Implicit hybrid simulation of magnetic reconnection and the ion-temperature-gradient-driven instability

Cheng, Jianhua

Graduate Thesis Or Dissertation

Implicit hybrid simulation of magnetic reconnection and the ion-temperature-gradient-driven instability Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/8336h193d

Abstract

This thesis presents a second-order accurate, semi-implicit δf hybrid simulation with Lorentz force ions and fluid electrons. This model includes full ion kinetic effects and is suitable for studying magnetohydrodynamics (MHD) scale physics. We report the first particle-in-cell simulation of nonlinear ion Landau damping of ion acoustic waves, and the results agree with theory. The numerical damping associated with the implicit time advance is also analyzed. We have investigated the full evolution of resistive tearing mode. The linear growth rate is in reasonable agreement with resistive MHD theory. The nonlinear growth and saturation stage has been observed and compared quantitatively with the resistive MHD theory. The simulation shows that current sheets of large aspect ratio tend to develop multiple islands and eventually coalesce to a single elongated island. During this process, significant ion heating inside the island was observed. The simulation shows that over 50% of the dissipated magnetic energy is converted into the kinetic energy of ions for a current sheet with sufficiently large aspect ratios, which is comparable with previous experimental measurements. We also compared the simulation to the extended-MHD NIMROD code for the ion-temperature-gradient-driven instability. The hybrid kinetic and fluid calculations agree well near the marginal stability point, but disagree as k_⊥ρ_i or ρ_i/L_Ti increases where the kinetic effects become important. Good agreement between the models for the shape of the unstable global eigenfunction is reported. The results help quantify how far fluid calculations can be extended accurately into the kinetic regime.

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