CHA Evaporation System Cryo Pump Regeneration

Normal Shutdown

The system should be periodically regenerated to keep pumping speeds high. The following describes how to take the system down when the pump still running properly.

1. If there is liquid N2 in the cold trap, clear the cold trap. This may be done either by waiting until the N2 is gone or by using a special device to clear the trap.
2. Make sure that the trap is at room temperature.
3. Pump until IG1 is < 10^-7 without the aid of liquid N2.
4. Open up the right side panel of the e-beam and connect the Cryo-purge plug. (This is a pair of white plug connector directly below the cryo-pump.)
5. Switch the Cryo-power off and the Cryo-Regenerate switch to PURGE. The REGENERATE light will come on. When the system is up to atmospheric pressure the LN2 trap will be lifted up. The purge step takes at least 2 hr. to complete. Shutdown when the vacuum is lost and the pump has heated up. In the case of unexpected failure, go to step 4 above.

System Clean-up

1. After the system has reached atmospheric pressure, remove the over pressure valve at the bottom of the cryo pump.
2. Remove the "O"-rings from the over pressure valve and grease.
3. Replace the "O"-rings and valve.
4. Remove the LN2 trap. Clean the trap. Grease the "O"-ring.
5. Replace the LN2 trap.
6. Remove the debris screen and clean and grease the Hi-Vac valve.
7. Replace Hi-Vac valve and debris screen.

Note: Do NOT use IPA on the "O"-rings as it will tend to cause them to get brittle. After greasing "O"-ring wipe with clean texwipe.

Restarting the System

1. Make sure that all of the parts have been reassembled and replaced correctly.
2. Switch the Cryo-Regenerate switch to ROUGHING. Allow system to pump down to about 50 mTorr.
3. Switch the Cryo-Regenerate switch to PURGE. Allow the system to come back up to atmospheric pressure.
4. Cycle through Steps 1 and 2 about 4 to 5 times.
5. Pump the system down to where the pressure gauge slows to a near stop. This should be < 50 mTorr at this time.
6. Switch the Cryo-Regenerate switch to OFF. Wait as the system leaks back up. When the pressure quits rising, switch back to ROUGHING.
7. Repeat step #5 until the leak-back rate is < 5 mTorr/min.
8. Switch the Cryo-Regenerate switch to OFF.
9. Switch the Cryo-Power switch to ON. The compressor will start and the system will start to pump down. After the Cryo-vacuum gauge has been off the low end of the scale for a min. or two, it is safe to turn on IG1. Once the system pumps down to the 10^-8 Torr range the system is ready to use.