Parallel Collisionless Shocks in strongly Magnetized Electron-Ion Plasma. I. Temperature anisotropies

Abstract

Collisionless electron-ion shocks are fundamental to astrophysical plasmas, yet their behavior in strong magnetic fields remains poorly understood. Using Particle-in-Cell (PIC) simulations with the SHARP-1D3V code, we investigate the role of the ion magnetization parameter ${\sigma }_i$ in parallel shock transitions. Strongly magnetized converging flows (${\sigma }_i>1$) exhibit lower density compression ratios ($R\sim 2$), smaller entropy jumps, and suppressed particle acceleration, while maintaining pressure anisotropy stability due to conserved perpendicular temperatures across the transition region, alongside increased parallel temperatures. In contrast, weakly magnetized shocks drive downstream mirror and firehose instabilities due to ion temperature anisotropy, which are suppressed in strongly magnetized cases. Additionally, weakly magnetized shocks exhibit the onset of a supra-thermal population induced by shock-drift acceleration, with most of the upstream kinetic energy thermalized for both electrons and ions in the downstream region. Our results demonstrate that perpendicular temperatures for both species are conserved in weakly and strongly magnetized cases and highlight deviations from standard ideal magnetohydrodynamic (MHD) behavior in strongly magnetized cases. These findings provide critical insights into the role of magnetic fields in parallel collisionless astrophysical shocks.

11 pages, 6 figures. Accepted to ApJ. Link to animations for simulations at http://mohamadshalaby.github.io/Pshock_Sig01.html

References in corpus (25)

• Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar wind
• Particle Acceleration in Relativistic Magnetized Collisionless Electron-Ion Shocks
• The microphysics of collisionless shock waves
• Rayleigh-Taylor Instabilities in Young Supernova Remnants Undergoing Efficient Particle Acceleration
• Proton Temperature Anisotropy Variations in Inner Heliosphere Estimated with First Parker Solar Probe Observations
• Temperature Anisotropy in a Shocked Plasma: Mirror-Mode Instabilities in the Heliosheath
• How large can the electron to proton mass ratio be in Particle-In-Cell simulations of unstable systems?
• PIC Simulation Methods for Cosmic Radiation and Plasma Instabilities
• Simulation of the growth of the 3D Rayleigh-Taylor instability in Supernova Remnants using an expanding reference frame
• SHARP: A Spatially Higher-order, Relativistic Particle-in-Cell Code
• A new cosmic ray-driven instability
• Loading Relativistic Maxwell Distributions in Particle Simulations
• Importance of resolving the spectral support of beam-plasma instabilities in simulations
• Growth of beam-plasma instabilities in the presence of background inhomogeneity
• The growth of the longitudinal beam-plasma instability in the presence of an inhomogeneous background
• Density jump as a function of magnetic field strength for parallel collisionless shocks in pair plasmas
• Weibel instability beyond bi-Maxwellian anisotropy
• Localized enhancements of energetic particles at oblique collisionless shocks
• On the Generation of Compressible Mirror-mode Fluctuations in the Inner Heliosheath
• Deciphering the physical basis of the intermediate-scale instability
• The Temperature Anisotropy and Helium Abundance Features of Alfvénic Slow Solar Wind Observed by Parker Solar Probe, Helios, and Wind Missions
• Density jump as a function of magnetic field for collisionless shocks in pair plasmas: the perpendicular case
• In-situ Measurement of the Energy Fraction in Supra-thermal and Energetic Particles at ACE, Wind, and PSP Interplanetary Shocks
• Modified jump conditions for parallel collisionless shocks
• Energy Dissipation in Strong Collisionless Shocks: The Crucial Role of Ion-to-Electron Scale Separation in Particle-in-Cell Simulations