Jaehong Park† , Chuang Ren, Eric G. Blackman, and Xianglong Kong
Whether an efficient collisionless temperature equilibration mechanism exists for a two-temperature ion-electron plasma, with Ti>T_e, is important for understanding astrophysical phenomena such as two-temperature accretion flows and relativistic collisionless shocks in GRBs. Here we study whether the two-stream, Weibel, and oblique instabilities driven by ion counter-streaming and/or temperature anisotropy can be such a mechanism. PIC simulations with different ion-electron mass ratios show that the Weibel instability alone induces only a weak electron-ion coupling in either non-magnetized or magnetized plasmas [Ren et al.(2007)] and the two-stream instability alone also provides a weak coupling. We provide 2D PIC simulation results to show interplay among these instabilities and that distinct stages with different dominant modes occur during the nonlinear evolution period. Although 2D results show stronger electron-ion coupling than 1D instabilities, it is still too weak to rule out existing two-temperature accretion solutions. We also numerically solve non-relativistic quasi-linear equations for 1D Weibel plus 1D two-stream modes to compare the results with 2D PIC simulations.
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