2005 Highlights

2006 Highlights

2007 Highlights

April 25, 2008

On April 15, 2008 Leonid E. Zakharov gave a PPPL Experimental Seminar entitled, "Where is the edge in toroidal plasmas?" The abstract follows. It is believed that, by definition, the plasma edge is the separatrix that separates the confinement zone from the convection dominated plasma periphery. Another belief is that the H-mode has a miraculous "edge transport barrier" providing a steep temperature pedestal in front of the last closed magnetic surface. Both these beliefs are in conflict with DIII-D experiments with Resonant Magnetic Perturbations. The recent discovery of unconditional instability of the so-called Wall Touching Kink Modes (and their edge version Takahashi Kink Modes) gives a basis for a self-consistent understanding of the plasma edge and its MHD activity observed in DIII-D experiments.

Dr. Yuri Petrov from Prairie View A&M University visited PPPL on
April 24-25. His visit was hosted by Dr. S. Zweben. Dr. Petrov gave
a Joint Theory/PS&T seminar entitled "Status of Rotamak program at
Prairie View." Two Rotamak devices, where the steady plasma current
is driven by applied Rotating Magnetic Field (RMF), are being
operated at Prairie View A&M University: one with a spherical and
another with a cylindrical chamber. We discuss latest experiments on
plasma reshaping in cylindrical Rotamak. During 40-ms plasma
discharge, a pulse current is briefly fed to a magnetic coil located
at the midplane (middle coil). The internal magnetic field is
scanned with pick-up coils in almost all cross-section of plasma. The
use of the middle coil allows switching from D-shape to doublet shape
plasma and back. We also compare main results of experiments in
spherical and cylindrical chambers, in particular, the structure of
self-generated toroidal magnetic field. The evidence is presented
that in Rotamak-ST case (with external toroidal magnetic field) the
mechanism of RMF penetration is different from that in Rotamak-FRC
(no external tor. field); it is more efficient due to whistler wave
excitation.

T.S. Hahm attended an International Workshop on Multiscale Methods
for Fluid and Plasma Turbulence: Applications to Magnetically
Confined Plasmas in Fusion Devices which has been held at Centre
International de Recontres Mathematiques, Marseille, France. He
presented an overview talk entitled "Gyrokinetic Description of
Tokamak Core Turbulence; Theory, Simulation, and Comparisons to
Experiments" which is based on his collaboration with GTS team, GTC
team, and NSTX team.

Dr. A. Reiman hosted a National Stellarator Physics Teleconference on
April 24. Dr. J. Talmadge from the University of Wisconsin presented
a seminar on "Experimental Tests of Quasisymmetry in HSX." The HSX
stellarator has an underlying symmetry of |B| that makes the drift
trajectories look like those in a helically symmetric field. This
property of the field has been confirmed by a study of the grad-B
drift of passing particles, by measuring the components of the field
driven by the Pfirsch-Schlueter current, and by verifying that the
bootstrap current decreases the rotational transform in the device.
The quasisymmetric field has a large effective rotational transform,
and this has been confirmed by the small drift of passing particles
from the flux surfaces, and by the consequent reduced magnitude of
the Pfirsch-Schlueter and bootstrap currents. Experiments with ECH
heating at 0.5 T have demonstrated a reduction of particle, momentum and heat transport with quasisymmetry. The experiment has been upgraded to B=1.0 T, for which the nonthermal component is small. Te up to 2.5 keV has been observed. A multimode model of the transport which uses stellarator neoclassical transport plus a modified Weiland model for the anomalous transport agrees well with the temperature profile and confinement time.

April 18, 2008

Prof. A. Boozer from Columbia University gave a Theory seminar entitled 'Perturbed Equilibria.' The response of plasmas to small external magnetic perturbations is an important issue for both the tokamak and the stellarator programs. Tokamak applications include (1) Control of magnetic field errors (errors ten thousand times smaller than the main field can cause disruptions).  (2) Control of edge localized modes (ELMs) and resistive wall modes (RWMs).  (3) Determination of the level and the effects of the toroidal torques produced by toroidal asymmetries.  Stellarator applications include: (1) Information useful for plasma and coil design.  (2) Specification of allowable construction tolerances.  (3) Assessment of intrinsic islands and magnetic surface quality.  Ideal MHD stability codes, such as DCON and CAS3D, give the fundamental information, but appropriate postprocessors for these codes are required for the applications.  Jong-Kyu Park has written and implemented IPEC, which is the required postprocessor for the DCON code, and Carolin Nuehrenberg has appropriately modified the CAS3D code.  The methods and the results will be discussed with an emphasis on the areas in which the fundamental understanding has been changed by these new computational capabilities

April 11, 2008

Theory Group

Dr. E. Startsev gave a Theory seminar entitled "Dynamics of
electromagnetic two-stream interaction processes during longitudinal
and transverse compression of an intense ion beam pulse propagating
through background plasma." To achieve maximum energy density charged particle beam must be compressed radially and longitudinally while its space-charge is neutralized by background plasma. The beam
propagating in plasma is subject to electrostatic two-stream
instability and electromagnetic Weibel instability. The electrostatic
two-stream instability may lead to longitudinal bunching of the beam
pulse and eventual longitudinal beam heating. Consequently, this
could degrade longitudinal compression of the beam. Similarly, the
electromagnetic Weibel instability may cause transverse filamentation
of the beam, which may degrade transverse compression. To achieve
stronger transverse focusing, it has been proposed to pass the beam
through a strong solenoidal magnetic field. The solenoidal magnetic
field can extend long distance away from the solenoid into the
neutralizing plasma where the beam is compressed longitudinally. In
this paper, we review how transverse and longitudinal compression
changes the dynamics of two-stream and Weibel instabilities. We also
discuss how these instabilities are modified by the solenoidal
magnetic field.

