We have measured the distribution of components of the steady magnetic fields and radiofrequency (RF) magnetic fields on a grid of points within the toroidal RF current drive device RYTHMAC, R0=0.375 m, a=0.075 m and from these measurements calculated the steady-current density distribution and the driving term distribution. With total RF power of about 130 kW at f=500 kHz coupled by currents phased 90 degrees apart in helical antennas to produce moving RF fields, the (j*b)/nee driving terms are strong, equivalent to tens of volts per metre, yet the driven current densities are relatively low, of the order of 10 kA m-2; the distribution of each is uneven and antenna-related. The interpretation is that the plasma which is actually prepared by the same RF power as that used for the current drive is highly resistive. In addition to the steady-current drive information, the experimental data on the RF fields reveal strong nonlinear effects producing strong b field harmonics at 2f, 35, 4f, etc.
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