CHA Resistive 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 the HI-VAC ion gauge tube pressure is < 10^-7 without the aid of liquid N2.
4. Open up the lower right side panel of the evaporator and connect the Cryo-purge plug. (This is a pair of white plug connector directly below the cryo-pump.)
5. Manually open the purge gas valve. It is inline with the automatic cryo purge valve, and should be normally closed.
6. Open the breaker for the Cryo-pump and move the SHUTTER switch to AUTO the top unlabled lamp will come on indicating N2 flow into the cyro pump. Purge for at least 4 hours. 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 apply a very thin coating of vacuum grease.
3. Replace the "O"-rings and valve.
4. Remove the LN2 trap. Clean the trap. Apply a very thin coating of vacuum grease to 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. Manually open the secondary Fore line valve. This valve is right behind the cryo pump.
3. On the Granville-Phillips ion gauge controller move the CHAMBER-FORE switch to FORE. This will allow you to monitor the foreline thermal couple reading.
4. Stop purging the Cryo pump by taking the MANUAL-OFF-AUTO switch to OFF.
5. Take the AUTO TECH-II controller to MANUAL, and move the FOREline switch to OPEN. All other valves should be SHUT. The roughing pump is now evacuating the cryo-pump.
6. Shut the FOREline switch when the pressure is about 50 mTorr.
7. Repeat the next steps at least four times, and until the leak rate is less than 5 mTorr/minute.
   1. Purge the Cryo pump by taking the MANUAL-OFF-AUTO switch to AUTO.
   2. When the cryo pump reaches atmospheric pressure, stop the purge by taking the MANUAL-OFF-AUTO switch to OFF.
   3. Evacuate the Cryo pump by taking the FOREline switch to OPEN.
   4. When the cryo pressure is down to where the pressure gauge stops. (It should be less than 50 mTorr) Shut the FOREline switch.
   5. Measure the system leak rate, if it is more than about 5 mTorr/minute repeat these steps.

8. Shut the Cryo-Pump breaker. The compressor will start and the system will start to pump down.
9. Shut the Manual foreline valve, and the manual cryo purge valve. Disconnect the Cryo purge plug.
10. On the Granville-Phillips ion gauge controller move the CHAMBER-HI-VAC switch to HI-VAC. This will allow you to monitor the cryo pump's ion gauge reading. Do not press the FILAMENT button until the cryo pump has been running for about 15 minutes.
11. Place the AUTO TECH-II controller back to AUTOMATIC, but make sure the Cycle switch stays in STANDBY until the cryo-pump is fully operational and the HI-VAC ion gauge is in the 10^-8 Torr range.
12. Reset the system back to the standard idle condition.