Experimental observations of the amplitude and frequency of low frequency magnetic field and soft X-ray fluctuations in the reversed field pinch (RFP) ZT-40M, which has toroidal and poloidal gaps in its stabilizing shell, have shown that for high values of the pinch parameter these fluctuations can be strongly affected by the configuration of the toroidal field circuit. Parallel connection of coil sections improves the toroidal flux uniformity, which results in a reduction of the fluctuation level, the toroidal loop voltage and the implied energy losses compared with those of coils connected in a series or series-parallel configuration. These results indicate that the operation of RFP experiments with shell gaps and field coils well removed from the plasma can be further improved by the addition of close fitting, parallel connected, low current coils.
Time-extended inductive tokamak discharges with differentially-tilted toroidal field coils