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VIS (IX)
takafumi.ushiba - 0:01 Friday 18 June 2021 (17157) Print this report
Alignment recovery of ITMX

[Tamaki, Ushiba with help of Miyo]

As I reported in klog17152, the inclination of ITMX was changed after removal of the first contact especially for pitch inclination.
First, we recovered the alignment by using moving mass on MN stage but it couldn't due to the lack of the range, which is close to the limit due to the alignment work posted in klog16863.
So, I onece fixed the suspension and move the ballast masses for alignment and offload of moving mass.

After this work, we can align the ITMX with respect to the TM OpLev reference.
Then, we centered all the MN OpLev (TILT, LEN, ROL, TRA, VER).
In this night, we (Miyo-kun) run the script to measure the TF of the suspension for health check.

Note: During this work, I noticed actuator magnets hit the coil before suspension hit the earthquake stops and one magnet (MNH3) obtained some forces.
As far as my visual inspection, the magnet looks healthy but we need to investigate it by measuring the TF.
Also, I learned the gap between MN and earthquake stops from MNR should be close in order not to touch the magnet to the coil bobins, so I set the gap between them roughly 3 mm in this time.

Comments to this report:
kouseki.miyo - 8:25 Friday 18 June 2021 (17158) Print this report

Fig. 1,2 shows the comparison of MN transfer function before (ref370 in June 16) and after (ref387 in June 17) the FC work. Shape of TFs are changed after I measured in Jun 16. Additoinaly, horizontal ones are not measured well. We need to investigate such strange behavior.

For further invesitigation, I measure TFs about coil-sensor basis as shown in Fig. 3,4. I think these TFs are measured clealy although the horizontal TFs (L, T, and Y) are not measured well.

Images attached to this comment
takafumi.ushiba - 17:44 Friday 18 June 2021 (17164) Print this report

I checked current photosensor spectrum and found that MN H2 photosensor has a strange noise spectrum after yesterday work (see fig1).
Red and blue represent the spectra before (9am, 17 of June) and after the work (5pm today), respectively.
As you can see, MN H2 noise becomes roughly 10 times larger.

I also checked the time series data around the work and found the strange jump of DC output from photosensor on H2 at around 3pm (see fig2).
I will investigate photosensor H2 in the next week.

Images attached to this comment
tomotada.akutsu - 20:41 Friday 18 June 2021 (17169) Print this report

OMG... Nice carefulness to find this, but can imagine the toughness from now on...

takafumi.ushiba - 18:36 Monday 21 June 2021 (17192) Print this report

[Tomaru, Ushiba]

Today, we checked the cables of MNH2 photosensors and found that one cable doesn't seem to be connected well (When we touch that cable, the output fluctuates a lot).
Other than that cable, we found no strange behaviour, so we decided to repair that cable and see noise level is recoverred.

We thought we repaired it inside the cryostat but found that it is difficult due to the accessibility, darkness, and so on.
So, we decided to take out the photosensor and repaired the cable.

Cable repairement was finished but not yet reinstalled.
We will do it tomorrow morning.

Note: Since the repairement was not et finished, we locked the suspension to the secrity flame.
So, please do not shake and control the suspension tonight.

takafumi.ushiba - 19:17 Tuesday 22 June 2021 (17221) Print this report

[Tomaru, Ushiba]

We reinstalled the fixed MNH2 sensor on the IX payload.
Attached shows the spectra of MN photosensors when before first contact removal (blue), after that (black), and after repairement (red).
As you can see, MNH2 spectrum comes back.

So, next step is to check the transfer function of suspension with these sensors again.

Images attached to this comment
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