P1.6 Cryostat cool down

• Phase : 1
• Status : Draft
• Category : Unpack, Assemble, and Verification (C1)
• Recurrence : once
• Duration : 0.5 day

Description

• Cooldown the cryostat.

Prerequisites

• SHARK-NIR connected to LBT network.
• Electronics cabinets on.
• Needs vacuum pumping at the beginning (vacuum pressure of 10e-5 Torr is good (see the cryostat manual SHARK-NIR_SO-MAN-001)).

Procedure

• Start the cryostat cooling down sequence (see the cryostat manual SHARK-NIR_SO-MAN-001).
• Check how the system performance every 30 minutes.

Templates

Success criteria

• Cryostat cooled down without any issues.
• The temperature at the detector is stable at ~78K.

Notes

• 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

• Liquid Nitrogen refill is required in the cleanroom. For the first fill, 40L of LN2 is required. For refill, every 48 hours, 15-18L of LN2 is required (see Notes section above for more details).
• Vacuum pump and support for cooling down the cryostat. We do not yet have the dimensions of the vacuum pump (available from LBTO) and how the LN2 refill will take place. If they will be done using long hoses then both vacuum pump and LN2 tank can stay outside the clean tent (see Notes section above for more details).
• We will require UPS connected to the turbo pump when pumping vacuum in the cryostat. UPS which can hold the power for 15 minutes would be sufficient. In case of a power outage, within 15 minutes, one of the SHARK-NIR team members can go to the pump and close the valve preserving the vacuum within the cryostat.

Date performed and by whom