Kimura, Yasui (Pleas add details as a comment)
(1) We Connected 5 TMPs(#13, 6, 8, 40, 28).
(2) We stopped 3 ion pumps(#6, 8, 28)
(3) Stop two cryocooler for the payload(P-54, P-56) and one cryocooler for teh radiation shield(P-55).
*We did not turned on 8K shield heater for IX because Kimura-sama found an issue for the medm screen for the heter control.
at 15:46 GVbsx and GVbsy were closed by the interlock system triggered by increase of the vacuum pressure in mainly IY.
at 15:50 GViy was closed.
Finally the vacuum pressure reached the order of 10^-3Pa.
We decided we do not open GVbsy and GViy today.
[Kimura]
Attaching the partial pressure plots for five Q-masses measured immediately after shutting down the cryo-coolers for payloads at four locations (IXC, EXC, IYC, EYC) and the radiation shield cryo-coolers.
The primary component of the pressure rise in each cryostat is nitrogen, consistent with the overall pressure increase trend shown in each plot.
The reason for the brief hydrogen release immediately after shutdown is unknown.
As of 23:00, the pressure trend has reversed from increasing to decreasing, as shown in each plot.
[Kimura]
Attached are plots of gas partial pressures at five locations (BS, IXC, IYC, EXC, EYC).
The total pressure at IYC decreased to the 1x10^-4 Pa range, but the plot confirms that the main component of the partial pressure changed from nitrogen to oxygen.
Total pressure at the other locations decreased to the ~10^-5 Pa range.
BS: 3.98 x 10^-5 Pa
IXC: 2.46 x 10^-5 Pa
EXC: 1.45 x 10^-5 Pa
EYC: 1.11 x 10^-5 Pa
The payload cryo-coolers and radiation shield cryo-coolers for IXC and IYC were shut down around 14:53 on December 8, 2025.
Following the shutdown, pressure inside the cryostats increased. Consequently, the ion pumps were stopped and switched to TMP vacuum pumping.
Since the vaccum pressure level in IY decresed at 3E-5Pa, I opened GViy at 8:36 AM.
I also opened GVbsy at 8:58 after changing the setting value of the GV interlock to 5.9E-5Pa which is the same value used other GV interlock system.
At 11:56 AM, the vacuum pressure in IYC suddenly increased and reached 2E-4 Pa. The GV interlock closed GViy.
The vacuum pressure rapidly decreased 4E-5 Pa which is lower than the set value of the GV interlock. So I opened GViy at 12:26.
I checked 5 TMPs around IY and confirmed they operated normally.
Nakagaki, Yasui
We stopped the other cryocooler for radiation shield(P-53) at 10:26.
The compressor operating time was 23360.2h.
Nakagaki, Yasui
We stopped two duct shield cryocoolers.
9:57 Yfs (The compressor operating time was 24008.4h)
9:57 Yfa (The compressor operating time was 26226.1h)
GVitmy was closed by the interlock at 19:09 on December 27, 2025, because the vacuum pressure at Y_00 reached 1E-3 Pa.
After closing GVitmy, the vacuum pressure in IYA (Top-Left of the attached figure) is still 1E-3 Pa.
GVbsy and GVbsx was closed by the interlock at 10:27 on December 28, 2025, because the vacuum pressure at BSY reached 1E-3 Pa.
We also turned on heater of both side of IYC at 19:40, because the temperature of this duct shield was enough higher than 150K.
The heater power is about 8W.
Fig. 1: IY-Arm side
FIg. 2: IY-BS side
Since the temperatures at the cold heads of the cryocoolers for the duct shields of IYC reached the room temperature, we turned off both sides of the duct shield heaters at 9:45 a.m. on January 5th, 2026.
I turned off the heater at the top of the inner ratioation shield.