KAGRA Logbook

VIS (SR2)

fabian.arellano - 7:00 Tuesday 05 February 2019 (7964)

SR2 height

Yesterday I set the height of the SR2 optic. I checked set it using Terada-san's reference with the laser level. The positions of the BF and F1 keystones were set very close to zero. According to my calculation of the temperature and bouyancy corrections (they will be added in another entry) it should be possible to move them back to zero with their respective fishing rods once in vacuum and at 25 ºC which as requested. The temperature yesterday was 26.1 ºC

Details of the measurement will follow and now I only point out the highlight that the F0 required to be 0.9 mm lower than expected. The origin of this discrepancy is likely the roll of the RM reported in my original measurment (7741). Yesterday I measured the height at the left side, which originally was higher by 0.7 mm w.r.t. Tereda-san's reference. The right side was 0.5 mm below. Given the diameter of the recoil mass to be 290 mm, the roll was 4.1 mrad. As far as I understand having the roll close to zero is not a vital but we still should investigate whenever possible. I remember checking the roll of the IM with the OSEMs (w.r.t. the IRM) to have a small value.

Today I shoud measure both sides and adjust F0 accordingly.

We also found the IP went out of aligment. Maybe because of the increase in temperature. We will adjust today.

Comments to this report:

fabian.arellano - 11:45 Wednesday 06 February 2019 (7980)

On Tuesday 5th of February (yesterday) I checked the height of the optic again taking into account the information of the roll of the recoil mass (entry 7741).

Given that we decided not to compensate the bouyancy effect of all the GAS filters using F0 exclisively but to do it at each filter, I did the following in order to set the height:

Set the BF LVDT to zero.
Set the F1 LVDT to zero.
Set the F0 LVDT to -1.1 mm.

The -1.1 mm displacement of F0 LVDT accounts for the 1 mm we moved the system up with the jacks (old strategy to account for the bouyancy) and for the 0.1 mm the optic was higher w.r.t. Terada-san's reference. Given the roll of the recoil mass (RM), in this conditions the -X side of the (RM) should be 0.6 mm above the reference.

I took a look of the height usign the laser level and the reference and I saw the RM to be where I was expecting. Namely, approximately 0.6 mm above the reference. See picture attached.

Images attached to this comment

fabian.arellano - 13:40 Wednesday 06 February 2019 (7991)

Yesterday we also checked the alignment of the IP and it was in good conditions, so we didn't adjust it. Likely, during the previous assesment the physical stops had not been withdrawn properly.