Abstract
Runaway electron populations seeded from the hot tail generated by the rapid cooling in plasma-terminating disruptions are a serious concern for next-step tokamak devices such as ITER. Here, we present a comprehensive treatment of the thermal quench, including the superthermal electron dynamics, heat and particle transport, atomic physics, and radial losses due to magnetic perturbations: processes that are strongly linked and essential for the evaluation of the runaway seed in disruptions mitigated by material injection. We identify limits on the injected impurity density and magnetic perturbation level for which the runaway seed current is acceptable without excessive thermal energy being lost to the wall via particle impact. The consistent modeling of generation and losses shows that runaway beams tend to form near the edge of the plasma, where they could be deconfined via external perturbations.
Highlights
One of the crucial problems facing magnetic fusion devices with large plasma currents is the occurrence of plasma-terminating disruptions [1]
Runaway electron populations seeded from the hot tail generated by the rapid cooling in plasmaterminating disruptions are a serious concern for next-step tokamak devices such as ITER
We present a comprehensive treatment of the thermal quench, including the superthermal electron dynamics, heat and particle transport, atomic physics, and radial losses due to magnetic perturbations: processes that are strongly linked and essential for the evaluation of the runaway seed in disruptions mitigated by material injection
Summary
The associated induced electric field, which in turn drives the runaway generation. We present an integrated model of thermal quench dynamics, including hot-tail generation and losses due to magnetic perturbations, and use it to explore viable scenarios with combined deuterium and neon injection. We model the current evolution together with the magnetic field fluctuation induced energy and particle transport, as the injected material and bulk plasma evolve into a cold free electron population and hot population, with densities ncold and nhot, respectively. NRE is the density of electrons having momentum p > pmax and E is the electric field parallel to the magnetic field, which in the cylindrical approximation evolves at radius r according to μ0. The temperature of the cold electron population is determined from the associated energy density Wcold 1⁄4 ð3=2ÞncoldTcold, which is evolved according to
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