NIRSPEC Cryogenic Procedures

NIRSPEC is cooled continuously by use of Closed-Cycle Refrigeration (CCR). A compressor unit in the K2 machine room provides pressurized He gas to two cold heads on-board NIRSPEC. If this system is inoperable for more than about 15 minutes, then NIRSPEC may require a lengthy 10 day cooling cycle to become operable again.
  1. Loss of CCR Cooling: Emergency Procedures
  2. Loss of CCR Cooling: Vacuum Procedures
  3. Reading Cryogenic Temperatures
  4. E-mail CCR alarm
  1. Loss of CCR Cooling: Emergency Procedures

    2. In the event of CCR shutdown, it is very important to assess the status of the NIRSPEC main dewar vacuum prior to restarting the CCR compressor unit.

    1. Verify CCR shutdown by inspection of unit 3; static pressure will be high (235-270 PSI), and the green indicator light will be off.
      Image of CCR Unit 3.
    2. Go up to NIRSPEC. Read the Edwards vacuum gauge display. Gauge 3 (termed Lo-Vac) should be displayed.
      Image of Edwards vacuum gauge display

      If the vacuum is:

      • Less than 1x10e-1, then it is safe to restart the CCR compressor. Be expeditious; it would be helpful to have an assistant waiting at the compressor to save valuable time.
      • Greater than 1x10e-1, the DO NOT restart the compressor. NIRSPEC must be vacuum pumped before cooling is restarted. Vacuum pumping should begin as soon as possible, otherwise NIRSPEC will continue to warm up and will require a complete cool down cycle. Read on.

  2. Loss of CCR Cooling: Vacuum Procedure

    1. Connect the pump to the NIRSPEC vacuum valve fitting.
    2. Start rough pumping the line. Open the NIRSPEC vacuum valve as soon as the line is a factor of 10 below the NIRSPEC vacuum reading.
    3. When the vacuum reaches 4x10e-2 (40 millitorr), start the turbo pump. At this time the CCR compressor unit 3 can be restarted.
    4. Monitor the NIRSPEC vacuum. When it is less than 1x10e-4, valve off the pump. Verify that the vacuum continues to drop with the CCR running.

  3. Reading Cryogenic Temperatures

    4. To read the nirspec cryogenic temperatures, log on to waimea as "nspeceng" and type "cryotemps". The result is: 

    8:20am waimea:xnirspec> cryotemps
 
**************************************************
Temp 1 - Rotator Motor                 = 55.080000
Temp 2 - 350 2nd Stage Cold Head       = 12.450000
Temp 3 - Optical Plate                 = 53.990000
Temp 4 - Top of Image Rotator          = 76.990000
Temp 5 - LN2 Can                       = 54.720000
Temp 6 - 1050 Cold Head                = 46.100000
Temp 7 - SCAM                          = 57.110000
Temp 8 - Top of TMA                    = 55.210000
Temp 9 - ALADDIN                       = 29.190000
Temp 10- Cold Strap                    = 31.650000
**************************************************

    Note that every sensor reads below liquid nitrogen temperatures (77 K).

  4. Example of the e-mail alarm message

    5. This message is sent to a group of people including IS's, OA's and facility staff when Temp 2 above exceeds 15 K. This should be an indication that the CCR has stopped operating. 

    ********************************************************************
        ATTENTION!  ATTENTION!  URGENT!  PLEASE PAY ATTENTION!
********************************************************************
 
  The CCR cooling system for NIRSPEC has apparantly halted.  If this
  system is not restarted IMMEDIATELY, the instrument will warm up,
  which means that it WILL NOT BE USABLE FOR 2 WEEKS!
 
  It is EXTREMELY URGENT to get this system restarted.  It may have
  halted for the following reasons:
 
        1. The building glycol (not instrument) system has gone down.
        2. The CCR controller/compressor has lost power.
        3. A leak has developed in the He lines. 
 
 ********************************************************************
        KEEP READING - THIS IS VERY IMPORTANT!  
 
  If the CCR compressor has been down for more than 10 minutes, then
  NIRSPEC may have lost a good vacuum.  Check the vacuum gauge readout
  (the grey box with black face/LCD readout located on NIRSPEC's frame
  near the floor; labeled "Edwards Pirani").
 
      If the pressure is GREATER than 1 x 10^-1 Torr (100 mT),
       DO NOT RESTART CCR UNIT #3 WITHOUT TOM BIDA'S APPROVAL. 
 
 ********************************************************************
 
        Inspect CCR Unit 3 in the Keck-2 Machine Room AND
                Read the NIRSPEC Vacuum RIGHT AWAY!
 
     CALL Dennis McBride (161), and/or Tom Bida (165, 883-9565) ASAP.