Versions Compared

Version Old Version 1 New Version 2
Changes made by

Carlos Alvarez

Carlos Alvarez

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

Introduction

...

Based on previous experience, it takes about 2 hours since the CCR system is turned off for the first stage of CH2 to reach 55K. We are planning to lower the temperature of the optical bench and radiation shield a few days before the ATS power shutdown to gain a few hours before the CH2 first stage temperature reaches 55K.

Procedure Before power down

...

  • Current cold head speed settings are:

    • waikoko-new{nirc1}81: gshow -s nirc2 ch1spd ch2spd
      CH1SPD = 333.330 mvolts
      CH2SPD = 250.000 mvolts

  • Current cold head speed read backs are:

    • waikoko-new{nirc1}82: gshow -s nirc2 ch1spdrbv ch2spdrbv
      CH1SPDRBV = 985.000 mvolts
      CH2SPDRBV = 932.000 mvolts

  • These are translated into RPM as follows, where CHSPD range is 100 to 3500 mV and CHSPDRBV range is 0 to 5000 mV:

    • Cold head speed setting in RPM: R [RPM] = 24 + 0.012 x CHSPD [mV]

      • CH1 = 28 RPM

      • CH2 = 27 RPM

    • Cold head back speed in RPM: R [RPM] = 0.024 x CHSPDRBV [mV]

      • CH1 = 23 RPM

      • CH2 = 22 RPM

  • We will start by setting the both cold head speeds to 75% of their maximum operation speed and adjust depending on behavior:

    • modify -s nirc2 ch1spd=2400 ch2spd=2400

  • Current temperature values are:

    • waikoko-new{nirc1}83: showtemps
      tdetblck = 28.875 degK
      tgetter = 4.678 degK
      thead2lo = 11.149 degK
      tcamera = 51.002 degK
      tcoll = 50.515 degK
      tbench = 50.624 degK
      tshield = 155.980 degK
      thead1 = 140.070 degK

      tc_setpa = 29.00
      tempdet = 28.978 degK

      tc_setpb = 50.00
      thead2hi = 49.982 degK

      htrdetblck = 24.300 percent
      htrhead2hi = 16.900 percent

    • We will set the control temperatures as follows and monitor the behavior:

      • modify -s nirc2 thead1=100K

      • modify -s nirc2 thead2hi=40K

...

  1. K2AO enclosure:

    1. Archon controller (AO room)

    2. Signal Analyzer USB (AO room - no need to power this up)

    3. Calibration lamp power supply (AO vault)

    4. Private network switch (AO vault)

    5. DGH A1000 units 1, 2, and 3 (AO vault)

    6. Auto-pump system (AO room)

    7. Lakeshore 340 (AO vault - Temperature control)

    8. Lakeshore 218 (AO vault - Temperature monitoring)

    9. Motor power supply (AO vault)

    10. Emulex TS (AO vault)

  2. Keck-2 Machinery Room

    1. NIRC2 CCR speed controller

  3. Keck-2 Computer Room:

    1. vm-nirc2

    2. waikoko-new

    3. waikoko

    4. waikoko Fortra 4-Slot disk U60

    5. waikoko Andataco GigaRAID 3000

    6. AT-MC15 10base converter

    7. Emulex TS for CCR

    8. DGH A1000 for CCR

    9. SCSI fiber optic extender (no need to power this up)

Procedure during power down

...

  1. If the power comes back up before the auto-pump system trigger temperature has been reached (55K on the CH2 first stage), then the NIRC2 temperature monitoring and control system will bring the temperatures down to their nominal values without any human intervention required.

  2. If the power comes back up when the CH2 first stage temperature is slightly above the auto-pump system trigger temperature, then the auto-pump system will kick in and we can follow the procedure described in https://www2.keck.hawaii.edu/inst/nirc2/technical/alarm55.html to bring the system back to its normal state.

  3. If the power comes back up when the CH2 when the pressure inside the dewar has reached 1E-4 Torr5 mbar, then we will need to perform a full NIRC2 warm up procedure.

...

Once all the systems are running, evaluate which scenario we are on , and determine how to proceed .Eventuallybased on:

  • The CH2 first stage temperature and other temperatures inside the dewar.

  • Whether the auto-vacuum system has been started or not.

  • Pressure inside the dewar.

One critical aspect of the decision making is to determine when the pressure inside the dewar is high enough that a full warm up will be required (Scenario #3). Based on the NIRC2 Maintenance Procedures (https://www2.keck.hawaii.edu/inst/nirc2/technical/NIRC2MaintainenceProcedures.pdf), sections “Evacuating D82” and “Cooling D82”, respectively: 

“The cold heads can be turned on when the vacuum has reached the desired state. Note that the pressure will never fall much below 1E-3 mbar at ambient temperature.” “After cooling, the getter should bring the pressure to about 1E-7 mbar or below.”

Therefore, I think ~1E-4 mbar would be a safe value for the “pressure of no return”, i.e. pressure beyond which we will need to fully warm up the instrument. Does this sound like a reasonable threshold?

Once the instrument is fully recovered, set the cold head speeds and control temperatures back to their normal operation values.

...

My real concern is with the mechanisms. The motor power supply is on a UPS, and for all I know, the motors have not been homed for more than a decade [they have been homed at least twice in the last 5 years]. If the motors lose power then their status will be unknown. Also the computer will be down, so that it will not have the motor status. I would be good if you do not have to home the mechanisms, because they might get stuck.  Since the motors have power off brakes, they will hold position until they are commanded to move. I suggest that you interrogate all of the motors and record their positions on something nonvolatile, like paper. You should check the Smart Motor manual and also the low level motor command instructions on command computer and see if the positions and other parameters can be loaded on to the motors [we can do this via keywords and low-level commands are available on waikoko - see https://www2.keck.hawaii.edu/inst/nirc2/technical/motor_commands.html]. As I understand it, there have been operation system changes and software changes, so I hope that the fundamental commands are available [fundamental commands are available].

The most important thing is for the UPS to supply the motor PS for as long as possible, all of the other electronics can be shut down. If you have to home the mechanisms, good luck [we have powered down and homed motors in the recent past, so will not have an UPS for the motor Power Supply]. The most worrying are the roller screws, CAM, GRS, SLS, and SLM.

...