Dr. E. Belova gave a Theory seminar entitled "Numerical simulations
of NBI driven GAE modes in NSTX." Hybrid 3D code HYM is used to
investigate beam ion effects on MHD modes in a NSTX, aiming at
simulations of NSTX shots where chirping frequency GAE/CAE modes have been observed. The thermal plasma is modeled using the MHD equations, and full-orbit delta-f kinetic description is used for the beam ions. The simulations show that for large neutral beam injection velocities and strong anisotropy in the pitch-angle distribution, many Alfven modes are excited. Unstable GAEs modes for 2<n<7 and weakly unstable CAE for n>7 are observed. Scaling of the growth rate of GAE mode with beam ion density is stronger than linear due to significant
modification of plasma equilibrium profiles. Profile modification is
due to self-consistent beam ion effects, and it has indirect effect
on the stability. It was demonstrated that phase velocity of the
unstable GAE mode has opposite sign compared to the beam injection
velocity, and the resonant particles satisfy Doppler-shifted
cyclotron resonant conditions. Dependence of the growth rate on
dissipation parameters is studied. Nonlinear simulations show that
the GAE instability saturates at low amplitude.

CPPG Group

A conference call was held between the PPPL CEMM team and the RPI
SCOREC center with regard to the status of the software development
that SCOREC is performing in support of the M3D-C1 code. Items that
have been successfully completed by SCOREC included (1)
Generalization of the SCOREC adaptive meshing routines so that they
can be applied to a complex scalar field for use with the 3D
eigenmode capability, (2) Generalization of the sparse matrix solver
invoked by the SCOREC routines so that now, as an option, PETSc
iterative solvers can be called instead of the SuperLU_Dist direct
solver. This now works for the complete 8-variable model, as well as
for each of the reduced models. The primary new capability that is
under development is a generalization of the SCOREC interface
routines so that boundary conditions can be correctly applied for non-
rectangular domains. This will allow M3D-C1 to take advantage of the
extensive meshing capability that SCOREC has for complex geometries.

April 4, 2008

Theory Group

The PPPL Theory department was well represented at the 2008
International Sherwood Fusion Theory Conference held at Boulder CO,
March 31 to April 2, 2008. There were four oral presentations, by
Drs. N. Gorelenkov, J. Johnson (emeritus), and H. Qin; and by a
graduate student Jong-Kyu Park. Mr. Park was a recipient of an award
for an outstanding presentation by a graduate student. The title of
his talk was, "Tokamak plasma response to external magnetic
perturbations."

Christine Nguyen, a graduate student at the Euroatom association in
Cadarache visited PPPL on April 4. Her visit was hosted by Dr. T. S.
Hahm. Christine gave a Theory seminar entitled "Low frequency modes
triggered by fast particles in Tore-Supra." The recent observation of
MHD modes destabilized by fast supra-thermal particles in Tore-Supra
has triggered a theoretical and experimental program designed to
model those modes and understand their interaction with fast particle
populations. For the success of burning plasmas, this study is of
major importance to understand and control the confinement of alpha
particles, whose resonant interaction with MHD modes may be
detrimental for plasma yields. Two particular types of instabilities
are currently investigated in Tore-Supra, following the experimental
observations of low-frequency modes: the Beta Alfvén Eigenmode (BAE)
and the electron fishbone.

Using a variational formalism coupled to a Fourier mode
decomposition, and a gyrokinetic-MHD model for the plasma, the BAE
dispersion has been derived and found consistent with F. Zonca et al.
earlier derivation in the ballooning representation. In particular,
this derivation allows to identify Tore-Supra observed modes as BAEs
despite the ambiguity linked to the BAE/GAM degeneracy, and to
calculate a threshold for BAE destabilization. This calculated
threshold has been compared with experimental observations, using in
particular the Monte-Carlo code PION to access the fast ion
distribution function. This comparison validates the consideration of
ion Landau damping of the mode sidebands as a main damping process.

Experiments designed to study electron fishbone modes have been
conducted, and display a puzzling behavior that provides some insight
in the interaction of those modes with the supra-thermal electron
distribution. Some modes, observed with the ECE diagnostic are
consistent with the traditional characteristics of precessional
fishbone modes, and appear to be characterized by frequency jumps
associated with a fast electron phase space redistribution. This
redistribution of fast electrons is likely to lead to a modification
of the q profile, which may have an impact on transport.

Leonid Zakharov gave a talk (March 24, 26, and April 3) to Department
of Physics (UW), Nuclear Plasma and Radiological Engineering Dept.
(UI at Urbana-Champaign), and Tech-X Corporation on "Lithium Wall
Fusion and its 3 Step Program toward a Reactor Development Facility"
as a response to the Orbach/Bodman initiative for domestic fusion and
as a future program for PPPL on spherical tokamaks.

