Structure of a Large-Radius Pinch Discharge
A large-radius pinch discharge produces a series of cylindrically symmetric, inwardly propagating current sheets and associated magnetic fields in a form convenient for detailed study of the j x B interactions basic to all schemes of electromagnetic gas acceleration. The discharge is examined by streak and Kerr cell photography, magnetic probes, spectroscopy, microwaves, and terminal measurements of current and voltage fluctuations, in order to determine the detailed distribution of the currents and fields as functions of radius and time. The initiation of the main discharge in a uniform peripheral ring is found to be primarily an inductive effect, conditioned somewhat by the presence of the adjacent insulator surface. Spectrograms of discharges in argon, nitrogen, and helium show singly and doubly ionized species indicating that particles of energy in excess of 25 ev are participating in the breakdown. A precursor front is observed to propagate ahead of the first current sheet and is identified tentatively as a gasdynamic shock. Another precursor, propagating many times faster, preionizes the gas slightly, prior to the arrival of the first current sheet. (auth)