R. Nazikian (Princeton Plasma Physics Laboratory) provided the following report:
The fourth Energetic Particle ITPA (International Tokamak Physics Activity) meeting was held in Garching, Germany on April 26-28, 2010, and included over thirty speakers with several remote participants from the US and the EU. The meeting was divided into four topical areas; linear and non linear benchmarking of Alfven eigenmode codes, ITER fast particle diagnostics and 3-D magnetic-field effects on fast ion confinement.
Significant progress has taken place since the first ITPA meeting on the linear benchmarking of toroidal Alfven eigenmode (TAE) spatial structure and damping. The analysis of damping rates was used to compare with experimental damping rate measurements on JET. It was found that full gyrokinetic codes generally predicted higher damping rates than perturbative MHD codes in cases with no continuum damping. The gyrokinetic codes contain a more self-consistent description of the coupling of the Alfven eigenmodes to kinetic Alfven waves. The linear gyrokinetic calculations were more consistent with the experimental observations of higher damping rates in JET plasmas where continuum damping was avoided. Interestingly, analysis with the LIGKA code (IPP, Garching) showed that very high-resolution electron density profile measurements are needed in order to determine the role of edge continuum damping. Plans were discussed for drafting an IAEA paper on the linear benchmark analysis.
A nonlinear benchmark study was performed for an analytical large-aspectratio tokamak equilibrium. The objective of the benchmark study was to compare the nonlinear simulations against linear TAE eigenmode calculations. Several codes were used in the benchmark study. The main result was that all of the codes identified the most unstable mode as a nonperturbative energetic particle mode (EPM) rather than the TAE. In addition, not all the codes could identify the TAE when the instability drive was below the EPM threshold. For this reason, it was decided that the nonlinear benchmark should be performed against a linear nonperturbative eigenmode calculation. The results of the comparison between the nonperturbative linear and nonlinear codes will be presented at the next ITPA meeting.