CPPG Group

S. Jardin and R. Samtaney organized and participated in the SciDAC
CPES and CEMM Meetings and the Sherwood Theory meeting this week.
Samtaney presented talks on "Updates on AMR and Fully Implicit MHD,"
"Kinetic-MHD coupled simulation of ELM cycles," and "AMR simulations
of pellet injection using a level-set approach with Cartesian grids"
and Jardin presented talks on "M3D-C1 update and new results on 2-
fluid reconnection with a guide field." Complete copies of the 20
presentations made at the CEMM meeting are available at: ttp://w3.pppl.gov/cemm under the "workshops" page.

March 28, 2008

Theory Group

Jong-Kyu Park, a graduate student at PPPL, gave a Theory seminar
entitles "Tokamak Plasma Response to External Magnetic Perturbation."
Tokamak plasmas are sensitive to external magnetic perturbations as
small as |δB|/B ~ 10e{-4} can be important. An asymmetric external
magnetic perturbation changes the plasma equilibrium, and the
asymmetry of the equilibrium current contributes to the perturbed
magnetic field. The linear Ideal Perturbed Equilibrium Code (IPEC)
finds the perturbed non-axisymmetric tokamak equilibrium with the
same p and q profiles. Often the magnetic field strength is changed
little at fixed points in space, but the wobble of the magnetic
surfaces causes a large variation in the field strength that perturbs
the action J and, therefore, the particle drift motion. The non-
axisymmetry of the equilibrium currents tends to give: (1) Strong
poloidal coupling - The magnetic perturbation tends to be locally
close to resonant with the magnetic field lines because that gives
the largest distortion in the equilibrium plasma currents. (2)
Amplification of the external perturbation - the perturbed magnetic
field can either be amplified or shielded by the perturbed plasma
current, but the most important perturbations are those that are
amplified by the non-axisymmetric distortions of the equilibrium
plasma currents. The IPEC code has (1) resolved paradoxes in error
field correction on NSTX and DIII-D (Physical Review Letters 99,
195003), (2) shown that ELM control coils in ITER could be designed
to greatly reduce asymmetries in the central plasma while producing a
strong perturbation at the plasma edge, (3) found that NSTX
experiments on rotating error fields indicate strong plasma shielding
due to the Maxwell limit on the torque. This work was a collaborative
effort, notably with Drs A. Boozer and J. Menard.

Igor Kaganovich visited UCLA and gave a talk on beam transport
through a background plasma in a magnetic field. The talk was well
received and future collaboration on experimental observation of
predicted theoretical effects is discussed.

CPPG Group

Stephane Ethier gave a mini-course entitled "Introduction to Parallel
Debugging" at Princeton University as part of the Program in
Integrative Information, Computer and Application Sciences (PICASso).
The tutorial was attended by graduate students and researchers from
many science departments.

March 21, 2008

Theory Group

Prof. Adam Burrows from Princeton University (Department of
Astrophysical Sciences) visited PPPL on March 20. His visit was
hosted by Dr. G. Hammett. Prof. Burrows presented a Theory seminar
entitled "Computational Supernova Theory." To address the theoretical
supernova explosion problem with physical fidelity requires the
development and use of sophisticated numerical radiation/hydrodynamic
codes that simulate the multi-dimensional flow in a variety of Mach-
number regimes. Though the latest simulations incorporate rotation,
multi-group radiative transfer, and magnetic fields, they are not yet
general-relativistic, do not solve the Boltzmann equation in its full
multi-D context, and are not fully 3D in space. One must eventually
do the calculations in six-dimensional phase space (plus time), and
such seven-dimensional calculations are currently beyond reach.
Nevertheless, there has been much recent progress and this progress
has been informed by numerical experiments that will only get better
in the next 3-5 years. In this talk, he discussed the latest physical
ideas in the theory of the mechanism of core-collapse supernovae and
the variety of results that have emerged from recent massive
computations. Moreover, he described what more might need to be done
to solve in credible fashion the enigma of stellar death and
supernova explosion.

Dr. A. Reiman hosted a National Stellarator Physics Teleconference on
March 20. Dr. S. Nishimura from NIFS (Japan) presented a seminar on
“Recent progress in the stellarator moment equation approach”. The
aim of this work is ultimately to provide a full calculation of the
neoclassical fluxes in stellarators. The work presented is an
extension of and further application of a formalism published in H.
Sugama and S. Nishimura, Phys. Plasmas 9 (2002). The approach
developed in that paper was compared with an earlier approach of
Taguchi, and it was shown that the new approach has the advantage
that it conserves momentum even when a truncated expansion is used
for the distribution function, so that it recovers intrinsic
ambipolarity for symmetric systems. This makes the method
particularly well suited to calculations for quasi-symmetric
stellarators. The method has been extended to include near-resonant
Fourier modes, allowing the study of physics in the neighborhood of
magnetic islands.

Dr. W. W. Lee has recently been appointed as an adjunct professor at
Columbia University and is currently teaching a course on "Kinetic
Theory and Modeling of Plasmas" in the Department of Applied Physics
and Applied Mathematics. He is the PI of Multiscale Gyrokinetics of
Plasmas, an ASCR project on Multiscale Mathematics Research and
Education. His project was invited by DOE to re-compete for the next
funding cycle.

CPPG Group

Jin Chen has sped up the production version of the M3D code being
used by J. Breslau in the sawtooth studies by a factor of 30% over
the previous versions on the NERSC Franklin computer. The improved
code, which gives identical results to the older version, takes
advantage of symmetries in the elliptic operators to give converged
solutions in many fewer iterations. We expect this improved version
to save over 1 M hours of NERSC compute hours over the course of the
year. The utilization of the symmetry properties of the operators
also paves the way for even bigger speedups once the algebraic
multigrid package HYPRE is linked into the PETSc library on Franklin.

