Gas control and wall conditioning in TMX

The Tandem Mirror Experiment (TMX) is a magnetic fusion research device at the Lawrence Livermore Laboratory, which confines a center-cell plasma between two higher density end-plug plasmas. The end-plug plasmas are separated from the metal end walls by an end-fan chamber. This paper describes how to minimize the power lost through charge-exchange and electron conduction. To isolate the end-plug plasma from the end wall, wall conditioning, gas pumping, and magnetic-field expansion are used in the end-fan chamber. The plasma density is reduced from above 10/sup 13/cm/sup -3/ in the end-plug to well below 10/sup 10/cm/sup -3/ at the end wall. A peak plasma potential of more than 1 kV above the grounded end wall is maintained in steady-state and gas buildup near the end wall is avoided. Gas flow in the end plug is controlled and the end-plug walls are conditioned so that the end-plug plasma is not eroded by large fluxes of cold gas. Wall conditioning in the center cell provides reproducible conditions. The center cell is fueled by gas from a gas box or a pulsed valve.