Observation of hot electron ring instabilities in ELMO Bumpy Torus

Abstract

A high-frequency hot electron instability is observed in ELMO Bumpy Torus (EBT) plasmas when the hot electron-to-ion density ratio exceeds 0.4. Both the real frequency and the imaginary frequency are larger than the ion cyclotron frequency. The azimuthal mode number (m) is 7, and the instability rotates in the hot electron curvature drift direction. This instability is identified as a curvature-driven mode. When it is strongly excited, the equilibrium of the hot electron annuli and confined plasmas are destroyed (disruption). Ion heating and neutron bursts are associated with this instability.