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.