Interpretation of Pisces-A RF Antenna system experimental results

The paper describes experimental data from RF coupling experiments using one to four coil antenna arrays that encircle a linear magnetized plasma column. Experimental results using single turn coil that produce symmetric (i.e. m=0), dipole (m=1), and radial RF magnetic fields for coupling to ion waves are compared. By operating without a Faraday shield, it was observed for the first time that the plasma resistive load seen by these different antenna types tends to increase with the number of turns to at least the second power. A four-turn m=0 coil experienced a record 3-5 Ω loading, corresponding to over 90% power coupling to the plasma. A four-turn m=1 coil experienced up to 1-1.5 Ω loading, also higher than previous observations. First time observations using a two coil array of m=0 coil are also reported. As predicted, the loading decreases with increasing phase between coil from 0° to 180°. Experiments using four coil arrays were difficult to optimize and interpret primarily due to complexity of the manual tuning. To facilitate this optimization in the future, a proposed feedback control system that automatically matches load variations between 0.2 and 10 Ω is described