Magnitude of Short-Wavelength Electric Field Fluctuations in Simulations of Collisionless Plasma Shocks

Large-amplitude electrostatic fluctuations are routinely observed by spacecraft upon traversal of collisionless shocks in the heliosphere. Kinetic simulations of shocks have struggled to reproduce the amplitude of such fluctuations, complicating efforts to understand their influence on energy dissipation and shock structure. In this contribution, 1D particle-in-cell simulations with realistic proton-to-electron mass ratio are used to show that in cases with upstream electron temperature exceeding the ion temperature , the magnitude of the fluctuations increases with the ratio ω_pe/Ω_ce of electron plasma-to-cyclotron frequency ratio, reaching realistic values at ω_pe/Ω_ce=32 for the cases considered. The large-amplitude fluctuations are shown to be associated with ion phase-space holes. In the cases where upstream temperature ratio is reversed, the magnitude of the fluctuations remains small.