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Entry  Fri Mar 18 19:34:35 2022, Radhika, DailyProgress, Cryo vacuum chamber, Megastat cooldown 3/18 - adding indium gaskets to copper bar joints 8x
    Reply  Thu Mar 24 16:08:35 2022, Radhika, DailyProgress, Cryo vacuum chamber, Megastat cooldown 3/18 - adding indium gaskets to copper bar joints cooldown_0319_vs_0310.pdf
Message ID: 2736     Entry time: Thu Mar 24 16:08:35 2022     In reply to: 2734
Author: Radhika 
Type: DailyProgress 
Category: Cryo vacuum chamber 
Subject: Megastat cooldown 3/18 - adding indium gaskets to copper bar joints 

The data from this cooldown is attached (labeled 03/19 - UTC time), compared to the run started on 03/10. In between these 2 cooldowns, the greased joints were replaced with indium joints on both sides of the copper bars (cold head to copper bar, copper bar to flexible strap). 

Observations:
1. The outer shield is in weaker conductive contact with the cold plate than before. Due to the resting of the outer shield (no clamping), the amount of contact is expected to vary run to run.
2. The cold head seems to be experiencing a larger heat load than compared to the previous run. The inner shield does get slightly colder, but this could be attributed to less cooling power being diverted to the outer shield. It is unclear what additional elements could be receiving this extra cooling power.
3. The steady-state temperature difference between the cold head and inner shield is much smaller than in previous runs (23K to 10K). Since this offset is determined by steady-state heat loads along the conductive pathway to the inner shield, it isn't immediately clear why this would have decreased
4. The test mass cooldown trend stays nearly identical to the previous run, despite the aforementioned differences. This seems to confirm that there is some heat leaking from the outer shield to the test mass, which balances the extra cooling power from the inner shield. 

Efforts to update the model (indium links) and analyze these runs is ongoing. Accurate analysis rests on understanding points 2 and 3. above, since the current model predicts a much larger steady-state offset between the cold head and inner shield.

I plan to devote some time to this analysis before planning another Megastat cooldown.

Attachment 1: cooldown_0319_vs_0310.pdf  31 kB  Uploaded Thu Mar 24 17:11:08 2022  | Hide | Hide all
cooldown_0319_vs_0310.pdf
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