We are delighted to invite Derek Schaeffer, from Princeton University, to discuss his recent work on magnetised collisionless shocks as part of the Plasma Seminar series.  Derek will be joining us remotely on Zoom (details to follow), but for those in College we will also be broadcasting the talk in 741.

Abstract:

Magnetized collisionless shocks are ubiquitous in space and astrophysical plasmas, from Earth’s bow shock to extreme environments such as supernova remnants and black hole jets.  The highly non-linear kinetic physics of these phenomena remains poorly understood, including the mechanisms by which particles are shock-accelerated to some of the highest energies observed in the cosmos.  Despite decades of spacecraft and remote sensing observations, as well as numerical simulations, many key questions remain unanswered.  Recent advances in high-powered lasers, strong external magnetic fields, and advanced diagnostics have enabled laboratory experiments to begin exploring collisionless shocks in a controlled environment.

We present results from experiments and simulations on the formation and evolution of quasi-perpendicular collisionless shocks created through the interaction of a super-magnetosonic laser-driven magnetic piston and magnetized ambient plasma.  Time-resolved, two-dimensional imaging of plasma density and magnetic fields shows the formation and evolution of a high-Mach-number shock for the first time [1].  By directly probing particle velocity distributions, additional measurements reveal the coupling interactions between the piston and ambient plasmas that are key steps in the formation of magnetized collisionless shocks [2].  The experimental results are well-supported by particle-in-cell simulations, which further detail the shock formation process, the role of collisionality, and the dynamics of multi-ion-species plasmas [3]. 

[1] D.B. Schaeffer, W. Fox, D. Haberberger et al., Physical Review Letters 119, 025001 (2017).
[2] D.B. Schaeffer, W. Fox, R.K. Follett et al., Physical Review Letters 122, 245001 (2019).
[3] D.B. Schaeffer, W. Fox, J. Matteucci et al., Physics of Plasmas 27, 042901 (2020).