Experimental Study of the Magnetic Piston-Shock Wave Problem in a Collisionless Plasma

The time-dependent problem of piston and shock wave formation in a low density (collision-free) magnetized plasma has been experimentally studied in a high voltage theta pinch. The applied field strongly interacts with the plasma: either exciting instabilities that cause a fast resistive penetration and very low force density, or exerting a sufficiently large force density to produce high Mach number (5-20) shock waves. The data on piston formation is discussed in terms of a magnetic field-dependent resistivity such as might be expected from an ion plasma drift wave instability. The piston ejects ions possibly by the interaction of ions with ion plasma waves. The shock wave is seen to evolve from an initially one-dimensional disturbance.