Application of a gold neutral beam probe and an end-loss energy component analyzer to space potential measurements in a tandem mirror

A Gold Neutral Beam Probe (GNBP) has been investigated from an active diagnostic point of view, and found to be the best way to measure potentials of the barrier and central cell plasmas in the GAMMA 10 tandem mirror. The thermal barrier potential was determined directly by the simultaneous measurements of the on-axis space potentials at both of these locations. Two-dimensional space potentials were obtained by adjusting the energy of the probing beams so that measurements were made along different chords through the plasma cross-section. A newly developed diagnostic device, a cylindrical End-Loss Energy Component Analyzer (ELECA), was also used to measure the plug potential, and was suitable for determining the distribution functions of end-loss ions. This diagnostic can also be useful as a compact energy analyzer for a beam probe diagnostic