March 14, 2008

Theory Group

On March 11, Daren Stotler and Bill Davis ran the Robot Ramble
competition at the New Jersey Science Olympiad State Tournament in
which teams of students from 24 New Jersey High Schools designed and
built a robot to pick up various objects and place them into a box.

Prof. Gennady Shvets from the University of Texas at Austin visited
PPPL on March 12-13. His visit was hosted by Dr. I. Kaganovich.
Prof. Shvets presented a Theory seminar entitled "Filamentation of
high-current beams in plasmas: physics and applications to Fast
Ignition." The filamentation (a.k.a Weibel) instability of high-
current beams propagating in background plasmas is one of the most
basic and long-studied collective plasma processes. The dynamics and
energetics of its nonlinear saturation is important for both
laboratory and astrophysical plasmas. The Weibel instability is
likely to play an important role in the Fast Ignitor scenario because
it may result in the collective energy loss of a relativistic
electron beam in both coronal and core plasma regions. Collisionless
Weibel instability has been suggested as an important mechanism for
relativistic collisionless shock formation in gamma ray bursts. The
theoretical framework predicting the long-term evolution, structure,
and coalescence energetics of beam/return current filaments during
the Weibel instability of an electron beam in a collisionless plasma
is developed. The strongly nonlinear stage of the instability, during
which the beam density of filaments is compressed to the background
plasma density, and the ambient plasma is fully evacuated was
emphasized. The analytic and numerical results demonstrate that the
beam filaments can carry super-Alfvenic currents by assuming current
and density profiles similar to the Hammer-Rostoker equilibrium. This
has profound implications for the long-term evolution of the magnetic
field and beam current and explains the long-standing puzzle: why
magnetic field energy initially increases, but eventually decreases
during the collisionless Weibel instability.

CPPG Group

E. Feibush, C. Ludescher, and R. Andre have developed a new ElVis-
based web service for preparing and running TRANSP between NSTX
shots. The client menu enables specifying a time slice or time
dependent run based on a shot number. The client connects to server
side software that retrieves shot data from MDSplus and prepares the
input data files for the TRANSP run. The user can select EFIT
options, specify run parameters, and edit the namelist through the
graphical user interface. As a run is prepared, graphs are generated
showing the shot profile trajectories being input. The user then
starts the TRANSP run from the client. The run can be previewed on
the Fusion Grid Monitor and the final results are displayed by
running RPLOT from within ElVis. Data preparation typically
produces 30 to 40 graphs. New features were added to ElVis to enable
working with an increasing number of graphs. You can find out more
about ElVis from http://w3.pppl.gov/elvis.

R. Samtaney, D. McCune, and P. Henderson attended the 2008 FES
Network Requirements Workshop at Gaithersburg, MD on March 13-14.
They participated in discussions of network requirements to meet the
needs of the SciDAC and related codes at PPPL, likely needs of a
future Fusion Simulation Project, as well as requirements based on
overseas experimental project collaborations, and possible future
requirements stemming from an ITER remote control and analysis center
located in the United States.

March 7, 2008

Theory Group

Dr. A. Reiman hosted a National Stellarator Physics Teleconference on March 6. Dr. M. Yokoyama, representing the LHD Stellarator Group (Japan), presented a seminar on "Recent progress of high-ion- temperature experiments in LHD." A low-energy positive-ion NBI system with perpendicular beam injection became operational in FY 2005, and it achieved 40-keV 7 MW injection in FY2006. This has supplemented the 14 MW of tangential NBI power previously available, and has allowed LHD to achieve ion temperatures exceeding 6 keV at average electron densities of 10^(19) per cubic meter. The ion temperatures achieved in LHD are continuing to rise as these experiments continue.

CPPG Group

J. Chen and the M3D group have been awarded 2 Million additional processor-hours (beyond their yearly 4.1 Million hour allocation) on the new NERSC Franklin Supercomputer to participate in the scaling reimbursement program. This program reimburses all charges for selected production runs made at NERSC that use over 2416 processors (which is 1/8 the size of the machine). The purpose of the reimbursement program is to encourage some of the large production users at NERSC to optimize their codes to routinely use thousands of processors for production runs.

Stephane Ethier attended the "ALCF Incite Getting Started" workshop held by the Argonne Leadership Class Facility at the Argonne National Laboratory (ANL). The goal of the workshop was to introduce the Incite recipients to the new Blue Gene/P platform recently acquired by the ALCF and help them port their codes. The final configuration of the BG/P system will comprise of over 130,000 processor cores and run at a peak performance of 500 TFlops. Ethier successfully ported the highly scalable Gyrokinetic Toroidal Code (GTC) and ran it on BG/ P in mixed mode MPI-OpenMP, which is the preferred way of exploiting the new multi-threading capability of the Blue Gene platform within each of its multi-core nodes.

