Computer control of the titanium Getter system on the Tandem Mirror Experiment-Upgrade (TMX-U)

Gettering has been a standard technique for achieving high-quality vacuum in fusion experiments for some time. On Lawrence Livermore National Laboratory's Tandem Mirror Experiment (TMX-U), an extensive gettering system is utilized with liquid-nitrogen-cooled panels to provide the fast pumping during each physics experiment. The getter wires are a 85% titanium and 15% tantalum alloy directly heated by an electrical current. TMX-U has 162 getter power-supply channels; each channel supplies approximately 106 A of regulated power to each getter for a 60-s cycle. In the vacuum vessel, the getter wires are organized into ''poles'' or arrays. On each pole there are six getter wires, each cabled to the exterior of the vessel. This arrangement allows the power supplies to be switched from getter wire to getter wire as the individual wires deteriorate after 200 to 300 gettering cycles and in this way, the system is effectively regettered without raising the vessel to atmospheric pressure for maintenance. To control the getter power supplies, the authors will install a computer system to operate the system and document the performance of each getter circuit. This computer system will control the 162 power supplies via a Computer Automated Measurement and Control (CAMAC) architecture with a fiber-optic serial highway. Getter wire history will be stored on the built-in 10 megabyte disc drive with new entries backed up daily on a floppy disc. Overall, this system will allow positive tracking of getter wire condition, document the total gettering performance, and predict getter maintenance/changeover cycles. How the authors will employ the computer system to enhance the getter system is the subject of this paper