Plasma start-up, sustainment and stabilization by currents along a poloidal magnetic field

The stability and heating effects of induced low frequency poloidal currents in the internal ring device F IV A have been studied. Density fluctuations are stabilized already at low power poloidal currents. At higher levels the temperature is increased. The start-up process is more efficient and works at lower filling pressures than without poloidal currents, resulting in lower plasma density and higher temperature. Rotating plasmas with density of 1.5x10/sp21/ m/sp-3/ were obtained for a filling pressure of 6 mtorr. At the lowest filling pressures, 0.2 mtorr, a non-rotating plasma, sustained only by the poloidal current, with a density of 1.5x10/sp20/m/sp-3/ and a temperature of 7 eV was produced. At this low density, the plasma is permeable to neutral gas, as opposed to the impermeable plasmas in the earlier experiments with this device. The stabilizing effect seems to be related to the applied toroidal magnetic field rather than the induced poloidal current. (authors)