Measured Temperature in the WIRCam Cryovessel on the Telescope

The WIRCam cryovessel was integrated at the CFHT in December 2004. Cryogenic tests were performed and temperatures were monitored during the cryostat cool-down. In the meantime, a transient analysis of the thermal model was computed. The hypotheses of the thermal model are identical to the experimental conditions on the Mauna Kea summit:

• Camera pointing in vertically (orientation of the gravity vector in the software).

Figure 3 compares the thermal model to the measurements of the current system for different parts of the cryostat. The getter temperature and the optical barrel (detector side) temperature measurements are compared to the thermal model. Figure 3 shows a reasonably good agreement between the thermal model and the measurements. This clearly validates the interest in thermal modeling for this kind of instrument. In particular, the barrel temperature as a function of time is well fitted by the thermal model. The deviation between the thermal model and the measurements is higher for the Getter, because there are interfaces in the cold finger that are not fully described. Nonetheless, the global behavior of the model reflects with a relatively good accuracy the measurements.

Figure 3. Comparisons between the WIRCam thermal model and the measured temperatures profile as a function of time during the cooling down at the Mauna Kea summit. The getter and the optical barrels temperatures are presented here.

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