Temperature Relaxation Rates in Strongly Magnetized Plasmas

Strongly magnetized plasmas, which are characterized by having a gyrofrequency larger than the plasma frequency, are known to exhibit novel transport properties. Previous works studying pure electron plasmas have shown that strong magnetization significantly inhibits energy exchange between parallel and perpendicular directions, leading to a prolonged time for the relaxation of temperature anisotropy. In this work, we extend the study of temperature relaxation rates to electron-ion plasmas. A time evolution equation is obtained for the temperatures and temperature anisotropies of both species. It is found that when electrons are strongly magnetized and ions are only weakly magnetized, the magnetic field strongly suppresses the perpendicular energy exchange rate of electrons, whereas the parallel exchange rate slightly increases in magnitude compared to the unmagnetized values. However, the ion perpendicular and parallel energy exchange rates slightly increase in magnitude compared to the unmagnetized values. Consequently, during equilibration electron parallel temperature rapidly aligns with the ion temperature, while the electron perpendicular temperature remains an adiabatic invariant. Total electron and ion temperatures relax to the equilibrium temperature much slower, as determined by the electron perpendicular energy exchange rate.