Magnetized collisionless shocks on the Large Plasma Device

A new laser experiment to study the interaction of an energetic laser plasma with a large magnetized ambient plasma is now operational at the Large Plasma Device (LAPD) at the University of California Los Angeles (UCLA). A rapidly exploding, and super-Alfvénic (MA>2) plasma-plume is created by irradiating a solid target within the preformed magnetized plasma with an energetic laser pulse (200 J in 20 ns). The ambient plasma (1013 cm-3, 5 eV) is current free, stationary, quiescent, and large enough (17x0.5 m) to support Alfvén waves. Laminar electric fields created by the streaming of laser-plasma ions across the magnetic field couple energy and momentum to the ambient ions until a magnetosonic shock forms and separates from the piston (i.e. the diamagnetic cavity formed by the laser plasma). The collisionless coupling and the formation and structure of the shock are measured with plasma probes and Doppler spectroscopy. Hybrid simulations reproduce the features observed in the experiment and show the presence of reflected ions, which provide the dissipation for the shocks. The results will be discussed in the context of debris-ambient coupling in space and astrophysical explosions and other laboratory experiments.