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Weekly Highlights~
Apr 20
Theory Group
Members from the Theory Department attended the 2012 International Sherwood Fusion Theory
Conference, in Atlanta, Georgia on March 31-April 3. Allen Boozer gave a plenary talk titled,"Rotation of Tokamak Halo Currents", and C.S. Chang, gave a plenary talk titled " Unveiling the
Kinetic Mechanism of RMP Penetration". Ilya Dodin presented a talk titled "Axiomatic
Approach to Wave-particle Interactions and its Applications to Waves with Trapped Particles".
Guoyong Fu presented three posters and the following department members, H. Mynick, W. W.
Lee and S. Ethier, Nikolai Gorelenkov, Greg Hammett, Roscoe White, Luca Guazzotto and
Theory Graduate Student Jessica Baumgaertel presented posters.
Theory department members also attended the 2012 Transport Taskforce Workshop in
Annapolis, Maryland on April 10-13. C. S. Chang, gave a plenary talk titled "Bootstrap Current
for Edge Pedestal Plasma in Diverted Tokamak Geometry" Seung-Hoe Ku presented a talk titled"Intrinsic Momentum Generation and Inward Transport in Realistic Diverted Tokamak
Geometry with Neutral Recycling" and Wenjun Deng presented a talk titled, “Gyrokinetic
Particle Simulations of Reversed Shear Alfv en eigenmodes in DIII-D tokamak". Guoyong Fu
gave an oral presentation titled "M3D-K Simulation of Beam-Driven Alfven Modes in DIIID"
and Theory Graduate student Katy Ghantous gave an oral presentation titled "Revisiting Line
Broadened QL Burst Model: Applications on TAE-EP Interaction". Weixing Wang, presented a
poster titled "Flow Shear Driven Turbulence and Transport in Tokamak Plasmas".
On April 16, Dr. Natalia Tronko gave a special theory seminar entitled "A Close Guiding-center
Look at Gyrokinetic Theory." Two representations of higher order Hamiltonian guiding-center
theory were identified, symplectic and Hamiltonian. The higher order effects were derived in the
symplectic representation using guiding-center Banos hierarchy to help guide the derivation.
Magnetic moment invariance was shown to guarantee the equivalence of the two representations.
Guiding-center polarization and magnetization were shown to arise naturally from higher-order
guiding-center theory within the two-step perturbative approach to nonlinear gyrokinetic theory,
i.e. particle to guiding-center, and guiding-center to gyrocenter.
On April 19, Professor Anatoly Spitkovsky, gave a theory seminar on "Plasma Physics of
Collisionless Shocks: from Astrophysics to Laboratory." Outstanding issues in plasma physics
that govern the structure of collisionless shocks and their ability to accelerate particles were
discussed. Shock properties as function of flow composition and velocity were addressed in
context of large scale ab-initio kinetic simulations. Also discussed was the progress at creating
collisionless shocks on the Omega laser, and physical constraints that need to be satisfied by
such experiments at high-energy density facilities.
COMPUTATIONAL PLASMA PHYSICS GROUP
S. Jardin attended the workshop "Computational Challenges in Magnetized Plasma" at the
UCLA Institute for Pure and Applied Mathematics (IPAM). He presented an invited overview
lecture: "Multiple Timescale Simulations of Global Macroscopic Dynamics of Magnetized
Plasma". Most of the material from this talk can be found in the PPPL report: PPPL-4717 (2012)
which has now been accepted for publication in the IOP Journal "Computational Science and
Discovery".
Apr 13
Theory Group
On April 5, Dr. Maxime Lesur gave a seminar on "Phase-Space Turbulence, and Nonlinear
Instabilities Driven by Self-Organized Structures." A new theory was described in which the
growth of coherent phase-space structures, called holes and clumps, can drive the wave by direct
momentum exchange due to dissipation. Also discussed was numerical evidence of breakdown
of the quasi-linear theory in the presence of structures, which showed that coalescing holes
survive much longer than the classical quasilinear diffusion time and dominate the nonlinear
evolution.
On April 6, Prof. Zhihong Lin gave a special theory seminar on "Gyrokinetic Particle
Simulations of Kinetic-MHD processes." The presentation summarized the status of firstprinciple
simulations of kinetic-MHD processes using the gyrokinetic particle code (GTC).
Recent progress in the studies of nonlinear wave-particle interactions underlying the transport
processes was also outlined, including: convective flux driven by the constraint of the
longitudinal invariant in the trapped electron mode turbulence; nonlinear frequency oscillation of
Alfven eigenmodes induced by phase space coherent structures; and scaling of energetic particle
transport due to wave-particle decorrelation and orbit-averaging.
The paper "Magnetohydrodynamic Simulations of Edge Poloidal Flows" by L. Guazzotto and R.
Betti was accepted for publication in Nuclear Fusion.
Allan Reiman wrote, and submitted to DOE, the Second Quarter Report on the FY 2012 FES Theory Milestone. The work in the second quarter focused on equilibrium calculations for two DIII-D shots by four codes: VMEC, IPEC, MARS and the linearized version of M3D-C1. Significant differences were seen between the nonlinear and linearized equilibrium solutions, and progress was made in developing an understanding of the sources of those differences. The participants in the second quarter research were N. Ferraro (GA), M. Lanctot (LLNL), E. Lazarus (ORNL), S. Lazerson (PPPL), J.K. Park (PPPL), A. Reiman (PPPL), and A. Turnbull (GA).
COMPUTATIONAL PLASMA PHYSICS GROUP
The split-implicit algorithm in the3D nonlinear extended MHD code M3D-C1 involves three
independent large sparse-matrix solves each time step for (1) the velocity matrix, (2) the pressure
matrix, and (3) the magnetic field matrix. When the normalized ion skin depth, d_i, is non-zero
(i.e. two-fluid MHD) the magnetic field matrix becomes non-normal (non-symmetric with
complex eigenvalues) and the iterative solve becomes time-consuming and may not converge at
all for certain parameters. We have computed all the eigenvalues of the magnetic field matrix for
some typical cases with non-zero d_i and found that while the same block-Jacobi preconditioner
used in the velocity matrix solve reduces the spectral radius of a problem with over 3500
degrees-of-freedom (DOF) from over 10^8 to around 30, the matrix solve using GMRES will not
converge for d_i larger than about 0.05. We have now introduced another preconditioner stage
(based on the differential approximation form of the equations) that further reduces the spectral
radius somewhat (about a factor of 2), but more importantly, introduces large symmetric terms
into the matrix, making it less non-normal. With this new preconditioner, all cases of physical
interest will now converge in an acceptable number of iterations.
At the request of the UKAEA MAST team, the `get_fbm' program (TRANSP post-processing
software) has been extended to include an option to produce simulated 2-D distributions of
neutron production rates over the plasma cross-section. These are now output in convenient
NetCDF format on the irregular spatial grid used in the Monte Carlo NUBEAM package, with
the cylindrical (R,Z) coordinates of the grid vertices being specified. This new capability was
requested to help with the interpretation of data from the most recent experimental campaign in
which a new neutron camera was installed.
Mar 30
Theory Group
On March 21, Dr. Gregory Kagan gave a special theory seminar on "Neoclassical Theory in a Tokamak Pedestal." Kinetic calculation to find pedestal modification to the conventional neoclassical prediction for the banana regime main ion flow, as well as the zonal flow residual, was discussed in the context of evaluation of the main ion orbits while accounting for the radial electric field inherently present in a subsonic H-mode tokamak pedestal. Theoretically deduced impurity flow and the bootstrap current from the kinetic calculations was compared with the boron flow measurements in the banana regime C-Mod pedestals. The results show that accounting for the radial electric field effect on the main ion orbits improves agreement between theory and experiment. The comparison supports the conclusion that the bootstrap current is enhanced in banana regime pedestal and verifies the role of the radial electric field in modifying the main ion flow.
On March 22, Dr. Edward Startsev gave a theory seminar on "Finite-Beta Simulation of
Microinstabilities." A new scheme for gyrokinetic particle simulation of high beta plasmas was
discussed. In the new scheme the perturbed particle response, associated with the quasi-static
bending of the magnetic field lines, is separated out from the total particle response. The finitebeta
stabilization of drift-waves and ion temperature gradient modes was demonstrated using a
simple gyrokinetic particle code based on realistic fusion plasma parameters. The proposed
scheme is most suitable for studying shear-Alfven physics in general geometry using straight
field line coordinates, for microturbulence and magnetic reconnection problems. Problems
associated with the resolution of electron skin depth when beta is much larger than the electron
to ion mass ratio were also addressed, together with possible solutions.
A paper titled "Nature of Energetic Ion Transport by Ion Temperature Gradient Driven
Turbulence and Size Scaling” by a PPPL former visiting student Jugal Chowdhury (from
Institute for Plasma Research, India), and W. X. Wang, S. Ethier, J. Manickam and R. Ganesh
(IPP, India) has been accepted for publication in Physics of Plasmas. The paper reports
interesting results regarding ITG turbulence driven energetic particle transport obtained
from global gyrokinetic nonlinear simulations using the GTS code. The measured transport and
its nature show dependence on the system size of the tokamak expressed as the ratio of plasma
minor radius to the thermal ion Larmor radius. It increases with system size initially and then
tends to saturate at larger system size. The nature of transport, on the other hand, exhibits
nondiffusive character for smaller system size, and gradually becomes diffusive as the system
size becomes larger. This work was mainly carried out during Jugal Chowdhury's visit at the
PPPL theory department.
On March 27, Professor Scott Parker gave a special theory seminar on "Bootstrap Current
Destabilization of the Kinetic Ballooning Mode in the Tokamak Edge Pedestal." Results obtained using global gyrokinetic simulations were used to demonstrate that the high-n kinetic
ballooning mode (KBM) is the dominant instability in the tokamak edge pedestal assuming the
bootstrap current locally flattens the q-profile in the steep pressure gradient region. In addition to
KBM, an intermediate-n electromagnetic mode was found to be unstable whose features are
similar to the MHD peeling-ballooning mode. This mode, called "kinetic peeling ballooning
mode" (KPBM) was stabilized when the magnetic shear was weak in a small region near the
steep pressure gradient, while the high-n KBM became unstable. Collisions decreased the KBM's
critical beta and increased the growth rate. The simulations were carried out using the global
electromagnetic GEM code, including kinetic electrons, electron-ion collisions and the effects of
realistic magnetic geometry.
COMPUTATIONAL PLASMA PHYSICS GROUP
Stephane Ethier gave an invited talk entitled "Computational Advances in Gyrokinetic Particlein
Cell Simulations" at the "Accelerating Computational Science Symposium 2012" held in
Washington, DC, on March 29-30. The purpose of this Symposium, which was sponsored by the
Department of Energy and by the National Science Foundation, was to advance our
understanding of how extreme-scale hybrid-computing architectures are accelerating progress in
scientific research.
Mar 23
Theory Group
A paper entitled "Coupled Core-Edge Simulations of H-mode Buildup Using the Fusion Application for Core-Edge Transport Simulations (FACETS) Code" by A. Hakim et. al was published in Physics of Plasmas, 19 032505 (2012) (URL: http://dx.doi.org/10.1063/1.3693148). This paper reports results from coupled core-edge simulations of density and temperature evolution of a DIII-D discharge and studies the impact of gas puff on pedestal profile evolution
COMPUTATIONAL PLASMA PHYSICS GROUP
Stephane Ethier gave a mini-course entitled "Introduction to Parallel Debugging" as part of the
series of mini-courses hosted by the Princeton Institute for Computational Science and
Engineering (PICSciE). The lecture introduced the Princeton University participants to different
approaches in tackling the task of debugging parallel applications, including the use of advanced
parallel debuggers, such as Totalview and DDT.
Mar 16
THEORY GROUP
On March 13, Daren Stotler, Bill Davis and Greg Tchilinguirian ran the Robot Arm competition
at the New Jersey Science Olympiad State Tournament. Each of the 23 high school teams
participating in Robot Arm designed and built a stationary robot capable of picking up various
objects and placing them in one of four "goal" boxes.
On March 15, Feng Wang and Wei Shen gave a joint seminar on 'Simulation of Non-Resonant
King Mode and Fast Ion Transport in NSTX' and 'M3D-K Simulations of Sawteeth and
Energetic Particle Transport in Tokamaks', respectively. In the first part of the seminar, Feng
Wang discussed results obtained from nonlinear MHD simulations using the M3D code,
initialized with measured NSTX plasma profiles. It was found that when the rotation velocity is
near the experimental level, its effect on equilibrium and linear stability is small. In the nonlinear
regime the (m=1,n =1) mode is also weakly affected. However, with finite rotation the width of
the saturated (m=2,n=1) island is greatly reduced as compared to that of non-rotating case. The
simulated Soft X-Ray (SXR) emission from M3D agreed qualitatively with the measurement.
The fast ion transport was also investigated using the M3D-K code. The initial simulation results
show that the fast beam ion distribution is flattened radially due to the saturated (1,1) mode. In
the second part of the seminar, Wei Shen discussed nonlinear simulations of sawteeth and
energetic particle transport simulations using the M3D-K code. MHD simulations showed
repeated sawtooth cycles due to a resistive (1,1) internal kink mode for a model tokamak
equilibrium with a broader pressure profile. However, sawteeth did not occur for a peaked
pressure profile. In this case, a steady state saturated (1,1) mode follows the initial sawtooth
crash. Test particle simulations were also carried out to study the energetic particle transport due
to a sawtooth crash. The results show that energetic particle distribution is flattened depending
on pitch angle and energy. For trapped particles, the redistribution occurs for particle energy
below a critical value.
COMPUTATIONAL PLASMA PHYSICS GROUP
A new visualization has been developed of the 3D vector field of plasma flow computed by
global gyrokinetic simulations with the GTS code. The visualization shows the direction,
magnitude and structure of turbulence-generated intrinsic rotation in tokamak for each time step.
Color-coded vectors are drawn at each grid point on poloidal planes. Technical highlights
include transferring large amounts of data from NERSC to PPPL using multiple streams, parallel
rendering by the VisIt software, and multiple nx client sessions connecting to a persistent server
session. The animated movies were assembled with software developed at PPPL. A workflow is
in place for producing visualizations of new simulations. Work performed by E. Feibush, S.
Ethier, and W. Wang.
Stephane Ethier attended the Nu-FuSE project meeting in Edinburgh, UK. Nu-FuSE is an
international project (funded through the G8 Research Councils Initiative on Multilateral
Research Funding) looking to significantly improve computational modeling capabilities to the
level required by the new generation of fusion reactors. The project, still in its first year and
making good progress, is led by Professor Graeme Ackland at The University of Edinburgh, and
includes research teams in Cadarache (France, and also the location of the next generation of
Fusion reactors, ITER), Edinburgh (UK), Princeton (USA), Garching and Juelich (Germany),
Keldysh Institute of Applied Mathematics (Russia), and Tsukuba (Japan). Dr. Ethier made two
presentations during the workshop: "Computational Advances in Large-Scale Gyrokinetic
Particle-in-cell Codes for Tokamak Fusion Simulations", and "Confinement Physics of Fusion
Grade Plasmas: Scientific and Associated 'Path to Exascale' HPC Challenges".
