Routine filing

• The outer liquid N2 dewar should be filled every day
• The inner liquid N2 dewar every two days.
• The outer vessel hold time is 23 hours.

Important: If you want to fill only once per day, fill in the afternoon. Filling in the morning creates a risk that the outer vessel may run out before the end of observing.

Note: The inner vessel does not have a hose connection for Clio2. This picture needs updating.

Filling the Dewars

Outer Dewar

An LN2 bottle is pulled over, and the metal rod inserted into the dewar. A solid metal rod from the top drawer of the Clio electronics rack is used to restrain a loop of the elastic filling tube. When the LN2 is turned on, this prevents the metal filling tube shooting out of the tank. Holding it lightly in place until the cold vapour freezes the tube in place, it takes about 5 minutes to fill the LN2 tank. The sign of a full tank is LN2 overflowing and spurting out of the tank.

Inner Dewar

The inner dewar will have very little boil off of liquid nitrogen each day. A fill time of 30-60 seconds is not unsual.

Temperature of the dewars is checked at the digital thermometer display on the Clio Electronics rack. The left top number shows the detector temperature. The right top number shows the optics temperature. The right bottom number shows what percentage of the total heater output is being used to stabilize the detector.