Tcam images of ITMX and ITMY seemed to change drastically from yesterday.
Figure 1 and 2 show the Tcam images of ITMX and ITMY today and yesterday, respectively.
It might be due to frosting on mirrors by increasing vapor pressure of water molecules due to warming up of duct shields.
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Fig. 1 shows vapor pressure of several materials.
According to this figure, the temperature at which H2O evaporates is
170K@1E-3Pa,
160K@1E-4Pa,
150K@1E-3Pa.
Fig. 2 shows changes of vacuum pressure in several places.
After 12/26, when the duct shield cryocoolers were turned off, the pressure increased from 1E-5Pa to around 1E-3Pa, so it is thought that it was necessary to keep the temperature of the mirror at about 170K to prevent water adsorption.
Fig. 3 shows summary of temperature of cryogenic payloads at 6:32.
165K@IX/Y
174K@EX
168K@EY
If there is no water adsorption in EX/Y, IX/Y may also see water starting to evaporate with a temperature increase of several K.
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