Mar 9
THEORY GROUP
On March 6, Dr. Slava Lukin of Naval Research Laboratory gave a seminar on "Simulations of
magnetic reconnection in laboratory and space with the HiFi multi-fluid modeling framework."
The methods and underlying principles used in the development of this implicit spectral element
multi-fluid framework were described together with its various domains of applicability. Results
for 2D reconnection in single-fluid MHD with anomalous resistivity, in Hall MHD, in plasmaneutral
two-fluid MHD, as well as fully 3D reconnection in single-fluid and Hall MHD through a
moving reconnection region were discussed. The 3D simulations were presented in context
of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and
oriented to form a single magnetic field null at its center. Correlation between the reconnection
region and the magnetic null were observed, together with stronger reconnection in plasmas with
lower thermal to magnetic pressure ratio.
COMPUTATIONAL PLASMA PHYSICS GROUP
S. Jardin attended the combined US-Japan Workshop on MHD and ITPA/MHD meeting at the
NIFS Institute in Japan. He made a presentation at the former on "Transport timescale
calculations of sawteeth and other m=1 activity in tokamaks" and gave a report at the latter on
Working Group WG-10: "Halo Current Modeling", for which he is the Chair.
Stephane Ethier attended the "Industry-National Laboratory Workshop on Modeling and
Simulation" held in Austin, Texas. This is the second in a series of workshops organized by DOE
to increase industry awareness of relevant research capabilities within the DOE national
laboratory system, deepen the national laboratories’ understanding of the technical challenges
facing industry, and identify and improve paths forward for collaboration. Dr. Ethier presented a
poster describing PPPL's major activities in the realm of modeling and simulation, from
engineering design and industrial plasma simulations to advanced physics calculations with
large-scale parallel codes.
Feb 24
THEORY GROUP
Professor Jim Drake of University of Maryland gave a seminar on February 22 entitled, "Particle Acceleration During Magnetic Reconnection." Models for heating and production of energetic particles were discussed in two distinct environments: impulsive flares, and the sectored regions of the heliosheath (regions with radially periodic reversal of azimuthal magnetic field). Multiisland reconnection model was suggested to be necessary to explain the observations in both cases. For the case of solar flares the model was used to explain the recent observations that all electrons in the flaring region undergo acceleration, and that the acceleration of high mass-tocharge ions is more efficient. As for the sectored regions of the heliosheath, the Voyager spacecraft has revealed that the termination shock is not the source of anomalous cosmic rays. Here the model suggests that the source of the anomalous cosmic rays may be the compressed sectored structure of the heliospheric magnetic field which undergoes collisionless reconnection. The high beta environment of the heliosheath leads to magnetic island dynamics that differ greatly from the low beta environment of flares but in both cases Fermi reflection in contracting islands drives the plasma towards the marginal firehose condition, which ultimately controls the spectra of energetic particles.
COMPUTATIONAL PLASMA PHYSICS GROUP
An Audio Web conference call was held this week between the TRANSP code developers (and
some users) at PPPL, MIT, and JET. Jim Conboy from JET gave a web presentation on"TRANSP at JET". A number of issues were discussed regarding the deployment of parallel
TORIC and NUBEAM within TRANSP at the two sites and maintaining compatibility. Also
discussed were the obstacles encountered when trying to use TRANSP at PPPL from JET.
Among the actions taken were steps to install the exact same TRANSP version used at JET as a
branch of the repository at PPPL so that compatibility can be tested on the PPPL unix system
before being committed into the PPPL TRANSP SVN repository.
Feb 17
THEORY
On February 13, Dr. Robert Hager gave a Special Theory Seminar entitled "Nonlinear dispersion relation of the geodesic acoustic modes." He discussed results obtained using two-fluid turbulence simulation code NLET. Some topics covered were frequency shift of geodesic acoustic modes (GAMs) and energy input induced by turbulence; dependence of radial phase velocity, in nonlinear stage, on up-down asymmetric equilibrium magnetic field; variation of GAM and turbulence intensity with the direction of radial phase velocity with respect to magnetic drifts. If the equilibrium magnetic field is up-down asymmetric, his simulations showed periodic bursts of turbulence and GAM activity which he used to interpret the experimentally observed pulsations during the I phase in ASDEX Upgrade and the periodic turbulence suppression in NSTX.
COMPUTATIONAL PLASMA PHYSICS GROUP
A major restructuring of the nonlinear operating mode of the M3D-C1 code was accomplished this week. The normal algorithm used in the code is the "split implicit method" where the velocity field at the new time level is first solved for, and then the magnetic field and pressures are advanced. We have added new options to allow the magnetic field and pressure advance to be either combined or done separately, and an option to allow equations to advance the electron and ion temperatures instead of the pressures. The first option resulted in a 20% speedup in many cases because it is more efficient to invert two smaller matrices than one large one. The second option was necessary to obtain a numerically stable time advance in the presence of a nonuniform density and large parallel electron thermal conductivity. These improvements were done in close collaboration with N. Ferraro of General Atomics.
S. Jardin participated in a conference call with representatives from ITER, India and the ITER Organization (IO) regarding the use of the TSC code to calculate the generation of runaway electrons during an impurity-pellet induced plasma disruption and the subsequent control of the runaway beam. The team from ITER, India has begun a series of TSC simulations using a high resolution model of the ITER plasma and surrounding structure and coils and the existing TSC pellet and runaway electron models. Plans for an IAEA paper on this work, and on subsequent experimental calibrations using JT-60 and DIII-D data were discussed.
Jin Chen attended SIAM Parallel Processing for Scientific Computing (Feb 14-17, 2012) and reported on an algorithm and numerical implementation for calculating eigenvalues from the M3D-C1 3 dimensional nonlinear MHD simulation, both before and after the pre-conditioner is applied. In the near future, she has plans to test the SS method using contour integration to speed up the convergence.
Feb 10
COMPUTATIONAL PLASMA PHYSICS GROUP
Stephane Ethier attended the annual NERSC Users' Group (NUG) meeting held at the NERSC facilities in Oakland, California. The three-day meeting consisted of two days of user training on all topics related to computing at NERSC, followed by a one-day business meeting during which participants learned about NERSC's current and future activities. It is also an opportunity for the users to give direct feedback to the NERSC staff and administrators about their overall experience with working on the NERSC systems. The business meeting was very informative and well attended by most members of the NUG Executive Committee, of which Dr. Ethier is the chair.
Feb 3
COMPUTATIONAL PLASMA PHYSICS GROUP
Several modifications and improvements have been made to the Tokamak Simulation Code (TSC) as requested by different research groups. A capability has been added to switch from "non surface-averaged transport" to "surface-averaged" transport at restart time. This was requested for modeling NSTX discharges that begin as CHI discharges and transition to OH discharges. A capability was restored to model impurity pellet injection [as done in Jardin, et al, "A fast shutdown technique for large tokamaks, NF 40 923 (2000)] as requested by ITER, India. A capability was added to import LHCD heating and current drive profiles from GENRAY via the SWIM framework.
J. Chen succeeded in calculating all the eigenvalues of the implicit M3D-C1 matrix for a small nonlinear 3D application both before and after the preconditioner was applied. This allows us to quantitatively measure the effectiveness of the preconditioner. We were thus able to show how dramatically effective the SuperLU_dist-based block Jacobi preconditioner is in reducing the condition number (ratio of the largest to smallest eigenvalue) from over 10^15 to approximately 30. After preconditioning, the matrix equation is solved in just 10's of iterations using the PETSc iterative solver GMRES.
X. Yuan visited G. Stabler and others at General Atomics regarding the TGLF transport module and its incorporation into transport codes. As a result of that visit, both sides now agree that there is adequate agreement in the fluxes computed by TGLF as installed in XPTOR (GA) and PTSOLVER (PPPL). PPPL and GA also jointly modified TGLF to make it parallel in the wavenumber evaluations. There were also discussions regarding transferring the capability of PTSOLVER to be parallel over flux surfaces to XPTOR
Jan 27
THEORY GROUP
On January 26, Dr Leonid Malyshkin of the Department of Astronomy and Astrophysics at the University of Chicago presented a Theory Department seminar entitled "Two-fluid Physics of Magnetic Reconnection". Magnetic reconnection is sometimes fast and sometimes slow in laboratory and astrophysical plasmas, depending on the plasma collisionality and the mechanism by which the magnetic field lines are broken. Highlighting the importance of understanding what drives the fast and slow regimes, Dr. Malyshkin presented a theoretical model he developed of two-fluid MHD reconnection to explain the physical processes which are central for distinguishing the two regimes. In the slow reconnection regime the resistive and Hall terms are important, while the electron inertia does not play any role. In the fast reconnection regime the electron inertia terms are important. He summarized how it is possible that the presence of the two reconnection regimes can provide an explanation for the initial slow build up and subsequent rapid release of magnetic energy observed in cosmic and laboratory plasmas.
COMPUTATIONAL PLASMA PHYSICS GROUP
The M3D-C1 code is now running on the recently installed PPPL computer Greene (named after
the late PPPL physicist John Greene). Production runs are being performed using the 256
processors that each have 8GB of memory. Since the memory per processor is approximately 3
times that of the Hopper computer at NERSC, this allows us to run the same jobs that require
768p on Hopper. Typical runs use 16 planes (16 Hermite cubic elements in the toroidal direction)
with the mesh points on each plane spread across 16 processors, with good efficiency and load
balancing. The availability of this resource is proving invaluable in further M3D-C1 development, in particular in the optimization of the nonlinear implicit algorithms when density
evolution and two-fluid effects are present.
Dr. Jai Sachdev from Combusion Research and Flow Technology presented a CPPG Seminar
on: "Numerical Solution of a Dilute and Disperse Gas-Particle Flow". In this seminar, the
equations governing the motion of a dilute and disperse gas-particle flow, the mathematical
characteristics of these equations, and methods for their solution were presented. Numerical
results were also described that demonstrate the capabilities of different approaches for the
solution of coupled gas-particle flows.
January 20
THEORY GROUP
There were four Theory seminars during the week of January 16. On January 16, Dr. William Daughton of LANL presented a seminar entitled "Spontaneous Generation of Turbulence in Magnetic Reconnection" in which he discussed results of 3D simulations of magnetic reconnection using the VPIC simulation code and highlighted the complex differences the extra dimensionality introduces over the 2D system.
On January 17, Dr Xin Wang of the Institute for Fusion Theory and SImulations of Zhejiang University gave a seminar entitled "Nonlinear dynamics of Beta-induced Alfven eigenmode excited by Energetic particles in Tokamak plasmas" in which she discussed nonlinear BAE simulations excited by purely circulating energetic particles in Tokamak plasmas using an extended version of the Hybrid Magetohydrodynamic Gyrokinetic Code (XHMGC).
On the
same day, Dr Zhiyong Wang (also of Zhejiang University) presented a seminar entitled "Spatialtemporal
evolution of the nonlinear DW-GAM system" which highlighted work investigating the
effects of plasma nonuniformities such as the GAM (Geodesic Acoustic Mode) continuum,
nonuniform DW frequency and nonuniform pump wave amplitude on GAM/KGAM excitation.
The final seminar entitled "Capitalizing on a better understanding of plasma turbulence" was
presented by Professor Frank Jenko of the Max Planck Institute for Plasma Physics in Garching
on January 18. During the seminar he discussed the basic character of plasma turbulence in
comparison with that of fluid turbulence. He discussed the limits of quasilinear theory in
describing the characteristics of the plasma turbulence and how this useful approach must be
complimented by simulations (such as from the GENE code) in order to elucidate nonlinear
effects and how the insight gained can be used to develop advanced transport models.
COMPUTATIONAL PLASMA PHYSICS GROUP
The ADAS310_FORTRAN_DRIVER has now been implemented and validated in the energetic
ion program NUBEAM. It is based on the ADAS310 program from ADAS (Atomic Data and
Analysis Structure) library. The program calculates the exited population structure, effective
ionization and charge-exchange coefficients of the hydrogen atom(ions) and its isotopes in an
impure plasma. A very many n-bundle-n approximation is used. The
ADAS310_FORTRAN_DRIVER provides users with atomic physics data computed using the
excited state model. To use this option in NUBEAM together with TRANSP, the
variables LEV_NBIDEP=2 and NSIGEXC=3 need to be set in the namelist.
January 13
As the POC for the FES FY 2012 Theory Milestone, Allan Reiman submitted the first quarter
report on the milestone to DOE on January 6. The work on the milestone focuses on
understanding experiments on the DIII-D tokamak in which relatively small nonaxisymmetric fields are imposed for the purpose of suppressing edge localized modes (ELMs). There are 17 participants involved in the project from four different DOE laboratories and three universities.
ELMs pose a threat to ITER, and the only method that has been demonstrated to suppress ELMs without reducing global plasma confinement is the imposition of a nonaxisymmetric field as
pioneered by DIII-D. There is as yet no first-principles understanding of this effect. A firstprinciples understanding would greatly increase our confidence in extrapolating these results to
ITER. The milestones for the first quarter have three elements: 1) Develop a preliminary
coordinated research plan among the groups that will be contributing to this research;
2) Assemble data from at least two DIII-D ELM suppression experiments in a form that can be used by 3D equilibrium codes; and 3) Provide a theoretical assessment of measurement options for ITER as-built field errors.
January 6
The paper entitled "Electron acceleration in a geomagnetic Field Line Resonance" by P.A.
Damiano and J.R. Johnson has been accepted for publication in the journal Geophysical
Research Letters. In this paper, a 2D hybrid MHD-kinetic electron model in dipolar coordinates
was used to conduct the first kinetic simulation of a global scale Field Line Resonance system
(standing shear Alfven wave along the Earth's closed dipolar magnetic field lines) for realistic
magnetospheric electron temperatures of a keV. It was found that mirror force effects self
consistently lead to the formation of field aligned potential drops that accelerate electrons to
greater than the keV energies needed to power auroral emissions. It was also determined that the
wave energy dissipated in the electron acceleration was sufficient to damp an undriven resonance
structure in under two Alfven periods.
Dec 16
Theory Group
Dr. Harry Mynick presented the Plasma Physics Seminar at the MIT PFSC, entitled "Reducing Turbulent Transport in Stellarators and Tokamaks Through Shaping", on work done in collaboration with Neil Pomphrey, Pavlos Xanthopoulos (IPP-Greifswald), and Matt Lucia.
