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

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. When 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 E x 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 stationary 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.

Physical Roles of Interstellar-Origin Pickup Ions at the Heliospheric Termination Shock: Impact on the Shock Front Microstructures and Nonstationarity

“…Similar results for runs 2 and 3 are shown in Figures 5(b) (PUI%=10) and (c) (PUI%=25), respectively. Results are summarized as follows.(1) As PUI% increases, the time variation of B y,max and E x,max persists, but the fluctuations' amplitude becomes weaker.(2) The time-averaged values of B y,max and E x,max decrease as PUI% increases; then, since the cross-shock potential becomes lower, more directly transmitted SWIs and PUIs are expected for higher PUI% case, which has been confirmed in previous PIC simulations (Matsukiyo & Scholer 2011;Yang et al 2012a). (3) Only the time-averaged value of the downstream ratio B y,max /B DS (green) is almost independent ofPUI%.…”

“…Herein, the shock is produced by the injection method as in previous PIC simulations ( Lee et al 2005;Matsukiyo et al 2007;Yang et al 2012a). In order to reproduce self-consistently the impacts of PUIs, three particlespecies are introduced within our PIC code: electrons, SWIs, and PUIs.…”

IMPACT OF PICKUP IONS ON THE SHOCK FRONT NONSTATIONARITY AND ENERGY DISSIPATION OF THE HELIOSPHERIC TERMINATION SHOCK: TWO-DIMENSIONAL FULL PARTICLE SIMULATIONS AND COMPARISON WITHVOYAGER 2OBSERVATIONS

“…We use a 2-D electromagnetic PIC code to simulate the evolving structures of supercritical, collisionless, perpendicular shocks with PUIs. Simulations of nonstationary shocks have been performed by 1-D PIC codes where PUIs are included (Chapman et al 2005;Matsukiyo & Scholer 2011;Yang et al 2012a). In this paper, we expand our simulation code to 2-D in order to investigate the ripples of the shock front.…”

“…Selfreformation of the shock front was predicted by both hybrid simulations (Hellinger et al 2002;Lembege et al 2009;Yuan et al 2009;Tiu 2011;Su et al 2012) andPIC simulations (Lembege &Dawson 1987;Hada et al 2003;Scholer et al 2003;Nishimura et al 2003;Lee et al 2005a;Yang et al 2009Yang et al , 2013 for large Mach number and low β i shocks, where β i is the ratio of the thermal pressure of ions to the magnetic pressure. Even in the presence of PUIs, the self-reformation can still be retrieved in some conditions (Lee et al 2005b;Chapman et al 2005;Oka et al 2011;Yang et al 2012a;Matsukiyo & Scholer 2014). For the heliospheric TS, the values of β i and the Mach number are relatively low and high, respectively.…”

Simulations of pickup ion mediated quasi‐perpendicular shocks: Implications for the heliospheric termination shock

“…PIC simulations of the TS started about a decade ago [ Lee et al , ; Matsukiyo et al , ; Matsukiyo and Scholer , ; Yang et al , ]. The above mentioned basic features reproduced by the hybrid simulations are also confirmed by the PIC simulations.…”