Laser-driven, magnetized quasi-perpendicular collisionless shocks on the Large Plasma Device

Abstract

Articles you may be interested inVisualizing electromagnetic fields in laser-produced counter-streaming plasma experiments for collisionless shock laboratory astrophysicsa) Phys. Plasmas 20, 056313 (2013); 10.1063/1.4804548Ion acceleration from laser-driven electrostatic shocksa) Phys. Plasmas 20, 056304 (2013);The interaction of a laser-driven super-Alfv enic magnetic piston with a large, preformed magnetized ambient plasma has been studied by utilizing a unique experimental platform that couples the Raptor kJ-class laser system [Niemann et al., J. Instrum. 7, P03010 (2012)] to the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875] at the University of California, Los Angeles. This platform provides experimental conditions of relevance to space and astrophysical magnetic collisionless shocks and, in particular, allows a detailed study of the microphysics of shock formation, including piston-ambient ion collisionless coupling. An overview of the platform and its capabilities is given, and recent experimental results on the coupling of energy between piston and ambient ions and the formation of collisionless shocks are presented and compared to theoretical and computational work. In particular, a magnetosonic pulse consistent with a low-Mach number collisionless shock is observed in a quasi-perpendicular geometry in both experiments and simulations. V C 2014 AIP Publishing LLC.

Observation of collisionless shocks in a large current‐free laboratory plasma

“…When the plasma discharge reaches a steady state (5 ms after breakdown), an exploding plasma cloud is produced by irradiating a solid polyethylene (C 2 H 4 ) target embedded inside the magnetized plasma with an energetic laser pulse (200 J at 1053 nm, 25 ns pulse width) at a laser intensity of 10 13 W/cm 2 . Thomson scattering spectra obtained with a second probe laser (532 nm, 8 J, 5 ns) yield an electron density n e =8.0 ± 1.5 × 10 16 cm −3 and temperature T e = 7.5 ± 0.5 eV 250 ns after the laser pulse at 2.5 ± 0.4 cm from the target [ Schaeffer et al , ]. Comparison of self‐emission spectra with synthetic, nonlocal thermal equilibrium, time‐dependent spectra in combination with the measured plasma parameters yield an average charge state of Z = 4.1, implying C +4 is the dominant debris charge state.…”

Fast gated imaging of the collisionless interaction of a laser-produced and magnetized ambient plasma

“…Collisionless magnetized shocks are often studied in the laboratory by observing the interaction between a laser-produced plasma (LPP) and an ambient background plasma [3,4]. As the LPP expands, currents along the edge expel the background magnetic field, creating a diamagnetic cavity or "bubble" that serves as an electromagnetic piston to drive a shock in the ambient plasma [5,6]. High laser energies are required to produce the large pistons necessary to drive super Alfvénic shocks, limiting experiments to relatively small data sets.…”

Collisionless momentum transfer in space and astrophysical explosions

“…However, this process has never before been observed in a laboratory setting. Despite numerous experiments utilizing laser-produced plasmas to simulate space and astrophysical explosions 22 , including noteworthy recent studies that successfully generated magnetized collisionless shocks 23,24 and measured the electrostatic component of the electric field structure associated with an explosive plasma cloud 25,26 , none of these efforts examined the ion dynamics in sufficient detail to confirm Larmor coupling as a participating momentum exchange mechanism.…”