Skip to main content
Open Access Publications from the University of California

UC Irvine

UC Irvine Previously Published Works bannerUC Irvine

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

  • Author(s): Fredrickson, ED
  • Bell, RE
  • Darrow, DS
  • Fu, GY
  • Gorelenkov, NN
  • LeBlanc, BP
  • Medley, SS
  • Menard, JE
  • Park, H
  • Roquemore, AL
  • Heidbrink, WW
  • Sabbagh, SA
  • Stutman, D
  • Tritz, K
  • Crocker, NA
  • Kubota, S
  • Peebles, W
  • Lee, KC
  • Levinton, FM
  • et al.

Published Web Location Commons 'BY' version 4.0 license

A wide variety of fast ion driven instabilities are excited during neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX) [Nucl. Fusion 40, 557 (2000)] due to the large ratio of fast ion velocity to Alfván velocity, Vfast VAlfvén, and high fast ion beta. The ratio Vfast VAlfvén in ITER [Nucl. Fusion 39, 2137 (1999)] and NSTX is comparable. The modes can be divided into three categories: chirping energetic particle modes (EPM) in the frequency range 0 to 120 kHz, the toroidal Alfván eigenmodes (TAE) with a frequency range of 50 kHz to 200 kHz, and the compressional and global Alfván eigenmodes (CAE and GAE, respectively) between 300 kHz and the ion cyclotron frequency. Fast ion driven modes are of particular interest because of their potential to cause substantial fast ion losses. In all regimes of NBI heated operation we see transient neutron rate drops, correlated with bursts of TAE or fishbone-like EPMs. The fast ion loss events are predominantly correlated with the EPMs, although losses are also seen with bursts of multiple, large amplitude TAE. The latter is of particular significance for ITER; the transport of fast ions from the expected resonance overlap in phase space of a "sea" of large amplitude TAE is the kind of physics expected in ITER. The internal structure and amplitude of the TAE and EPMs has been measured with quadrature reflectometry and soft x-ray cameras. The TAE bursts have internal amplitudes of ñ n=1% and toroidal mode numbers 21 and can have a toroidal mode number n>1. The range of the frequency chirp can be quite large and the resonance can be through a fishbone-like precessional drift resonance, or through a bounce resonance. © 2006 American Institute of Physics.

Many UC-authored scholarly publications are freely available on this site because of the UC's open access policies. Let us know how this access is important for you.

Main Content
Current View