Sumitomo Marathon CP-8 - Regeneration: Evacuation Phase; Regeneration: Cooldown Phase; Vacuum Baking

Operation
35
Purging with nitrogen only:
1. Use a nitrogen supply to break the vacuum and warm up the cryopump. The nitrogen
supply pressure should be high enough to open the pressure-relief valve, but less than 105
kPa (15 psig).
2. Stop the purge when the cold second-stage panel reaches 280 K.
Purging with nitrogen and an outside heat source:
1. Follow Step 1 in "Purging with nitrogen only:” A heater should be placed in direct contact
with the external surface of the cryopump enclosure and operated with a thermostat set at
60 - 70°C (140 - 160°F). A 250 Watt, 208 V blanket heater with a 130°F thermostat is
available from SCAI, P/N 267358C. See the Parts section.
2. When the second-stage panel temperature reaches 310 K, turn off the heater. Stop the
purge.
Regeneration: Evacuation Phase
Evacuate the cryopump to a pressure of 5 x 10
-2
torr (50 microns of mercury). See Figure 12.
SCAI recommends running the roughing pump for at least 30 minutes at 5 x 10
-2
torr to fully
desorb gases from the charcoal. Dry nitrogen gas may be bled through the purge port or into
the roughing pump manifold to prevent the pressure from going below 5 x 10
-2
torr and oil
backstreaming into the cryopump.
Before proceeding with the cooldown phase, SCAI recommends checking the rate of pressure
rise in the cryopump vacuum enclosure. Close the roughing valve and the purge valve, if open.
Monitor the pressure in the cryopump vacuum enclosure. If the pressure rises faster than 1 x
10
-2
torr/min (10 microns/minute), rough pump the cryopump for an additional 10 minutes and
repeat the test.
Regeneration: Cooldown Phase
Begin cooling down the cryopump with the main vacuum chamber gate valve closed. Monitor
the pressure inside the cryopump chamber. If it rises above 0.1 torr, (100 microns), turn off
the cryopump and evacuate the cryopump chamber until the internal pressure reaches 5 x 10
-2
torr. Turn on the cryopump by starting the compressor or reconnecting the cold head cable if
the cryopump is in a multiple-cryopump system.
Vacuum Baking
PREVENT EQUIPMENT DAMAGE. Do not heat standard cryopanels and
cylinder assemblies above 80°C (176°F).
Do not heat ultra-high vacuum cryopumps above 150°C (300°F).
If pressures below 10
-7
Torr are required, it is recommended to vacuum bake the vacuum
chamber walls and the cryopump vacuum enclosure to drive off water vapor that has adsorbed
onto them. During this process, a vacuum of less than 1 torr is preferred. Cryopanels and
cylinder assemblies may be heated to 80° C.