Instability analysis of asymmetric counter-streaming plasmas in parallel magnetized collisionless shock experiments

Collisionless shocks are ubiquitous in our universe and serve as natural sites for accelerating cosmic rays to PeV energies via diffusive shock acceleration. Recent numerical and observational studies have found that cosmic ray acceleration is most efficient for large Alfvénic Mach Number M_A (M_A>100 for supernova remnants (SNR)), and when the magnetic field is quasi-parallel to the shock propagation direction. Recent experiments conducted on the OMEGA-EP laser facility studied the formation of collisionless shocks in these large M_A, quasiparallel environments [1]. We use experimental plasma conditions to initialize first principle kinetic, particle-in-cell (PIC) simulations aimed at identifying the dominant streaming instabilities - in particular the ion-Weibel & non-resonant (NRI) instabilities - capable of driving shock formation in the experimental platform. These simulations are complemented with first-principles analytic theory, and demonstrate that the ion-Weibel instability is indeed present and matches experimental measurements taken within the first 3ns of the interaction. Additional work explores the role of other streaming instabilities and the experimental modifications required to accelerate the onset of shock formation.

1 S. Bolaños, et al. 2024, Phys. Rev. E 110.