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Message ID: 2794     Entry time: Thu Jul 14 18:15:41 2022
Author: Radhika 
Type: DailyProgress 
Category: Emissivity estimation 
Subject: Undoped Si wafer cooldown in Megastat 

[Stephen, Clare, Hiya, Radhika]

On Thursday 7/14 we started a cooldown of an undoped Si wafer in Megastat. Our goals were to swap out the glass wafer from the previous cooldown for the new undoped Si wafer, to verify that there is sufficient radiative coupling between thin Si and the inner shield. This way we ensure that our cooldown data can be fit for the wafer's emissivity. 

When we opened up the chamber, we noticed some of the aquadag-coated foil was touching the bottom face of the glass wafer [bottom edge of wafer in Attachment 1]. This is a potential conductive short, and analyzing the cooldown data will reveal how significant the conduction was. We also noticed several aquadag flakes on the ceramic ball bearings/wafer [Attachment 1]. Stephen pointed out ways to improve the clamping of one end of the base plate to the cold plate, given that the hole spacings of the two did not line up (explained in 2792). We mapped out a new bolting/clamping approach for the baseplate using metal spacers instead of folded Al foil [Attachment 2]. We applied grease to the bottom surface of the baseplate and then bolted/clamped it down to the cold plate [Attachment 3].

We removed the glass wafer and debonded the varnish from the RTD. We then re-varnished this RTD to the undoped Si wafer [Attachment 4] and placed it on top of the ceramic ball bearings on the bolted/clamped baseplate [Attachment 5].

Lastly, we trimmed off excess aquadag-coated Al foil to ensure there would be no future shorting to the wafer. We then verified all RTDs were responsive and closed up the chamber.

The vacuum pump was turned on at 5:35pm, and the cryocooler was turned on at 6pm. 

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