Polarized radial magnetic fields and outward plasma fluxes during shallow-reversal discharges in the ZT-40M reversed-field pinch

The characteristics of edge-region electromagnetic disturbances and of pulsed radial fluxes of plasma to the liner as well as the detailed interrelationship among these processes have been studied on the ZT-40M reversed-field pinch in its normal, shallow-reversal operating regime. The dominant magnetic disturbances are spiky (pulsewidth approx.5--10 μs) low-amplitude (Vertical BarB/sub r//B/sub theta/Vertical Bar< or approx. =10-2)= poloidally symmetric radial-field structures intersecting the vacuum wall and precessing toroidally in the anti-I/sub phi/ sense. The effect of even slight toroidal-field reversal (Vertical BarB/sub phi/(a)Vertical Barroughly-equalB/sub theta/(a)/10) is to polarize these radial-field spikes preferentially positive (i.e., B/sub r/>0) and to increase the speed of the minority (B/sub r/<0) while decreasing the speed of the majority (B/sub r/>0) spikes. Synchronous with the polarized B/sub r/ spikes are intense radially outward fluxes of plasma (instantaneously > or approx. =1022 m-2 s-1) leading to recurrent, large amplitude (Vertical BarΔn/n> or approx. =25%) depletion of the density in the outer quarter of minor radius. The resulting time-averaged global loss-rate per particle is significant (approx.103 s-1)