Mr. Zhirui Wang from RFX Padua visited PPPL from November 23 to December 6. He had
broad discussions with Weixing Wang, Jong-Kyu Park and other theorists and experimentalists
at the PPPL on kinetic effects on MHD instabilities. He presented a Theory Seminar entitled“Physical understanding of resistive wall modes in reversed field pinch plasmas and comparison
with tokamak”. The physics of kinetic effects on the Resistive Wall Mode (RWM) stability arestudied and compared between Reversed Field Pinch (RFP) and Tokamak configurations. The
toroidal kinetic hybrid stability code MARS-K is upgraded with an extensive energy analysis
module for the study. In tokamak, the kinetic stabilization on the pressure driven RWM is
provided by the precession resonance of thermal trapped particles, which requires very slow, or
vanishing plasma rotation. In RFP, instead, the stabilization of RWM comes from the transit
resonance of passing ions (i.e. the ion acoustic Landau damping) in high beta plasmas. The
required rotation for kinetic stabilization is in the ion acoustic speed range or even higher
(depending on the toroidal mode number and wall position). The trapped particles do not play a
significant role in the kinetic stabilization in RFP plasmas. Detailed numerical analysis based on
the perturbed potential energy components have been performed to obtain the understanding of
kinetic physics in the two different systems. The physics of the active stabilization of feedback
control on RWM in RFP is also studied based on the cylindrical MHD model. The study, via
both analytical and numerical analysis, provides the physical understanding on the response of
the unstable plasmas to the feedback control in RFPs. The linear solutions of time evolution of
RWM instability under various feedback scenarios are given out.
A lecture paper "Excitation of Alfvén Modes by Energetic Particles in Magnetic Fusion" by N.N.
Gorelenkov will soon appear in the proceedings of this year international ITER summer school
held in Cadarache, France on June 2011. The paper deals with the most recent advances in the
area of energetic particles spanning from the TFTR first DT campaign to the ITER planned
experiments. Both theory and computation progresses are reviewed.
On November 25 - December 7, Leonid E. Zakharov visited Peking University, Graduate
University of Chinese Academy of Sciences in Beijing and Institute of Plasma Physics in Hefei.
He was shown three special divertor tiles on EAST tokamak installed following his suggestion in
July for Hiro current measurements during vertical disruptions. Full information was presented
to him on different kinds of damages of in-vessel components by disruptions: several broken
water cooling pipes, tiles supports, and unexpected hair-thin holes in water pipes due to runaway
electrons from the previous experimental campaign on EAST. A schedule for flowing liquid
lithium system for HT-7 and EAST was determined.
Leonid Zakharov gave a talk on "Understanding Disruption in Tokamaks" to ASIPP and to
physics seminar at Peking University. He also described the scope of work on simulations of the
free surface liquid lithium flow to the Prof. Ming-Jiu Ni group in College of Physical
Sciences of Beijing Graduate University.
COMPUTATIONAL PLASMA PHYSICS GROUP
Stephane Ethier gave a two-part tutorial entitled "Introduction to Mixed Parallel Programming with MPI and OpenMP" at Princeton University as part of the technical mini-course series from the Princeton Institute for Computational Science and Engineering (PICSciE). Over two practiceoriented sessions, participants learned to exploit the power of parallel computing on a distributed memory system using message passing (MPI), as well as on a shared memory multicore node using OpenMP. Attendees were also introduced to mixing these two methods together in the same application, which is the favored approach for achieving high scalability on the largest computers currently available. This popular mini-course was attended by Princeton University's graduate students and research scientists from diverse science departments.
The NERSC computer time allocations were announced this week and PPPL scientists were awarded a total of 63,115,000 hours of supercomputer time for FY 2012. The awards went to the following principle investigators: S. Cohen, “FRC simulations with the LSP PIC code” (15,000 hr); R. Davidson, “Simulations of field-reversed configuration and other compact tori plasmas” (50,000 hr); R. Davidson, “Nonlinear delta-f particle simulation of collective effects for heavy ion fusion drivers and high intensity particle accelerators” (50,000 hrs); D. Mikkelsen,“Experimental tests of gyrokinetic simulations of microturbulence” (8,000,000 hrs); C.S. Chang,“Center for plasma edge simulation” (37,500,000 hrs); G. Fu, “Center for simulation of energetic particles” (4,500,000 hrs); S. Jardin, “3D extended MHD simulation of fusion plasmas” (4,000,000 hrs); and W. Lee, “Turbulent transport and multiscale gyrokinetic simulation” (9,000,000 hrs).
Dec 2
Theory Group
Dr. H. Strauss (HRS Fusion) and R. Paccagnella (RFX Padua) visited PPPL this week to consult
with J. Breslau and others in the PPPL Theory Division on the modeling of the forces produced
by plasma disruptions on the vessel wall, and projection of these forces to ITER using the M3D
code. Dr. Strauss is the principal on a subcontract to address the ITER proposal “3D MHD
simulation of VDEs for detailed evaluation of toroidal peaking factor (TPF) and associated
electro-magnetic load”. Dr. Paccagnella is the principal on a similar subcontract being handled
by the European agency F4E. The focus of this work is to (1) utilize the massively parallel
capabilities of M3D to greatly increase the resolution and time-scale separation of earlier work
performed on a workstation version of M3D, and to (2) increase the physical realism of the halo
model in M3D.
Roselyne Tchoua (ORNL) visited PPPL November 29-30 to learn about MDSplus and to plan
extensions to the eSiMon simulation monitoring system (developed by the Center for Plasma
Edge Simulation) to provide access to MDSplus data and tools. During her stay, she met with
Eliot Feibush, Daren Stotler, Stan Kaye, and Devon Battaglia. She also had discussions on the
ADIOS adaptable I/O system with Guo-Yong Fu, Stephane Ethier, and Jin Chen.
On November 22, Dr. Gregory von Nessi of the Australian National University presented a
Theory Department Seminar entitled "Tokamak Equilibria Validation: Reconciling Theory and
Observation via Bayesian Inference and BEAST". During his presentation, Dr von Nessi, gave
an overview of a new technique for reconciling force-balance models with diagnostic
observations via the statistical theory of Bayesian analysis. This method forms the backbone of a
new data analysis code called BEAST (Bayesian Equilibrium Analysis and Simulation
Technique) and is based on refactoring the force-balance relation into two different forward
models, each associated with a set of 'fractional' observations. These pairs of models and sets of
observations are subsequently used in the Bayesian inference of the plasma equilibrium. By
using a variant of the nested sampling algorithm, the evidence of the inferred posterior
distribution is calculated and provides a value which is sensitive to how much the inferred
equilibrium differs from a force-balance solution. Results of the model were presented for
discharges on the Mega-Ampere Spherical Tokamak (MAST), which are calculated using pickup
coil, flux loop and Motional-Stark Effect (MSE) diagnostic observations. These results
encompass inferences made utilizing both standard Grad-Shafranov (GS) and flow-modified GS
force-balance models. Finally, the interpretation of these results were discussed in the context of
Bayesian model comparison and BEAST outputs.
On December 1, Dr, Timothy Stoltzfus-Dueck of the Max Planck Institute, Greifswald, Germany
presented a Theory Department seminar entitled " Transport-driven Toroidal Rotation in the
Tokamak Edge". The edge of H-mode tokamak plasmas without external momentum input
almost always rotates toroidally in the co-current direction, which has prompted a theoretical
search for non-diffusive momentum transport mechanisms. In contrast to these efforts, Dr.
Stoltzfus-Duek presented work that treats a model kinetic ion equation for the pedestal and SOL
(Scrape Off Layer) containing only parallel free streaming, magnetic drifts, and spatially
inhomogeneous but purely diffusive transport. The solution demonstrates that passing-ion orbits
and spatially inhomogeneous diffusion interact to cause a variation of the orbit-averaged
diffusivities that depends on the sign of the parallel velocity, typically resulting in preferential
transport of counter-current ions. If the plasma at the boundary with the core is allowed to rotate
toroidally to annihilate toroidal momentum transport, the resulting pedestal-top rotation reaches
experimentally relevant values and exhibits several features in qualitative agreement with
experiment. It is almost always in the co-current direction, with a rate that is proportional to
pedestal-top ion temperature over poloidal field strength and the gradient scale length for the
intensity of potential fluctuations, thus inversely proportional to plasma current in accord with
Rice scaling. It is independent of the toroidal velocity and its radial gradient, representing a
residual stress. The given scaling implies co-current spin-up at the transition to H-mode, as ion
temperature increases and the gradients steepen. Untested predictions of the model include a
sensitivity of the rotation to the major-radial position of the X-point, with a more inboard Xpoint
leading to stronger co-current rotation. Beyond intrinsic rotation predictions, comparison of
heat and momentum transport reveals that neutral beam injection must be significantly
unbalanced in the counter-current direction to cause zero toroidal rotation at the pedestal top.
COMPUTATIONAL PLASMA PHYSICS GROUP
Both the tshare and pshare versions of TRANSP now have a new option for a shielded beam current calculation in the Monte Carlo neutral beam package NUBEAM. The model was recently derived and submitted for publication in Nuclear Fusion by Honda M., Kikuchi M., Azumi M. "Collisionality dependence on shielding factor of beam driven current" Eqs. 16 – 18 (submitted October 2011). The fit takes into account the collisionality dependence of the shielding factor at arbitrary aspect ratio. The new shielding calculation is invoked by setting NMCURB=4 in the TRANSP namelist. Initial preliminary studies by Budny of a D3D discharge shows that the NMCURB=4 setting gives a result for the beam-driven current that is intermediate between the values obtained with NMCURB=2 and NMCURB=3 (LinLiu).
The article “Review of Implicit Methods for the Magnetohydrodynamic Description of
Magnetically Confined Plasmas” by S. C. Jardin is now available online: J. Comput. Phys. 231
(2012) pp. 822-838. This appears in a special JCP issue on Computational Plasma Physics. The
article traces the development of modern algorithms for obtaining implicit solutions of the MHD
equations to their roots in algorithms used in the 1960s and 1970s. These modern algorithms
make possible the simulation of slowly growing (compared to the Alfven time) global
instabilities in today’s fusion experiments.
Nov 25
Theory Group
Many researchers from the Theory Department attended the Annual Meeting of the APS Division of Plasma Physics in Salt Lake City, UT Nov. 14-18. Allen Boozer presented a tutorial talk " Physics of Tokamak Disruption Simulations". Leonid Zakharov gave an invited talk " Understanding Disruptions in Tokamaks" and Andrey Zhmoginov, Theory department graduate student presented an invited talk "Alpha-channeling in Mirror Machines".
Dr. Jay Johnson gave a space plasma seminar at Dartmouth College about "Modeling Wave Propagation, Dissipation, and Mode Conversion in Space Plasmas" on November 8. While there, he collaborated with Richard Denton on hybrid simulations of whistler waves and Jim Labelle on mode conversion of Langmuir waves in ionospheric density gradients.
Nov 18
COMPUTATIONAL PLASMA PHYSICS GROUP
A TRANSP Users Group meeting was held at the annual APS-DPP meeting. The meeting discussed new options available in TRANSP such as the ability to invoke the RF routines in parallel, improved atomic physics packages in NUBEAM, a new nonlinear solver for TGLF, and a new free-boundary equilibrium capability. Approximately 25 users from the US and abroad attended the meeting. Presentations by the TRANSP team were followed by a discussion with the users regarding what new capabilities were desired and the best way of implementing them.
R. Andre, X. Yuan, and S. Jardin attended the DPP-APS meeting and made presentations on:"Status of TRANSP/PTRANSP", "A modular, parallel, multi-region predictive transport
equation solver, installed and available in PTRANSP", and "Multiple Timescale Calculations of
Sawteeth in Tokamak Plasmas" respectively.
Stephane Ethier attended the SC'11 conference on supercomputing held in Seattle, WA. He was
co-author on three papers presented at the conference: "Gyrokinetic Toroidal Simulations on
Leading Multi- and Manycore HPC Systems", K. Madduri et al., "ISABELA-QA: Query-driven
Data Analytics over ISABELA-compressed Extreme-Scale Scientific Data",
S. Lakshminarasimhan et al., and "Multithreaded Global Address Space Communication
Techniques for Gyrokinetic Fusion Applications on Ultra-Scale Platforms", R. Preissl et al.
Nov 4
THEORY GROUP
On November 3, Leonid E. Zhakarov gave a Theory Department seminar entitled "Scalable
Flowing Liquid Lithium System (FLiLi) for Tokamaks" where he presented a practical system
for the implementation of a flowing liquid lithium layer in tokamaks. The suggested scheme
satisfies all requirements for FLiLi for development of the LiWall Fusion regime on existing
devices and for its utilization in future tokamaks with a burning plasma. The thin LiLi layer is
insensitive to MHD effects and yet unknown j �� B forces, transparent to the heat flux an
sufficient for plasma pumping. The FLiLi system is scalable in both poloidal and toroidal
directions, compact, and has minimal necessary LiLi inventory in the machine.
COMPUTATIONAL PLASMA PHYSICS GROUP
Stephane Ethier gave an invited talk at the 2011 international Conference on Computational
Physics held in Gatlinburg, Tenessee. This annual conference is dedicated to presenting an
overview of the most recent developments and opportunities in computational physics across a
broad range of topical areas and from around the world. Dr. Ethier's presentation was entitled"Computational advances in large-scale gyrokinetic particle-in-cell simulations of tokamak fusion devices".
Oct 28
Theory Group
Jay Johnson and the space physics group hosted a NASA LWS team meeting on "Integrating
kinetic effects in global models" at PPPL on October 24-25. The group discussed collaborative
projects considering comparative studies of reconnection in global systems using MHD, Hall-
MHD, and fully kinetic models. The team also considered how to best include wave-particle
interactions that control temperature anisotropies in global models of the solar wind and
planetary magnetospheres. Sixteen members of the team attended from University of New
Hamsphire; University of Maryland; Johns Hopkins University, APL; NASA Goddard Space
Flight Center; NASA Headquarters; Naval Research Laboratory; University of California,
Berkeley; and PPPL.
On October 27, Prof Huishan Cai of the Department of Modern Physics, University of Science
and Technology, Heifei, China presented a Theory Department seminar entitled "Influence of
energetic ions on tearing modes". During his presentation, Professor Cai summarized the
disruptive effects of tearing modes on tokamak plasmas. He discussed how fast ions generated
by neutral beam injection are being investigated as a method of controlling these modes. In
contrast with the stability effects of trapped energetic ions on tearing modes, the effects of
circulating energetic ions (CEI) on tearing modes depend on the toroidal circulating direction,
and are closely related to the momentum of the energetic ions. CEI provide an additional source
or sink of momentum to affect tearing modes. For co-circulating energetic ions (co-CEI), where
the circulating direction is the same as the plasma toroidal current, tearing modes can be
stabilized if the momentum of energetic ions is large enough. On the other hand, the growth of
tearing modes can be enhanced by countercirculating energetic ions. Professor Cai additionally
pointed out the possibility to suppress the island growth of neoclassical tearing modes by co- CEI. (Cai et al., PRL, 106, 075002, 2011).
