Measurement of NSLS distributed diode sputter ion pump characteristics

For the DI pump to have acceptable pumping speed, the pump must be glow discharge conditioned after the 150 C max vacuum bakeout. Other DI pump conditioning procedures have not been investigated. Glow discharge conditioning of the system using the DI pump anode significantly improves the pumping speed at low pressures and high pressure pumping speed is slightly improved. The NSLS DI pump speed is not linear with pressure even though the average current is. Pumping speed drops to less than 25% of the high pressure speed at pressures below 10(-9) torr, depending on the pump condition. The pumping speed is sufficiently close to its calculated value at high pressure. These results agree with actual ring experience with the distributed pump. The DI pump is most efficient pumping distributed gas loads from beam operation rather than gas loads introduced at the ends of the pump. Most of the gas load is distributed adjacent to the pump during beam operation due to synchrotron radiation included desorption.