Excitation of the beta-induced Alfvén eigenmodes by a magnetic island

Abstract

It is shown that a pair of counter-propagating, tearing-parity, beta-induced Alfvén eigenmodes (BAEs) with low mode numbers can be excited in the presence of a magnetic island of the same helicity. The instability mechanism consists of the reversal of ion Landau damping due to island-induced modification of the equilibrium distribution function. This instability seems to be responsible for the BAE excitation in ohmic plasmas with tearing mode activity at the FTU tokamak (Buratti P. et al 2005 Nucl. Fusion 45 1446 ).