Computational Plasma Physics Group
The M3D-C1 nonlinear simulation code has been used to calculate a sequence of sawtooth
events in a tokamak of the shape of CMOD with a Spitzer resistivity profile and an analytic
transport model. A loop voltage is applied to the boundary to sustain the current. After about
10^5 Alfven times the system becomes perfectly periodic with the sawtooth occurring at regular
intervals. E. Feibush (CPPG) and A. Sanderson (U. Utah) have used the Visit visualization tool
to create a movie of the evolution of a pressure contour during one of these periods. The movie
can be viewed at (requires QuickTime): http://w3.pppl.gov/cemm/Highlights/iso006b.mov.
This sequence is being used as a baseline for which to study the effects of the transport model, 2-
fluid terms, and kinetic effects on the sawtooth period, crash time, and other characteristics.
Marina Gorelenkova held an informal design review on her project to include 3D geometry for
the halo neutrals in the NUBEAM Monte-Carlo neutral-beam simulations used in TRANSP.
Participating were Sid Medley, Stan Kaye, Daren Stotler, Bill Heidbrink (remotely), and Robert
Akers (remotely).
Oct 21
Computational Plasma Physics Group
Marina Gorelenkova hosted Dr.Stuart Loch (Assistant Professor at Auburn University) and
Dr.Martin O'Mullane (Professor of Physics, University of Strathclyde) on October 17-18.
Dr.Loch and Dr.O'Mullane had presentation on The Atomic Data and Analysis Structure
(ADAS) activities and future development. Stuart and Martin worked with Daren Stotler, C.S
Chang's group, Vlad Soukhanovskii, Daniel Clayton, Marina Gorelenkova, Brentley Stratton and
few other physicists.
Oct 14
Theory Group
Greg Hammett recently spend a couple of weeks visiting Oxford and Culham, interacting with
Professor Alex Schekochihin, Professor Steve Cowley, Professor Bill Dorland, Michael Barnes,
Ian Abel, Edmund Highcock, and others on gyrokinetic theory and simulations of plasma
turbulence, including topics such as momentum transport and possible transitions from
gyroBohm to Bohm scaling. (This trip was supported in part by Oxford University and
Schekochihin's grant from the Leverhulme Trust.). He gave a talk for a UK Fusion theory
meeting at Culham/JET summarizing recent work with PPPL graduate students on GYRO
simulations of ETG turbulence in NSTX and improved algorithms for transport solvers (J. L.
Peterson), improved algorithms for gyrokinetic stellarator simulations in the GS2 code (J.
Baumgaertel), and on simulations of density-gradient-driven turbulence in improvedconfinement
regimes expected with lithium walls (E. Granstedt).
Graduate student Luc Peterson published an article, "Bringing Star Power to Earth," on plasma
physics, fusion energy and his graduate research in Imagine Magazine, a publication of the Johns
Hopkins Center for Talented Youth that aims to provide gifted students in grades 7-12 insight,
perspectives and opportunities in fields they may wish to explore. Mr. Peterson's article appears
in the September/October 2011 issue on Physics and Astronomy.
A paper titled ""Radial Transport of Energetic Ions in the Presence of Trapped Electron Mode
Turbulence By a PPPL former visiting student Jugal Chowdhury (from Institute for Plasma
Research, India), and W. X. Wang, S. Ethier, J. Manickam and R. Ganesh (IPP, India) has been
accepted for publication in Physics of Plasmas. In this paper the nature of transport of hot ions is
studied in the presence of microturbulence generated by the trapped electron mode in a Tokamak
using massively parallel, first principle based global nonlinear gyrokinetic simulation, and with
the help of a passive tracer method. Passing and trapped hot ions are observed to exhibit inverse
and inverse square scaling with energy, while those with isotropic pitch distribution are found to
exhibit inverse dependence on energy. For all types of hot ions, namely, isotropic, passing and
trapped, the radial transport appears to be subdiffusive for the parameters considered.
On October 13, Dr. Jacob Bortnik of NJIT and UCLA presented a Theory Department seminar
entitled "Some Open Problems Related to Wave Modeling in the Context of the RBSP Mission".
More than 50 years after the discovery of the radiation belts, many of the key physical processes
that control the structure and dynamics of these high energy electrons remain poorly understood,
poorly quantified, or both. An emerging consensus recently stated that the long-held view of
electron energization by inward radial diffusion was insufficient to account for the dynamics and
phase space density gradients that are typically observed, and that the operative process most
likely involves a combination of several different types of plasma waves. During his
presentation, Dr Bortnik briefly reviewed the role that waves play in controlling radiation beltdynamics. He described recent work on the origin and modeling of lasmaspheric hiss, that
attributes the unexpected source of the hiss to electromagnetic chorus wave emissions which
can propagate into the plasmasphere from tens of thousands of kilometers away (Bortnik et al.,
Nature, 2008). He highlighted a few of the upcoming missions and the key problems that that
will be studied over the next few years with emphasis on the Radiation Belt Storm Probes
mission, scheduled for launch in the Fall of 2012.
Computational Plasma Physics Group
Marina Gorelenkova attended the ADAS international workshop at Auburn University, Alabama
on October 5-8. The Atomic Data and Analysis Structure (ADAS) is an interconnected set of
computer codes and data collections for modeling the radiating properties of ions and atoms in
plasmas. She gave a talk "TRANSP/NUBEAM: atomic physics updates and issues" and had
fruitful discussions with Dr. M.O'Mullane(CCFE), Dr. O.Marchuk(Institut fuer Klimaforschung
Plasmaphysik IV Forschungszentrum Juelich). She also participated in the ADAS steering
committee meeting.
Stephane Ethier attended the DOE-ASCR Exascale Research Principal Investigators meeting in
Annapolis, MD. Dr. Ethier is a co-PI on an ASCR-funded Exascale Software Stack (X-Stack)
project led by Dr. Sam Williams of the Future Technologies Group at LBNL. The project
explores new optimizations for the particle-in-cell (PIC) algorithm as the computing technology
moves towards exascale.
S. Jardin attended the ITPA meeting on MHD and Disruptions in Padua, Italy and made a
presentation on "Nonlinear calculations of sawteeth and helical states in tokamaks". He also
reported on the progress for Working Group-10, "Halo current modeling", for which he is the
group head.
Oct 7
Theory Group
Daren Stotler attended the XSAMS (XML Schema for Atoms, Molecules and Solids) meeting at
the National Institute of Standards and Technology in Gaithersburg, Maryland on October 3-5.
The XSAMS schema promises to provide a single, comprehensive standard for exchanging
atomic physics and plasma-material interaction data between data producers and consumers.
Igor Kaganovich was invited to be a key note speaker at the TRR24 workshop on "Physics of
Complex Plasmas" in Germany (see file http://www.tr24.uni-greifswald.de/WS/flyer-TR24-
Workshop.pdf). He was also invited to visit University of Greifswald and The Leibniz Institute
for Plasma Science and Technology, (see http://www.inp-greifswald.de/webn.
nsf/index?OpenPage&Language=eng). He was given a tour of facilities and met with the
Directors.
Jin Chen attended XE6 Workshop at SNL September 27-28. The workshop features achieving
good scaling on future Multi-Core MPP system using Hybrid OpenMP-MPI programming.
Dr. Chris Chaston of the Space Sciences Laboratory at UC Berkeley visited PPPL on September
29-30. In addition to presenting the Colloquium on September 29, he was involved in research
discussions with the Space Physics Group. These discussions led to his collaboration with Jay
Johnson and Peter Damiano on a proposal to be submitted to the National Science Foundation,s
Geospace Environment Modeling program.
Sep 23
Theory Group
On September 22, Francesca Poli of PPPL gave a Theory Department seminar entitled, "Stability
and performance of ITER steady stated scenarios with ITBs". Non-inductive steady state
scenarios on ITER will need to operate with Internal Transport Barriers (ITBs) in order to reach
adequate fusion gain at typical currents of 9 MA. The large pressure gradients at the location of
the internal barrier are conducive to the development of ideal MHD instabilities that may limit
the plasma performance and lead to plasma disruptions. In her talk, Dr Poli presented five fully
non-inductive scenarios with various combinations of heating and current drive sources and
plasma currents in the range of 7 to 10 MA. For each configuration, the linear, ideal MHD
stability was analyzed for variations of the Greenwald fraction and of the pressure peaking factor
around the operating point aiming at defining an operational space for stable, steady state
operations at optimized performance. It was shown that lower hybrid heating is desirable to
maintain the safety factor profile above 1.5 and that these plasmas have better performance and
more favorable MHD stability properties. Operating with moderate ITBs at 2/3 of the minor
radius leads to safety factor profiles with minimum above 2, which significantly improves
stability and extends the operational space up to and above beta_N~3.
The US-Japan Joint Institute for Fusion Theory Workshop on ``Turbulent and Neoclassical Flow
Generation and Associated Transport Dynamics=94 was hosted by PPPL on September 9-10 at
Long Branch, New Jersey. A number of PPPL researchers, graduate students and visitors
participated the workshop. Choong-Seock Chang, Luca Guazzotto, Hantao Ji, John A. Krommes,
Seung-Hoe Ku, Jong-Kyo Park, Wayne Solomon, Weixing Wang, Jinlin Xie and Stewart J.
Zweben from PPPL presented talks at the workshop.
The paper "Magnetohydrodynamic Mechanism for Pedestal Formation" by L. Guazzotto and R.
Betti was published in Physical Review Letters.
On September 11-16, Leonid Zakharov visited Max Planck Institute of Plasma Physics in
Garching. He discussed experiments with high pressure gas injection on ASDEX Upgrade and
gave presentations on "Progress in understanding disruptions in tokamaks" and "Basics of
LiWall Fusion". Topics of discussion after the talks included the halo current based
interpretation of vertical instability and diffusion based confinement regime. The recent version
of the ASTRA code was obtained from IPP.
Sep 16
Theory Group
PPPL was the host for the International Conference on Numerical Simulation of Plasmas
(ICNSP) [http://icnsp2011.pppl.gov], which took place at the Jersey Shore (Long Branch, NJ),
September 7-9. There were 125 papers presented (45 orals and 80 posters) at this biennial
conference, which covered six disciplines: Magnetic & Inertial Fusion Plasmas, Space &
Astrophysical Plasmas High Intensity Beams & Laser Plasma Interactions, Low-temperature
Plasmas, Numerical Methods & High Performance Computing, and Scientific Visualization.
There were 18 papers presented at the conference from PPPL (4 orals and 14 posters) with many
student observers from the Lab as well. W. W. Lee gave the John Dawson Prize presentation,
entitled: “Surfing the Waves: a Particle Pusher's Personal Perspective”. The organizers of the
conference were Riccardo Betti, Stephane Ethier, Wei-li Lee, and Ed Startsev. Jennifer Jones,
Barbara Sarfaty - Carl Scimeca provided the help before and during the conference.
Eun-Hwa Kim attended a meeting in Fukuoka, Japan on "Physical Processes in Non-Uniform
Finite Magnetospheric Systems---50 years of Tamao's Resonant Mode Coupling Theory" from
Sept 12-15. She presented an invited talk on Electromagnetic Ion Cyclotron Waves at Mercury.
Guoyong Fu and Nikolai Gorelenkov attended The IAEA Technical Meeting on Energetic
Particles in Magnetic Confinement Systems held on September 7-10 and the ITPA Energetic
Particles Topical Group Meeting held on Sept. 12-13 in Austin, Texas. Dr. Fu gave an invited
talk titled "Nonlinear Theory and Simulation of Energetic Particle-induced Qeodesic Acoustic
Mode" at the first meeting. He also gave a talk at the second meeting titled "M3D-K simulations
of beam-driven Alfven eigenmodes in DIII-D plasmas".
Seung-Hoe Ku gave an invited talk , entitled “Utilizing extreme scale HPC for full-f gyrokinetic
particle simulation in realistic diverted tokamak geometry ” at 22nd ICNSP at Long Branch, NJ.
Sep 9
Theory Group
On August 25, Leonid A. Zakharov gave the PPPL Theory Department seminar on the "MHD
energy principle for tokamaks", where he showed that the MHD energy principle can be
expressed in terms of magnetic field perturbations. The advantages of this representation are: (a)
a direct interface with the equilibrium codes and mitigation of the convergence problem, and (b)
the applicability to perturbed equilibrium studies for understanding the thermal quench and
schemes of runaway electron suppression during disruptions. Also, robust stability of the plasma
edge in the LiWF regime (predicted in 2005 and later confirmed by many experiments) is
evident from the new form of energy principle.
On September 6, Professor Zhengming Sheng of the Laboratory for Laser Plasmas and
Department of Physics, Shanghai Jaiotong University presented a special Theory department
seminar entitled "Charged particle acceleration and radiation from ultra-intense laser-plasma
nteractions". During his presentation, Professor Sheng summarized the basic concepts and
introduced some recent progress of his group on laser plasma acceleration and radiation. The
interaction of ultra-short intense laser pulses with plasmas has been a subject of significant
interest in the last 20 years with the invention of the CPA (Chirped Pulse Amplification) laser
technology. Such interaction shows highly-nonlinear features, where both kinetic and collective
effects for particles are important and the relativistic nonlinearity becomes significant. In
particular, the large laser field itself and the induced electrostatic fields (waves) are so high that
both electrons and ions can be accelerated quickly under different conditions. For example, it
becomes possible to accelerate charged particles to GeV energies over a short distance of a few
centimeters. Meanwhile, the interaction of such lasers with different targets can result in
electromagnetic radiation ranging from THz to gamma-rays. These particle beams and radiation
sources are collimated and are suitable for a range of applications.
COMPUTATIONAL PLASMA PHYSICS GROUP
Several staff attended the International Conference on the Numerical Simulation of Plasmas this
week in Long Branch, NJ. S. Ethier presented a poster on "Optimizing Gyrokinetic PIC Codes
for Extreme Scale Computing", and S. Jardin gave a talk on “Multiple Timescale Calculations of
Sawteeth and other Global Macroscopic Dynamics of Tokamaks”.
Sep 2
Theory Group
Dr. Wei-li Lee, has been awarded the 2011 John Dawson Prize for Numerical Simulation of
Plasmas. The award reflects on seminal contributions of Dr. Lee to the area of gyrokinetic
simulations in plasma physics. An award ceremony presenting the prize will be held during the
International Conference on Numerical Simulation of Plasmas in Long Branch, New Jersey,
September 7-9.
Riccardo Betti gave a review invited talk on hydrodynamic instabilities at the Turbulent Mixing
and Beyond meeting. The meeting took place at the Abdus Salam International Center for
Theoretical Physics (ICTP), Trieste, Italy, on August 21-28. Betti's invited talk reviewed the
theory of the Rayleigh-Taylor instability in the presence of mass ablation.
A paper titled "Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes" by
N.N. Gorelenkov, R. Nazikian and G. Kramer has been accepted for publication in Physics of
Plasmas. In this paper the authors elaborate on methods to find the solutions of the so called
RSAE (reversed shear Alfven eigenmodes) modes and its physics. These modes are known to be
among the most dangerous for fast ion confinement. The theory of their existence in a special
case when the magnetic shear profile is reversed and the value of q min is slightly above m/n
ratio is developed. With the help of MHD code NOVA the paper explains the relations of the
MHD theory to the oscillations, observed in experiments and modes obtained using kinetic
approximations.
