Titanium sublimation pumping systems and performance on the tandem mirror experiment-upgrade (TMX-U)

This paper presents a brief history of the TMX-U Titanium Sublimation Pumping process (gettering). Titanium sublimation pumps offer an economical means of pumping chemically active gases (especially hydrogen) at high speeds, and serve as additional pumps, along with liquid nitrogen-cooled panels, to provide pumping during each physics experiment. The getter wires are 85% titanium and 15% tantalum alloy. The Ti-Ta alloy is heated by the passage of current until titanium begins to evaporate. This vapor condenses on the cold surfaces surrounding it and forms an absorption layer which binds the available chemically active gas particles. Saturated layers are covered by further depositions of Ti. Each getter delivers approximately 106 amperes of regulated power for a 60-second getter cycle. In the vacuum vessel, the wires are arranged in arrays of 6, 5, and 2, each cabled to the exterior of the vessel. This alloys for the advancement of the wires. We follow a current schedule allowing a proper deposition rate which extended our average shot, per wire, to exceed 250+. This allows quality gettering in the system effectively, without raising the vessel to atmospheric pressure because of deteriorated wires. Because of the size of the system, a complex computer program was written which is run-time compiled, and then run by the computer. With the multi-tasking capability of the computer, five programs are used in operation and run simultaneously. All getter wire history, deposition, and system notes are stored on the external disc drive. The progress and performance in the four years the system has been used, two year manually controlled, and two computer controlled will be covered. Emphasis on the computer control system and its by-products, which enhance the operation of the TMX-U, will be the subject of this paper