[mTakahashi, Ushiba(remote)]
We stopped ITMX payload cryocooler (REF2, P-54) at 13:45 JST.
Cold head temperature started increasing just after stopping (fig1).
The other payload cryocooler (REF4, P-56) was already turned off, so there is no operating payload cryocooler for ITMX now.
I checked the temperature of the 80K_SHIELD_TOP, and it was 121 K. It will take one week or more to reach the critical temperature.
Even if it reaches the critical temperature, the expected vacuum level enhancement will be comparable to the vacuum level of X_00 around -21 days, which is the timing without operation of REF2/4 cryocoolers.
[Kimura]
H2O in the residual gas component tends to increase due to the temperature rise associated with the stopping cryocooler for ITMX payload.
A trend graph of Q-mass measurement is attached for reference. The H2 peak in the graph indicates the time when the cryocooler was stopped.
[Kimura]
The increasing trend of H2O in the residual gas component still continues.
For reference, two trend graphs of Q-mass measurements for IXC and BS are attached.
The partial pressure of H2O did not change in the Q-mass on the BS side, suggesting that the H2O component did not flow into the ITMY side due to ITMX heating.
The temps at the 1st heads of the REF2/4 cryocoolers are around 142K (< 157K (Tc)). Not near, but not so far. H2O is now coming from these areas outside the inner shields. So, I hope H2O frosting on mirrors will not be serious.
The 1st stage of the REF4/2 cryocooler (4K_REF2/4_50K_HEAD) is now approaching the Tc. So slight H2O release will be expected.
By the way, the recent warm-up speeds of REF2/4 2nd stages (4K_REF2/4_4K_HEAD) are different, while the recent warm-up speeds of the REF2/4 1st stages (4K_REF2/4_50K_HEAD) are similar. This means that the REF2 2nd stage has more heat invasion than REF4.
All MN_DAMP_{L, R, Y, V, P}_INMON seem to be going back to values that were recorded before the operation of cryocoolers for the cryopayload (~ 22 days ago).
For example, many ty-raps are used to bundle wires, as in photo 1 for cryopayloads. I guess these have rather large stress in them because they are fastened tightly, especially at the cryogenic temperature. Are there any accidents of the ty-raps' break in the past cooling?
The IFO lock was stopped around the earthquake timing? yesterday.
I also checked the photosensor outputs. Then, P and V also seemed to drift to the original positions. Actually, the pitch seemed to be misaligned judging from the GR trans image.
[Kimura]
At about 2:00 a.m. on May 25, the increasing trend of H2O in the residual gas component in the IXC stopped and began to decrease.
For reference, two trend graphs of Q-mass measurements in the IXC are attached.
