Hirata, TakahashiR, Kohara (ATC), Tsuzuki (ATC), Yasugaki (ATC), Ebizuka (Riken), Suzuki (TMT), Akutsu, Aso

We measured the surface figure of the 85% 2-inch SRM with different shim thicknesses to find the suitable mounting configuration.

Conclusion

Consistent with Hirose-san’s report, we concluded that using a 1.4 mm thick shim is appropriate.

Note: We were initially concerned that a 1.4 mm shim might provide insufficient pressure to hold the mirror. However, even when the mount was rotated to various orientations, no displacement of the mirror was observed. In addition, the O-ring adheres to the glass surface and helps maintain the mirror position without requiring strong compression. In practice, when we pulled the ⑤ part out of the mirror mount assembly, the O-ring and the mirror came out attached as a single unit.

Measurement Setup

We used a Zygo GPI-XP interferometer with the following configuration.

A λ/10 reference flat was installed in the interferometer. The SRM under test was mounted in a holder, which was supported by two posts and attached to an adjustment stage combining an XYZ stage and a goniometer.
The temperature of the room was 22.8C, which is similar to the temperature in the KAGRA tunnel.

Results

Shim thickness = 1.4mm

We assembled the SRM holder with 1.4mm thick shims first. This is the recommended thickness in Hirose-san's report.
(We used a combination of two 0.5mm shims and four 0.1mm shims)

The surface figure is beautifully spherical as shown below on the left.
The right hand figure shows the surface figure with the power term removed.

The fitted power term is 571.511nm which translates into the RoC of 462.8m. (Note that the RoC specification of SRM is 458m+/-20m)
The residual RMS after the subtraction of the Zernike terms up to power is 10.728nm. (Note that in Hirose-san's report, this value was 13.3nm for 1.4mm shims).

Shim thickness = 1.3mm

We then removed 0.1mm shims to make the total thickness 1.3mm.

The measured results show clear astigmatism.
The RoC from the power term is 450m. The residual RMS is 103.4nm. While the RoC is still within the tolerance of the specification, the residual RMS is 10 times larger than the 1.4mm case.
This is very similar to the 1.3mm result in Hirose-san's report.

Left: only piston and tilt removed,  Right: power is also removed

Shim thickness = 1.4mm again

We then put the 0.1mm shims back to measure the 1.4mm case again to check the repeatability.

The result is fairly consistent with the previous 1.4mm measurement.
RoC = 458.0m, residual RMS = 13.2nm

Left: only piston and tilt removed,  Right: power is also removed

Closing Remarks

The obtained results are remarkably consistent with Hirose-san's results.
Also it is quite repeatable.
Note that we have two sets of the SRM mirror mount assembly. What we used this time is a different one from the one Hirose-san used. Still the results are quite similar to each other.
There must be a good mechanical reason for this behavior.

I finished the replacement of the Pastavi server at Kashiwa (in computer room of daini sougou tou). Now the new server is working well for the Pastavi.
From the user side, the usage is same as previous. The way to access the server is written in the document.

I tested most of the options in several modes including the noise budget mode. As I checked, the options is available on the new environment.
If you faced any issue, please share the information with me.

The remained task is to develop the new scheme to handle several job by using HTCondor.

Date: 2026/03/19

Member: Dan Chen, Shingo Hido, Misato Onishi

We performed our usual WSK calibration at UToyama.

The results look no problem.

Results

Comparison with Previous Results

Comparing with previous results, no significant issues were found.
Attached graph is the result summary including the latest measured data.

[Kimura and M. Takahasi]

 On March 18, we switched  form TMP to the Ion pump of the #36 vacuum pump unit at the Y-end .

After the activation of the #36 Ion pump, we turned off the #36 TMP and dry pump

[Kimura and M. Takahashi]

 On March 18, we completed maintenance work on the duct-shield cryo-coolers for the  EYC.
We are planning to restart the duct-shield cryo-coolers starting March 23, which will also serve as a test run.

