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.

The high-energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactor and reduce its lifetime. Therefore, it is important to find methods for decreasing the generation of runaway electrons and their energy. Tokamak limiter biasing is one of the methods for controlling the radial electric field and can induce the transition to an improved confinement state. In this paper, the generation of runaway electrons and the energy they can obtain is investigated theoretically. Moreover, in order to apply radial biasing, emissive limiter biasing is utilized. This biasing limiter can apply ±380 V in the cold and hot (emissive) states to the plasma and can result in an increase of negative bias current in the hot state. In fact, in this experiment, the researchers try to decrease the generation of runaway electrons and their energy by using emissive limiter biasing inserted in the IR-T1 tokamak. The mean energy of these electrons was obtained by hard x-ray spectroscopy.

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