Zeroeth Cooldown: August 2001

NIFS was assembled and readied for its first cooldown on Friday August 24 2001.

The cryostat contained the cold work surface plate and the radiation shields, but not the spectrograph or the On-Instrument Wavefront Sensor.

The cryostat was evaculated for the next 72 hours and reached a pressure of ~1.5×10^-5 mbar.

The large Leybold cryocoolers were switched on at 1:00 pm on Monday August 27. The cryocoolers were run very slowly for the first hour to check operation and once cooling-proper began, the cryocooler speed was increased to ~ 2 Hz.

Internal temperatures then fell steadily for the following 32 hours and levelled out after 40 hours. The center of the cold work surface plate reached a minimum temperature of ~ 46.1 K. The getter reached ~ 9.2 K. Both are well below the required final operating temperature. The pressure inside the cryostat fell to ~ 7.2×10^-6 mbar.

The cryocoolers were slowed to ~ 1.25 Hz which is the expected operational speed and the center of the cold work surface plate rose slightly to ~ 48.2 K. Temperatures remained steady for the next 20 hours. The servo-controlled heater system in the center of the cold work surface plate was then tested at various power levels. Full power on the control heater lifted the cold work surface plate temperature by ~ 20 K.

For this test, we used a new and large recirculating water chiller to cool the helium compressors. A leak in the pump rotary shaft seal of this unit developed early in the test. After running for 80 hours, this leak became serious and we risked loss of cooling water to the helium compressors, each of which dissipates ~ 5 kW. We reluctantly shut down the cryocoolers at 4:15 pm on Thursday 30 August.

NIFS was back up to ambient temperature 35 hours after the cryocoolers were shut down. No internal heating was used during the warmup.

Peter Conroy lowering the cold work surface plate into the cryostat.	Colin Vest and Dave Mitchell assembling the cryostat.	Colin Vest attaching the cold work surface plate.
Assembling the first cryocooler.	Assembling the second cryocooler.	Pumping the cryostat.
Ready to begin the cooldown.	Cooldown begins.	Differential pressure switched and helium compressors.
Assembled cryostat.	Assembled cryostat.	Cryocooler head.
Control electronics in rack.	Mark Jarnyk checking temperatures.	Temperature control screen.
First cooldown temperature plots.

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