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Structure of cosmic ray-modified perpendicular shocks




Kinetic diffusion of cosmic rays ahead of perpendicular shocks induces charge non-neutrality, which is mostly, yet not completely, screened by the bulk plasma via polarization drift current. Hydrodynamic shear instabilities as well as the modified Buneman instability of the polarization current generate the turbulence necessary for a Fermi-type acceleration. Thus, similar to the case of parallel shocks, in perpendicular shocks the diffusing cosmic rays generate unstable plasma currents that in turn excite turbulence. This allows for a self-consistent evolution of a shock-cosmic ray system. In the kinetic regime of the modified Buneman instability, electrons may be heated in the cosmic ray precursor.