April 4-6

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Author: Kaixuan Fan
Requested Type: Poster
Submitted: 2022-03-02 07:21:34

Co-authors: X.Q.Xu, B.Zhu, P.F. Li

Contact Info:
Peking University
Yiheyuan Road No.5, Haidian di
Beijing, Beijing   100871

Abstract Text:
New kinetic Landau-Fluid closures, based on the cut-off Maxwellian distribution is derived. A special static case is considered (the frequency ω=0). In the strong collisional regime, our model reduces to Braginskii’s heat flux model, and the transport is local. In the weak collisional regime, our model indicates that the heat flux is non-local and recovers Hammett-Perkins model while the value of the cut-off velocity approaches to infinity. We compare the thermal transport coefficient χ of Maxwellian, cut-off Maxwellian and super-Gaussian distribution. The results show that the reduction of the high-speed tail particles leads to the corresponding reduction of the thermal transport coefficient χ across the entire range of collisionality, more reduction of the free streaming transport toward the weak collisional regime. In the collisionless limit, χ approaches to zero for the cut-off Maxwellian and the super-Gaussian distribution, but remains finite for Maxwellian distribution. χ is complex if the cut-off Maxwellian distribution is asymmetric. The Im(χ) approaches to different convergent values in both collisionless and strong collisional limit respectively. It yields an additional streaming heat flux in comparison with the symmetric cut-off Maxwellian distribution. Furthermore, due to the asymmetric distribution, there is a background heat flux q_0 though there is no perturbation. The derived Landau-Fluid closures are general for fluid moment models, and applicable for the cut-off Maxwellian distribution in an open magnetic field line region, such as the Scape-Off-Layer (SOL) of Tokamak plasmas, in the thermal quench plasmas during a tokamak disruption, and the super-Gaussian electron distribution function due to inverse bremsstrahlung heating in laser-plasma studies.