Towards a parallel collisionless shock in LAPD

Abstract

Abstract. Using a high-energy laser to produce a super-Alfvénic carbon-ion beam in a strongly magnetized helium plasma, we expect to be able to observe the formation of a collisionless parallel shock inside the Large Plasma Device. We compare early magneticfield measurements of the resonant right-hand instability with analytical predictions and find excellent agreement. Hybrid simulations show that the carbon ions couple to the background plasma and compress it, although so far the background ions are mainly accelerated perpendicular to the mean-field direction. IntroductionCollisionless shocks are a virtually ubiquitous phenomenon in space, from planetary bow shocks in our solar system [1,2,3,4,5] to the shocks occurring in supernova remnants [6,7] and presumably the jets of active galactic nuclei [8]. Our understanding of the complex process of shock formation has greatly improved since Sagdeev's seminal paper [9], thanks to both satellite observations [10,11] and numerical simulations [12,13]. Yet the complicated three-dimensional structure that one would predict for a parallel shock on theoretical grounds [14] is difficult to confirm, either because of the nature of one-or few-point satellite measurements or because three-dimensional kinetic simulations are computationally too expensive.To avoid these particular difficulties, our group is working on producing a parallel collisionless shock in a laser-plasma experiment at the Large Plasma Device (LAPD) [15]. Simulations assuming a quasi-one-dimensional carbon front [16] showed that the available energy density is sufficient to observe the early stages of collisionless-shock formation. In this proceeding, we present measurements of the resonant right-hand instability in our experiment and compare them with predictions of shock-formation theory [17]. This research continues previous work on the generation and investigation of a perpendicular collisionless shock [18,19].

Observations of a field-aligned ion/ion-beam instability in a magnetized laboratory plasma

“…A dispersion relation for the RHI generated by interacting bi-Maxwellian beams can be derived from linear Vlasov theory [30,31]. Applying the inertia-less electron limit (Ω e ω − kv e ) and assuming that the beams are temperature-isotropic leads to the following simplified normalized dispersion relation (for k × B 0 = 0 and q c = 1) in the stationary-electron frame [32]:…”

“…Simulations of each experiment were conducted using a hybrid code [27,32] that represented ions with a particle-in-cell (PIC) technique and electrons as an MHD fluid. Two carbon debris species (C +3 and C +4 ) were initialized with a velocity distribution matching the experimental measurements.…”

Multi-scale simulations of particle acceleration in astrophysical systems

“…Since these experiments, the effort in producing and studying magnetized shocks has continued, exploring e.g. the possibility to produce parallel shocks (Weidl et al, 2017), or to use the Biermann-Battery process to magnetize the plasmas (Umeda et al, 2019).…”