The evolution of a low temperature linear discharge plasma

The time evolution of a low temperature, large linear discharge in a confining magnetic field has been followed from the initial plasma formation to the afterglow. Extensive diagnostics such as Thomson scattering, interferometry, emission line spectroscopy and Langmuir probes were used to study plasma in the density and temperature range 1013 < Nsub(e) < 1015 cm-3, 0.5 < Tsub(e) < 3 eV. Diagnostics of the gas breakdown phase indicate that the plasma forms in channels and shows evidence of current filaments. After the plasma current is clamped, the plasma mixes and becomes spatially homogeneous in the axial direction with boundary layers of only a few centimeters. The afterglow plasma density decays exponentially with a decay time proportional to the square root of ion mass, as predicted by models of end loss from a theta pinch. The observed decay times are about a factor of three larger than those anticipated for such models, due to end stoppering by the electrodes. (author)