40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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Message ID: 2559     Entry time: Wed Apr 21 09:42:35 2021
Author: Stephen, rana 
Type: Things to Buy 
Category: Cryo vacuum chamber 
Subject: Reimagining QIL Cryo Vacuum Chamber 

WIP log entry - working on getting all of our ideas down on the page, then will sort and elaborate.

We met to discuss a range of topics relating to the path ahead for the Cryo Vacuum Chamber. This reconsideration of the current state of things is necessary as the chamber needs to become the workhorse for PD characterization efforts soon, in addition to a range of other tests (large suspension tests will be conducted in a different chamber, yet to be designed)

  1. Pumping station should be moved away from table, with long roughing lines perhaps coming down from above using some ceiling-mounted cable tray or similar.
  2. Primary pumping line to chamber is large and overkill in terms of conductance. Can move to a longer, more flexible, smaller diameter connection (may need to adapt using CF zero-length flange).
  3. Pumping of the external volume may be managed by valve arrangement and direct connection of both volumes to the turbo pump. Valve out the external volume once the pressure is low, and the pressure should hold well enough for conductive losses to be minimal.
  4. Viewports seem suitable, no issues throughout. I learned about common coating behavior, namely that reflectance is generally at half the wavelength of transmission, so if I see a green reflection it suggests transmission at IR. Neat!
  5. Cabling into chamber for temp sensors is pretty scary. Noticed the kink in the cable bundle caused by the flexible part of the cable extending longer than the grip of the connector's stiffening. Needs to be reassembled with the stiff cabling under the grip (could extend the grip, shorten the flexible leads, etc.) to avoid the kink.
  6. External volume feels like a misdirected design.
    1. For general case, consider mounting the cryocooler directly to chamber. Avoid losses related to thermal linkages from cold head of cryocooler to baseplate (diagram will be supplied, Rana was especially concerned that the V clamping arrangement didn't have adequate contact area in the line contacts)
    2. For vibration-sensitive experiments, would be good to have a flexible bellows reducing vibrational energy through the vacuum skin, and flexible strap reducing vibrational energy to the baseplate.
    3.  For contamination-sensitive experiments, would be necessary to implement a feedthrough as currently, but seems overkill for current slate of experiments.
    4. The intention seems to have been to devise a scaleable solution that would work for Mariner, but we are currently very far from realizing that (cryocooler needs to be Stirling cycle for vibration, no validation yet of adequate thermal conductivity through the external volume to the baseplate, etc.)
  7. Thermal straps with Mylar shielding is not the optimal implementation. Something like a rigid copper bar provides better conductivity, and can be shielded by G10 tubing with Aluminum metallization on the OD. If a flexible connection is required (for example, vibration isolation or positional uncertainty) a thermal strap may also be shielded in this sort of conduit.
  8. Need to replace the V-groove copper connections with something with much more surface area. V-grooves are nearly 1D contact lines, so they are probably the mian cooling rate limiter at the moment. Need to get some new parts fabbed ASAP to continue working on this cryostat.
  9. Vent valve should be a leak valve with a controlled, small conductance, perhaps backed by a filter. Want to allow slow, controlled venting.
  10. Skyhook Crane should be on its cart wheels for easy relocation away from the experiments.
  11. Skyhook should be replaced by a simple hoist mounted to ceiling of enclosure. Would require stiffening of some members of the enclosure's ceiling, but would permit easier access with fewer traffic jams.
  12. Yellow solvent cabinet should be removed. Solvents should be stored under fume hood.
  13. Would be great to get a stand (ie wire shelving, but heavy duty) which could hold the compressor, hold the pumping station, and provide a single location for any other items that need to be interfaced. All connections would be routed over the walkway via a run of cable rack.
  14. Moving the chamber to the center of the table width would be helpful to opening up access to more ports. Currently located in a corner, such that only half of ports are accessible. This is an extra reason that the Sky Hook should be remounted to its wheeled base.
  15. Should put all controllers on a rack, rather than consuming optical table space. All necessary serial comm cabling could then run to this singular location. We can use the rack next to the sink which has the NIM racks. The rack is completely unused right now. Need to get some rack parts to put some shelving in there.
  16. Documentation of ongoing thoughts, design efforts, modifications, etc. can be contained at the wiki!
  17. What is currently installed? Some insights from the wiki (ie gauges, pumps, viewports) should be elevated into a comprehensive diagram with a bill of materials or similar.
  18. In the diagram need to note all instruments so that Radhika can include it in her work to interface with the DAQ. i.e. no more photos and screenshots to record data.
  19. Where am I? A floorplan for this experiment (current and planned) would be worth some time, now that we are considering specific improvements.

Will sort the above into some sort of timeline (such as short term / long term).

Ruminations about the future chamber for suspension work:

  1. Stirling cryocooler for vibration isolation
  2. Straight-sided construction (i.e. rectangular prism) for more usable footprint inside
  3. If vertical (i.e. lid) use counterbalance and hinge for easy opening without hoist or crane; might need side ports large enough for hand access, since the height will be prohibitive to reach all the way down to the baseplate.
  4. Horizontal (i.e. door) might be preferred, especially with the volume in the form of a rectangular prism. This would allow access throughout the height of the chamber.
  5. Usual vacuum vendors should be able to help bring the design from a sketch to a quote, so start those conversations.
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