Magnetohydrodynamic behaviour during core transport barrier experiments with ion Bernstein wave heating in PBX-M: II n=m-1 and n=m modes
Two new types of high frequency (HF) magnetohydrodynamic (MHD) mode activity are observed when a core transport barrier is formed during ion Bernstein wave (IBW) heating in PBX-M. These modes seem to be mainly responsible for the soft saturation in the strength of the core transport barrier. The two types of HF mode activity are determined by the presence or absence of a strong 1/1 mode. The m numbers of both of these modes vary between 4 and 13. They all seem to be coupled and rotate as a rigid body. The n=m-1 modes seemed to be narrowly localized on their corresponding rational surface (ie q=m/(m-1). The modes are ballooning-like, and their amplitudes increase with increasing beta. Calculations with the CASTOR code show that the n=m-1 modes are most probably pressure driven tearing modes, but the possibility of kinetic ballooning modes (KBM) cannot be fully excluded. The n=m modes appear on or around the q=1 surface, and are localized at the X point of the 1/1 mode island. The frequency offset of the n=m modes, which is too low for a toroidal Alfvén eigenmode (TAE), is shown to be consistent with beta-induced toroidal Alfvén eigenmodes (BAE).
Bibliographic Reference: Article: Nuclear Fusion, Vol. 38 (1998) No. 6, pp. 861-884
Record Number: 199811034 / Last updated on: 1998-09-15
Original language: en
Available languages: en