Interchange and infernal fishbone modes in plasmas with tangentially injected beams

Abstract

New energetic particle mode instabilities of fishbone type are predicted. The considered instabilities are driven by circulating energetic ions. They can arise in plasmas of tokamaks and spherical tori with weak magnetic shear in the wide core region and strong shear at the periphery, provided that the central safety factor is close to the ratio m∕n, where m and n are the poloidal mode number and toroidal mode number, respectively. The instability with m=n=1 has a mainly interchange-like radial structure, whereas the radial structure of instabilities with m∕n>1 is mainly similar to that of the infernal magnetohydrodynamics (MHD) mode; the differences between the fishbone mode structures and MHD mode structures are considerable only in the vicinity of the local Alfvén resonance.