Inversely operated aluminum alloy distributed ion pump

Abstract

The distributed ion pump (DIP) for the accumulation ring (AR) for TRISTAN is described. The elements of the DIP are newly designed and fabricated. The cathode consists of titanium (Ti) rods and the anode is five aluminum (Al) plates with punched holes 12 mm in diameter. The unit of the DIP is 50 cm long and 5.3 cm wide. There are 62 holes in the unit. Five units are connected and installed in a bending magnet (B) chamber. Both the cathode and the anode are insulated from the chamber. The insulation makes it possible to measure only the current between the anode and the cathode. Therefore, the insulation enables us to use the DIP as an ultrahigh vacuum gauge. The initial pumping curve shows that the ultimate pressure is 9×10−11 Torr at 2000-h operation after several conditioning processes were applied. The processes are a higher magnetic field application (4–11 kG), bakings, a higher voltage application (5–12 kV), and argon glow discharge (dc, ac). Pressure improvement of one order was obtained after baking (140 °C, 64 h). Pressure improvement of a factor of 2 was obtained by the higher magnetic or electric field application. However, pressure deterioration was observed after the argon discharge. The DIP was operated for different magnetic fields simulating beam injection and acceleration. By changing the polarity of the power supply, pumping speed was measured for two cases: Ti cathode and Al anode, and Ti anode and Al cathode. For the latter, a different discharge pattern was observed. Before baking, the pumping speed for nitrogen was 150 l/s at 10−7 Torr and 5 kG and after baking, 310 l/s at 10−8 Torr at a field higher than 3 kG. The DIP of the AR has been operated successfully for more than five years. While the DIP was in operation, pressure in the AR was reduced by about one order. The base pressure is ∼1×10−9 Torr without baking.