40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  ATF eLog  Not logged in ELOG logo
Message ID: 2539     Entry time: Tue Mar 16 18:45:43 2021
Author: Aidan 
Type: DailyProgress 
Category: 2um Photodiodes 
Subject: Cryo cool down and temperature rise - JPL PD LN2 (5 hours to rise) 

I pumped the chamber down and added LN2 today. The pressure was slowly rising - it was about 20m Torr in the chamber when I added the LN2. Per Raymond's instructions, I added about a third of a container of LN2. This got the temperature down to about 89K (when I had 20W running in the heater). It stayed there for about 25-30 minutes.

I turned off the heater and left the LN2 to boil off. You could see the cloud coming out of the top (the plume height would increase proportionally to the heat in the heater).

Eventually the LN2 evaporated and the shield temperature started to increase back to room temperature. As of this post it is 282K (which took about 5 hours).

The PD thermistor is not currently registering. However, the temperature of the PD can be inferred from the shield temperature (see aLOG 2517).

The rate of increase in temperature was much faster than the previous test - see second time series. I wonder if the thermal mass of the shields in the Feb 2020 test was cooled down a lot more due to 5 hours at 80K in that test - thus reducing the overall ambient load on the inner shield ...


Attachment 1: Screen_Shot_2021-03-16_at_6.44.09_PM.png  69 kB  Uploaded Tue Mar 16 19:50:44 2021  | Hide | Hide all
Attachment 2: IMG_1397.jpg  1.919 MB  Uploaded Tue Mar 16 19:52:24 2021  | Hide | Hide all
Attachment 3: Screen_Shot_2021-03-16_at_7.09.34_PM.png  74 kB  Uploaded Tue Mar 16 20:11:38 2021  | Hide | Hide all
ELOG V3.1.3-