Observation of the generation and evolution of long-lived runaway electron beams during major disruptions in the HuanLiuqi-2A tokamak

Abstract

In an experimental study of the runaway electron generation during major disruptions in the HuanLiuqi-2A (commonly referred to as HL-2A) [L. W. Yan, Nucl. Fusion 51, 094016 (2011)] tokamak, detailed time and space resolved x-ray images of the long-lived runaway electron beam in flight have been observed and these allow a detailed analysis of the generation and evolution of the disruption produced runaway electron beam in a major disruption, where the conversion efficiency of pre-disruption plasma current into runaway current is up to 55% on HL-2A tokamak. Moreover, a delay of about 7 ms between the start of the disruption and the formation of runaway electron beam has been found. With the aid of the Equilibrium FIT (EFIT) code, magnetic configuration reconstruction has made possible a detailed observation of the magnetic flux geometry evolution during major disruptions. The EFIT magnetic configuration reconstructions show that the delay is due to the transient strong deformation of the magnetic configuration in the initial stage of the current quench, which may provide a possibility of suppressing or mitigating the runaway electron beam during this period by massive gas injection or other methods.