The paper entitled "ULF Wave Absorption at Mercury" by E.-H. Kim, J. Johnson and K.-D. Lee
has been published to Geophysical Research Letter.
(see http://www.agu.org/pubs/crossref/2011/2011GL048621.shtml
COMPUTATIONAL PLASMA PHYSICS GROUP
A modular, parallel, multi-regional, implicit transport equation solver (PT_SOLVER) built over
the Plasma State and other publicly available (NTCC) libraries has been developed. It integrates
the highly nonlinear time-dependent equations for ion, and electron temperatures, and angular
momentum with implicit Newton iteration methods. The user controls choice of transport models
attached to the solver, with neoclassical models of Chang-Hinlton, and NCLASS and/or
turbulent models available. Implemented turbulent transport models include GLF23, TGLF and
ETG models. For the more expensive transport coefficient models such as TGLF, a multi-level,
communicator splitting method is used to parallelize the computation of transport coefficients
using MPI, which allows the code to run on parallel supercomputers. Once the verification
activities are concluded, this module (PT_SOLVER) will be installed as the primary transport
equation solver in PTRANSP.
PLASMA
Aug 26th
COMPUTATIONAL PLASMA PHYSICS GROUP
The MODPALEO model, containing the PALEO subroutine which calculates the electron thermal transport according to the Paleoclassical transport model of Jim Callen, et al. was added to the NTCC Modules Library, ttp://w3.pppl.gov/ntcc/. Authors: Lixiang Luo, Tariq Rafiq, Arnold Kritz, Lehigh University It was observed this summer, as a result of a careful benchmarking exercise by a student Intern, that the linear growth rate of a resistive instability calculated by M3D-C1 when using a full MHD model on an adapted mesh could be slightly different when different numbers of processors were used in the calculation. This discrepancy did not occur for a uniform mesh, or for any of the reduced MHD models. This week, we have identified that significant differences are present in certain velocity variables after the first iteration for the full MHD model when using an adapted mesh. Using this new data, we are now working with our meshing partners at the SCOREC center at RPI to identify and correct the source of this discrepancy.
Aug 19
Theory Group
Wenjun Deng of the Department of Physics and Astronomy at the University of California
Irvine, gave a Theory Department seminar entitled "Gyrokinetic particle simulations of reversed
shear Alfven eigenmode in DIII-D tokamak". In his talk, Mr. Deng presented the
electromagnetic gyrokinetic simulation model used in the gyrokinetic toroidal code (GTC) which
reduces to ideal MHD theory in the long wavelength limit. He summarized the application of the
code to the study of the reversed shear Alfven eigenmode (RSAE) (Deng et al, Physics of
Plasmas, 2010). The damping rates measured from the antenna excitation and from the initial
perturbation simulation were found to agree very well. The RSAE excited by fast ions showed an
exponential growth. The finite Larmor radius effects of the fast ions were found to significantly
reduce the growth rate. With kinetic thermal ions and electron pressure, the mode frequency
increased due to the elevation of the Alfven continuum by the geodesic compressibility. For
simple geometries with concentric-circular flux surfaces and large aspect ratio, the non-existance
of the RSAE when the parallel equilibrium current is taken into account (as derived from ideal
MHD theory) was confirmed. In a realistic geometry, the RSAE can exist even in the presence of
equilibrium current due to toroidal coupling and other geometric effects. Simulations of the
DIII-D discharge 142111 near 750ms showed that the RSAE exists even without fast ion drive.
The mode structure, frequency, and growth rate obtained from GTC simulations are close to
those given by GYRO and TAEFL simulations.
Jay Johnson led an international team meeting on "Plasma Entry and Transport in the Plasma Sheet" Aug 8-12 at the International Space Science Institute in Bern, Switzerland. The team discussed observational constraints on plasma entry processes at the Earth's magnetopause such as entropy, dawn-dusk asymmetries, and conservation of the electron to ion temperature ratio even when particles are heated by an order or magnitude. The international team has also been invited to write a review paper on plasma entry and transport processes. The paper entitled ULF wave absorption at Mercury by Kim, Johnson, and Lee, has been accepted to Geophysical Research Letter. The abstract is: The field line resonance at Mercury is expected to occur when the ion-ion hybrid (IIH) and/or Alfven resonance conditions are satisfied. However, the relative efficiency of wave energy absorption at these resonances has not been studied in the context of Mercurys magnetosphere. To understand the efficiency of wave absorption, we evaluate absorption coefficients at the IIH and Alfven resonances for variable concentrations of sodium and azimuthal and field-aligned wave numbers in 1D multi-ion plasmas. The results show that wave absorption is much more efficient at the IIH resonance than at the Alfven resonance at Mercury. Our results suggest that the mode conversion efficiency is sensitive to the azimuthal and field aligned wave numbers as well as heavy ion concentration ratio. Therefore, the radial profile of field-line resonances at Mercury can exhibit complex, discontinuous structure.
The paper "Magnetohydrodynamic mechanism for pedestal formation, L. Guazzotto and R.
Betti" was accepted for publication in PRL.
COMPUTATIONAL PLASMA PHYSICS GROUP
Checkpointing (for restarting a calculation) is becoming more and more critical in large scale
computation. Traditionally one file per processor is written/read, but this is not efficient or even
allowable when thousands of processes are used since every process competes for IO and there are limits on the maximum number of files allowable. ADIOS (Adaptable IO System (ADIOS) has been developed at ORNL for this purpose. It efficiently coordinates all MPI processes to
write all the checkpoint data into a single file. It also provides flexibility for processing the
checkpointed data outside of the running simulation. Jin Chen has now integrated ADIOS-1.3
into M3DC1. This resulted in significant improvements in convenience and performance,
particularly for large jobs on Hopper at NERSC.
Arnold Kritz and three others from the Lehigh U. predictive transport group visited PPPL for
discussions related to simulations performed with PTRANSP and the SWIM IPS. A number of
issues that arose in benchmarking the two codes were resolved. A planning session was held
regarding extending the SWIM IPS to include toroidal momentum transport and extending
PTRANSP to include more general particle transport. These extensions will aid in performing more extensive benchmark calculations in the future, as well as in performing more realistic simulations of ITER and other devices.
Bryan Weinstein and Jeffrey Liu completed their Science Undergraduate Laboratory Internships
under the direction of Eliot Feibush and Harry Mynick. The students developed a graphical user
interface to the Plasma Apprentice formulary developed by Harry Mynick. The user interface is
written in Java and connects to Mathematica for expression evaluation.
Parag Srivastava completed his Science Education Internship under the direction of Eliot Feibush
and Gerrit Kramer. Parag developed visualizations and analysis of the results from the SPIRAL
code. The user interface enables selection of trapped or passing particles for graphing any pair
of the 60 parameters computed by the code.
Christina Efthimion completed her PPPL Summer Internship under the direction of Stephane
Ethier and William Tang. The project consisted in exploring new algorithms to set up the
poloidal grid in PPPL's Gyrokinetic Tokamak Simulation code (GTS).
A video conference was held between Jim Conboy (JET), John Wright (MIT, PSFC) and the
PPPL TRANSP developers regarding the status and future developmental path for both serial
and parallel TORIC within TRANSP. A TRANSP specific version of TORIC is kept in a branch
of the TORIC SVN repository at IPP in Garching. The same source code is also kept in a
directory of the TRANSP SVN repository at PPPL. Plans were made for Jim Conboy to initially
synchronize the two versions of the TRANSP/TORIC source code, incorporating his own
modifications as well, and for the PPPL TRANSP developers to have direct access to the IPP
SVN repo in the future so that they could keep their SVN repo version in sync with the IPP
version. Several bug fixes were also discussed.
Stephane Ethier attended the five-day summer school on "Proven Algorithmic Techniques for
Many-core Processors" organized by the Virtual School of Computational Science and
Engineering (VSCSE). NSF-funded VSCSE is a national virtual organization whose goal is to
develop and deliver a computational science curriculum that accelerates the ability of faculty,
staff, and students to use emerging computational resources to advance science and engineering.
The lectures were delivered to several geographically-distributed sites via audio-video broadcast.
Princeton University hosted one of those sites at the Lewis library through PICSciE. The highly
technical lectures focused on algorithms and methods to efficiently program and use GPU
processors.
Aug 5
THEORY
Leonid Zakharov visited the People’s Republic of China (Wuhan, Hefei, Chengdu, Beijing) from
July 10-27. In HUST (Huazhong University of Science and Technology, Wuhan) he discussed
the possibility of installation of ITER-mimicking tiles on the local J-TEXT device for measuring
Hiro currents during plasma disruptions. Zakharov gave a presentation on "Progress in
Understanding and Simulations of Disruptions in Tokamaks". In ASIPP (Institute of Plasma
Physics of Chinese Academy of Sciences, Hefei) he proposed modification of 6 divertor target
tiles for the first measurement of Hiro currents during Vertical Disruption Events in tokamaks.
At the HT-7 data analysis workshop Zakharov gave a presentation entitled "Design Guidance for
Flowing Lithium Systems in Tokamaks", where for the first time a practical Flowing Liquid
Lithium System (developed with Peter Yushmanov) was disclosed. In SWIP (South West
Institute of Physics, Chengdu), Zakharov discussed the possibility or making a low voltage (10-
15 kV)/high current (15-20A)) Neutral Beam Source for LTX device in PPPL. Zakharov gave a
presentation to the SWIP Center for Fusion Studies on "Progress in Understanding Disruptions in
Tokamaks". Waveforms of magnetic measurements from HL-2A device in SWIP were providedto the visitor. In Peking University (Beijing), Zakharov discussed with Professor Ming-Jiu Ni the
MHD physics of the liquid metal blanket of tokamaks. Finally, Zakharov made a presentation at
the Fusion Simulation Center of Peking University on "Lithium Wall Fusion Regime and the
Next Step in Chinese Magnetic Fusion".
July 22
Theory Group
Eliot Feibush and Bill Tang attended the DOE Computational Science Graduate Fellowship Conference in Arlington, VA July 20 - 22. They presented PPPL as a DOE site where fellows can perform a laboratory practicum for students to broaden their experience beyond thesis search.
W. W. Lee gave a keynote talk in the Science Session of the TeraGrid Conference on Extreme Digital Discovery at Salt Lake City, Utah, July 18-21. The title of Lee's talk was "Kinetic Simulation of Magnetic Fusion Plasmas on High Performance Computing Platforms." The
TeraGrid project, after ten years of service to the national science and engineering community, will be succeeded by a new National Science Foundation program called XSEDE -- the Extreme Science and Engineering Digital Environment. A closer collaboration between PPPL and XSEDE in the future is to be explored.
Prof. Dmitri Uzdensky of the University of Colorado Boulder gave a Theory Department seminar entitled "Plasmoid-dominated magnetic reconnection". During his presentation, Prof. Uzdensky discussed how analytical and numerical results have illustrated that long thin
Current layers, the hallmark of the classical Sweet-Parker (SP) resistive MHD model are violently unstable to secondary tearing instability when the systems global Lundquist number S exceeds a critical value Sc ~ 104. As a result, these layers are replaced by hierarchical multiscale chains of numerous secondary islands (plasmoids; flux ropes in 3D). He presented a new conceptual analytical model of reconnection in the plasmoid-dominated regime, as well as the related recent numerical work. The model analyses the interplay of the plasmoids' production,
growth, ejection, and coalescence with the key results that (1) the global effective reconnection rate is fast, of order 0.01 of the Alfven rate, independent of S for S > Sc ; (2) the distribution of plasmoid fluxes is the inverse-square law; (3) there is a finite probability of emergence of anomalously large "monster" plasmoids that can disrupt the chain. Prof Uzdensky also described how the plasmoid hierarchy hastens the transition from collisional to collisionless limits, blurring the distinction between the two regimes.
July 8 & 15
Theory Group
R. Betti gave a theory seminar at General Atomics on "Two-Dimensional Magnetohydrodynamic Simulations of Poloidal Flows in Tokamaks and Pedestal Formation." He also taught three lectures on implosion hydrodynamics at the Summer School in high-energy density physics organized by the Fusion Science Center for Extreme States of Matter at the University of California San Diego.
CPPG Group
The subroutine "innerc" has been added to the NTCC modules library. This routine implements the solution of the inner region equations in the asymptotic matching solution for tearing modes as formulated in the 1970s by Glasser, Greene, and Johnson. The highly accurate routine follows the procedure given in Glasser, Jardin, Tesauro Phys. Fluids 27 (5), May 1984.This routine, originally written in the early 1980's has been resurrected and modernized by a graduate intern, Thomas Scaffidi, from the Ecole Normale Superieure, Paris, France. It has recently been verified both by comparing with published solutions, and also by comparing with linear tearing mode solutions from the M3D-C1 code in simplified geometry. A paper describing this benchmarking is in preparation.
July 1
Theory Group
Drs. N. Gorelenkov and N. Fisch gave lectures to the international ITER summer school held in Aux-en-Provence, France from June 20-24 to an audience of young researches and students. Two lectures focused on the recent achievements in the area of fast ion physics, their confinement, Alfven instability studies and the possibility to use them to make more efficient fusion reactor. Several other lecturers from UK, Europe, US, India and Russia were also present.
June 24
Theory Group
Professor Bruce Scott of the Max-Planck-IPP (and EURATOM Associates) presented two Theory Department seminars. In the first, entitled "Energy Consistency and Momentum Conservation in Gyrokinetics", Professor Scott briefly reviewed the modern theory of gyrokinetics where the dynamics is described in terms of a Lagrangian with canonical structure -Dependent field variables appear only in the time component. The gyrokinetic and associated field equations are derived from the same Lagrangian by varying gyrocenter coordinate positions and field amplitudes. Energetic consistency follows from the general symmetry implied by the support of the equations by the Lagrangian. The Noether theorem indicates what is conserved and both local and global conservation forms were given. The conversion from canonical to plasma momentum uses the charge conservation equation which follows from continuity. Professor Scott emphasized the specific role of the time-dependent polarization current and explained that in the plasma momentum form, the original motivation for considering higher-order drifts is removed exactly. The correspondence to the MHD momentum conservation law was also given. The results are automatically valid for any ordering since all ordering is done in the construction of the Lagrangian in the beginning and none is done thereafter.
In the second presentation "entitled "Axisymmetric Electromagnetic Gyrokinetic Computation" Prof. Scott discussed simulating the tokamak edge layer using a total-f electromagnetic gyrokinetic field theory model (FEFI) based on an "MHD Lagrangian" designed to capture shear-Alfven (reduced) MHD and equilibrium flows on a banana width scale. Dr. Scott illustrated that without collisions, the neoclassical control case determines the necessary resolution to conserve energy/momentum and also produce negligible transport. In this context "neoclassical" refers to the time scale assumption of flows in 2D divergence balance, nearly but not exactly incompressible as variations within the flux surface of all quantities is allowed. With collisions the bootstrap current is found self consistently. Professor Scott also described ongoing attempts to turn FEFI into a comprehensive equilibrium and turbulence model.
