Ion Temperature Effects on Electrostatic Instabilities in Partially Magnetized Plasmas*

In partially magnetized plasmas, the ion temperature can be an appreciable fraction of the electron temperature. Within partially magnetized plasmas, there are kinetic instabilities that are driven by the E×B drift of electrons, such as electron cyclotron drift instability (ECDI) and modified two-stream instability (MTSI).  The electrostatic plasma waves generated by ECDI and MTSI may resonate with the warm ion population, affecting the waves’ dispersion. The kinetic dispersion relation, accounting for warm, unmagnetized ions and warm, magnetized electrons, is solved via complex root-finding for both ECDI and MTSI modes [Phys. Plasmas 30, 032108 (2023)]. The nonzero ion temperature causes ion Landau damping, decreasing the growth rate of the instabilities. It is found that short wavelength ECDI modes are more strongly affected by this damping than long wavelength MTSI modes. In addition, the kinetic dispersion relation is assessed in comparison to the fluid MTSI proposed by McBride et al. [Phys. Fluids 15 2367–2383 (1972)]. Here, we formulate a kinetic MTSI theory by relaxing the conditions proposed by McBride et al. The kinetic MTSI description allows us to study the electron and ion Landau damping effects, which the fluid limit neglects.