NIRSPEC Cryogenic Procedures Page
  • Emergency
  • Standard

    Emergency 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.

    3. 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.

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

      [nspeceng@nirspec ~]$ cryotemps
      ======================================================================
       Service  =   NSDEWAR                  NIRSPEC Temperatures (K) 
      ======================================================================
       Keyword      Location                                          Temp  
      ----------------------------------------------------------------------
       BENCH1INVAL  Bench-1-temp-value                                50.411
       BENCH2INVAL  Bench-2-temp-value                                50.084
       CCR1050VAL   Cold-head-1050-temp-value                         45.838
       CCR350VAL    Cold-head-350-temp-value                          16.089
       LN2CANVAL    LN2-can-temp-value                               480.000
       OPTPLATEVAL  Optical-plate-temp-value                          55.658
       ROTMOTVAL    Rotator-motor-temp-value                          56.975
       ROTTOPVAL    Top-of-rotator-temp-value                         75.188
       SCAMASICVAL  SCAM-ASIC-temp-value                              51.134
       SCAMFILTVAL  SCAM-filter-wheel-temp-value                      53.200
       SCAMTEMP1VAL SCAM-temp-value                                   30.001
       SCAMTEMP2VAL SCAM-temp-value                                   29.904
       SPECASICVAL  SPEC-ASIC-temp-value                              60.883
       SPECTEMP1VAL SPEC-temp-value                                   30.000
       SPECTEMP2VAL SPEC-temp-value                                   29.930
       TMAVAL       Three-mirror-antistigmat-temp-value               57.180
      ======================================================================
       Service  =   NSDEWAR            NIRSPEC Controlled Temperatures (K) 
      ======================================================================
      Location HtrMode             HtrRng    Htr%   Target    Temp1    Temp2
      ----------------------------------------------------------------------
        Bench1 Closed-loop-PID        Low    29.7   50.000   50.409    0.000
        Bench2 Closed-loop-PID        Low    37.8   50.000   50.409    0.000
          SCAM Closed-loop-PID     Medium    42.2   30.000   30.001   29.904
          SPEC Closed-loop-PID        Low    23.3   30.000   30.000   29.931
      ======================================================================
      
      

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

    6. Example of the e-mail alarm message
    7. 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.
      

    Standard Cryogenic Procedures

    Planned cryo cycles on NIRSPEC require some coordination between summit and HQ staff, to ensure that everything gets done in the right order. The steps below include suggestions as to who can carry them out most easily, but these are only suggestions. Experience shows that the whole process is usually smoother when both summit and HQ staff are involved.

    1. Procedure for a planned warmup
      1. Move NIRSPEC into stow if not already there.
      2. Lock out unwanted activity. (For Instrument Scientist) Stop all VNC sessions corresponding to numbered accounts. E.g. log into nspec1@nirspec. Then issue the command "kvnc stop servers". Do this for ALL VNC sessions that are up and running. This will prevent random astronomers from attempting to start the NIRSPEC software or move motors while the instrument is not at thermal equilibrium. Be sure to make a note of the new password, so you can reverse the change later! Send an email to the "instrument" alias to announce that you have done this.


    2. Procedure for a planned cooldown
      1. Pump for as long as practical. (IT) Before cooling down, pump the dewar for 4-5 days if possible.
      2. Bake the getters. (IT) Make a note of the vacuum reading on the pump (and dewar if possible) before beginning this step. During the first day of pumping, connect a DC power supply to the banana jacks on the rear module leg (by the vacuum valve) to power the heaters in the getter material on the cold heads. The heaters are two 25-ohm resistors wired in parallel adjust the power supply so that the total DC power supplied to both heaters (voltage times current) is about 12.5 watts or 6.25 watts per resistor. Make a note of the vacuum reading on the pump (and dewar if possible) after the heaters have been on for at least a half-hour.
      3. Turn off getter heaters. (IT) Run the getter heaters as described above for only about 24 hours, then continue pumping.
      4. Decide when to start CCRs. (IS) This decision will usually be dictated by the observing schedule. It's best to allow 12 full days of CCR operation before the first science night. Subject to that constraint, pump the dewar for as long as practical before starting the CCRs.
      5. Lock out unwanted activity. (IS) If this has not already been done as part of the warmup, log on to the HQ workstation hanauma as user nirspec and change the password using the unix command yppasswd. This will prevent random astronomers from attempting to start the NIRSPEC software or move motors while the instrument is not at thermal equilibrium. Be sure to make a note of the new password, so you can reverse the change later! Send an email to the "instrument" alias to announce that you have done this.
      6. Configure the software on waimea. (IS) Log in to the instrument host waimea as user nirspec and perform the following steps:
        1. Make sure waimea is healthy. Check the time since the last reboot with the unix command uptime. If it's been more than a week, reboot waimea before proceeding. This will help prevent crashes that would interrupt temperature logging while NIRSPEC is warming up.
        2. Get the server running. Check the status of the server with the unix command ct, and verify that you see three server processes running. If you see none, start the server with the command runserver. If there are 1 or 2 processes running, or if the server won't start normally, see the troubleshooting page for help.
        3. Start temperature logging. If you had to restart the server in the previous step, then any cryo logging that was running before is now dead. Check for any lingering processes with the command:
          • psgrep logcryo
          Kill any suspended logcryo jobs found. If there is not a working logcryo job running, start it. In the home directory of the nirspec account on waimea issue the command:
          • logcryo > logs/cryotemps.warmup.[date] &
          to start the temperature logging process. This will record the temperatures on all the dewar sensors, every five minutes, in the file you just created. For the [date] part of the filename, use some identifier that will include the day, month and year such as 23jul01.
        4. Turn up the Aladdin detector temperature setpoint. To protect the Aladdin detector from condensation, it must not ever be the coldest point in the system. The normal temperature setpoint is 30 Kelvin. Set it up to 300K with the following command:
          • m change.detector.temp=300
          The detector block heaters do not have enough power to take it to 300K, but setting the temperature to 300 will run the heaters flat out, which will keep the Aladdin about 10-15 degrees K warmer than the rest of the system.
      7. Touch base. (IS) Contact the summit Instrument Technician on duty to confirm that all the steps above have been completed, and that NIRSPEC is ready for cooling down.
      8. Check the vacuum. (IT) Turn on the Varian SenTorr vacuum gauge controller, and after it stabilizes make a note of the vacuum reading on the "high vacuum" channel. Also note the vacuum reading on the pump. Touch base with the responsible Instrument Scientist to confirm that the vacuum is good enough to restart CCR cooling.
      9. Stop pumping. (IT) Close the dewar vacuum valve, and turn off the pump.
      10. Start the CCRs. (IT) In the Keck 2 mechanical room, switch on the CCR compressor No. 3 that serves NIRSPEC. Immediately advise the responsible Instrument Scientist as to the time the CCRs were turned on, and as to the vacuum reading on the Varian SenTorr gauge controller before and after.
Last modified: 12/03/2021 01:39
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