Distributed Sputter-Ion Pumps for Use in Low Magnetic Fields

Measurements of the ignition characteristic of large diameter anode cells indicate a more than proportional increase of cell radius for a given reduction of Bi. Considerations of conductance have lead to an open anode configuration with several layers of perforated metal sheets. The pumping speed is found to be larger than for anodes with conventional cylinders. Moreover, since the electrons can move more freely inside the anode the discharge ignites at a lower magnetic field. Scaling from our measurements on model pumps, we expect to obtain with a single row of anode cells, designed to ignite at a field below 0.02 T, a linear pumping speed of about 60 l/sm at a transition field of about 0.1 T.