KAGRA Logbook

VIS (PR3)

fabian.arellano - 21:45 Thursday 11 March 2021 (16239)

Test of PR3 mirror pitch stability using the Donald Trump method.

With Hirata-san.

We tried the Donald Trump method to recover the alignment of the IM. We did it from the control room using the OSEMs as a reference for pitch and then we did it in the clean room using an oplev to measure pitch.

From the control room

We selected as a reference orientation of the IM the one it had when there is no actuation on the BF. In this case the position of the BF keystone was about 940 um.
In this condition V1 was out of range but V2 and V3 were functional.
The values of the OSEMs before and after the Trupm procedure were
- V2: 227 µm → 50 µm.
- V3:190 µm → -13 µm.
Because these OSEMs are sensitive to roll also, to calculate the change in their readouts related to pitch, we must consider the average before and after:
- Before: 208.5 µm.
- After: 18.5 µm.
- Difference: s = -190 µm.
The distance from the OSEMs V2 and V3 to the suspension rod (see details in this diagram) is R = 48 mm.
Then, the change in pitch ( S / R ) = -3.9 mrad. This number is consistent with what we measured when we glued the wire and disturbed the alignment (3.8 mrad). See this notebook page (not in klog yet).

In situ

We set up an oplev with a laser level and a ruler.

The details of the calculation are in this other notebook page.
The change in pitch was measured to be 33.4 mrad!
There are videos of the position of the oplev before, during and after the procedure.

There is also the calculatio using V2 and V3 OSEMs but I'm sleepy now. I'll add it tomorrow.

Comments to this report:

fabian.arellano - 11:27 Friday 12 March 2021 (16247)

This is the calculation I didn't write yesterday because I was sleepy.

As reported, we monitored the change in pitch produced by the Trupm procedure with the oplev, but we can also use the OSEMs.

The values of the OSEMs before and after the Trupm procedure were
- V2: 41 µm → 228 µm.
- V3: -19 µm → 188 µm.
Because these OSEMs are sensitive to roll also, to calculate the change in their readouts related to pitch, we must consider the average before and after:
- Before: 11 µm.
- After: 208 µm.
- Difference: S = 197 µm.
The distance from the OSEMs V2 and V3 to the suspension rod (see details in this diagram) is R = 48 mm.
Then, the change in pitch ( S / R ) = 4.1 mrad. This number is consistent with what we measured when we glued the wire and disturbed the alignment (3.8 mrad, see this notebook page ) and also with the measurement carried yesterday morning from the control room (-3.9 mrad).

Images attached to this comment

fabian.arellano - 12:29 Friday 12 March 2021 (16246)

With Hirata-san

See pictures in album PR3 Remedying Work.

After subjecting the suspension to the Trump procedure, today we inspected it visually just to make sure everything was well.

We did not find anything wrong.
The only change was the rotation of the H2 OSEM flag, which can be seen from before and after pictures. We haven't fixed it yet.
We also inspected the wire breakers. See pictures with today's date in the album.
We inspected the places where we put the adhesive on the wire. We did not notice any obvious change. Again see pictures with today's date in the album.

At the end of the session we turned on the oplev laser level and checked that the beam was still in the same place. It was indeed, namely close to 103 mm. See yesterday's entry notebook entry here.