Laser-Driven Collisionless Shockwaves in Magnetized High-Energy-Density Laboratory Plasmas

Derek Schaeffer

University of California, Los Angeles

Tuesday, September 12, 2023

12:00pm

NW17-218 Hybrid

PSFC Seminars

Abstract: As a fundamental process for converting kinetic to thermal energy, collisionless shocks are ubiquitous throughout the heliosphere and astrophysical systems, from Earth's magnetosphere to supernova remnants. While these shocks have been studied for decades by spacecraft, telescopes, and numerical simulations, there remain key open questions in the fundamental physics of collisionless shocks, such as: How do shocks accelerate particles to extremely high energies? or How is energy partitioned between particles across a shock?

In this talk, I will discuss results from high-energy-density experiments and simulations on the formation of supercritical collisionless shocks created through the interaction of a supersonic laser-driven magnetic piston and magnetized ambient plasma.  Through proton and refractive imaging, we observe for the first time a fast, high-Mach-number shock, comparable to some of the strongest shocks in the heliosphere.  By probing particle velocity distributions with Thomson scattering, we directly measure the coupling interactions between the piston and ambient plasmas that are critical steps in the formation of magnetized collisionless shocks.  Particle-in-cell simulations constrained by experimental data further detail the shock formation process and predict key signatures that are observed in experiments.  I will also discuss how the development of this experimental platform can complement, and in some cases overcome, the limitations of similar measurements undertaken by spacecraft missions and can allow novel investigations of energy partitioning and particle acceleration in shocks.

Bio: Derek Schaeffer is an Assistant Professor in the Department of Physics & Astronomy at the University of California, Los Angeles.  He received his BA in Physics and Philosophy from Cornell University and his PhD in Physics from UCLA.  He did his postdoctoral work at Princeton in high-energy-density laboratory astrophysics, where he was one of the primary developers of pioneering laboratory experiments that utilize high-energy lasers to generate astrophysically-relevant collisionless shocks in high-energy-density plasmas.  His research focuses on experiments and numerical simulations of the interaction of magnetized plasmas and strongly driven high-energy-density flows, with applications to astrophysical phenomena, particle acceleration, and inertial fusion energy.