Tandem mirror experiment-upgrade vacuum system: a new configuration and operating parameters

The Tandem Mirror Experiment-Upgrade (TMX-U) vacuum system has been installed and operating since December 1981. In 1982 and early 1983 the performance of the internal, dynamic pumping system was evaluated during physics experiments. The plasma region gas loads caused the pressure to exceed that allowable for achieving thermal barrier plasmas. The unified, multiple-beamline concept used on TMX-U to pump the neutral-beam injector gas was modified. The modifications to the system were designed to reduce conductance between the injectors and the plasma region to better use the differential pumping in the pumping regions. The modifications made were a smaller cross section neutralizer, replacing apertures with ducts between regions, eliminating the injector scrape-off in the plasma region, relocating the neutral beam dumps, and eliminating the gaps around various penetrations