Summary: Things look OK (after some adjustments).
sliders.png is the latest snapshot of the suspension sliders.
What was done:
This morning, no SQZ reflection was visible in AS camera at all (except for SRM reflection). After getting confused, what I did was the following.
Make sure that SR and PR chain optics are aligned except SRM and PRM.
Asked Sheila to revert ZM4 back to the last the last known good alignment (Tuesday June 30 1300 Pacific, alog 90831). Reverted PR3, PR2, SR2 and SR3 back to the last known good alignment according to OSEMs. This only had a minor impact.
- Misalign ITMX, align ITMY.
- Moved ITMY until the ITMY reflection went back roughly to the old position on the AS camera (not on June 30 but earlier on June 25 in alog 90759 because there was not screenshot on June 30).
- Moved BS until the ITMY reflection went back roughly to the position I remember on the ISCT1 REFL camera.
- Align ITMX and move it until the ITMX reflection went roughly on top of ITMY reflection on both cameras. See PXL_20260707_193654789TS.mp4.
- Aligned PRM and saw PRC fringes (I won't call it flashing but it's a great sign).
As of now, F2 and F3 BS M1 stage DAC are using about 8e6 counts or about 6% of the full DAC range, everything else is smaller (DAC_now.png, top middle and top right).
It's worth noting that, before I did the above, I accidentally "aligned" ITMs and BS using a similar method as the above without knowing that SR2 was misaligned (SR2 had equivalent P and Y offset of 200/1.875~107urad and 300/2.681~112urad), and brought the ITMX and Y reflection into AS and ISCT1 cameras successfully. Even then, F2 DAC output was about 12e7 or about 9% of the full DAC range (DAC_whenAlignedToMisalignedSR2.png).
The conclusion is:
We have plenty of headroom for BS DAC as of now, and even if our SQZ beam alignment is significantly different from "true" in-vac alignment, and/or the sqz injection path is not co-aligned with IMC injection path, BS can be tweaked accordingly to provide "true" alignment.
Other things to add:
As of now, numbers don't add up in general, though that won't change my conclusion. If you want to disentangle the information, following is a summary table of the slider offsets, OSEM_DAMP_IN at the top stage, ISI (ST1 CPS) and HEPI (IPS) at the time of last good alignment ("back then") VS after I was done. All numbers are in urad.
ISI and HEPI Rz motions were used directly as YAW motions of the cage.
For Ry for ITMX and Rx for ITMY, the sign seen from the optic are the opposite. I flipped the sign of ITMY RX "diff" in the table such that positive "diff" for "PIT" for SEI for both ITMs means that the HR side of the cage points down. The sign-flipped numbers are followed with "(*)" in the table. If the optic itself just follows the local gravity without any change in the suspension, I'd expect "ISI+HEPI" PIT diff to be the negative of OSEM_DAMP_IN PIT.
For BS PIT, I gave up converting as it's a combination of RX and RY.
| Sliders | Sliders | Sliders | OSEM_DAMP_IN | OSEM_DAMP_IN | OSEM_DAMP_IN | ISI | ISI | ISI | HEPI | HEPI | HEPI | ISI+HEPI | |
| back then | now | diff | back then | now | diff | back then | now | diff | back then | now | diff | diff | |
| BS PIT | 107 | -0.9 | -107.9 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| BS YAW | 390 | 385.0 | -5 | --- | --- | --- | -20.924 | -15.691 | 5.2 | 8.7 | 10.1 | 1.4 | 6.6 |
| ITMX PIT | -96 | -72.0 | +24 | 509 | 469 | -40 | -29.97 | 10.81 | 40.8 | -16.1 | -15.6 | 0.5 | 41.3 |
| ITMX YAW | 104 | 103.0 | -1 | -15 | -17 | -2 | 9.292 | 25.80 | 16.51 | 73.4 | 73.4 | 0 | 16.5 |
| ITMY PIT | -70.3 | -23.2 | +47.1 | 81 | 91 | 10 | 0.42 | -56.71 | 57.1(*) | 10.1 | 9.8 | 0.3(*) | 57.4(*) |
| ITMY YAW | -17.7 | 43.3 | +61 | 301 | 357 | 56 | -49.87 | -38.38 | 11.5 | -6.8 | -7.0 | -0.2 | 11.3 |
For the numbers used, see ISI_HEPI.png for ISI ST1 CPS and HEPI IPS. BS_ITMs.png and BS_ITMs_now.png show the top level OSEM_DAMP_IN and sliders, the only difference in these two plots is the time scale. In all of these, vertical marker indicates the last known good alignment on June 30, Y1 the "back then" level. A big jump in everything at t~-5d is the ISI unlocking, but the supensions kept drifting since.
BS sliders are uncalibrated, and OSEM numbers are not useful because they seem to have been reset at some point. Also I haven't bothered to convert ISI CPS RX and RY to BS cage PIT. So BS numbers aren't that useful except that YAW didn't move much.
ITMX PIT makes sense. SEI tilted the cage in PIT by 41urad (i.e. -41urad in top OSEM if SUS followed local gravity). SUS drifted by about negative 20 to 30 urad since then (ITMs_drift_after_ISI_unlock.png). I used the slider of positive 24urad to undo the drift to bring the PIT measured by SUS back to -41urad-ish. The PIT of the optic was brought back to "back then" level.
Other DOFs don't make sense to me. Nevertheless I'm not worried about the available range of BS actuation.
To repeat myself, we have both ITMX and ITMY reflection in both cameras, we see PRC fringes when PRM was aligned, and we were able to make the alignment OK even when SR2 was misaligned. Things look OK now and we have plenty of BS actuation range.
