Firehose Instability in Astrophysical and Space Environments

The firehose instability is driven by a pressure anisotropy in a magnetized plasma when the plasma has T??? > T???, that is, the temperature along the magnetic field is higher than the perpendicular temperature. Such condition occurs commonly in astrophysical and space environments, for instance, when there are beams aligned with the background magnetic field. Recently, it was argued that around weak quasi-perpendicular shocks in high-?? plasmas of the intracluster medium, shock-reflected electrons propagating upstream cause the temperature anisotropy of T??? > T???. This electron temperature anisotropy can trigger the electron firehose instability (EFI). In the study, the kinetic properties of the EFI are first examined by the linear stability analysis based on the kinetic Vlasov-Maxwell theory and then further investigated by 2D Particle-in-Cell (PIC) simulations, especially focusing on those in high-?? (??~100) plasmas. We then discuss the implication of our work on electron acceleration in ICM shocks in clusters of galaxies