Dr. Jeronimo Garcia presented a CPPG seminar on "ITER steady-state analysis with the CRONOS suite of codes." The speaker described integrated simulations using the CRONOS suite of codes, developed at CEA-Cadarache, which were used to study the physics involved in the Internal Transport Barrier (ITB) sustainment and to identify the main obstacles for the establishment of a steady-state scenario in ITER. It was demonstrated that any current drive inside the ITB leads to a progressive shrinking and disappearance of the barrier, which means that Neutral Beam Current Drive, which is naturally localized in the central part of the plasma, proves to be of little use in these scenarios. Dr. Garcia has been at PPPL the last 3 weeks carrying out a successful effort to benchmark the CRONOS codes against the TSC/ TRANSP codes.

Harper Langston from NYU presented a CPPG seminar on "A Kernel- Independent FMM-Based Elliptic PDE Solver in Complex Geometries with Non-homogeneous Force Distributions." The speaker described the application of fast-multipole-method solvers to complex geometries using an embedded boundary solver approach.

February 29, 2008

Theory Group

Dr. N.N. Gorelenkov presented a colloquium at the Applied Physics & Mathematics Department of Columbia University, NY, titled "Energetic Particles and Alfven Instabilities in Magnetic Fusion." In this talk Dr. Gorelenkov considered various experimental and theoretical advances in the field of energetic particle (EP) research. These advances helped to validate theoretical and numerical tools to make robust predictions on EP driven effects for future experiments with burning fusion plasmas, such as for ITER tokamak. Several non- conventional issues due to energetic particles were highlighted, such as alpha channeling and the prospect of building efficient tokamak based reactor, where fusion alphas should not be confined to improve its effectiveness.

CPPG Group

Dr. Kathy Yelick, the new Director of NERSC, presented a CPPG seminar on "The Future of NERSC." In her talk, she highlighted some of the science activities performed at NERSC and described two new strategic directions for the next 10 years. The first significantly expands the support for analysis of large scientific data sets through a combination of hardware, software, and service activities. The second is to re-think high end computing system design from a power- efficiency perspective, which is necessary to reach the target of Exascale computing. She discussed initial efforts in these two areas, both using an application-driven approach to finding a general solution to these problems.

S. Jardin attended the 11th meeting of the ITPA MHD Topical group, IEA Large Tokamak workshop, and US-Japan workshop on "MHD Behavior and Control of Burning Plamsa." He made three presentations that highlighted recent ITER relevant CEMM simulations, the physics of two- fluid magnetic reconnection, and a proposal for the NIMROD/M3D sawtooth calculation to be used as an international benchmark calculation for non-linear MHD. He also had a number of meetings with members of the Japan and IO ITER teams related to advice and consultation on the TSC simulations of plasma disruptions and scenario development in ITER being performed by those teams. Discussions were also held regarding PPPL performing a 3D simulation of the mechanism recently proposed by L. Zakharov of a large n=1 kink mode occurring in a disrupting plasma in contact with a first wall.

February 22, 2008

Theory Group

Dr. Guoyong Fu gave a Theory seminar entitled "1) Energetic Particle-induced Geodesic Acoustic Mode. 2) Introduction to CSEPP." 1) He reported that a new Energetic Particle-induced Geodesic Acoustic Modes (to be called EGAM), was discovered in recent numerical simulations using the particle/MHD hybrid code M3D. The new mode was found to be excited by energetic particles with free energy associated with anisotropic particle distribution function. The mode had a global radial structure peaked at the center of plasma and had a frequency inside the GAM frequency continuum. An integral equation was derived for EGAM including the non-perturbative effects of energetic particles. Analysis shows that energetic particles can either enhance or reduce the EGAM frequency depending on details of particle distribution such as particle energy and pitch angle distribution. In the limit of isotropic distribution and large energetic particle temperature, the energetic particle pressure reduces the GAM frequency unlike the thermal species. Furthermore, the effects of finite orbit width of the energetic particles determine the radial mode structure of the global EGAM. 2) A brief introduction was given to CSEPP which stands for “Center for gyrokinetic/MHD hybrid Simulation of Energetic Particle Physics”.  CSEPP has been recently formed with members from PPPL, IFS, University of Colorado and Oak Ridge National Laboratory. The aim of the center is predictive nonlinear simulations of energetic particle-driven modes and energetic particle transport in burning plasmas such as ITER.

CPPG Group

The PPPL Linux cluster is in the process of being upgraded to a new operating system, RedHat 4, and several machines are now available now with the new software.  TRANSP/PTRANSP have now been ported to this new environment and built with the newly installed 64 bit fortran compiler Pathscale 3.1.  All benchmarks run correctly, and significant serial performance improvements are noted.  On equivalent hardware, the TRANSP Monte Carlo benchmark ran in 0.47 hours compared to 0.66 hours in the old environment (RedHat 3 with lf95 6.2c 32 bit fortran), an improvement of over 28%.  A TRANSP RF wave code benchmark showed even greater speed up: 0.44 hours vs. 0.75 hours, an improvement of over 41%.  These changes are believed to be due to improvements in the software—faster kernel, newer compiler. An effort is now underway to place Fusion Grid TRANSP run production onto the upgraded systems. Thanks to the PPPL Computer Division for putting together this important Linux Cluster upgrade.

