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Entry  Tue Apr 5 16:47:46 2022, Radhika, DailyProgress, , Rerun of cooldown with indium gaskets in copper bar joints 9x
    Reply  Wed Apr 6 10:31:55 2022, rana, DailyProgress, , Rerun of cooldown with indium gaskets in copper bar joints 
Message ID: 2749     Entry time: Tue Apr 5 16:47:46 2022     Reply to this: 2750
Author: Radhika 
Type: DailyProgress 
Category:  
Subject: Rerun of cooldown with indium gaskets in copper bar joints 

[Radhika, Stephen]

On Thursday 3/31 we opened up with a goal to diagnose and fix the heater connection (previously reporting an error). Upon opening, we realized the steel wires suspending the test mass had snapped, and the test mass was sitting on the cold plate [Attachments 1, 2]. The mirror had fallen off one face of the test mass, and the heater had also debonded from the other face [Attachments 3, 4]. Our suspicion was that the wires somehow got sliced by the metal zip tie whose function was to mechanically secure the heater in place. Since it did not serve this function anyway and caused more harm, we decided to ditch the zip tie moving forward. 

Procedure (3/31-4/1):

  • Removed suspension frame and fallen test mass from chamber
  • Addressed debonded heater
    • Cleaned up varnish from where the heater had been previously bonded [Attachments 5, 6]
    • Re-varnished heater to the test mass face
      • We did not rebond the mirror to the opposite face, since it doesn't currently serve a purpose
  • Addressed snapped suspension
    • Removed old steel wires
    • Cut 2 new wires, adjusted to desired length, and tightened them in place
  • Re-inserted the test mass into suspension, and placed the whole system back into the chamber [Attachments 7-9] 
  • Tested the heater output before closing up

The vacuum pump was started ~4:15pm on 4/1, followed by the cryocooler at 5pm. 

On 4/5, I realized the CTC100 log did not contain any data from the weekend cooldown. I expected it would record the data locally even if the workstations were powered off, but this turned out not to be the case. I turned off the cryocooler at 11:45am, with the heater set to 295K. We will redo the cooldown once the chamber gets close to RT.

During the above investigation, I realized the CTC100 channel values were stale - the values are not being updated and all the channels are showing ~255K. None of the RTDs on the CTC100 front panel were are reporting this temperature, so something is getting in the way of proper telnet connection. The warmup waiting period will give me time to diagnose and debug the issue.

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