MODS CCD Dewar Vacuum Pump-Down Procedure

From Bruce Atwood (2011 Aug 1):

On Tuesday night I pumped MODS I Blue and Black (a.k.a. Red) Dewars. I was able to read the pressures by connecting the Dewar-mounted MircoIon+ heads to the aluminizing system through a 100ft Cat5 cable. MODS was on the cart. I think basically the same procedure could be used with MODS on the telescope if the new 20ft KF-25 line is used. Once you figure out the best access it is a straight forward process. The procedure given below is not exactly what I did but what I would have done if I had known what I learned about accessing the various parts.

This is very definitely not a primmer on how to use the Varian 936. RTFM (or ask), the friendly manual is in the LBT CAN.

The initial pressures were 403 mTorr Blue, 376 mTorr Red. Final pressures were 4 mTorr Blue and 8 mTorr Red.

Abbreviations:

    BHE     Blue Head Electronics
    RHE     Red Head Electronics
     LD     Varian 936 leak detector
    SSL     Flexible KF-16 Stainless Steel vacuum Line, total length ~8'
    RDV     Vacuum Valve on the Red Dewar
    BDV     Vacuum Valve on the Blue Dewar
   RMI+     MircoIon+ vacuum gauge on the Red Dewar
   BMI+     MircoIon+ vacuum gauge on the Blue Dewar

1. Check that the RD and BD are warm. This could be by reading the temperatures, if the computer system is up, or by knowing the last time they were filled.

2. Open the door on the blue side and both doors on the red side.

3. Through the Blue Door remove the cap on the valve and connect the SSL to the BDV. Remember where you put the cap.

4. Set the LD transfer pressure to hold, pump the SSL, don't open the BDV at this time.

5. From inside the instrument disconnect the RJ45 cable that runs from the BMI+ to the BHE at the BHE and connect it to the line to the aluminizing system through a RJ45 hub.

6. Read and record the pressures

7. Open the BDV.

8. When the pressure in the test port is low enough let the leak detector transfer to high vacuum mode.

9. Pump for ~45 minutes at which time the pressure, as read from the BMI+, should be a few mTorr. Record the final pressure.

10. Close the BDV, vent the SSL through the LD, remove the line at the BDV, reinstall the cap, and move the LD to the red side.

11. Poke the SSL through the red side door towards the top of the Black Dewar. You will need to get the end almost all the way across the top of the Black Dewar so that you can reach it from inside.

12. From inside the instrument, standing between the dichroic drum and the red camera, remove the cap from the BDV and connect the SSL. Do not open the RD Valve at this time.

13. From inside the instrument reconnect the RJ45 cable from the BMI+ to the BHE.

14. From inside the instrument disconnect the RJ45 cable that runs from the RMI+ to the RHE at the RHE and connect it to the line to the aluminizing system through a RJ45 hub.

15. From outside the instrument set the LD transfer pressure to hold and pump SSL.

16. Read and record the pressure in the pressure as read by the RMI+

17. From inside the instrument open the RDV.

18. When the pressure is low enough let the LD transfer to high vacuum mode.

19. Pump for ~45 minutes, the pressure, as read by the RMI+, should be a few mTorr. Record the final pressure.

20. From inside the instrument close the RD valve, do not remove the line at this time.

21. From outside the instrument vent the line through the LD.

22. Back inside the instrument remove the SSL from the RDV and reinstall the cap on the RDV.

23. Reconnect the RJ45 cable from the RMI+ to the RHE.

24. Extract the cat5 cable and hub, close the doors.

25. Properly shut down the LD

-- RichardPogge - 29 Jul 2011