Theta Pinch Collisionless Shock Experiment on the Big Red Ball

A high-beta theta pinch collisionless shock experiment was performed on the big red ball. Cylindrical VPIC simulations were used to interpret experimental results. Hall-MHD in this cylindrical geometry mostly succeeds in explaining results via the following mechanism: the fast theta-pinch field affects the magnetized electron fluid, creating an ExB drift inward. The resultant charge separation serves to pull ions inward, with ion inertia slowing the current layer. Reflected ions that move at twice the piston speed are observed, as are resonant ions that ‘surf’ the compressing wave inward. The experiment and simulation were repeated in the strongly magnetized regime and compared with pure MHD. Whether the reflected ions could lead to a collisionless shock through Buneman, Weibel, or other instabilities is explored.