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It seems that the green-handled regulator on the QT manifold should not be open too much. This will make the MFC letting in the helium to the cold heads fluctuated a lot which is not optimal for cooling. During cooldown mode you want a large flow running in and out of the dewar with the goal of around 60 slm going in and 24 slm going out. In order for this to work the pressure in the cold heads much stay slightly above the dewar pressure so flow continuously runs to the dewar to cool things down. The black-handled needle valve should be open a lot (maybe all the way) to keep the flow through this area as high as possible. This will lead to lots of frost and ice build up on the dewar neck. This should not be a problem but should be checked and defrosted regularly. When everything is set appropriately the accumulation of liquid should happen in about 24 hours.
Cooldown Mode Settings
- Open the NV501 (A/B) as much as it doesn't affect producing a lot of ice on the Dewar neck. This will allow a higher flow circulation between the Dewar and coldheads.
- In the "Cooldown Mode Settings": Set the outlet flow to 24slm and End mode cold head temperature to 3K
- Reduce PRV501 (A/B) (green-hand valve) to barely provide the flow that FC501(A/B) flow controller asking for.
Liqefy Mode Settings
1. Close the NV501 (A/B) until there is no ice accumulation on Dewar neck
Questions
a.) Is there a downside to having the needle valve open too much during the dewar cooldown?
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