Fast particle modifications to equilibria and resulting changes to Alfvén wave modes in tokamaks

Abstract

We quantify the impact of poloidal and toroidal rotation, anisotropy and energetic particle pressure produced by neutral beam injected energetic particles on the magnetic configuration and wave modes in tokamaks. Specifically, we focus on the class of spherical tokamaks, for which the impact of neutral beam heating is larger due to the relatively low toroidal field and large trapped particle fraction. Recently, (Hole et al 2011 Plasma Phys. Control. Fusion 53 074021) we have used Bayesian inference techniques to compute rotating MAST equilibria, and thereby compute toroidal and poloidal Mach numbers and their uncertainties, as well as computed MAST anisotropic equilibria in the presence of neutral beam heating. Motivated by this work, we compute the impact of rotation and anisotropy on magnetohydrodynamic (MHD) waves of the plasma. Specifically, we determine how a change in q profile due to rotation and anisotropy could affect frequency scalings of the Alfvén continuum, Alfvén gap modes and compressional Alfvén eigenmodes. We also use Bayesian inference to infer energetic particle pressure, and compare the result with the inferred pressure from high-fidelity TRANSP simulations.