[Kimura and M. Takahashi]
 As part of maintenance work on the cryogenic cooling units, we removed two valve units from the radiation shield cryo-coolers (P-53 and P-55) of EYC.
The removed valve units were packaged and returned to the manufacturing plant, where they will be disassembled and inspected.

 We plan to remove the remaining valve units from the IXC, IYC, and EXC radiation shield cryo-coolers early next week.

KAGRA Pcal-X updates (2026/03/18)

Workers: Kohei Mitsuhashi, Dan Chen

We performed monthly Pcal-X calibration on 2026/03/18.

After the calibration, we updated EPICS parameters related to the Pcal-X system. No issues were found.

I offloaded the F0 and F1 GAS filters with the FRs.

[Kimura and Yasui]

Parts replaced during maintenance work
1. Absorber in the helium compressor
2. Filter unit at the supply side
3. Gas replacement inside the cold head in accordance with SHI work procedures
4. Disassembly and maintenance of the valve unit at the SHI factory
5. Gas replacement in the compressor and flexible tubing
(1) Helium gas used: G-1 grade
(2) Filling pressure: 14.8 bar

A CAL Tcam session was performed to obtain beam position information necessary for Pcal. The parameters have already been updated, and SDF has been accepted.

Operator: Shingo Hido, Kohei Mitsuhashi, Dan Chen

Update Time: 2026/03/18 07:41:38

This work is continued from klog36589

## GAS control modification

According to yesterday's results related to GAS, there seem to be gain peaking at 3-4 Hz. So I reduced {F0,F1,BF} gains to -6dB. After that I measured their OLTFs when SR2 is in the LOCK_ACQUISITION state. Fig.1,2,3 show the results. Unfortunately, OLTF could not be measured well maybe due to the coupling between GAS controls. Acoording to loop suppression (IN2/EXC), their controls seem to work well and the peaking around 3-4Hz becomes smaller. Fig.4 shows the error/feedback spectra. The peaking seems to be disappeared although each residual GAS motion seems to be not changed so much.

## IM DAMP roll off modification

I also modified the roll off filters for IM DAMP {L, P, R, Y}. As for T and V, elliptic filter was also not used in SR3. So I did not touch them in this time. (Maybe it is better to change)

I measured the OLTFs after the modification. Figure.5, 6, 7, and 8 show the OLTFs of IM DAMP {L,P,R,Y}. Also Fig. 9 and 10 show the error/feedback spectra. the feedback above 10 Hz was rolled off successfully.

[Kimura and Yasui]

 At around 10:00 a.m. on March 17, we stopped the vacuum pumping in the Q-mass piping, opened the cryostat-side GV, and connected the Q-mass.
The pressure inside the piping before opening the cryostat-side GV was 1.8×10⁻⁴ Pa, and after opening the GV, it was 4.4×10⁻⁵ Pa.
 We then installed an analysis unit on the Q-mass piping. The final pressure inside the piping was 3.5 × 10⁻⁵ Pa.
We then removed the vacuum pumping unit from the piping.

[Kimura and Yasui]

 On March 17, we completed maintenance work on the duct-shield cryo-coolers for IXC and IYC.
Maintenance work on the duct-shield cryo-coolers for EXC and EYC is also scheduled to be completed by the end of this week.
We are planning to restart the duct-shield cryo-coolers starting March 23, which will also serve as a test run.

Workers: Kohei Mitsuhashi, Dan Chen

We performed monthly Pcal-Y calibration on 2026/03/17.

After the calibration, we updated EPICS parameters related to the Pcal-Y system. No issues were found.

A CAL Tcam session was performed to obtain beam position information necessary for Pcal. The parameters have already been updated, and SDF has been accepted.

Operator: Kohei Mitsuhashi, Dan Chen

Update Time: 2026/03/17 15:31:24

I offloaded the F2 and BF GAS filters with the FRs.