Collisionless shock formation and electron acceleration in the laboratory (A. Grassi - SLAC, USA)
LERMA-LPP-LULI Plasma Physics Seminars
Collisionless shocks are ubiquitous in the Universe and play an important role in the slow down of plasma flows, magnetic field generation/amplification, and particle acceleration. Depending on the plasma conditions, different plasma processes are believed to mediate shock formation and particle injection, however, these are not yet fully understood. Kinetic plasma simulations and high-energy-density (HED) laser-plasma experiments can help probe different plasma conditions and validate models for shock acceleration.
I will present the results of recent laser-driven experiments performed at the National Ignition Facility (NIF) that have observed for the first time the formation of high-Mach number turbulent collisionless shocks and nonthermal electron acceleration to relativistic energies. I will also discuss the comparison of the experimental results with large-scale particle-in-cell (PIC) simulations, which help reveal the microphysics of shock formation and the details of electron injection. The simulations take into account the time-dependent density and velocity profiles of the flows, that are inferred from hydrodynamical simulations and observed in the experimental Thomson scattering data.
This study demonstrates that inhomogeneous ablation plasma profiles increase the coherent length of magnetic field structures and make shock formation more efficient. It also indicates that high-Mach number turbulent shocks can be effective at injecting electrons from the thermal pool to nonthermal energies within the shock transition. Our results open a new path for the study of the shock acceleration physics in the laboratory that can greatly complement astrophysical observations and help validate theoretical and numerical models.
Salle 509 - couloir 24-34, 5ème étage - Sorbonne Université, campus Pierre et Marie Curie - 14:00