Experimental tests of a large noncircular RFP

Within a large noncircular conducting shell, originally that of the Wisconsin Levitated Octupole, the authors have examined reversed-field-pinch (RFP) plasmas in order to (1) investigate plasma control aspects of a large RFP (R=1.4 m, average minor radius=0.5 m), (2) establish that an RFP with noncircular boundary can be sustained by dynamo activity, (3) examine the effect of poloidal magnetic field curvature on RFP stability (the shell contains a 35% indentation at the midplane), and (4) investigate the possibility of obtaining sustained RFP plasmas in a poloidal divertor configuration. The device is unconventional in that the 5 cm thick aluminum vacuum steel vessel with single poloidal and toroidal gaps serves as both the vacuum liner and conducting shell. The poloidal gap is protected with a 20 cm wide ceramic strip and self-reversed RFP plasmas are initiated with a toroidal loop voltage of --200 volts/turn. The best plasmas have peak currents of 300 kA and are sustained 10 msec (over ten resistive diffusion times). The conductivity temperature is --20 eV while the impurity carbon doppler width temperature is --60 eV. Unlike typical RFP experiments, no reduction in fluctuation level accompanies the toroidal field-reversal