Mach Number Dependence of Ion-scale Kinetic Instability at Collisionless Perpendicular Shock: Condition for Weibel-dominated Shock

Abstract

We investigate ion-scale kinetic plasma instabilities at the collisionless shock using linear theory and nonlinear Particle-in-Cell (PIC) simulations. We focus on the Alfvén-ion-cyclotron (AIC), mirror, and Weibel instabilities, which are all driven unstable by the effective temperature anisotropy induced by the shock-reflected ions within the transition layer of a strictly perpendicular shock. We conduct linear dispersion analysis with a homogeneous plasma model to mimic the shock transition layer by adopting a ring distribution with finite thermal spread to represent the velocity distribution of the reflected ions. We find that, for wave propagation parallel to the ambient magnetic field, the AIC instability at lower Alfvén Mach numbers tends to transition to the Weibel instability at higher Alfvén Mach numbers. The instability property is, however, also strongly affected by the sound Mach number. We conclude that the instability at a strong shock with Alfvén and sound Mach numbers both in excess of $\sim 20-40$ may be considered as Weibel-like in the sense that the reflected ions behave essentially unmagnetized. Two-dimensional PIC simulations confirm the linear theory and find that, with typical parameters of young supernova remnant shocks, the ring distribution model produces magnetic fluctuations of the order of the background magnetic field, which is smaller than those observed in previous PIC simulations for Weibel-dominated shocks. This indicates that the assumption of the gyrotropic reflected ion distribution may not be adequate to quantitatively predict nonlinear behaviors of the dynamics in high Mach number shocks.

18 pages, 14 figures. Accepted for publication in Physics of Plasmas

References in corpus (12)

• Particle acceleration in relativistic collisionless shocks: Fermi process at last?
• Saturation mechanism of the Weibel instability in weakly magnetized plasmas
• Electron Shock Surfing Acceleration in Multidimensions: Two-dimensional Particle-In-Cell Simulation of Collisionless Perpendicular Shock
• Electron Surfing and Drift Accelerations in a Weibel-dominated High-Mach-number Shock
• Nonrelativistic collisionless shocks in weakly magnetized electron--ion plasmas: two-dimensional particle-in-cell simulation of perpendicular shock
• Observational Evidence for Stochastic Shock Drift Acceleration of Electrons at the Earth's Bow Shock
• Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region
• Magnetic field amplification by the Weibel instability at planetary and astrophysical high-Mach-number shocks
• Nonlinear dynamics of the ion Weibel-filamentation instability: an analytical model for the evolution of the plasma and spectral properties
• Absence of Electron Surfing Acceleration in a Two-Dimensional Simulation
• Kinetic simulations of nonrelativistic perpendicular shocks of young supernova remnants. I. Electron shock-surfing acceleration
• The Dynamics of a High Mach Number Quasi-Perpendicular Shock: MMS Observations

Cited by in corpus (6)

• Theory of Electron Injection at Oblique Shock of Finite Thickness
• Enhanced Magnetic Field Amplification by Ion-Beam Weibel Instability in Weakly Magnetized Astrophysical Shocks
• Weibel-dominated quasi-perpendicular shock: hybrid simulations and in situ observations
• Electron Weibel instability and~quasi-magnetostatic structures in~an~expanding collisionless plasma
• Criteria for ion acceleration in laboratory magnetized quasi-perpendicular collisionless shocks: when are 2D simulations enough?
• Energy partition in collisionless counterstreaming plasmas