High voltage processing of the SLC Polarized Electron Gun

The SLC polarized electron gun operates at 120 kV with very low dark current to maintain the ultra high vacuum (UHV). This strict requirement protects the extremely sensitive photocathode from contaminants caused by high voltage (HV) activity. Thorough HV processing is thus required. X-ray sensitive photographic film, a nanoammeter in series with the gun power supply, a radiation meter, a sensitive residual gas analyzer and surface x-ray spectrometer were used to study areas in the gun where HV activity occurred. By reducing the electric field gradients, carefully preparing the HV surfaces and adhering to very strict clean assembly procedures, the authors found it possible to process the gun so as to reduce both the dark current at operating voltage and the probability of HV discharge. These HV preparation and processing techniques are described