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DECam Cryogenics: An introduction for CTIO

DECam Cryogenics: An introduction for CTIO. Brooke Gregory Materials at ftp:// ftp.ctio.noao.edu/pub/brooke/DECam_Cryo_Tutorial /. Liquid nitrogen as coolant. DECam 100 K; 7 bar = ~ 100 psi. PVT surface. Overview.

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DECam Cryogenics: An introduction for CTIO

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  1. DECam Cryogenics:An introduction for CTIO Brooke Gregory Materials at ftp://ftp.ctio.noao.edu/pub/brooke/DECam_Cryo_Tutorial/

  2. Liquid nitrogen as coolant DECam 100 K; 7 bar = ~ 100 psi

  3. PVT surface

  4. Overview The red and blue lines represent, for liquid LN2 and helium respectively, a pair of lines: supply and return.

  5. Dewar Valve Box and LN2 lines LN2 Reservoir LN2 Main Valvebox 4 U-Tubes Valvebox to stairwell 2 left to Coude room 2 right to telescope Location of vent valve Used during initial Cool down Purple is location of Dome ladder

  6. Cable tray path from stairwell to imager vessel in Coude room Supply and return lengths are the same Qty 4 – 40 foot LN2 hose lengths QTY 2- 50 foot LN2 hose length 50 foot lengths

  7. LN2 vessel + coldheads+gauge panel +valvebox

  8. Top of vessel + coldheads

  9. Valve box

  10. Gauge panel

  11. Connections to imager dewar

  12. LN2 system diagram (detailed) LN2_schematic_drawing 436677-B1_Rev.C.pdf (expands in Acrobat viewer on click)

  13. Component labels • SV – relief valves • VV – vacuum valve • MV – manual valve • PV – pneumatic valve • CV – check valve • RD – Rupture disk (relieve pressure @ 150 psi) • PI – pressure indicator • FI – flow indicator • TE – temperature sensor • Detailed valve list for system drawing

  14. Dewar vessel details

  15. Cryocooler “Stinger” (Aguijón)

  16. Cryomech AL300 coldhead

  17. Connection showing LN2 and vacuum seals

  18. Hose connections (Swagelock)

  19. Swagelock - section

  20. MDC ISO LF NW500 flange

  21. Structure of LN2 hoses

  22. Vacuum access tool Vacuum access tool

  23. Valve and Gauge Panel

  24. DECam Imager Cooldown – 13Oct10 • Initial state: DECam imager dewar ~warm (-60C) • LN2 in storage dewar, LN2 pump off • Vent return line at valve box; fill with LN2 from LS160. (Storage dewar pressure ~150 psi: Not familiar low pressure (15-20 psi) dewars. CTIO has ordered two high pressure dewars for DECam). • This purges the lines and relieves the LN2 pump of the work to circulate the LN2 during cooldown. • Run this way, cooling lines with external LN2 until liquid appears at vent (sign that tubes are really cold ~ -60 C) • Open valve on Valve box to Imager. (Differential pressure surprise.) • 10:15 am - Open vent valve. Flow starts driven by dewar pressure (~100 psi)

  25. Cooldown continued… • CCs off until pump is started. (They tend to decrease the pressure in the storage dewar; we want flow.) • Pressure starts to drop. Add LN2 from storage dewar after purging connection hose. • Dewar fills while lines are cooled. • 11:10 am - 60 – 71 % fill; stop filling; close vent; braids at -80 C; focal plane at -10 C; • Start CCs. (Control: open loop with heaters in dewar to control pressure – at 100 psi in Chile.) • 11:42 - Start LN2 circulation pump. • 12:15 – Things are pretty stable at control pressure (75 psi in this test); differential pressure about 7.5 psi, control leads to ~10 sec period oscillation with 1.5 psi pressure amplitude; pump at 61 Hz (see control screen).

  26. Open discussion of Scenarios • Departure from normal operating conditions – safety; what to do?: • Electrical power failure (loss of cooling, loss of circulation) • Loss of temperature regulation: (over cooling) • Failure of compressors • Failure of coldheads • Failure of vacuum in LN2 lines • Failure of vacuum in LN2 dewar

  27. Some Reference Documents • In the local directory: • Cryocooler specs AL300 Specification Sheet .pdf • Cryocooler manual AL300 CP970 (NEW MANUAL 6-13-07).pdf • Cryocooler system drawing AL300 SYSTEM DRAWING.pdf • In des-docdb: • LN2 Cryo safety documentation. (To be updated for CTIO system as delivered.): • http://des-docdb.fnal.gov:8080/cgi-bin/ShowDocument?docid=4994 • Routing utilities on the telescope at CTIO: • http://des-docdb.fnal.gov:8080/cgi-bin/ShowDocument?docid=4278 • Neslab chiller used to cool the monsoon crates. It references other documents also: • http://des-docdb.fnal.gov:8080/cgi-bin/ShowDocument?docid=4753 • PF Cage cooling system: • http://des-docdb.fnal.gov:8080/cgi-bin/ShowDocument?docid=3763 • Water/glycol interface with CTIO: • http://des-docdb.fnal.gov:8080/cgi-bin/ShowDocument?docid=4907 • Any drawing numbers referenced in the documents can be found here • http://www-admscad.fnal.gov/MSDMain/cgi-bin/TP_PPDifind-web.pl • (des-docdb access requires des, 70chips)

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