As discussed during the 21 Jan 2022 meeting, the next cryostat run will seek the fastest radiative cooling (again, see QIL/2706) through the following configuration choices:
- move heater to test mass
- add thermal grease to inner shield - coldplate interface (clamped joint)
Actions completed 27, 28, and 31 Jan 2022
- Vent.
- Remove Test Mass in frame.
- For simplicity, we snipped the RTD lead (we didn't want to have to redo the cryovarnish joint).
- Of course, the joint failed during the repairs so we had to redo the workpiece RTD cryovarnish joint anyway!
- Use cryovarnish to affix heater.
- Removed aquadag in area of joint using IPA-soaked Alpha wipe and scrubbing motion.
- First, varnished cigarette paper anchor pad, then added heater.
- We allowed the cryovarnish to cure overnight between the 27th and 28th, then allowed the joint to hang in its vertical orientation over the weekend to confirm its integrity.
- Use conventional pin-socket arrangement to add junction to heater leads and workpiece RTD leads.
- Confirm all RTD leads are functional, and repair crimp joints and Kapton tape insulation where needed.
- Clean up aquadag flakes on coldplate.
- Remove inner shield, add Apiezon M thermal grease, and bolt down again.
- Touch up position of mylar shield on cold linkage, aluminum foil aperture covers.
- All apertures are covered except:
- Inner Shield: cold linkage (not an issue - partially occluded by copper bar, mylar tube extends into cold head view and mylar mitten)
- Outer Shield: electrical port, cold linkage (aperture has been extended to have additional area underneath the original circular aperture)
- Insert Test Mass in frame. Dog clamp down frame.
- Pump down, cool down.
- Pump down started at ~15:15.
- Cool down started at 15:44.
Model updates required to reflect new configuration:
- estimate conductive leak from 24 AWG heater leads to test mass
- model conductance of cryovarnish joint between heater and test mass - does cigarette paper make a difference?
- model greased joint of inner shield - cold plate interface
- confirm clamp load is adequate for effective greased joint, at room temp and cold temp!
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