Physics – Plasma Physics
Scientific paper
Oct 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aps..dppgi2001g&link_type=abstract
American Physical Society, 45th Annual Meeting of the Division of Plasma Physics, October 27-31, 2003, Albuquerque, New Mexico,
Physics
Plasma Physics
Scientific paper
A low-field, low aspect-ratio device such as NSTX is an excellent testbed to study the ITER relevant physics of fast particle confinement which is of major importance for burning plasmas. The low Alfven speed in NSTX offers a window to the super-Alfvenic regime expected in ITER. Effects such as the large FLR, orbit width, strong shaping and high thermal and fast-ion betas make this effort a greater challenge. We report on the linear stability of different Alfven eigenmode (AE) branches and compare theory with experimental data. Low frequency MHD activities 100kHz on NSTX are often observed and identified as the toroidicity- induced AEs (TAE) driven by beam ions. Sometimes they are accompanied by beam ion losses in H-mode, high q(0) plasmas. Numerical analysis using NOVA-K code shows a good agreement with the experimental data. The TAE instability was compared in experiments on NSTX and DIII-D. With very similar plasma conditions we tested the theoretical prediction that the toroidal mode number of the most unstable TAEs scales with the machine size, n a. In NSTX TAEs are observed with n=1-2, whereas in DIII-D n=4-7. The confirmation of n scaling validates the predictive capabilities of theoretical tools (NOVA-K) for studying ITER plasmas. In the high frequency range recent observations of rich sub-ion cyclotron frequency MHD activities in NSTX suggest that new instabilities are excited, which we identify as Global shear AEs (GAEs). Similar to the compressional AEs (CAEs), GAEs are destabilized by the Doppler shifted cyclotron resonance in the presence of 80 keV NBI. To simulate GAE/CAEs in realistic NSTX plasma conditions we have developed a nonlinear hybrid kinetic-MHD code, HYM, which is capable of computing the mode structure, saturation and energetic particle transport.
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