Characteristics of the NASA Lewis Bumpy Torus plasma generated with high positive or negative applied potentials

The toroidal ring of plasma contained in the NASA Lewis Bumpy Torus may be biased to positive or negative potentials approaching 50 kV by applying d.c. voltages of the respective polarity to 12 or fewer midplane electrode rings. The electric fields, which are responsible for raising the ions to high energies by E x B/B2 drift, then point radially outward or inward. The influence of electric field direction on ion kinetic temperatures and ion heating efficiency was investigated. Under equivalent conditions of magnetic field, deuterium background pressure, and midplane electrode voltage, the ion kinetic temperatures and ion heating efficiencies were virtually the same whether all 12 midplane electrodes were positive or negative. Deuterium ion kinetic temperatures of 340-2500 eV were observed. The ion heating efficiency ranged from 5 to 22%, increases with increasing background pressure or magnetic field, decreases with increasing anode voltage, and is higher in the high pressure than in the low pressure mode of operation. (author)