The theory of ion heating in a Q-machine Barium plasma by the electrostatic ion cyclotron instability is considered in some detail. Linear and quasi-linear theories are considered. The effect on resistivity of the instability is also considered. The ion temperature was observed, optically, to increase to a value in excess of 25 000°K by a mechanism attributable to a collisionless process. Energy transfer from the drifting electron current to the ions is analyzed explicitly. Detailed comparisons with experiments are presented.

We have observed and confirmed significant ion heating by the electrostatic ion-cyclotron instability in a barium plasma. We present spectroscopic evidence showing that this mechanism drastically alters the velocity distribution, demonstrating at least a highly nonlinear process and giving strong evidence for randomization of the particle motion. Experimental corroboration of a theory of Drummond and Rosenbluth is presentedWe report the direct observation of ion heating in a fully ionized barium plasma, as indicated by an order-of-magnitude increase in ion temperature (from 2500°Kto greater than 25 000°K) due to the current-driven electrostatic ion-cyclotron instability. 1 The instability was generated by a technique first used by Motley and D'Angelo in the Princeton University Plasma Physics Laboratory Q device, 2 the theory for which was subsequently developed by Drummond and Rosenbluth. 1 The experiment was performed in the Q machine at the University of California at Irvine. Perpendicular temperature measurements were made by spectroscopically observing the Doppler line broadening of light scattered by singly ionized barium after the techniques developed by Hinnov et al 3 The significance of these measurements is that this is the first demonstration of ion heating by this current-driven instability. 4 Historically, this series of measurements was undertaken in an attempt to explain the previous results of Hinnov et al. 3 They measured and reported anomalously high ion temperatures in a barium plasma but the heating mechanism was not understood. We repeated the earlier experiments and recovered some of their results. However, we noticed that high temperatures occured when the rhenium coating on the hot tungsten end plates, used to ionize the barium, 5 was uneven so that patches of tungsten appeared through the rhenium coating. As a consequence small areas of different work function were formed on the plates and we speculated that the localized emfs thus formed produced axial filaments of current (easily visible since the barium ions emit visible light). To test this hypothesis, and to identify the heating mechanism (which we were unable to do initially) we went to a single-ended Q machine with insulated buttons, as indicated schematically in Fig. 1(a). In this configuration the electrostatic ion-cyclotron instability was observed, easily identified from its spectrum, from its dependence on the magnetic field, and by recovering the results of Motley and D'Angelo, 2 most notably that the observed frequency is slightly higher than the ion-cyclotron frequency (typical values at onset: / ci = 5 kHz, / = 61 kHz, linewidth approximately 1 kHz). Several configurations were tried, varying from a single button to an BUTTON PROBE BARIUM OVEN TO FABRY-PEROT •5 FIG. 1. (a) Schematic of the experimental arrangement. The length L was 123 cm; the diameter, 5 cm, button diameter, 0.6 cm. The Fabry-Perot looked into a light dump also, (b) Typical low-temperature (T f ) Doppler broadening scan. a 0 is the 4934 A line of Ba n, ...

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Plasma erosion switches have been fielded on the PITHON generator during imploding plasma experiments. Theta pinch plasma guns were used to inject carbon plasmas of densities in the range of 1012–1014 cm3 between the electrodes of the vacuum power feed region, upstream from an imploding plasma load. Current monitors indicated that the erosion switches carried substantial current early in time, diverting it from the load. Late in the pulse the erosion switches opened, transferring the current to an imploding plasma with the effect of sharpening the current rise time at the load. Associated withthe sharper rise time was an improvement in the quality of the plasma implosions. The results of varying the density and total number of particles in the plasma of the switches are presented with regard to the effect on the current along the vacuum feed and on the behavior of vacuum flowing electrons.

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