ANALYSIS OF MAGNETOHYDRODYNAMIC INSTABILITIES IN TJ-II PLASMAS

Magnetohydrodynamic instabilities in the TJ-II stel-larator are being experimentally characterized in vari-ous plasma parameter regimes and heating scenarios. Magnetic field fluctuations data are collected, using var-ious Mirnov coil sets distributed at different toroidal sec-tors of the vacuum vessel, with frequency resolution up to 1 MHz. Specific analysis is carried out with the signals from a poloidal array of 15 coils measuring poloidal magnetic field fluctuations. The appearance of low-frequency modes (some tens of kilohertz) in electron cyclotron heated plasmas depends on the rotational trans-form profile and plasma density. In neutral beam injec-tion plasmas, high-frequency (150- to 300-kHz) modes have been found in plasmas with line densities in the range 0.6 1019 m3 to 3 1019 m3 and heated with on/off-axis electron cyclotron heating. They are good candidates for global Alfvén eigenmodes related to the low-order resonance n/m 3/2