Changes between Version 23 and Version 24 of docs/CommissioningPlan/P1.6

Timestamp:

02/23/22 18:04:50 (3 years ago)

Author:

kradhakrishnan

Comment:

--

docs/CommissioningPlan/P1.6

@@ -28 +28 @@
 - This activity can run in parallel with other cleanroom activities (which do not need a cold detector).
 - Vacuum Pump details, usage and LN2 fill/refill: First, we need to pump a guard vacuum on a dewar. This requires a pump capable of pressures below 1 mTorr. Although a diffusion pump is capable of providing a high vacuum, a turbo pump would be preferable. A pressure gauge capable of reading below the 1 mTorr range is also essential for determining the extent of high vacuum achieved. When we reach the guard vacuum on the dewar, we need to valve the dewar onto a turbo pump. If a turbo pump is not available, a diffusion pump is acceptable. If a diffusion pump is used, make sure that the pump's cold trap is filled with liquid nitrogen. Yes, the cryostat shall be pumped off from the day before LN2 refilling, and be on UPS (so if the power goes off the pump is still working, otherwise we risk losing the vacuum in the cryostat). The dewar to the pump interface is a KF-25 vacuum flange. Regarding the LN2, for the first fill, we would require 40L. For every refill in 48 hours, we would require about 15-18L of LN2.
+- The cryostat is equipped with a small amount of charcoal getter, which will become effective below 120K. For this reason, it is best to leave the dewar on the pump while filling with nitrogen, and until the charcoal itself has cooled. Since the pump will maintain the vacuum while the charcoal is cooling, the charcoal can then absorb what outgassing occurs once the dewar has been taken off the pump. No getter is required on turbo pump. The cryostat has to be vacuum pumped also after its installation at the telescope (still, no getter required).
 
 **LBTO support**