CPPG GROUP
The 2F 3D nonlinear MHD code M3D-C1 is now operational on the NERSC peta-flop system Hopper; a Cray XE6 with 153,216 computer cores. Initial benchmark run was performed with 96 processors to reproduce nonlinear sawtooth calculations performed on the PPPL computer, STIX, using a time-step dt=20 Alfven transit times. We then performed preliminary parallel scaling studies keeping the time-step fixed, but increasing both the number of finite-element nodes and the number of compute cores by a factor of 40 and the wall-clock time increased by only 40% to get to the same point in time. We had discussions with the PETSc group, the SCOREC team, and the SuperLU-dist group this week on analyzing the performance data, and expect to improve the parallel scaling performance and extend it to 10's of thousands of compute cores in the coming weeks. The higher resolution made possible by Hopper is enabling these sawtooth studies to be performed in a parameter regime that was previously inaccessible.
June 17
Theory Group
Dr. Gabriel Plunk of the University of Maryland gave a Theory Department seminar entitled "The generalized Fjortoft constraint for two dimensional gyrokinetics". In his presentation, Dr. Plunk initially summarized the result of the 1953 paper by Fjortoft, which established the simple argument for understanding the upscale transfer of energy that occurs in incompressible two-dimensional Navier-Stokes turbulence. This argument starts from the simple observation that the existence of a second quadratic invariant, "enstrophy," places a constraint on how energy can be redistributed spectrally under nonlinear interaction. This sets the stage for the famous "inverse cascade" of fluid turbulence. He then went on to explain how the gyrokinetic equation also conserves two quadratic quantities under nonlinear interactions. To isolate the effects of this property, he focused on the simple limit: the electrostatic two-dimensional gyrokinetic equation, with a homogeneous equilibrium. He showed that the relationship between the two invariants establishes a simple constraint on spectral transfer, in analogy to that of 2D Navier-Stokes turbulence. However, in the gyrokinetic case, the inverse transfer of energy (appropriately defined) is only one possible outcome. If suitably driven, a constrained dual forward cascade can also occur, revealing the possibility that large scales can be "forcibly" damped by fluctuations at much smaller scales. Dr. Plunk also discussed the consequences for zonal flows and other features of realistic saturated turbulence.
W. W. Lee gave a seminar, entitled "Recent Development in Gyrokinetic Theory and Simulation," at the Department of Physics and Astronomy, University of California at Irvine, last week. In his talk, three related topics in gyrokinetic theory and simulation were addressed: 1) The recent concern related to the validity of the gyrokinetic Vlasov--Poisson equations used in most of the existing gyrokinetic codes in the community, which contained only the terms associated with the lowest order in gyrokinetic ordering parameter Ξ΅; 2) A discussion on the newly developed electromagnetic gyrokinetic formulation for finite-Ξ² plasmas; 3) A demonstration of the new two-wieght PIC scheme, which could enable us to carry out simulations using first the Ξ´f scheme to minimize the intrinsic noise in PIC codes at the start of the simulation and gradually evolve into a full-F code in nonlinearly saturated stage of the simulation.
R. Betti served on the DOE Review Committee of the National Ignition Campaign chaired by the Undersecretary for Science Dr. S. Koonin. The two-day long review assessed the progress of the ICF program toward demonstrating thermonuclear ignition on the National Ignition Facility at Lawrence Livermore National Laboratory.
June 3
Theory Group
Professor Amita Das of the Institute for Plasma Research, Gujarat, India presented a Theory Department seminar entitled "Electron - Magnetohydrodynamic (EMHD) studies in an inhomogeneous plasma". The advent of high intensity femto-second laser pulses and the availability of fast diagnostic techniques have now made it possible that a plasma can be triggered at very fast electron time scales and its response at these fast time scales can now also be watched in considerable detail. These studies have therefore opened up an entirely new regime of studies of plasma phenomena. During her presentation, Prof. Das highlighted how these phenomena can be suitably depicted by the Electron Magnetohydrodynamics (EMHD) model, which is a simplified description for magnetized electron fluid in the presence of neutralizing stationary background ions. The model has been recently generalized (G-EMHD) to incorporate plasma density inhomogeneity and the salient features of his advanced version were discussed. Simulations using the G-EMHD model demonstrate the possibility of maneuvering the propagation and evolution of an electron current pulse in the plasma by an appropriate choice of plasma density inhomogeneity. Specifically, regions of high plasma density can trap electron current pulses, thereby providing a basis for a plasma tweezer like device for electron currents. The plasma inhomogeneity also helps in collimating and guiding the electron current pulses. Furthermore, the location of electron energy deposition in plasma medium can be maneuvered by an appropriate choice of the plasma density inhomogeneity and the relevance of this to the fast ignition scheme for laser fusion was discussed. A variety of PIC simulations, as well as several experimental observations, provide sufficient evidence in support of the mechanism presented based on the G-EMHD studies.
May 27
Theory Group
Riccardo Betti gave the Physics Colloquium at the University of California Los Angeles. His talk entitled "Conventional and Advanced Thermonuclear Ignition in Inertial Confinement Fusion" covered the essential physics of inertial fusion and the high-gain schemes for inertial fusion energy.
Professor Allen Boozer of Columbia University presented a Theory Department seminar entitled "Reconnection in Naturally Arising Magnetic Fields". During his presentation, Professor Boozer emphasized the distinction between reconnection processes in laboratory plasmas and naturally occurring systems. He discussed how the fundamental questions of reconnection theory are why is the observed dissipation of the magnetic field sometimes enhanced by ten or twenty orders of magnitude from its characteristic value and what is the trigger for the enhanced dissipation. Electrodynamics provides an answer-the exponential increase in the separation between neighboring magnetic field lines. In toroidal magnetic configurations with small islands this exponentiation occurs only near the X-points of the islands, though it occurs almost everywhere in regions of stochastic field lines. In naturally occurring magnetic structures X-points and islands are ill defined, but neighboring magnetic field lines generically change their separation by a factor of exp(S) within a segment of the magnetic system of length L. The exponentiation S is easily calculated field-line-by-field-line in any bounded region in which a magnetic field is known-for example in a numerical simulation-and S evolves even when the magnetic evolution is dissipationless. The exponential increase in the separation implies an exponential increase in derivatives across the magnetic field of quantities that vary slowly along the magnetic field lines. Some dissipative mechanisms are proportional to these derivatives squared, so the dissipation becomes exponentially large, proportional to exp(2S). Reconnection is naturally triggered in regions in which S ~ 20.
May 20~
Professor Alan Brizard of Saint Michael's College gave a Theory Department seminar entitled "On the Noether Derivation of the Gyrokinetic Energy-Momentum Conservation Laws". The variational formulation of the nonlinear gyrokinetic theory is based on a Lagrangian density that depends on the gyrocenter Vlasov distribution and the perturbed electric and magnetic fields. According to the Noether Theorem, the energy-momentum conservation laws are associated with symmetries of the gyrokinetic Lagrangian density with respect to time and space translations. During his seminar Prof. Brizard presented a tutorial on the Noether method and its applications in plasma physics illustrating the derivation of the exact energy-momentum conservation laws for the gyrokinetic Vlasov-Poisson equations with particular reference to the axisymmetric tokamak geometry (Brizard and Tronko, Physics of Plasmas, submitted 2011). Future work will extend this analysis to the electromagnetic case.
On May 15-19, 2011 Dr. Leonid E. Zakharov attended the 15th International Conference on Emerging Nuclear Energy Systems, San Francisco, CA. He gave a talk on "Fission-Fusion Research Facility
(FFRF) as a Practical Step Toward Hybrids" where potential burning plasma regimes for the next step device in China were described.
Dr. Harry Mynick presented a talk for the weekly 3D Task Force Meeting entitled "Transport simulations for the DIII-D double-null experiments". The talk is focused on transport assessments and was done in collaboration with Neil Pomphrey.
Drs. Hank Strauss of HRS Fusion and Roberto Paccagnella of Consorzio RFX concluded a two-week visit to PPPL in which they collaborated with Josh Breslau and Steve Jardin on expanding the ability of the free-boundary version of the M3D code to perform disruption studies for ITER.
May 13~
Theory Group
Andras Pataki of the Courant Institute of Mathematical Sciences (CIMS) at New York University gave a Theory Department seminar entitled, "Rapid Evaluation of the Fokker-Planck Collision Operator". In his presentation, he described a new high accuracy solver (developed in collaboration with L. Greengard) for the collision term in the Fokker Planck equation. This equation, which describes the evolution of the plasma over time, has a nonlinear term representing the collisions of various species of the plasma. Current plasma edge simulations do not take this collision effect into account, because of the difficulties in the accurate evaluation of this term. Using the Rosenbluth potential formalism, the collision operator can be written in terms of solutions of a Poisson and a biharmonic free space PDE. Due to the inherent axisymmetry of the input data, cylindrical coordinate solvers are preferred for efficient computation. Standard numerical techniques (based typically on finite differences and finite element approximations) encounter difficulties in achieving high order accuracy, especially in the computation of derivatives of the solution (required in the collision operator formulation), and in imposing radiation conditions at infinity. In his presentation, Mr Pataki illustrated that the new solver achieves arbitrary order accuracy in cylindrical coordinates based on a combination of separation of variables, Fourier analysis and the careful solution of the resulting radial ODE. A weak singularity arises in the continuous Fourier transform of the solution that can be handled effectively with special purpose quadrature rules and spectral accuracy can be achieved in derivatives without loss of precision.May 6~
Theory Group
Professsor Grame Ackland, FRSE and Head of Institute for Condensed Matter and Complex Systems School of Physics at the University of Edinburgh visited PPPL and Princeton University on May 3 for discussions on the G8 Exascale Project in Fusion Energy, for which he is the lead PI. Professor Ackland was hosted by Bill Tang, who is the US PI for this international HPC collaboration involving the US (Princeton University with hardware access at Argonne National Laboratory), EU [UK, France, Germany (with hardware access at the Juelich Supercomputing Center)], Japan, and Russia. The National Science Foundation (NSF) administers these awards in the US with the relevant announcement at: http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=1128080Professor Ackland had productive discussions with S. Ethier and D. Stotler at PPPL and also with Professor Emily Carter of Princeton University.
A paper titled “Generalized Courant–Snyder theory and Kapchinskij–Vladimirskij distribution for high-intensity beams in a coupled transverse focusing lattice” by Hong Qin and Ronald C. Davidson has been published on Physics of Plasmas. http://link.aip.org/link/doi/10.1063/1.3574919 . In this paper, the Courant–Snyder (CS) theory and the Kapchinskij–Vladimirskij (KV) distribution for high-intensity beams in an uncoupled focusing lattice are generalized to the case of coupled transverse dynamics. The envelope function is generalized to an envelope matrix, and the envelope equation becomes a matrix envelope equation with matrix operations that are noncommutative. In an uncoupled lattice, the KV distribution function, first analyzed in 1959, is the only known exact solution of the nonlinear Vlasov-Maxwell equations for high-intensity beams including self-fields in a self-consistent manner. The KV solution is generalized to high-intensity beams in a coupled transverse lattice using the generalized CS invariant. This solution projects to a rotating, pulsating elliptical beam in transverse configuration space. The fully self-consistent solution reduces the nonlinear Vlasov-Maxwell equations to a nonlinear matrix ordinary differential equation for the envelope matrix, which determines the geometry of the pulsating and rotating beam ellipse. These results provide us with a new theoretical tool to investigate the dynamics of high-intensity beams in a coupled transverse lattice. A strongly coupled lattice, a so-called N-rolling lattice, is studied as an example. It is found that strong coupling does not deteriorate the beam quality. Instead, the coupling induces beam rotation and reduces beam pulsation.
Ten members of the Theory Department attended the International Sherwood Theory Fusion Conference, May 2-4 in Austin, Texas. Invited and review talks were given by: John Krommes (Review), "The History and Present Status of Gyrokinetic Theory'', Weixing Wang (invited), "Gyrokinetic Turbulence Driven Plasma Flow and Origin of Empirical Scalings of Intrinsic Rotation in Tokamaks" and Roscoe White (invited), "Particle Distribution Modification by MHD Modes". Posters were presented by: Steve Jardin, "First Non-Linear 3D Results From the M3D-C1 Code", Janardhan Manickam, "Kink Dynamics and Halo Currents During VDEs", W.W. Lee, "On Darwin Gyrokinetics", Joshua Breslau, "A Method for Reconstructing Equilibrium Energetic Particle Distributions from NUBEAM", Leonid Zakharov, "Understanding Disruptions in Tokamaks" and Stuart Hudson, "Computation of Non-Axisymmetric Equilibria using a partially-relaxed,partially-constrained MHD equilibrium model". Luca Guazzotto, who is visiting the Theory Department from the University of Rochester, presented three posters; "Poloidal Flows in Tokamaks and MHD Pedestal Formation" by L. Guazzotto and R. Betti; Supersonic Equilibria with Minimized Poloidal Viscosity ("inviscid equilibria") by R. Betti and L. Guazzotto and "A Comprehensive Model for the Kinetic Linear Stability of Axisymmetric Plasmas", by L. Guazzotto, R. Betti, J. Berkery, and S. Sabbagh.
The members of the SciDAC Center for Extended Magnetohydrodynamic Modeling met on May 1, at the Sherwood Meeting Hotel to report on the progress on MHD modeling. The presentations have all been posted at: http://w3.pppl.gov/cemm/Sherwood2011/index.htm. This is the tenth consecutive year that CEMM meetings have been held in conjunction with both the APS DPP and Sherwood Theory meetings.
PPPL Graduate student Katy Ghantous, advised by Nikolai Gorelenkov, and working on the quasilinear theory due to Alfvenic instabilities, received a Sherwood student poster award.
April 30~
Theory Group
Dr. Jack Berkery from Columbia University/PPPL, gave a seminar entitled, "Resistive Wall Mode Kinetic Stability Theory Advancements for Refined Comparison With Experiments" on April 28. He presented the theory of RWM stabilization that invokes kinetic effects as energy dissipation mechanisms. In particular, rotational resonances between the mode, the plasma rotation, and thermal particle motions have been shown to explain RWM instability at intermediate rotation in NSTX. The inclusion of energetic particle effects refined the qualitative agreement between computed RWM marginal stability points and experimental results. He showed that it is important to take into account the anisotropy of neutral beam injected energetic ions to correctly account for their stabilizing effects. He also outlined the role of collisions in both dissipating the mode energy and also in damping the resonant kinetic effects. In future devices with lower collisionality, it is important to avoid unfavorable plasma rotation profiles through rotation control or active mode control.
Harry Mynick presented the Plasma Physics Seminar at the University of Wisconsin, entitled "Reducing Turbulent Transport in Toroidal configurations through shaping", on work done in collaboration with Neil Pomphrey and Pavlos Xanthopoulos (IPP-Greifswald).
