IYC test (temperature & frosting)
1) IYC cryostat looks to reach to stable temperature.
See the attached file of temperature distribution in IYC, with the reference of temperature distribution at Apr. 2019.
Apparently, 4K-3 refrigerator shows higher temperature of 22K, and this can imply that 4K-3 ref. is in semi-stable temperature.
We need to break thermal balance to solve this issue. So I turned off 4K-3 ref. at 4pm today.
Before tuned off 4K-3 ref., I checked frosting situation on the IYC mirror.
Attached file shows a picture taken by TCAM by irradiating LED light from OpLev port.
It is difficult to see mirror surface clearly, however, we could see actuator coil and magnet on mirror clearly, which exist at the back side of mirror from TCAM.
That is, I think there are no frosting on mirror surface.
After re-cool-down by 4K-3 ref., we need to check frosting on the mirror since absorbed gas can be released by warming up.
Non-image files attached to this report