Report on FY07 DOE Theory Milestone: Improve the simulation resolution of linear stability properties of Toroidal Alfven Eigenmodes driven by energetic particles and neutral beams in ITER by increasing the numbers of toroidal modes used to 15
Personnel involved in the preparation of this report: N. N. Gorelenkov,
R. V. Budny, C.E. Kessel, D. McCune, J. Manickam, PPPL
Collaborators: E.D. Fredrickson, G.-Y. Fu, G.J. Kramer, R. Nazikian, R. White, PPPL; H. L. Berk, IFS; J.
Snipes, MIT; W.W. Heidbrink, L. Chen, UC Irvine; A. Polevoi, ITER team & Kurchatov institute;
Quarterly milestones:
Q1 Develope ducial ITER numerical equilibria, using TRANSP, to determine the alpha-particle slowing down distributions and neutral beam ions for a range of operating regimes.
Q2 Analyze the normal shear discharges, performing a parameter scan to determine the linear stability of toroidal mode number n = 1-15 TAE modes.
Q3 Analyze the hybrid shear discharges, performing a parameter scan to determine the linear stability of toroidal mode number n = 1-15 TAE modes.
Q4 Analyze the reversed shear discharges, performing a parameter scan to determine the linear stability of toroidal mode number n = 1-15 TAE modes, and prepare a comprehensive review of the TAE stability of ITER discharges in the three operating regimes.
Qtr1 Report
Qtr 2 report
Qtr 3 Report
Qtr 4 Report
Final Report
Background
In a thermonuclear deuterium-tritium (D-T) tokamak plasma the 3:5MeV alpha particles must be trapped by the magnetic field so that their energy can be transferred, primarily through electron drag, to the background plasma. One purpose of burning plasma (BP) experiments is to demonstrate that this method of self-heating will be the dominant method of heating of fusion-energy-producing plasma. However, when the alpha particle partial pressure is significant, a physics issue arises, as to whether this pressure is capable of inducing collective behavior that may cause the premature loss of alpha particles. Should this be the case, two major problems may arise: (i) it may become difficult to sustain the plasma parameters close to those required for ignition and (ii) the flux of energetic alpha particles (~ 3:5MeV ) to the first wall of the experiment can cause severe wall damage. Indeed it has been demonstrated in present day (PD) experiments that the collective effects induced from energetic particles can result in premature energetic particle loss. However, it is difficult to extrapolate the results of PD experiments to BP experiments, for the following reasons. The fast particle distribution functions are often quite different. In PD experiments the energetic particle distribution are anisotropic whereas in a BP experiment the distribution function of fusion alpha particles would be isotropic. In addition, in a BP experiment the machine size to orbit width will be significantly larger, and the spectrum (and number) of unstable modes is likely to be broader in a BP compared with PD experiments. Thus even with continued study in PD experiments, extrapolation to reliable predictions for BP experiments may remain uncertain. However, theoretical modeling and simulation can provide predictions of the likely effects of the driven modes. It is generally believed that the Toroidal Alfven Eigenmodes (TAE's) [1{3] destabilized by fast ions, are the plasma waves most likely to cause significant difficulties for the containment of energetic alpha particles in fusion energy generating tokamak experiments. It has been experimentally established that in the presence of a strong enough energetic particle energy density, these modes will induce large losses of fast particles. It is also known that there exists a variety of conditions where these modes are stable or when unstable, do not induce anomalous loss.
This report describes the work performed to address the stability issue. We will perform a systematic study of various plasma scenarios, planned for ITER, in order to determine whether linear instability to the TAE's is expected under burning plasma conditions. Specifically, we will study TAE stability for the three proposed scenarios; elmy H-mode, hybrid and advanced tokamak conditions. TAEs with the toroidal mode number ranging up to the value fifteen will be investigated. With the use of analytic estimates, some extrapolation is possible to other temperature regimes of operation.
Executive summary. The first quarter milestone was achieved. In all, equilibria representing the evolution of
eleven distinct plasma conditions were developed. The Tokamak Startup Code, (TSC), and the plasma transport
simulation code, TRANSP, were used to develop ducial equilibria for the three main ITER scenarios; the elmy Hmode,
hybrid and advanced plasma regimes. The simulations addressed the evolution from start-up to steady-state, for
a period of thousand seconds. TSC was used to simulate the startup and control of the plasma boundary, and TRANSP
was used to obtain accurate particle distribution functions for the slowing down negative neutral beam injected, (NNBI),
ions as well as the thermonuclear alpha-particles. In addition to the three ducial ITER scenarios, eight additional
scenarios, with varying NNBI injection angle, were developed for the elmy H-mode and hybrid scenarios. This will
enable an evaluation of the potential of controlling the excitation of TAE modes by varying the injection angle.
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