COMPUTATIONAL PLASMA PHYSICS GROUP
The PPPL CPPG supports TRANSP run production on PPPL servers, for tokamak simulation. TRANSP jobs can be submitted from numerous sites around the world; there are currently over 115 registered users. The PPPL Linux server cluster has recently seen high levels of TRANSP/PTRANSP simulation activity. On many occasions, the total count of concurrent runs has exceeded 60, which includes many low-N MPI simulations. A recent snapshot (Thursday April 28) showed 61 runs, including 1 with 16 processors, 2 with 8 processors, 46 with 4 processors, and 12 serial jobs for a total of 228 processors concurrently engaged in TRANSP/PTRANSP production computing.
Stephane Ethier completed a two-week visit to IPP in Garching, Germany, to work with Dr. Bruce Scott on incorporating a series of specialized diagnostics into the global gyrokinetic PIC code GTC-P. The diagnostics, developed by Dr. Scott, are being used in gyrofluid and continuum gyrokinetic codes for studying the macroscopic characteristics of plasma microturbulence under various conditions. The implementation of those diagnostics into GTC-P will allow for direct code comparison and validation with experiments. This work is being carried out as part of a PPPL INCITE project
April 15th~
Theory Group
Several members from the Theory Department attended the 2011 Joint EU-US Transport Task Force Meeting, April 6-9 in San Diego, California. Guo-Yong Fu gave a talk titled "M3D-K simulations of beam-driven Alfven modes in NSTX" at the Energetic Particle Working Group Session, Jianying Lang gave an oral presentation entitled " M3D-K simulation of beam-driven Alfven eigenmodes in DIIID ", Harry Mynick presented a paper, entitled "Reduced turbulent transport in toroidal configurations through shaping", on work done in collaboration with Neil Pomphrey and Pavlos Xanthopoulos (IPP-Greifswald), Daren Stotler presented a poster entitled "Consistent Recycling in a Coupled Kinetic Plasma - Neutral Transport Code". Daren Stotler also participated in the Edge Coordinating Committee meeting at the same venue on April 5, Weixing Wang gave an oral presentation on "Electrostatic Turbulence Driven Plasma Current".April 8th~
Theory Group
Dr. A. Reiman gave a talk at the DIII-D task force meeting on March 30 describing Theory Department plans for applying stellarator codes to analysis of 3D DIII-D ELM suppression experiments. The STELLOPT code will evaluate a number of properties, including 3D ballooning stability and macroscopic stability. This will make use of the TERPSICHORE code, and will be done by N. Pomphrey in collaboration with A. Turnbull at GA and A. Cooper at CRPP, Lausanne, Switzerland. The ORBIT Monte Carlo code, developed by Dr. R. White, will be used by Dr. Pomphrey and Dr. H. Mynick to calculate 3D effects on neoclassical ion confinement.
The GENE gyrokinetic code will be used by Dr. Mynick to obtain information on the effect of the 3D fields on turbulent transport. The PIES code, which can calculate equilibria with islands and stochastic regions, will be applied by S. Lazerson, A. Reiman and D. Monticello.
A paper titled "Onset and Saturation of a Non-Resonant Internal Mode in NSTX and Implications for AT modes in ITER" by J.A. Breslau, M.S. Chance, J. Chen, G.Y. Fu, S. Gerhardt, N. Gorelenkov, S.C. Jardin, and J. Manickam has been accepted for publication in Nuclear Fusion. The article describes numerical modeling work performed with M3D and Several other PPPL codes that helped to elucidate the origin of an unexplained tearing mode that had been observed in NSTX. It arises from a non-resonant ideal MHD mode with toroidal mode number n=1 that is destabilized in the low shear equilibrium as the central safety factor approaches one. Nonlinear simulation demonstrates that this mode can lead to saturated 2,1 magnetic islands, as seen in the experiment.
April1st~
THEORY GroupThe letter "Drift-Kinetic Studies of Neoclassical Poloidal Rotation with Finite Orbits" [PPCF 52, 123001 (2010)] by R. A. Kolesnikov, W. X. Wang, F. L. Hinton (UCSD), G. Rewoldt and W. M. Tang was chosen as one of 25 research articles for the 2010 Highlights of Plasma Physics and Controlled Fusion. This letter reports a significant discrepancy of poloidal velocity from conventional theoretical predictions found in global neoclassical simulations with the GTC-NEO code. The difference is identified as being due to the presence of large ion orbits. In the case of a large aspect ratio tokamak configuration with steep toroidal flow profiles, a novel heuristic theory which estimates this nonlocal effect is presented. The dominant nonlocal mechanisms captured by the theory are associated with ion parallel flow modification due to the steep toroidal flow and radial electric field profiles. The carbon poloidal velocity observed in simulations with experimentally relevant parameters is in good agreement with the neoclassical theory modified by the newly identified nonlocal effects.
COMPUTATIONAL PLASMA PHYSICS GROUP
As had been requested by users, LSC in TRANSP has been upgraded to support multiple Lower Hybrid RF couplers running at different frequencies. There can be up to three couplers. This removes a restriction from an earlier version of the code that only allowed a single frequency of Lower Hybrid RF current drive to be present in a simulation. Details are available in the "TRANSP help" user documentation linked at the TRANSP website http://w3.pppl.gov/TRANSP. To access this feature please use the "tshare" production version of the code.
Stephane Ethier conducted a mini-course entitled "Introduction to Parallel Debugging", hosted by the Princeton Institute for Computational Science and Engineering (PICSciE). The mini-course, attended by both graduate students and researchers, introduced the Princeton University participants to different approaches to tackle the task of parallel debugging, including the use of advanced parallel debuggers, such as Totalview and DDT.
March 25th~
On March 22 Luca Guazzotto, who is long term visitor of the Theory Department from University of Rochester, gave a seminar at NYU entitled, "Equilibrium and Time-Dependent Simulations of Two-Dimensional Magnetohydrodynamic Tokamak Plasmas with Flow". The seminar is based on his recent work on this topic together with Riccardo Betti. In the talk, Dr. Guazzotto showed how transonic poloidal flows at equilibrium can only exist in the presence of tangential discontinuity in the density and velocity profiles, and how a static plasma will automatically develop discontinuous profiles if it is made to spin in the poloidal direction, regardless of the shape of the momentum source.Professor David Knudsen of the University of Calgary (and on leave at the NASA Goddard Space Flight Center) presented a Theory Department seminar entitled, "Auroral Arc Theories - The Missing Link". In his presentation he summarized the basic properties of auroral arcs and several of the proposed theories to account for their formation. In-situ and optical observations of visible auroral arcs - the most common pre-midnight auroral form - place tight restrictions on candidate theories. For example, electron energies within inverted-V arcs can reach 20-30 keV; these energies vary characteristically and often symmetrically with latitude; they have typical widths of order 20 km; they are highly elongated in longitude; they can occur as far south as the inner edge of the plasma sheet and as far north as the polar cap (though at lower energies); they often appear in multiple parallel sets of two to five or more; and although they sometimes oscillate, more often they exist with no basic change in form for several to tens of minutes. These basic properties have been well-known for many decades, yet most auroral theories address only a small subset - often only one - and no theory accounts for them all. As a result, there remains no consensus as to the essential mechanism(s) responsible for auroral arcs. One barrier to progress is a surprising lack of statistical information on basic arc behavior. Professor Knudsen presented initial work intended to remedy this situation, and discussed the implications for theories of auroral arcs, focusing in particular on zero-frequency electromagnetic structures known as "stationary inertial Alfven waves" [Knudsen, JGR, 1996].
March 18th~
Professor Roscoe White of PPPL presented a Theory Department Seminar entitled "Modification of particle distributions by MHD instabilities". The modification of particle distributions by magnetohydrodynamic modes is an important topic for magnetically confined plasmas. Low amplitude modes are known to be capable of producing significant modification of injected neutral beam profiles, and the same can be expected in burning plasmas for the alpha particle distributions. Flattening of a distribution due to phase mixing in an island or due to portions of phase space becoming stochastic is a process extremely rapid on the time scale of an experiment but still very long compared to the time scale of guiding center simulations. In his presentation, Prof. White introduced a new method of determining domains of phase space in which good KAM surfaces do not exist, giving exact resonance locations and island widths. The method was used for quickly finding the evolution of the particle distribution without carrying out a full guiding center simulation. As examples, profile flattening due to particle avalanche caused by island overlap and large scale flattening of a beam distribution in DIII-D due to a large spectrum of low amplitude TAE modes were considered.An article titled, "Characteristics of Turbulence-Driven Plasma Flow and Origin of Experimental Empirical Scalings of Intrinsic Rotation", by W. X. Wang, T. S. Hahm, S. Ethier, G. Rewoldt, W. M. Tang, W. W. Lee and P. H. Diamond (UCSD), has been accepted for publication in Physics of Plasmas. This paper details the global gyrokinetic simulation results of turbulent stress driven toroidal flow in understanding possible mechanisms for intrinsic rotation. Toroidal plasma flow driven by turbulent torque associated with nonlinear residual stress generation is shown to recover the observed key features of intrinsic rotation in experiments. Specifically, the turbulence-driven intrinsic rotation scales close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing empirical scaling obtained from a large experimental data base. The effect of magnetic shear on the symmetry breaking in the parallel wave number spectrum is identified.The origin of the current scaling is found to be the enhanced k// symmetry breaking induced by increased radial variation of the safety factor as the current decreases. The physics origin for the linear dependence of intrinsic rotation on the pressure gradient comes from the fact that both turbulence intensity and the zonal flow shear, which are two key ingredients for driving the residual stress, are increased with the strength of the turbulence drives, which are R/LTe and R/Lne for the collisionless trapped electron mode (CTEM). Highlighted results also include robust radial pinches in toroidal flow, heat and particle transport driven by CTEM turbulence, which emerge ``in phase", and are shown to play important roles in determining plasma profiles. Also discussed are experimental tests proposed to validate findings from these gyrokinetic simulations.
A paper "A Gyrokinetic Collision Operator for Magnetized Lorentz Plasmas" by Chang Liu, Hong Qin, et al is published in Physics of Plasma, 18, 032502 (2011). The first author, Chang Liu, is an incoming graduate student of the graduate program in plasma physics at PPPL. A gyrocenter collision operator for magnetized Lorentz plasmas is derived using the Fokker-Plank method. The gyrocenter collision operator consists of drift and diffusion terms in the gyrocenter coordinates, including the diffusion of the gyrocenter, which does not exist for the collision operator in the particle phase space coordinates. The gyrocenter collision operator also depends on the transverse electric field explicitly, which is crucial for the correct treatment of collisional effects and transport in the gyrocenter coordinates. The gyrocenter collision operator derived is applied to calculate the particle and heat transport fluxes in a magnetized Lorentz plasma with an electric field. The particle and heat transport fluxes calculated from our gyrocenter collision operator agree exactly with the classical Braginskii's result [ S. I. Braginskii, Reviews of Plasma Physics (Consultants Bureau, New York, 1965), Vol. 1, p. 205: P. Helander and D. J. Sigmar, Collisional Transport in Magnetized Plasmas (Cambridge University, Cambridge, 2002), p. 65 ], which validates the correctness of our collision operator. To calculate the transport fluxes correctly, it is necessary to apply the pullback transformation associated with gyrocenter coordinate transformation in the presence of collisions, which also serves as a practical algorithm for evaluating collisional particle and heat transport fluxes in the gyrocenter coordinates.
On March 15, Daren Stotler, Bill Davis and Greg Tchilinguirian ran the Sumo Bots competition at the New Jersey Science Olympiad State Tournament. Each of the 22 teams participating in Sumo Bots designed and built a robot, the primary objective of which was to push the opponent's robot out of the ring. Abe Massry (Wind Power), Ninaad Desai (Sound of Music) and Stephen DeLuca (Technical Problem Solving) helped run other events at the Tournament.
March 11th~
Dr. Bedros Afeyan of the Polymath Research Inc. gave a Theory Department seminar entitled, "Optimal Control of Laser-Plasma Instabilities in Plasmas Using STUD Pulses". If STUD pulses (Spike Trains of Uneven Duration or Delay) are used instead of continuous laser illumination of the plasma, and the laser pulses become "on" for a few inverse growth rates of the fastest instabilities with comparable delays or "off" times between the spikes, then it was shown that due a variety of favorable mechanisms, coherent wave-wave interaction instabilities can be kept under control. The growth of these instabilities can be kept linear and unable to turn into runaway processes as is often the case in current plasmas, such as Raman scattering on the NIF. In addition, STUD pulses allow the actual true control of crossed beam energy transfer whenever it is desired and can be disallowed when it is not desirable. This is achieved by temporal interleaving the pulse trains between cones of beams in indirect drive and in a spatially random subset of a larger number of overlapping beams in direct drive. During the presentation, theoretical and computational results were shown together with the innovative design elements of future experiments meant to validate the results.Riccardo Betti chaired the meeting of the Fusion Science Center on March 7-10 at the University of Rochester. About 50 participants from the US and Europe attended the meeting. The four day meeting included overview talks on the FSC activities and a three day topical session on Shock Ignition inertial confinement fusion.
March 4th~
Professor Don Batchelor of Oak Ridge National Lab presented a special Theory Department seminar entitled "Using the SWIM Integrated Plasma Simulator for Multi-physics Fusion". The SWIM (Simulation of Wave Interaction with Magnetohydrodynamics) center has the scientific objectives of improving the understanding of interactions that both RF wave and particle sources have on extended-MHD phenomena, and improving the capability for predicting and optimizing the performance of burning plasmas. The center has built an end-to-end computational system that allows physics codes to be able to function together in a parallel environment and connects them to utility software components and data management systems. This framework has been used to couple together state-of-the-art fusion energy codes to produce a unique multi-physics simulation capability. In his talk, Professor Batchelor presented a physicist's overview of the Integrated Plasma Simulator (IPS) and described applications. For example, the IPS is being employed to support ITER with operational scenario studies. A computational approach to coupling MHD with RF has also been developed, and initial numerical studies of RF effects on tearing modes with reduced models have been completed. Additionally, the IPS is being used to investigate the possibility of parallelization in the time domain of plasma turbulence calculations. The wide range of simulation work-flows that can be composed using the IPS was emphasized.
Dr. Walter Guttenfelder of PPPL presented the regular Theory Department seminar entitled, "Electromagnetic Transport From Microtearing Mode Turbulence in NSTX". In this presentation, Dr. Guttenfelder summarized first-of-a-kind non-linear gyrokinetic simulations of microtearing mode turbulence using the GYRO simulation code. The physically comprehensive simulations (including kinetic ions and electrons, electromagnetic perturbations, collisionality, and toroidal flow and flow shear) use parameters from a high beta NSTX discharge. The predicted electron thermal transport is comparable to experimental analysis, and it is dominated by the electromagnetic contribution of electrons free streaming along stochastic magnetic field line trajectories. The structure of the turbulence is distinctly different from traditional tokamak turbulence and initial ideas for experimentally diagnosing such characteristics, and the associated transport, were additionally presented.
