Analytic stability boundaries for compressional and global Alfvén eigenmodes driven by fast ions. II. Interaction via Landau resonance

Abstract

Conditions for net fast ion drive are derived for beam-driven, co-propagating, sub-cyclotron compressional (CAE) and global (GAE) Alfvén eigenmodes driven by the Landau resonance with super-Alfvénic fast ions. Approximations applicable to realistic neutral beam distributions and mode characteristics observed in spherical tokamaks enable the derivation of marginal stability conditions for these modes. Such conditions successfully reproduce the stability boundaries found from numerical integration of the exact expression for local fast ion drive/damping. Coupling between the CAE and GAE branches of the dispersion due to finite $\omega /{\omega }_{ci}$ and $k_{\parallel }/k_{\perp }$ is retained and found to be responsible for the existence of the GAE instability via this resonance. Encouraging agreement is demonstrated between the approximate stability criterion, simulation results, and a database of NSTX observations of co-CAEs.

Part 2 of 2. 14 pages, 5 figures

References in corpus (1)

• Analytic stability boundaries for compressional and global Alfvén eigenmodes driven by fast ions. I. Interaction via ordinary and anomalous cyclotron resonances

Cited by in corpus (3)

• Analytic stability boundaries for compressional and global Alfvén eigenmodes driven by fast ions. I. Interaction via ordinary and anomalous cyclotron resonances
• Hybrid simulations of sub-cyclotron compressional and global Alfvén Eigenmode stability in spherical tokamaks
• Theory and Simulations of Compressional and Global Alfven Eigenmode Stability in Spherical Tokamaks