Due to the amount of Tritium that exists in the 45R beam line, and a detectable release of this Tritium during pumping, the following procedure is used every time the beam line is shutdown for venting or regeneration:
Close gate valves and turn off ion gauges, glass tube and nude controlled by Fredericks Televac controller.
Turn off cryopump compressor and note the time.
After one hour rough each cold head until roughing vacuum is 100 microns, close roughing valves.
After half of an hour, repeat the roughing process to 100 microns.
After 15 minutes, repeat the roughing process to 100 microns.
After another 15 minutes, repeat the roughing process to 100 microns.
After 2 hours of total elapsed time, the cold heads should be warm and may be vented or pumped down for re-start.