Electron cyclotron microinstability in the foot of a perpendicular shock: A self-consistent PIC simulation

We have performed one-dimensional full particle simulations of perpendicular shocks and found that an electron cyclotron microinstability can develop in the foot during the self-reformation phase of low βi supercritical shocks. The instability is excited by the beam of reflected ions interacting with the incoming electrons. It exhibits a rapid growth, and propagates along the shock normal towards upstream. This instability, which does not require high Mach number, has a frequency comparable to the electron cyclotron frequency and a wavelength shorter than the electron inertia length. It basically results from the coupling of electron Bernstein waves with an ion beam mode carried by the reflected ions. Dispersion properties in the foot are analysed. We discuss the effects of varying parameters, in particular as the fake ion-to-electron mass ratio used in the simulations converges to more realistic values. Comparison with other microinstabilities evidenced in recent full particle simulations of shocks is outlined.