A hybrid simulation of contact discontinuity

Abstract

Contact discontinuities in a collisionless plasma are studied by hybrid simulations, in which ions are treated as particles and electrons are considered as a fluid. It is demonstrated that contact discontinuity with a stable density ramp can exist in cases with a finite electron temperature. An electron pressure gradient is present across the contact discontinuity, leading to the presence of a parallel electric field and hence field‐aligned potential increase (ΔΦ∥) in the transition region. By reflecting ions at the discontinuity, this parallel electric potential peak reduces the interpenetration between hot and cold ions and maintains a stable density ramp across the contact discontinuity. The ratio of the field‐aligned electric potential energy to ion thermal energy, eΔΦ∥/kTi, is found to be an increasing function of Te/Ti, where Te and Ti are respectively the electron and ion temperature.

A theoretical and simulation study of the contact discontinuities based on a Vlasov simulation code

“…Their hybrid simulation results are similar to the one obtained by Wu et al [1994]. But their full particle code simulation showed that the CD structure is unstable in the ion time scale.…”

“…[34] In summary, the stability of a CD, a long-term controversial issue [Wu et al, 1994;Lapenta and Brackbill, 1996], is reexamined analytically and numerically in this paper. Our analysis shows that the electron and the ion temperature profiles must be out of phase across the CD if the CD structure is to be stable in the electron time scale and with zero electron heat flux on either side of the CD.…”

“…[14] Note that a finite potential jump has been found in the previous CD simulations [Wu et al, 1994;Lapenta and Brackbill, 1996]. The initial conditions used in the previous simulation studies are characterized by [p i ] = [p e ] = 0 and the jumps of T i and T e are in phase across the CD.…”

“…[3] Although the jump condition of the CD is the simplest one among all the MHD shocks and discontinuities, the stability of the CD structure in the kinetic plasma simulations has become a controversial issue in the past 10 years [e.g., Wu et al, 1994;Lapenta and Brackbill, 1996].…”

“…[4] Wu et al [1994] studied the stability of the CD structure based on a hybrid simulation model [Swift and Lee, 1983]. The hybrid simulation treats ions as macro particles and electrons as a fluid.…”