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Message ID: 2594     Entry time: Fri Jun 25 09:47:33 2021
Author: Radhika 
Type: DailyProgress 
Category: Cryo vacuum chamber 
Subject: Cooldown data 

I've attached cooldown data from 6/21-6/24. Unexplicably, the CTC-100 stopped logging temperatures at ~50 hours after the start of cooling, or around 5pm Wednesday. The red logging indicator was definitely on at 3pm Wednesday, but it was off when I checked in Thursday afternoon. It must have somehow been disabled in between. On the bright side, the temperature of the workpiece stabilized at 66K. I had checked in at 53 hrs, 62 hrs, and 64 hrs and noted the temperatures by eye (green data points on attachment 2). 

The time constant for the workpiece is ~ 36.4 hrs, about the same as the previous run (tau = -40/ln(100/300)). While no improvements were made on this front (cooldown still very slow), it stabilized 6K below the previous run. 

The RTD at the cold head recorded a shoot-up in temperature right at the beginning of cooldown, which makes Stephen/me think that it debonded from the cold head. This temp reading would have been informative for our model, but we will verify it's status when we open up. We can find a better bonding mechanism for the next cooldown.

[Update] I let the chamber warm up over the weekend, and brought it up to room pressure on Monday 6/28. Next steps are to open up and investigate the cold head RTD and make improvements to bonding mechanism, if necessary. We will assess any other improvements (model driven) before the next cooldown.

Attachment 1: cooldown_6-21.pdf  16 kB  Uploaded Fri Jun 25 10:48:01 2021  | Hide | Hide all
Attachment 2: cooldown_model_vs_data_v2.pdf  22 kB  Uploaded Mon Jun 28 15:02:58 2021  | Hide | Hide all
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