Parametric study of non-relativistic electrostatic shocks and the structure of their transition layer

Abstract

Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell (PIC) simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant (SNR) shocks.

11 pages, 12 figures, accepted for publication in Physics of Plasmas

References in corpus (7)

• Particle acceleration in relativistic collisionless shocks: Fermi process at last?
• A Physical Relationship Between Electron-Proton Temperature Equilibration and Mach Number in Fast Collisionless Shocks
• Electron Shock Surfing Acceleration in Multidimensions: Two-dimensional Particle-In-Cell Simulation of Collisionless Perpendicular Shock
• Electrostatic and electromagnetic instabilities associated with electrostatic shocks: two-dimensional particle-in-cell simulation
• On the plasma temperature in supernova remnants with cosmic-ray modified shocks
• Nonrelativistic parallel shocks in unmagnetized and weakly magnetized plasmas
• Mach Number Dependence of Electron Heating in High Mach Number Quasiperpendicular Shocks

Cited by in corpus (7)

• Structure of a collisionless pair jet in a magnetized electron-proton plasma: flow-aligned magnetic field
• Modification of the formation of high-Mach number electrostatic shock-like structures by the ion acoustic instability
• The evolution of a slow electrostatic shock into a plasma shock mediated by electrostatic turbulence
• Collisional behaviors of astrophysical collisionless plasmas
• A thin-shell instability in collisionless plasma
• The interplay of the collisionless nonlinear thin-shell instability with the ion acoustic instability
• Conditions of structural transition for collisionless electrostatic shock