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: January 2003
Published in: Physics of Plasmas, Volume 10, Issue 7 (July 2003) pp. 2852-2862.
Spherical tokamaks, with their relatively low toroidal field, extend fast-ion-driven instability physics to parameter ranges not normally accessed in conventional tokamaks. The low field means that both the fast-ion Larmor radius normalized to the plasma minor radius and the ratio of the fast-ion velocity to the Alfvén speed are relatively large. The large Larmor radius of the ions enhances their interaction with instability modes, influencing the structure of the unstable mode spectrum. The relatively large fast-ion velocity allows for a larger population of fast ions to be in resonance with the mode, increasing the drive. It is therefore an important goal of the present proof-of-principle spherical tokamaks to evaluate the role of fast-ion-driven instabilities in fast-ion confinement. This paper presents the first observations of fast-ion losses resulting from toroidal Alfvén eigenmodes and a new, fishbone-like, energetic particle mode.