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CRY (Cryo-payload EX)
takahiro.miyamoto - 0:36 Wednesday 01 August 2018 (5663) Print this report
Oplev light quantity issue

Last week we found that oplev light quantity is reducing.

So at first we thought that this issue come from power supply of light source of the AC 100V.

So I checked this voltage, however we was not able to find any issue.
I confirmed the light brightness of the QPD side visually, and it was very weak.(Fig.1)
Then I confirmed the light brightness of the light source side visually too, and maybe I think it was not so bad.(Fig.2)
Therefore I thought that this issue come from light path, so I confirmed the view port.
As this result, we found the frost on the view port of the 4K shield.(Fig.3 : TM oplev QPD side)
We stopped the all 4K cryocooler for warming up.
After turning off these cryocooler, this frost is gradually vanishing.(Fig.4 : TM oplev light source side, Fig.5 : TM oplev QPD side)
Around ~16:50, we confirmed the light brightness became light.(Fig.6 : TM oplev QPD side)
Tomorrow We will check this view port again. 

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takahiro.miyamoto - 0:44 Wednesday 01 August 2018 (5664) Print this report

maybe this frost is nitrogen, because this vanished at ~40K.

according to the state diagram of the nitrogen, nitrogen  become gas at ~4*10^(-4)Pa. However this graph is not including less than 10^(-3) Pa, so this is guess.

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