Contributions to the cross shock electric field at supercritical perpendicular shocks: Impact of the pickup ions

TL;DR

This study uses particle-in-cell simulations to analyze how pickup ions and solar wind ions influence the cross shock electric field at supercritical perpendicular shocks, revealing different behaviors based on pickup ion density.

Contribution

It provides the first detailed analysis of pickup ions' impact on the cross shock electric field at supercritical perpendicular shocks using self-consistent PIC simulations.

Findings

At 25% pickup ion density, the shock front is nonstationary with a self-reforming process.

At 55% pickup ion density, the shock becomes stationary with a stable extended foot.

Pickup ions dominate the Lorentz term in the upstream foot region.

Abstract

A particle-in-cell code is used to examine contributions of the pickup ions (PIs) and the solar wind ions (SWs) to the cross shock electric field at the supercritical, perpendicular shocks. The code treats the pickup ions self-consistently as a third component. Herein, two different runs with relative pickup ion density of 25% and 55% are presented in this paper. Present preliminary results show that: (1) in the low percentage (25%) pickup ion case, the shock front is nonstationary. During the evolution of this perpendicular shock, a nonstationary foot resulting from the reflected solar wind ions is formed in front of the old ramp, and its amplitude becomes larger and larger. At last, the nonstationary foot grows up into a new ramp and exceeds the old one. Such a nonstationary process can be formed periodically. hen the new ramp begins to be formed in front of the old ramp, the Hall term mainly contributed by the solar wind ions becomes more and more important. The electric field Ex is dominated by the Hall term when the new ramp exceeds the old one. Furthermore, an extended and stationary foot in pickup ion gyro-scale is located upstream of the nonstationary/self-reforming region within the shock front, and is always dominated by the Lorentz term contributed by the pickup ions; (2) in the high percentage (55%) pickup ion case, the amplitude of the stationary foot is increased as expected. One striking point is that the nonstationary region of the shock front evidenced by the self-reformation disappears. Instead, a stationary extended foot dominated by Lorentz term contributed by the pickup ions, and a tationary ramp dominated by Hall term contributed by the solar wind ions are clearly evidenced. The significance of the cross electric field on ion dynamics is also discussed.