This post will host plots and trends from this radiative cooling run (QIL/2704).

Preliminarily, it looks like the reconfiguration to remove a hardware mistake or two led to a healthier run. The comparison below clarifies the two runs:

• QIL/2702 - conductive link between inner shield and outer shield (twisted pair from an RTD lead accidentally clamped); possibly another conductive link between outer shield and baseplate (outer shield more wobbly than usual on spacers)
  • this data set should only be used to study the impact of a known conductive link between inner and outer shields.
  • this run demonstrates that there will be more effective, faster cooling if the outer shield is conductively cooled!
• QIL/2704 - resolved above mistakes!
  • this data set may be used to gain understanding of the impact of emissivity changes to the inner surface of the inner shield.
  • may be compared to QIL/2695, a run that is equivalent except with a higher emissivity inner surface of the inner shield

Run ended with cryocooler shutdown at 12:27 pm (actual duration just under 92 hours). System will warm up with pumps on for the rest of the break, unless I am inspired to come in and run one of the next intended runs discussed in QIL/2704. I did not run any heat input test for this data set, as I am not planning to come in frequently enough to monitor the heating safely.

Data:

Attachment 1 compares QIL/2704 (solid) to QIL/2702 (dashed). As expected, the outer shield temperature from the latter run stays warm since the conductive short was resolved. Due to the reduction of the inner shield's thermal load, the inner shield is able to cool faster and plateau at a colder temperature. As Stephen pointed out, however, the test mass is not cooled as efficiently compared to when the outer shield was conductively cooled.

Fitting Results:

Attachment 2 is a current model diagram of the various components being considered, and their thermal couplings. Attachment 3 plots the fitted model (dashed) over the temperature data (solid). The fit parameters were the following emissivities: aluminum foil, rough aluminum, and aquadag. Notes from the fit:

1. With the conductive shorting of the outer shield resolved, the model (which considers only radiative cooling of the OS) is well fit to the OS temperature data. 

2. The inner shield model is missing some key term(s) affecting its time constant and steady state temperature.

3. The above error propagates to the test mass model (I believe). 

Given these caveats, the fit results are as follows: aquadag e = 0.92, Al foil e = 0.04, rough Al e = 0.19. These all initially seem reasonable, and I'm happy to see that the aquadag emissivity is higher than previously estimated.

Next steps:

1. Separate the cold plate from the inner shield, and model their conductive and radiative link. Also model the radiative link between the cold plate and the test mass.

2. Cover the test mass in foil (to best of our ability) to refine the radiative link between the test mass and inner shield. Doing so will mean both elements have the same emissivity, so there is only one unknown parameter.