Maintaining the level of liquid helium in the nose is critical to the operation of the target, and monitoring this level is one of a target operator's tasks. The level of liquid helium must remain above that of the target cups or the polarization will be lost and the material may be melted by the beam. The liquid level should be adjusted automatically by a PID loop, but it's crucial to watch this level to ensure the loop is working. These are the key indicators of the refrigerator to watch, and the two valves we use to control them during normal running:
Main Flow: Indicates the flow of gas being pulled out of the nose of the fridge.
This flow will indicate the heat load on the target in the form of boil of gas flow.
Run Valve: : Controls the flow of liquid helium from the separator into the nose, and therefore is used to maintain the level of liquid helium over the target cups.
Nose Level: Indicates the level of liquid helium in the nose where the tar-
get cells are located.
Separator Flow: Flow of gas being pulled from the separator, which acts
as a buffer of cold helium to send to the nose by pulling liquid helium from the
magnet Dewar.
Separator pump manual: n_0150.pdf
Separator Valve: Controls the separator flow, and is used to keep liquid
helium in the separator.
Separator Level: This indicated the level of liquid helium in the separator,
most generally this should be considered full.
The Pump Stack is two 7000 m3/hour in parallel backed by a 7000 m3/hour backed by a 755 m3/hour rotary vane.