Magnetized collisionless shocks are found where super-magnetosonic plasma flows interact in a pre-existing magnetic field, and are the most prevalent type of shocks in the universe, from planetary bow shocks and the heliopause to supernova remnants and galaxy clusters. These shocks are known to accelerate particles to extremely high energies, and are mediated by electromagnetic effects over characteristic length scales much shorter than the particle mean free path. Our understanding of these shocks has been traditionally based on spacecraft measurements and telescope observations, but these are limited to either the smallest or largest scales in uncontrolled plasma conditions. Consequently, many fundamental questions of shock physics remain unanswered, such as how energy is partitioned across a shock or how particles are accelerated by shocks.

By utilizing high-energy lasers and HED plasmas, these questions can be addressed in the lab, with the goal of complementing spacecraft and telescope data with well-controlled and diagnosed experiments.  The lasers ablate thin foils to drive supersonic piston plasmas, which sweep up ambient plasma and magnetic fields like a snowplow to drive a collisionless shock.  While these laboratory shocks occur over only a few millimeters and nanoseconds, orders of magnitude smaller than those seen in space, they match key dimensionless parameters like Mach number and scale size.  Combined with large particle-in-cell simulations, this allows direct comparisons between lab and astrophysical collisionless shocks.

We are currently performing experiments to study partilcle acceleration, shock heating, and shock structure on several of the world's largest HED facilities, including the Omega Laser Facility at the Laboratory for Laser Energetics (LLE), the National Ignition Facility (NIF) at Lawrence Livermore National Lab, and the Z Machine at Sandia National Labs.

Magnetized Transport in HED Plasmas

Anomalously fast diffusion of plasma across magnetic fields has long been recognized in magnetic fusion devices and laser plasmas. Micro-instabilities driven by gradients in plasma parameters give rise to convective flow patterns on meso to global scales, which leads to correspondingly enhanced diffusion coefficients. Alternative mechanisms such as the Nernst effect can similarly drive magnetic field transport.  While anomalous transport has been demonstrated in many HED plasma experiments, it is especially relevant to magnetized ICF schemes such as MagLIF, where this physics is not typically included in MHD design codes.

Relevant Publications

• S. Malko, et al. "Observation of a magneto-Rayleigh-Taylor instability in magnetically collimated plasma jets,"  Physical Review Research 6, 023330 (2024).