FourStar Software Documentation

Cooldown Procedure

Location of this document: http://instrumentation.obs.carnegiescience.edu/Software/FourStar/cooldown.html

  • Preparations
  • Filling The Shroud Dewar (Optics)
  • Filling The Detector Dewar
  • Operations Settings (Equilibrium)


    FourStar Warmup
    FourStar Software Documentation

    Preparations

    Please read the entire document before you start the cooldown and familiarize yourself with the FourStar Sensors.

    Note:It is recommended to test the detector system warm before cooling down the system to ensure that all components/cables are ok, but it is important that the JADE power is off during cooldown to avoid trapping charges in the H2RG arrays.

    Startup the FourStar software selecting just the Detector- and Optics-Temperature controllers, Front- and Back-Temperature monitors and the LN2-Controller (if available):

    Both tanks should be empty at this time and at ambient temperature. The turbo-pump should be connected to the system and the ion-pump off.

    Use the following settings on the temperature controllers:
    Setting Detector Temp.Controller (TC1) Optics Temp.Controller (TC2)
    Target [K] 75 199
    |Max| [K/min] 0.4 0.02
    Range [W] Off Off
    Meta On On

    Filling The Shroud Dewar (Optics Cooldown)

    Fill the Shroud tank first. If you are not in a rush to take data, it is recommended to wait filling the detector tank until the next day. This will allow the detector system to pre-cool slowly.

    Filling The Detector Dewar

    Before you start filling the detector tank you must set the Detector Temp.Controller Range to 50 [W]. This is also a good time to set the Optics Temp.Controller Range to 25 [W].

    Setting Detector Temp.Controller (TC1) Optics Temp.Controller (TC2)
    Target [K] 75 199
    |Max| [K/min] 0.4 0.02
    Range [W] 50 25
    Meta On On

    Note: The system should be under constant supervision during the detector system cooldown. This procedure takes about 4-6 hours, please plan ahead.

    Start filling the detector tank, while keeping an eye on the Detector Heater output. If the heater output starts oscillating then:

  • stop filling the tank and
  • set the Target temperature of the Detector Temp.Controller to the current temperature
    until the system stablizes. Filling the detector tank slowly during the first fill minimizes the likelyhood of oscillations.

    Once the heater output goes below 15% you should switch the heater range to 5 [W]. After about 5 hours the cooldown rate will be slowing down to a point where the heater will be effectively off, so you may switch the Range to the off position and let the detector temperature drift during the remainder of the cooldown procedure. Once this point is reached it is sufficient to only check the system status every few hours to ensure the tanks are not running out of LN2.
    The diagrams below shows a typical cooldown: [todo use latest cooldown]

    Once both tanks are cold you may turn-on the ion-pump. It is recommended to leave the system on the turbo-pump as long as possible.

    Operations Settings

    After about 4-5 days the optics temperature will reach 199 K and the Optics Heater will start controlling the temperature of the optics barrel. Please adjust the Target temperature of the Optics Temp.Controller to 200.
    The operational temperature for the detector is 80 [K] with a Detector Heater Range of 0.5 [W]. A few hours before you want to take data you should change the temperature controller settings to its operational (equilibrium) settings:

    Setting Detector Temp.Controller (TC1) Optics Temp.Controller (TC2)
    Target [K] 80 200
    |Max| [K/min] 0.1 0.02
    Range [W] 0.5 25
    Meta On On

    2012-01-30, Christoph C. Birk, Carnegie Observatories