Entropy modes in pair plasmas*

Unlike many instabilities that are absent in electron-positron plasmas due to their unique mass symmetry [1], we find that slab entropy modes -- an electromagnetic micro-instability driven by plasma inhomogeneity still persists in pair plasmas. In order to appropriately describe magnetized relatively low density electron-positron plasmas, our previous gyrokineitc analysis on the slab entropy modes [2] has been generalized to include electron finite Larmor radius (FLR) effects and Debye shielding effects. Both electron FLR and Debye shielding effects are stabilizing; in particularly, as Debye length $\lambda_D$ approaches electron/positron gyroradius $\rho$, entropy modes are largely suppressed. Analytical derivation of dispersion relation, stability analysis as well as nonlinear gyrokinetic simulations of this mode in pair plasmas will be presented.[1] Tsytovich and Wharton, Comments Plasma Phys. Controlled Fusion \textbf{4}, 91 (1978)[2] Rogers, Zhu and Francisquez, \textit{Phys. Plasmas} \textbf{25}, 052115 (2018)