Effect of limiter biasing on runaway electrons in tokamaks

Tokamak limiter biasing is one of the methods for controlling the radial electric field and can induce a transition to an improved confinement state. Moreover, the mean energy of runaway electrons and therefore emitted hard x-rays depends on fluctuations of plasma current and loop voltage, which can be controlled using limiter biasing. In this paper, we studied the effects of a biased limiter on loop voltage and hard x-rays. Hard x-ray emissions are produced by the collision of runaway electrons with limiters. Experiments were done by discharges in the range of a positive 180-380 V biased limiter.