Filling Dewars with liquid nitrogen (LN2)

Created: 02/29/96 by BvS
Updated: 09/21/19 by EF

The FAST dewar must be filled twice every 24 hours. Optimal times are just before starting observations and in the morning, immediately after finishing observations for the night. Note that the dewar must be filled irrespective of the success of your observations each night (e.g., solid clouds or no). You may need to fill it even if you are using TRES. If FAST is not on the telescope it is normally filled automatically. If the autofill system is not operating, you will be asked to fill FAST. Click here to print a new FAST Dewar Filling Form.

To fill the dewar on the telescope, first stow it. Then, disable the drives at the rack. Bring the roll-around dewar near the CCD dewar. You should wear the cryogenic protection (face shield, blue gloves and apron) that you will see inside the chamber to fill the dewar.
Insert the fill pipe into the hole at the bottom of the CCD dewar. ( Make sure you are using the correct fill pipe - each CCD dewar has a different fill pipe, which is usually labeled). You may need to fiddle with the fill pipe before it finds its proper insertion point inside and near the top of the dewar. Screw the cap down, then back it off one turn so that if ice forms you can wiggle the pipe up and down. SLOWLY open the flow valve on the roll-around dewar. The CCD dewar should fill in 5-10 minutes (timing varies depending on the dewar and the pressure in the roll-around dewar). The sign of a full CCD dewar is LN2 flowing out and spilling onto the floor. You should make sure to see this happen before you shut off the flow of LN2. Once you are sure that you have a good fill, shut off the valve. Then, wait a few minutes, to allow for defrosting, and take it out.

The TRES dewar fills automatically once every 24 hours, at 10AM. It should not require any attention from the observer.

The Keplercam dewar is filled automatically twice every 24 hours, at about 5:30 pm and 7:30 am, but varying seasonally to ensure the fills are not during observations. If you need to fill it manually, follow the instructions above and fill an online log on the 1.2m main page.

If you have any problems with the dewars, please notify the staff in your nightly log, so they can address them as soon as possible.