Abstract
The hot-tail (H-T) effect in disruption of impurity injections is considered. The contribution of the H-T effect to runaway electron (RE) current, which arises from fast thermal quenching, is studied using a two-dimensional Fokker–Planck simulation. It is found that in a high-density plasma the total RE current is reduced owing to the high collisionality. We also found that if the thermal quench is fast enough to invoke the H-T effect, the effect produces more seed REs than when the H-T effect is excluded even in high-density plasmas. In the high-density region () with fast thermal quenching, nevertheless the increment of the seed REs due to the H-T effect is generally small (tens of milliamperes) while the increment of the total RE current reached 2 MA owing to the avalanche effect.
Highlights
Disruption is one of the most serious events in tokamaks, since it induces huge electromagnetic force to the device and generates high-energy runaway electron (RE) which may cause the damage of plasma facing components [1]
The drop of the plasma temperature and the increase of the electron density and the effective charge during thermal quench owing to impurity injection are implemented
This is because we focus on not RE distribution in high energy region but the number of REs generated in disruptions
Summary
Disruption is one of the most serious events in tokamaks, since it induces huge electromagnetic force to the device and generates high-energy REs which may cause the damage of plasma facing components [1]. The collisional suppression [6] is one of the strategies This strategy aims to suppress the RE generation by the rapid increase of electron density. The collisional suppression, tends to shorten the thermal quench duration and may enhance the primary RE generation through the so-called “hot-tail (H-T) effect” [18,19]. Aim of this paper is the estimation of the RE current generated in the disruption mitigating plasma including H-T effect. The drop of the plasma temperature and the increase of the electron density and the effective charge during thermal quench owing to impurity injection are implemented . The RE current generation is suppressed with the increase of the electron density as expected.
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