Controlling the energy of runaway electrons by emissive limiter biasing in tokamaks

Abstract

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.

x-ray irradiation analysis based on wavelet transform in tokamak plasma

“…Such a suppression of hard x-ray emission by MHD oscillations was also observed in other tokamaks [15]. Also, other example of the effect of biasing on plasma fluctuations can be seen in the experiments performed on the IR-T1 tokamak [14,16,17].…”

Biased Limiter and RHF Effects on X-Ray Intensity and Mirnov Oscillations

“…The confinement time of runaway electrons decreases as MHD oscillation increases. According to (2), a decrease of confinement time of runaway electrons reduces runaway electron generation [13]. Control and decreasing of runaway electrons is important issue to minimize damage to the tokamak wall.…”

“…Then, the development of experimental methods to decrease the number and energy of runaway electron is an important subject. For this purpose, various methods, including enhancing the magnetic turbulence [11]- [13], increasing the plasma density [1], and applying lower hybrid waves [14], have been applied. If the amplitude of MHD oscillation exceeds a certain level, hard X-ray intensity terminates.…”

Edge biasing and its impact on the edge and SOL turbulence

“…Several authors have studied the effect of biasing in the edge or SOL region. The biasing in these regions can be done in several ways e.g., divertor biasing [8][9][10][11][12], limiter biasing [13][14][15][16], emissive probe biasing [17,18], and electrode biasing [19][20][21][22][23][24][25][26][27][28]. An experiment carried out on the ISTTOK tokamak has shown [29] that electrode biasing in the edge region is more effective in comparison to limiter biasing.…”