Timescale of fast thermal quench based on general thermal diffusion induced by stochastic magnetic fields

Abstract

The timescale of fast thermal quench (TQ) based on the stochastic magnetic fields induced thermal diffusion has been investigated. First, a general expression of electron thermal diffusivity induced by the stochastic magnetic fields is obtained via connecting the electron thermal diffusivities in multiple collisional regimes, which can be applicable to a wide range of collisional parameters. The dependence of this general diffusivity on the electron temperature, density, and the plasmas size is discussed. Then, under different tokamak parameters, the evolution of the electron temperature profile and the characteristic timescale of fast TQ are analyzed based on the general electron thermal diffusivity. It is found that the core electron temperature can rapidly collapse in less than 1 ms in the initial stage of TQ. The fast TQ timescale defined as the time interval for the core electron temperature dropping from 90% to 20% of the initial value is reduced (enhanced) by increasing the initial electron temperature (plasma size), which is qualitatively consistent with the experimental observations. However, the decay rate of electron temperature gets slower due to flattening of the electron temperature profile, and the scaling of fast TQ timescale with plasma size does not exactly follow the linear relation. This indicates that other fast transport mechanisms, such as heat convection, nonlocal transport, and so on may be necessary to maintain the fast decay rate of electron temperature.