Experimental study of the structure of the plasma-current sheath on the PF-1000 facility

The results of studies of the plasma-current sheath structure on the PF-1000 facility in the stage close to the instant of pinch formation are presented. The measurements were performed using various modifications of the calibrated magnetic probes. Studies of the influence of the probe shape and dimensions on the measurements accuracy were done. The current flowing in the converging sheath at a distance of 40 mm from the axis of the facility electrodes was measured. In the optimal operating modes, this current is equal to the total discharge current, which indicates the high efficiency of current transportation toward the axis. In such shots a compact high-quality sheath forms with shock wave in front of the magnetic piston. It is shown that the neutron yield depends on the current compressed onto the axis. This dependence agrees well with the known scaling, Yn ~ I4. The use of the total discharge current in constructing the current scaling, especially for facilities with a large stored energy, is unjustified.