Laboratory study of magnetized collisionless shock formation in an oblique geometry and the effect of the ion-electron collisions*

Collisionless shocks are ubiquitous in astrophysics and a possible source of the highest-energy cosmic rays (CRs) in our universe. Significant work has been done recently, that highlights the dependence of collisionless shock formation mechanisms on the amplitude of the ambient B-field and its orientation relative to the flow. Recent laboratory measurements of quasi-perpendicular shocks, a configuration with the B-field perpendicular to the flow, revealed the underlying acceleration mechanisms and the interaction between reflected and inflowing ions. However, other magnetic geometries, such as quasi-parallel and oblique, are less well understood.

We will present a new platform for the Janus Laser Facility to investigate the formation of oblique magnetized collisionless shocks. The new platform design relies on the interpenetration of a magnetized high-density (n_i~10¹⁹-10²⁰cm^-3) background plasma with a fast, low-density (n_i~10¹⁷- 10¹⁸ cm^-3) plasma. The dynamics of the interactions were observed using interferometry and streaked optical pyrometry diagnostics. The measurements suggest that a magnetized shock is formed early in the interaction of the two flows, within ~1.5 – 3 ns, driven by a magnetic piston. These measurements are compared with FLASH calculations to reveal the underlying mechanisms of the shock formation.