Today we continue the work on SDB2 bench.
We open the OMC shutter at 07h52 utc.
We decide to use B5_QD2 instead of B5_QD1 in order to shorten the optical path up to the galvo and increase the distance between the galvo and the QPD of B1s.
We displace the B5_QD2 quadrant by -150 mm in X. Its galvo was also translated by -125 mm along X. The distance between the galvo and the B5_QD2 oblong hole is now 275 mm.
With this reshuffling we should have preserved the Gouy phase tuning performed yesterday with B5_QD1. In other words the optical path length from the lens to the B5_QD1 should now be the same as the optical path length that we had adjusted yesterday between the lens and othe B5_QD2.
After this change we align the B1s beam on the B5_QD2 quadrant by acting on the picomotors of B5_M1 (-4200 steps in H, -14000 in V) and we managed to close the galvo loops as shown on Fig.1.
We placed a beam dump for the reflection from the quadrant.
We realigned the galvo and QPD B5_QD1 on the B5 beam. We acted on B5_M1 picomotors.
We realigned the beam on B5P_PD1 using the motors of B5_M3. Then we realigned the beam on B5_PD2 by adjusting laterally the photodiode position and acting with B5_M4 (see Fig.2).
Finally we realigned the B5 beam on the camera (see Fig.3) by displacing the camera by 5mm towards east and by vertically adjusting the beam position with the last folding mirror.
To be noted: we had difficulties in seeing a beam on B5_PD1. we suspect that its shutter was stuck in the close position. When it opened we could rapidly realign it.
During this intervention, the elements we have removed and/or added to the bench:
- Added: 6g for cable ties
- Added: 175g for the glass beam dump to block the beam going towards B5_QD1
- Removed: 11g for two screws and their washers
After summing all the added and removed weights on the bench, since yesterday, we conclude that we have added a total of 329.5 g.
To compensate for the extra weight we have removed 332g of counterweights.
We added some temporary weights in order to bring the bench height around +500 um.
We then balanced the bench and were able to close both the angular and position loops (Fig.4).
We performed alignment checks with the bench suspended and controlled in air:
* the beam position on the B1p, B1s, B5 camera did not change at first order, compared to the reference taken last monday before the intervention: Fig. 5,6,7.
* we checked that we obtain the expected power on the B1s and B5 photodiodes and quadrants, compared to what we had before the intervention. The only doubt is on B5-PD2 where we have now more power than we used to.
* we were able to close the galvo loops of B1s and B5 as earlier (Fig. 8).
* we checked the alignment of the B1s beam on the EDB bench. The beam was still passing through the two irises installed last monday and reaching the OMC. We checked that, when opening widely the irises aperture, we have a power of about 2.1 mW reaching the photodiode EDB_B1s in reflection of the OMC, which corresponds roughly to our expectations (Fig.9).
Finally, we added a beam dump in EDB, right after the telescope placed before the OMC. We oriented this beam dump in such a way that its reflection reaches another beam dump.
At the end of the activity on SDB2, we performed the following actions:
* close the doors of SDB2 with only one screw, keeping the temporary weights inside, and keeping the clips holding the door rings.
* close the OMC shutter
* reopen the SDB2 position loops (in preparation of the SDB1 tower venting).
* Open SDB1 angular controls
* Open OB suspension controls
* Open OMC temperature stabilization loop
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