Description
Major disruptions in tokamak plasmas can generate high-energy runaway electron (RE) beam, posing a significant threat to device safety. Massive impurity injection is a primary method for mitigating and dissipating runaway electrons, yet it faces the persistent challenge of achieving the Rosenbluth electron density required for complete RE generation suppression. In recent years, wave-runaway electron interactions, which can enhance the pitch-angle scattering of runaway electrons, have been considered a potential alternative approach for RE mitigation.
A newly developed Ion Cyclotron Emission (ICE) diagnostic on the J-TEXT tokamak enables measurements of high-frequency instabilities driven by fast or runaway electrons. Utilizing this ICE diagnostic, the studies of high-frequency instabilities excited by runaway electrons have been carried on J-TEXT. During the plasma current ramp-down phase, high-frequency waves in the range of MHz excited by runaway electrons have been successfully detected. Frequency chirping phenomena have been observed in the high-frequency waves associated with the excitation of the Parail-Pogutse instability. In low electron density disruption experiments, modes with frequencies in the range of kHz have been observed, along with modes whose frequencies are close to the fundamental and second harmonic of the ion cyclotron frequency at the low-field-side plasma edge.
Concurrently, studies on controlling runaway electron instabilities using Electron Cyclotron Waves (ECW) have been performed. Experimental results indicate that the application of ECW can suppress runaway electron beam instabilities. However, after the ECW is switched off, runaway electron beam instabilities can be excited. Furthermore, it was found that terminating the ECW can increase the density threshold for the onset of the Parail-Pogutse instability. These results provide valuable references for runaway electron mitigation in large-scale tokamak devices.