February 15, 2008

Theory Group

On February 5, Hong Qin presented a seminar at the Courant Institute
of Mathematical Sciences at New York University. The title of the
seminar is "weight growth due to resonant simulation particles and a
modified delta-f algorithm with smooth switching between delta-f and
total-f methods." When applying the standard delta-f particle-in-
cell (PIC) simulation method to simulate linear and nonlinear
collective instabilities with coherent structures, wave-particle
interaction may result in large weight growth for resonant or nearly-
resonant simulation particles. It is demonstrated that the large
noise associated with the large weight of nearly-resonant simulation
particles can produces significant error fields at the nonlinear
stage of the instability. To overcome this deleterious effect, a
modified delta-f method which contains a smooth switching algorithm
between the delta-f and total-f methods has been developed. Before
the switch, the simulation effectively makes use of the desirable low-
noise feature of the delta-f method for small weight to accurately
follow unstable mode structures. When the weight function becomes
large during the nonlinear phase, the low-noise advantage of the
delta-f method ceases to be significant and the simulation is
switched to the total-f method to avoid the large noise induced by
nearly-resonant simulation particles. This algorithm has been
successfully applied to simulation studies of the electrostatic
Harris instability driven by large temperature anisotropy in high
intensity charged particle beams typical of applications in high
current accelerators, including high energy density physics and heavy
ion fusion.

CPPG GROUP

Ravi Samtaney visited the Culham Science Center, UK and Imperial
College, UK from February 4-9, 2008. He presented a seminar at Culham
entitled "Overcoming spatial and temporal stiffness in MHD
simulations for fusion," and a tutorial on structured adaptive mesh
refinement methods for MHD at Imperial College. Discussions were
held on forced and unforced magnetic reconnection and plasmoid
formation therein.

S.C. Jardin presented a joint CPPG/Theory seminar on: "The M3D-C^1
Approach to Calculating Two-Fluid Equilibrium, Stability, and
Magnetic Reconnection in Magnetized Plasmas." The M3D-C^1 code is
based on high-order compact conformal finite elements with C^1
continuity on an unstructured adaptive grid. The efficient split-
implicit time advance is shown to be closely related to the ideal MHD
energy principle, and allows time steps several orders of magnitude
in excess of the Courant condition based on the Alfven or whistler
waves. The full model consists of eight 3D scalar variables. Two
energy-conserving subsets of the full equations exist: 2-variable 3D
toroidal resistive reduced MHD, and a 4-variable 3D toroidal two-
fluid MHD. The structure of the code makes linear calculations
exceptionally efficient.

R. Samtaney and D. Stotler (theory) as well as ten outside
participants attended a one-day mini-workshop on code coupling
activities at PPPL as part of the Center for Plasma Edge Simulations
(CPES). Discussions were held on coupling between the edge
gyrokinetic code XGC and the MHD codes M3D and NIMROD.

February 8, 2008

Theory Group

Prof. John Krommes gave a Theory seminar entitled "The remarkable
similarity between the scaling of kurtosis with squared skewness for
TORPEX density fluctuations and sea-surface temperature fluctuations:
Baby steps toward a theory". The striking similarity between certain
higher-order statistics of drift-interchange plasma turbulence in the
TORPEX device [B. Labit et al., Phys. Rev. Lett. 98, 255002 (2007)]
and sea-surface temperature fluctuations [P. Sura and P. D.
Sardeshmukh, J. Phys. Oceanogr. (2007), in press] is described. A
successful nonlinear Langevin theory due to sea-surface temperature
fluctuations is reviewed, then generalized to include linear wave
propagation; it is shown to make a reasonable prediction for the
shape of the kurtosis versus skewness curve for TORPEX. The
relevance of these somewhat naive calculations was discussed, and
future research directions were indicated.

February 1, 2008

Theory Group

A paper titled "A Variational Symplectic Integrator for the Guiding
Center Motion of Charged Particles for Long Time Simulations in
General Magnetic Fields" was published in Physical Review Letters [H.
Qin and X. Guan, Physical Review Letters 100, 035006 (2008)]. The
paper reported a newly developed variational symplectic integrator
for the guiding-center motion of charged particles in general
magnetic fields for long-time simulation studies of magnetized
plasmas. Instead of discretizing the differential equations of the
guiding-center motion, the action of the guiding-center motion is
discretized and minimized to obtain the iteration rules for advancing
the dynamics. The variational symplectic integrator conserves exactly
a discrete Lagrangian symplectic structure, and has better numerical
properties over long integration time, compared with standard
integrators, such as the standard and variable time-step fourth order
Runge-Kutta methods.

CPPG Group

Stephane Ethier attended the kick-off meeting of the SciDAC Center
for Gyrokinetic Particle Simulations of Turbulent Transport in
Burning Plasmas held at UC Irvine, in Irvine, CA. The focus of the
meeting was on the needs in code development, analysis, and
visualization for the project. Ethier gave a presentation entitled
"What to do with 100 billion particles".

Prof. Jinchao Xu from Pennsylvania State University presented a CPPG
seminar on "Nonconforming Finite Elements for High Order PDE Systems
and Relevant Algebraic Solvers." The finite element representation
uses local low-order polynomials to represent the solution in each
triangle or rectangle (in 2D). It is commonly believed that these
piecewise polynomials need to be constructed so that the derivatives
through order m-1 are continuous when applied to an equation with
2m^th order highest derivatives. Prof. Xu showed that in order for
the error to be comparable to other errors present in the finite
element method, only certain line integrals of the solution needed to
have (m-1)st order continuity. This relaxed requirement may be used
to replace the more complicated high continuity elements with simpler
elements that lead to matrices that require less computational effort
to invert.

