Operation of CESR distributed ion pumps at reduced voltage

A transverse single-beam instability is observed in CESR which has been found to arise from the DC static electric field leaking into the beam chamber from distributed ion pumps (DIPs). Further, a very large photoelectron current is measured in the DIPs which may impose a potential problem in future CESR upgrades. The purpose of this study was to investigate the possibility of lowering the DIP operating voltage without sacrifice of DIP pumping speed. A relatively constant DIP pumping speed was measured with the anode voltage ranging from the 'normal' operating voltage of 7.6 kV to as low as 1.8 kV, when there is beam stored in CESR. On the other hand, a higher (5 kV) minimum DIP anode voltage is needed to sustain effective pumping speed without beam present. A simple model is proposed to describe the operation of DIPs under the influence of the stored beam. As the result of this study, the majority of CESR DIP controllers have been modified to enable remote switching of the DIP anode voltage between 2.2 kV (for normal beam operation) and 6.6 kV for start-up or for long periods without stored beam.