High-Speed Pumping System Characteristics of 2 MW Neutral Beam Injector Based on Ti Gettering

The 15 kV, 2 MW neutral beam injector (NBI) was developed for C-2U magnetic trap experiments. Important part of the NBI is efficient pumping system which provided a good vacuum condition during beam pulse. The pressure rise during the NBI operation and accompanying gas flow to the fusion device is a negative factor both for the beam transportation and for fusion experiment. The high-speed pumping system based on four Ti-bar arc-discharge evaporators placed inside LN2-cooled volume was developed and successfully used in vacuum chamber of the 2 MW NBI. The results of calculations and tests are presented both at the room and at the LN2 temperatures of the gettered surface. Achieved pumping speeds are about 10(5) and 4.10(5) l/s correspondingly. Also gas capacitance of the gettered surface and conditions of uniform gettering were established.