January 25, 2008

Theory Group

The paper "Turbulent Equipartition Theory of Toroidal Momentum Pinch"
by T.S. Hahm, P.H. Diamond, O. Gurcan, and G. Rewoldt has been
accepted for publication in Physics of Plasmas. The paper which is
based on T.S. Hahm's invited talk at the APS-DPP '07, presents a
simple physics interpretation of the magnetic curvature driven
momentum pinch, which has been originally derived from gyrokinetic
equations [Phys. Plasmas 14, 072302 (2007)], in terms of the
turbulent equipartition (TEP) theory. This work also demonstrates
that the magnetic curvature modification of the parallel acceleration
in the laboratory frame, which is responsible for the momentum pinch,
is closely related to the Coriolis drift coupling to the perturbed
electric field in the rotating frame.

Ron Davidson, Mikhail Dorf, Hong Qin, Igor Kaganovich and Edward
Startsev participated in the Winter School on Warm Dense Matter held
at the Lawrence Berkeley National Laboratory on January 10 - 16. Ron
Davidson lectured on the role of the Warm Dense Matter (WDM) studies
as part of high energy density plasma physics. Igor Kaganovich
addressed the importance of considering negative ions in many WDM
phenomena. As an example, recent experiments to produce ball lighting
in the laboratory were discussed, where the burning of nanoscale
particles may be a key process responsible for the phenomena. These
particles are charged negatively in plasmas, which may explain why
the ball lighting keeps its shape after passing through narrow objects.

Dr. Hong Qin gave a Theory seminar entitled "Variational Symplectic
Integrator for the Guiding Center Motion of Charged Particles for
Long Time Simulations in General Magnetic Fields". A variational
symplectic integrator for the guiding center motion of charged
particles in general magnetic fields is developed for long time
simulation studies of magnetized plasmas. Instead of discretizing the
differential equations of the guiding center motion, the action of
the guiding center motion is discretized and minimized to obtain the
iteration rules for advancing the dynamics. The variational
symplectic integrator conserves exactly a discrete Lagrangian
symplectic structure, and has better numerical properties over long
integration time, compared with standard integrators, such as the
standard and variable time-step 4th order Runge-Kutta methods.
Standard integrators only guarantee the error to be small in each
time-step. The errors at different time-steps often accumulate
coherently, and result in a large error over a large number of time-
steps. The symplectic integrator conserves the symplectic structure
exactly, and guarantees that the energy error is bounded by a small
number for all the time-steps. Numerical examples with more than 25
million time-steps are given to demonstrate the superiority of the
variational symplectic integrator. This significant improvement in
long term simulation capability of gyrokinetics is a direct result of
the geometric formulation of the gyrokinetic theory using the modern
language of differential geometry [H. Qin, et al, Physics of Plasmas
14, 056110 (2007)].

CPPG Group

Devon Battaglia from Prof. Fonck's U. Wisconsin Pegasus group
concluded a 2-week stay at PPPL in which he learned to use the
Tokamak Simulation Code (TSC) and apply it to the current injection
experiments on Pegasus. He was successful in developing an input
file that allowed him to simulate many of the features of the
experiments in which current is injected on open field lines, which
under certain conditions can transition into a closed field line
configuration.

Mark Adams (Columbia University) presented a CPPG seminar on "Toward
optimal multigrid algebraic solvers in magnetohydrodynamics
simulations of fusion plasmas". He described progress in solving the
implicit resistive MHD equations, with application to a model problem
in resistive reconnection in the presence of a guide field.

Doug McCune, K. Indireshkumar (Kumar), and Greg Hammett (Theory)
attended the FACETS ALL-Hands Meeting in Boulder, Colorado. G.
Hammett led a discussion on improved implicit solvers for advective-
diffusive transport codes. D. McCune gave a presentation on the
Plasma State software that has recently undergone a major revision.
Detailed discussions were held between Alex Pletzer of Tech-X, Kumar,
and Doug McCune regarding incorporation of the Plasma State software
into the FACETS framework, thereby facilitating the integration of
the Monte Carlo NUBEAM software into FACETS as a component. The
Plasma State and NUBEAM component work represents an effective
collaboration between the SWIM and FACETS SciDAC Fusion Simulation
Project prototypes.

January 18, 2008

Theory Group

On January 16, T.S. Hahm gave a colloquium entitled "Recent Progress
in understanding Tokamak Core Turbulence and Transport." The abstract
of his talk follows: In the past decade, considerable progress in
understanding tokamak core turbulence and transport has been made
thanks to advances in experimental measurements, numerical
simulations, and nonlinear theory. In this presentation, after a
brief description of properties of tokamak core turbulence, a few
examples for which effective interactions among theorists and
experimentalists led to significant achievements will be illustrated.
Outstanding remaining problems will be discussed at the end.

CPPG Group

A new version of the Plasma State software has been developed and
made available to the SWIM SciDAC project and committed to the TRANSP/
PTRANSP CVS source code repository. The new software includes an
expandable machine description, which enables geometrical
specification of tokamak experiments: neutral beams, RF antennas,
etc. Machine description namelists are expected to provide a
resource for predictive simulation. The software is expected to be
used in the FACETS and CPES SciDAC projects as well as SWIM.

J. Chen, S. Jardin, J. Breslau and N. Ferraro traveled to the SCOREC
center at Rensselaer Polytechnic Institute (RPI) this week for an all
day meeting and tutorial related to the M3D-C1 project. Items
covered included routines for unstructured grid generation and
adaptive re-gridding, defining and applying boundary conditions in
arbitrary shaped domains, and SCOREC software modification required
to enable full 3D iterative solves.

