Wave Driven Fast Ion Loss in the National Spherical Torus Experiment
Authors: E.D. Fredrickson, C.Z. Cheng, D. Darrow, G. Fu, N.N. Gorelenkov, G. Kramer, S.S. Medley, J. Menard, L. Roquemore, D. Stutman, and R.B. White
Date of PPPL Report: August 2003
Presented at: the 30th European Physical Society Conference on Controlled Fusion and Plasma Physics, 7-11 July 2003, St. Petersburg, Russian Federation, Russia.
The study of fast ion instabilities in conventional aspect ratio tokamaks is motivated in large part by their potential to negatively impact the ignition threshold in fusion reactors by causing fast ion losses. Spherical tokamak's (ST), with intrinsically low magnetic fields, are particularly susceptible to fast ion driven instabilities. The 3.5 MeV alpha's from the D-T [deuterium-tritium] fusion reaction in proposed ST reactors will have velocities much higher than the Alfvén speed. The Larmor radius of the fusion alphas, normalized to the plasma size, will also be larger than for conventional aspect ratio tokamak reactors. The resulting longer wavelengths of the *AE instabilities will be more effective in driving fast ion loss. The change in magnetic topology also influences the mode structure, as in the case of the Compressional Alfvén Eigenmodes (CAE) seen on NSTX.