On Thursday 6/30 we worked towards a cooldown with a glass wafer rested on ceramic ball bearing supports. We used a glass wafer for this cooldown because it has a higher emissivity than a Si wafer, and therefore could be more easily validate our cryostat setup.
The procedure went as follows:
1. RTD preparation [Attachments 1, 2]
- Re-soldered the leads of the 3 RTDs we previously calibrated (2791)
- Bonded RTDs to the inner shield, outer shield, and glass wafer with varnish
*Note that we did not have any RTDs left to clamp to the coldhead
2. Wafer support structure [Attachments 3, 4]
- Applied grease to the bottom of the baseplate and bolted it down to the cold plate using 2 screws and a dog clamp. The hole spacings on the cold plate and base plate did not align align along the longer axis of the baseplate, so we needed the dog clamp to hold down one end. To get the dog clamp elevated to the right height, we folded a piece of aluminum foil until it was tall enough to rest the dog clamp flush on top of the base plate.
- Rested 3 ceramic ball bearings and wafer on top (*The ball bearings created enough clearance between the dog clamp and the wafer)
We closed up the chamber and started the vacuum pump [Attachments 5, 6], but soon after I realized the wafer RTD was glitching/shorting. I turned off the pump and re-opened the chamber, and upon inspection noticed that a few of the RTD lead pins were fraying. I replaced these pins and left for the day.
On Friday I verified that all RTDs were operating properly and closed up the chamber. The vacuum pump was started at 3:10pm and the cryocooler was switched on at 4:10pm on 7/1.