First Cooldown With Mechanisms: May 2002

NIFS was reassembled for its first mechanisms test in May 2002. The vacuum pump was switched on on Friday May 31. The cryostat temperatures took 90 hours to stabilize to 50 K. Initial impressions were that all mechanisms were operating correctly. This is the first time that all the mechanisms have been tested together with an integrated software system.

Once cold, the mechanisms were extensively tested using command scripts. Overall performance is satisfactory. However, a few issues have been identified.

• The grating turret operated for several days and then became stiff and no longer turns in one direction at normal speed (250 rpm on the motor). It does work at much reduced speed (120 rpm). The cause of this binding is unclear.
• The OIWFS gimbal mirror does not operate at the speed at which it was tested at the University of Hawaii (250 rpm). It can be run at 60 rpm on one axis and 120 rpm on the other axis. Determining the datum takes 40 min at these speeds.
• An inconsistency has been identified in the drive train gear ratios for the focal plane mask wheel and the filter wheel. Both mechanisms use non-integer gear ratios. This means that one revolution of the wheel corresponds to a non-integer number of turns of the drive pinion attached to the stepper motor. The datum position is determined from this drive pinion, so the datum position moves if the sum of the wheel motions exceeds one complete revolution. Solutions to this bug are being investigated.
• The detector housing temperature plateaued during the cool down and eventually reached its expected final temperature, but at a slower rate than expected. Warming the cold work surface plate temperature caused an unexpected increase in the detector housing temperature. It appears from this that the 20 K tie point is not getting as cold as expect, possibly due to a thermal short to the cold work surface plate where the copper shaft passes through the cold work surface plate.
• One cryocooler has developed an intermittent squeak of unknown origin.
• Water condenses easily on the outside of the cryostat window without the dry air supply connected.
• A thin layer of condensates has appeared on the radiation shield and pickoff probe after two weeks of cold operation. This may be contaminants from the manufacturing process that will eventually be pumped out of the cryostat.

Cold work surface plate being inserted in the NIFS cryostat.	Cryostat center section in the RSAA clean room.	Bob Miles working on the cryostat center section.
Radiation shields in cryostat center section.	Cryocoolers in cryostat.	Cryostat and lifting equipment.
Focal plane unit being assembled.	Focal plane unit being assembled.	Bob Miles assembling the OIWFS optable.
OIWFS optable in clean room.	Spectrograph side of cryostat.	Spectrograph side of cryostat.
Focal plane unit in cryostat.	Cryostat wiring.	Bob Miles and Col Vest looking for that screw.
Bob Miles and Col Vest again.	And again...	Bob Miles and Col Vest with the cryostat end section.
Preparing the cryostat end section.	Nearly there...	The last piece goes on the OIWFS side.
Spectrograph camera and grating turret in cryostat.	Spectrograph camera and detector housing in cryostat.	Wiring the spectrograph mechanisms.
Detector housing in cryostat.	More spectrograph spaghetti.	Detector housing removed from support structure.
Spectrograph skirt and cover.	Celebration!!!.	Peter Conroy starting the vacuum pump.
Cool down temperatures.

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