Runaway electrons generated during spontaneous disruptions in the EAST tokamak

The runaway electrons produced during spontaneous disruptions were studied when lower hybrid wave heating was used in the EAST tokamak. Up to 60% of the pre-disruptive plasma current can be transferred to runaway current in the disruptions when seed fast electrons exist in the plasma. The evolutions of the radial profile of the electric field and the runaway electron density are obtained with the aid of an one-dimensional self-consistent simulation model. The results clearly show the competition between the radial diffusion of the induced electric field and growth of the runaway current. They also indicate that the dominant runaway generation mechanism was of Dreicer type, and half of the decreasing magnetic energy was converted into runaway electron kinetic energy during the disruptions.