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VIS (SRM)
ryutaro.takahashi - 0:33 Tuesday 31 March 2026 (36675) Print this report
Investigation of BF GAS

[Washimi, Takahashi, Ushiba (remote)]

We investigated the strange BF behavior reported in klog36669. The situation had changed.

  • The movable range of the BF keystone was from +1335 to +2166 (um) in LVDT output; only 0.8mm. The setpoint is 0.
  • The measured transfer function (Pic. 1) and spectrum (Pic. 2) showed the damped resonance when the BF GAS was around 1500.
  • The RM position was higher than the reference level by 1.5mm (Pic. 3).

We found the lower stoppers (Pic. 4) for the BF keystone have gone down to near the lowest. It might be due to vibration from the stepper motor driving the FR.

  • We screwed up the stoppers (nuts). The movable range was extended from -1300 to +2284.
  • We could move the keystone to 0 with the FR.
  • The measured transfer functions (Pic. 5,6,7) and spectrum (Pic. 8) became natural.
  • The RM position was consistent with the reference level (Pic. 9).
Images attached to this report
Comments to this report:
ryutaro.takahashi - 20:46 Tuesday 31 March 2026 (36677) Print this report

[Washimi, Takahashi]

We went to the recovery work.

  • VAC staff opened the top chamber.
  • We checked the suspension. We found the IRM is touching the EQ stop at X-Y+ (Pic. 1).
  • We screwed out the stopper nuts for the BF keystone to the top of the stud bolts and glued them with TRA-BOND (Pics. 2, 3, 4).
  • We tried to align the TM using the Oplev. We found the F0 yaw FR was not working during the alignment. The pushing bolt head has been detached from the rotor bar (Pic. 5). The rotor was rotated by hand. Finally the TM was aligned.
  • We added the stopper nuts to make the double nuts for the F0 keystone (Pics. 6, 7, 8).
  • VAC staff closed the top chamber temporarily.
Images attached to this comment
ryutaro.takahashi - 8:41 Wednesday 01 April 2026 (36679) Print this report

The actuators in the IM H1/2/3 OSEMs are not working.

takaaki.yokozawa - 12:28 Wednesday 01 April 2026 (36687) Print this report
[YokozaWashimi, Ushiba(remote)]

> The actuators in the IM H1/2/3 OSEMs are not working.
We checked the signals outside of the SRM chamber.

By adding the 100cnt offset to
K1:VIS-SRM_IM_COILOUTF_H1_EXC
and checked the offset voltage by the voltage monitor.

OK : AI output
OK : input of the coil driver
OK : output of the coil driver
OK : Vmon of the coil driver

After confirmed the pay tripped state
(After this measurement, the state of the SRM guardian was pay tripped, Ushiba-san noticed it and fix them)
(When we turned on/off the coil driver, the software WD may set the tripped state, Ushiba-san changed the threshold of the software WD)
OK : H1 signal of the output of the satellite box .

So, we suspected that the inside of the camber, there would be some trouble.
tatsuki.washimi - 10:56 Thursday 02 April 2026 (36690) Print this report

I measured L & R for each IM H coils at the feedthroughs (with cross cables), pin 2-7, with the LCR meter at 100Hz

  H1 H2 H3
L [mH] 8.71 8.71 8.67
R [Ω] 19.8 19.8 19.6

 

ryutaro.takahashi - 23:13 Thursday 02 April 2026 (36694) Print this report

[Ushiba, Washimi, Takahashi]

We found that the H1 (Pic. 1) and H3 (Pic. 3) OSEM flags on the IM are touching the OSEM bodies on the IRM. The H2 (Pic. 2) OSEM flag was also close to the OSEM body.

Images attached to this comment
tomotada.akutsu - 0:09 Friday 03 April 2026 (36695) Print this report

By the way, we should have a jig, which was made at the beginning of 2024, to peacefuly rotate the flag so that the tip direction can align to the vertical direction.

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