PPPL hosted a CEMM conference call this week that was focused on
finalizing the new CEMM sawtooth benchmark problem. The new
benchmark starts from an analytically specified equilibrium with
constant loop voltage and self-consistent Ohmic heating and thermal
conduction. The nonlinear evolution includes Ohmic heating and an
applied loop voltage, with no artificial source terms in the
equations. Initial results on the linear stability of different
toroidal modes were presented.

January 11, 2008

Theory Group

The paper "An Iterative Semi-Implicit Scheme With Robust Damping" (http://arxiv.org/abs/0707.1121), by N. Loureiro and G.W. Hammett, has been accepted for publication in the Journal of Computational Physics. The paper presents an improved semi-implicit algorithm that can be useful for problems that contain high-frequency dynamics, discusses the relation with preconditioning for fully implicit algorithms, and demonstrates an application to gyrofluid magnetic reconnection.  Loureiro was a postdoc at PPPL for 2 years, through the University of Maryland, Center for Multiscale Plasma Dynamics, and has recently started working at Culham.
 
Dr. L. Zakharov gave a Theory seminar entitled "The kink mode during the disruptions in tokamaks". The talk explained the locked $m/n=1/1$ kink mode during the vertical disruption event when the plasma has an electrical contact with the plasma facing conducting surfaces. It was shown that the kink perturbation can be in equilibrium state even with a stable safety
factor $q > 1$, if the halo currents, excited by the kink mode, can flow through the conducting structure. This suggests a new explanation of the toroidal asymmetry in magnetic measurements and so-called sideway forces on the in-vessel components during the disruption event.
 
Dr. A. Reiman hosted a National Stellarator Theory Teleconference on Jan. 10.  Dr. J. Harris of Oak Ridge National Laboratory presented a seminar on "Super Dense Core Plasmas in the LHD Stellarator".  It has been found that a combination of pellet injection and low recycling on LHD allows the achievement of very high central densities, greater than 10**20 per cubic meter.  This is associated with improved core confinement.  It appears that one key feature of LHD associated with this regime is that the core is in the second stability regime for ballooning modes.  The regime may provide an attractive high-density reactor scenario.

December 21, Dec. 28, 2007 & January 4, 2008

Theory Group

A new version of the DG code was released this week to seven users at various institutions around the world. DG is a graphical user interface program used to define computational grids input to tokamak scrape-off layer and edge plasma simulation codes. Current applications of DG include B2-EIRENE simulations of the ITER divertor (Andre Kukushkin, ITER) and DEGAS 2 neutral transport simulations of NSTX experiments (Daren Stotler). The new release incorporated improvements made by Alan Chin, a SULI intern at PPPL the past two summers, and a complete update of the User's Manual by Daren Stotler.

Jay Johnson & Eun-Hwa Kim attended AGU fall meeting and GEM workshop on 12/9 - 12/14 in San Francisco, CA. Jay Johnson organized a session on "Entropy Constraints on Plasma Entry, Tail Transport, and Magnetospheric State Transitions" at the American Geophysical Union Meeting. The session highlighted the following important science questions: why is entropy not conserved along field lines during earthward convection?; what are the dynamics of entropy bubbles and what is their role in ring current injections?; what does non-conservation of entropy during substorms tell us about the dynamical transition between growth phase and expansion phase?; how does plasma entry from the solar wind and loading from the ionosphere affect total and local measurements of entropy and what transport processes are responsible for the significant changes in entropy observed in the magnetospheric system? Eun-Hwa Kim presented two papers, which were Kinetic Alfven wave at the low latitude boundary layer by Eun-Hwa Kim and Jay R Johnson and Mode Conversion of Langmuir to Electromagnetic Waves at Oblique Density Inhomogeneities by Iver H Cairns, Eun-Hwa Kim, and Peter A. Robinson.

CPPG Group

The M3D-C1 development effort has met a major milestone by completing and demonstrating an initial 3D toroidal linear stability capability. The linear option of the M3D-C1 code initializes from a steady state toroidal equilibrium computed by either a Grad-Shafranov solver, or by the 2D M3D-C1 code: a comprehensive 2-fluid non-linear 2D toroidal evolution code with flow. The linear option then uses an efficient implicit time advance to evolve a given toroidal harmonic in time in order to find any unstable eigenmodes. The linear code contains full 2-fluid physics described by 9 scalar 3D fields, including the Hall term and the gyroviscous tensor. A feature of the M3D-C1 approach is that there are several well-posed non-trivial subsets of equations that can be solved instead of the full set of 9 scalar variables. These are: (1) 2-variable reduced MHD and (2) the 4-field 2-fluid equations of [Hazeltine, et al. PF 28 2466 (1985)] and [Fitzpatrick et al, PoP 11 p4713 (2004)]. This capability is invaluable in both debugging the full code and in better understanding the results. The initial capability verification tests are with the 2-variable option. Future development effort will include verifying the 4 and 9 variable options, adaptive meshing, a resistive wall capability, and active feedback. The 2D M3D-C1 code and the linear 3D option both have demonstrated good scaling on parallel computing platforms. The structure of the software is such that it leads directly into a scalable nonlinear 3D capability. This work was done in collaboration with the CEMM SciDAC team, the SCOREC team at RPI, and with Princeton University graduate student N. Ferraro.