Leonid E. Zakharov participated in a two day workshop on "Stationary Fusion Neutron Sources" in Kurchatov Institute (Moscow) February 21-22. In his presentation, "Potential Burning Plasma Regimes for Tokamak Based VNS", he outlined the necessity of new plasma regimes for better confinement, stability and plasma-wall interaction for neutron sources based on tokamaks with a conventional aspect ratio 4 and 1 m thick blanket. In another presentation "ASTRA-ESC simulations for the LiWF regime in a Compact FNS-ST" he revealed a possibility of a very attractive "hot-ion" regime with Ti >3Te for a small plasma configuration R/a=0.5/0.3 with P_DT=0.2-0.8 MW.
Peter Damiano attended the American Geophysical Union Chapman conference on "The Relationship Between Auroral Phenomenology and Magnetospheric Processes" in Fairbanks Alaska (Feb 27 - Mar 4) and gave an oral presentation entitled "Characteristics of current saturation and electron energization in simulations of global scale Alfven waves".
Dr. Ilya Dodin of Princeton University, gave a Theory seminar entitled, "Ponderomotive Forces, Wave Dispersion, and Action Conservation" on March 3. His talk focused on two types of adiabatic effects. First is fundamental properties of nonlinear forces on particles due to waves and second is the particle influence on waves. He presented the derivation of a general nonlinear dispersion relation for arbitrary stationary waves in plasma, which includes the kinetic effects without solving the Vlasov equation and the frequency shifts due to trapped particles. He finally showed the application of adiabatic conservation laws to plasmas undergoing densification in various contexts. Existing results pertaining to slow transformation of linear waves in such plasmas are generalized and corrected.
The paper " Nonlinear Simulation of Toroidal Alfven Eigenmode with Microturbulence-induced Radial Diffusion" by Jianying Lang and Guo-Yong Fu, has been accepted for publication in the Physics of Plasmas. The abstract reads as follows: "It is shown analytically and numerically that microturbulence-induced diffusivity can affect nonlinear saturation of energetic particle driven modes in the similar way as collisional pitch angle scattering does. Introducing a simple diffusion operator to the code, our numerical results have shown that a single Toroidal Alfven Eigenmode (TAE) can saturate at a steady state with sufficiently high diffusion rate. The calculated saturation level scales with the radial diffusion rate by the same scaling of pitch angle scattering. A criterion is derived to judge the importance of microturbulence-induced radial diffusion effect comparing to the collisional pitch angle scattering effect. According to the criterion, we find that the micro-turbulence induced diffusion has a stronger effect than the Coulomb collision on the TAE saturation in present tokamak devices and future burning plasmas (ITER)".
February 18, 2011
THEORY GROUP
Riccardo Betti was a member of the DIII-D Program Advisory Committee that met at General Atomics on February 15-17. The PAC reviewed the DIII-D experimental and theory programs and made recommendations to the DIII-D team.
John Krommes was nominated Outstanding Referee for Physical Reviews and Physical Review Letters. Initiated in 2008, the Outstanding Referee program expresses appreciation for the essential work that anonymous peer reviewers do for APS journals. Each year a small percentage of 45,000 active referees are selected and honored with the Outstanding Referee designation. Selections are made based on the number, quality, and timeliness of referee reports as collected in a database over the last 23 years. The program recognizes about 150 referees each year.
Professor George Tynan of the Department of Mechanical and Aerospace Engineering at the University of California at San Diego (UCSD) gave a Theory department seminar entitled "Turbulent momentum transport in magnetized plasmas: results from linear devices and thoughts for studies on toroidal confinement devices". Turbulent momentum transport is thought to play an important role in the formation of sheared ExB flows in confined plasmas and thus may be a key piece of important macroscopic transport phenomena such as critical gradient behavior and transport barrier formation. In addition, recent experiment and theory suggest it may play a crucial role in the formation of so-called "intrinsic rotation" in confined plasmas, where the plasma acquires a net rotation in the absence of external momentum input. Thus turbulent momentum transport studies are of fundamental importance for magnetic fusion. In his presentation, Professor Tynan provided an overview of studies of turbulent momentum transport in a linear plasma device. Using a mixture of multi-point probe studies, digital signal processing techniques and fast imaging diagnostics, he showed how coherent drift waves transition into a turbulent spectrum, and how coherent sheared zonal flows arise from the turbulence during this transition. The results showed the key role that turbulent symmetry breaking plays in the formation of large scale ordered flows out of turbulence, and suggested several laboratory and confinement device experiments.
Five members of the Theory Department participated in the FSP planning workshop from February 8-11 in San Diego: Daren Stotler, Doug McCune, Guo-Yong Fu, Weixing Wang, and Allan Reiman.
COMPUTATIONAL PLASMA PHYSICS GROUP
Stephane Ethier participated in the "Juelich Blue Gene/P Extreme Scaling Workshop" held at the Juelich Supercomputing Center in Juelich, Germany. The purpose of the three-day workshop was to give application teams an opportunity to scale their code across the full Blue Gene/P system JUGENE, which consists of 72 racks with a total of 294,912 cores - the highest number of cores world-wide. The benchmark version of the gyrokinetic kinetic particle-in-cell code GTC successfully ran on the full system, pushing over 14 billion particles per second per time step. The test run used 95 billion particles.
February 11, 2011
THEORY
Professor Bruno Coppi of MIT gave a Theory department seminar entitled, "Attractive Properties of the I-Confinment Regime and Interpretation: Relevance to the Ignitor Experiment". In his presentation he summarized the theoretical model (Coppi et al., PRL, 17, 1966, 377-379) that can account for the characteristics and effects of the plasma mode around 200 kHz that is excited in connection with the onset of the I Confinement Regime. The mode is associated with the presence of a heavy particle (impurity) population near the edge of the plasma column and the theory correctly predicts the direction of the mode phase velocity (that of the electron diamagnetic velocity). The driving factor for the mode is the temperature gradient of the main ion population combined with the finiteness of the impurity population temperature. The main effects of the mode is to transport the impurity population outward (increasing their density gradient) and the main ion population inward while allowing an outward flow of the thermal energy of the hotter plasma. This characteristic of impurity confinement makes the confinement regime of particular interest for experiments aimed at producing plasmas close to ignition conditions. In the last part of his talk, Professor Coppi presented an overview of the Ignitor experiment (to be constructed in Russia) that will be able to expand on experiments studying the I-Mode Confinement Regime that have been conducted with the Alcator C-Mod experiment at MIT.
February 4, 2011
THEORY GROUP
Professor C.Z. (Frank) Cheng of National Cheng Kung University in Taiwan, gave a Theory seminar entitled, "Observation Features and Physical Mechanisms of Substorms". Professor Cheng started his presentation by giving an overview of the space plasma physics related research efforts currently underway (and under development) at Cheng Kung University. He then presented his official seminar summarizing the observational characteristics and physical mechanisms behind magnetospheric substorms. In particular, he highlighted the fine structure observed in the onset arc and the associated magnetic fluctuations evident in the Pi1 and Pi2 frequency ranges (as measured from ground based magnetometers) and their exponential growing behaviors evident before the onset of the substorm expansion phase. He discussed the kinetic ballooning instability as a possible physical mechanism for substorm onset in the magnetosphere and the formation of the auroral breakup arc in the ionosphere. He also presented the nonlinear evolution of the onset arc breakup and magnetic fluctuations into turbulent states, the current disruption and magnetic field dipolarization processes and the dispersionless particle injection during the expansion phase.
COMPUTATIONAL PLASMA PHYSICS GROUP
A new version of ElFresco, the full-wave reflectometer simulation code, has been released by Ernest Valeo, Gerrit Kramer, and Eliot Feibush. The model of the transmitter antenna has been expanded so users can specify a 2-D array for the incident electric field. Visualizations have been added for the incoming and outgoing data in the paraxial region. Both plasma profile and wave field data can be displayed with a variety of presentation types: color map plots, contour plots, indexed plots, and surface plots. Managing and monitoring simulation runs has also been improved.
A new capability for modeling electron cyclotron heating and current drive ( ECRH and ECCD) has been added to the TSC code. All heating systems, NB, ICRH, LH, and ECRH can now be applied in a single simulation run. For each of these, the user has the choice of using the internal TSC model for heating and current drive, or using a more detailed model through the SWIM IPS (or a coupled LSC calculation for LH).
January 28, 2011
Theory Group
A paper titled, “Trapped Electron Mode Turbulence Driven Intrinsic Rotation in Tokamak Plasmas”, by W. X. Wang, T. S. Hahm, S. Ethier, L. E. Zakharov and P. H. Diamond, has been accepted for publication in Physical Review Letters. In this letter, recent progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported with emphasis on electron thermal transport dominated regimes. The turbulence driven intrinsic torque associated with nonlinear residual stress generation by the fluctuation intensity and the intensity gradient in the presence of zonal flow shear induced asymmetry in the parallel wave number spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current. These results qualitatively reproduce empirical scalings of intrinsic rotation observed in various experiments. The origin of current scaling is found to be due to enhanced k// symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The physics origin for the linear dependence of intrinsic torque on pressure gradient is that both turbulence intensity and the zonal flow shear, which are two key ingredients for driving residual stress, increase with the strength of turbulence drive, which is R0/LTe and R0/Lne for the trapped electron mode.
On January 25, Daniel Raburn defended his Ph.D. thesis, which was done under the supervision of A. Reiman and D. Monticello and with the collaboration of E. Fredrickson and R. Samtaney. The work implemented a Jacobian-Free Newton-Krylov scheme for converging the PIES 3D equilibrium code. The new scheme was found to be about an order of magnitude faster than the Picard algorithm that had previously been used. The modified code was applied to calculate the saturated island widths for neoclassical tearing mode (NTM) experiments in the TFTR tokamak where the island width was carefully measured. The calculations were found to agree with the experimental data within the error bars.
CPPG Group
A highly simplified model for density prediction has been demonstrated in PTRANSP, using a Plasma State based solver. The model, which uses a prescribed density profile shape and a two parameter 0d scaling, was implemented to develop and test PTRANSP's capability to receive a
density solution from a portable solver module coded without dependence on PTRANSP internals.
January 21, 2011
THEORY GROUPDr. Peter Porazik of the University of California at Irvine presented a Theory Department seminar entitled, "Gyrokinetic Particle Simulation of the Drift Compressional Modes in the Magnetosphere". In the presentation, he summarized the development of a global gyrokinetic particle-in-cell simulation model that has been successfully verified against the shear Alfven wave, ion acoustic wave and the drift compressional wave. A numerical scheme has been developed for gyrokinetic simulations of low frequency compressional modes to study the linear and nonlinear properties of the drift compressional mode. Linear gyrokinetic simulations were performed to investigate the effects of the kinetic ions and finite Larmor radius (FLR) on the frequency and growth rate. It was found that FLR effects reduce the linear growth rate significantly but change little the real frequency. Global simulations were also conducted to resolve the structure of the perturbation along the equilibrium magnetic field and it was found that the global eigenmode structures are even along the field line and broadened by the FLR effects in the radial direction.
COMPUTATIONAL PLASMA PHYSICS GROUP
The M3D-C1 code project has met a major developmental milestone in that it has performed its first 3D fully nonlinear tokamak simulation. The calculation was of a predominantly m=1 n=1 resistive internal kink mode in non-circular (toroidal) tokamak geometry. The growth rate of the most unstable mode when in the linear regime agreed to within a few percent with a previous linear calculation. This initial demonstration calculation was done with a reduced subset of the full MHD equations with only 8 toroidal planes on stix.pppl.gov, but demonstrated that the 3D unstructured meshing, partitioning, and communication software is fully functional. The next step is to extend this to the full 2F MHD equations (which is coded but needs to be verified) and to optimize the sparse-matrix solvers to enable finer meshes. This work was done in close collaboration with the SCOREC center at RPI, and with Nate Ferraro at General Atomics (ORISE).
S. Jardin served on a review panel for the Institute of Plasma Physics (IPP) in Garching, Germany on Jan 12-14. The panel, known as the Fachbeirat, is formed by and reports to the Max Plank Society of Germany.
January 14, 2011
THEORY GROUP
Feng Wang, a graduate student from Dalian University of Technology in Dalian, China, has begun his visit to PPPL’s theory department from January 7, for 18 months. He will work with Drs. Guoyong Fu and Josh Breslau on nonlinear simulations of MHD modes and energetic particle-driven Alfven instabilities as part of his Ph.D. thesis research. Feng Wang’s visit is partly supported by a scholarship from the China Scholarship Council.Professor Chuang Ren of the Department of Mechanical Engineering at the University of Rochester presented a Theory Department seminar on January 13 entitled "Particle-in-Cell Simulations using graphics cards". Graphics Processing Units (GPU's), which are the graphics cards in most PC's and computer gaming platforms, are among the most powerful computing devices now available. In recent years, the adaption of scientific codes to harness the computing power of these chips has become an active area of research. This effort has been aided by the development of parallel computing architectures for GPU's such as CUDA (by NVIDIA). Recently, using CUDA, Professor's Ren's group has developed a Particle-in-Cell code (X. Kong et al., JCP 230, 1676, 2011) with charge conserving current deposition that can run 30-100 times faster on a GPU than on a CPU. On the NVIDIA GeForce GTX-280 graphics card, the GPU PIC code can achieve a one-particle-step process time of between 1.9 - 5.1 nanoseconds in 2D and between 5.7-21 nanoseconds in 3D, depending on plasma temperature. Besides the formulation and performance characteristics of the GPU PIC code, Professor Ren also discussed the issues they encountered in the development of the adaptation including thread assignment, reduction of algorithm branching and writing conflicts, shared memory usage and parallel particle sorting.
December 24, 2010- January 7, 2011
THEORY GROUP
W. W. Lee, as an adjunct professor at the Department of Applied Physics and Applied Mathematics, Columbia University, has just finished teaching a graduate/upper undergraduate level course on "Kinetic Theory and Simulation of Kinetic Plasmas" for the Fall Semester of the 2010-2011 academic year. The topics included: various reduced descriptions for the Vlasov-Maxwell system, wave-particle interactions, collisional effects, gyrokinetic equations and their relationship to MHD, microinstabilities and the various simulation methods for plasmas. A one-dimensional Particle-In-Cell code using MATLAB was used for the course.
Jia Zhu, a graduate student from Zhejiang University in China, has finished his eight-month long visit to PPPL Theory Department from April 23-December 23, 2010, and returned to China. During his visit, he worked with Dr. Guoyong Fu on nonlinear simulations of energetic particle-driven Alfven modes in tokamak plasmas as a part of his Ph.D. thesis studies. A reduced model code has been built where the mode structures of Alfven modes such as TAEs are fixed and mode amplitudes and phases are evolved due to wave particle interaction between energetic particles and Alfven waves. The initial simulation results compare well with NOVA-K code and M3D-K code for the linear growth rate of an n=1 TAE mode. Work is in progress to benchmark the code in the nonlinear regime and to investigate the nonlinear saturation of multiple Alfven modes driven by fast ion.
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