Morning locking to PRMI, oplev damping solution, Afternoon L2P decoupling, DRMI

Sheila, Elenna, Jenne

Morning locking notes

• Jenne completed initial alignment by running green initial alignment and through manual initial alignment for X arm IR, PRX, MICH dark, SR align, and SRY. Except for SR2 align, all alignment was touched up by hand.
• We tried locking PRMI once without oplev damping, however we lost ALS with a large beamsplitter kick.
• The second time we tried locking with oplev damping (using oplev as sensor), and we were successful. PRMI locked for 10 minutes. I touched up the PRM and BS alignment. Sheila still measured a large amount of motion at 0.45 Hz. We think this motion is due to length to pitch coupling on M2.
• I tried engaging the L2P decoupling filter in M2 drivealign. We lost lock due to a 19 Hz ringup in MICH. We are not sure if this was caused by the L2P filter or if MICH is unstable. We will remeasure.
• After that we had two lockloss on the first PRMI flash. This flash is coincident with oplev damping ramping on, but we realized it is because the damping is not on before the LSC starts triggering. I moved the oplev damping to engage as "prep DRMI" in the ISC DRMI guardian, so it will hopefully help.

At this time we held in down to allow relay tube work, and used the time to measure the oplev damping and try switching to using M3 wit for lower stage damping instead.

I measured the oplev damping OLGs, pitch and yaw. The reference traces use the oplev as the sensor for the damping, and the live traces use the M3 wit as the sensor but a different matrix value that Sheila calculated based on this alog.

We then switched to M2 damping using M3 wits as the sensor, and compared the BS spectra with no lower stage damping, oplev damping, and wit damping, comparison here. We see good suppression of the modes and less sensor noise injection on the M3 wits.

Here is a screenshot of the "OLDAMP" settings we want to use on M2. I want to clarify that even though we are now using the M3 wits as the sensor, the damping is still running through the oplev damping bank on M2.

At this point, we decided to break further and allow Filiberto to update the resistors on the M1 QOSEMs, so our lockloss transient from saturation is reduced.

***

After Fil and Oli finished the sat amp changes, we began locking again. We locked PRMI with M3 wit damping engaged before the triggering occurred so there was no lockloss. Once locked, the guardian disengages the lower stage damping.

Sheila measured the BS motion using oplev and M3 wit without the L2P decoupling engaged but the wit damping off. She checked the MICH and PRCL OLGs and we saw that they were fine. MICH UGF is 8.5 Hz, PRCL is 60 Hz.

I engaged the L2P decoupling, and we saw that low frequency pitch motion was reduced. However, there was still a large 0.45 Hz peak. With the  M3 wit damping reengaged, the peak is reduced. See plot

Recipe for successful PRMI: M3 wit damping engaged, L2P decoupling engaged. Once we can reengage MICH ASC, we can turn off the M3 wit damping. I have SDFed the filters for BBSS M2 L2P decoupling 1 2

There is a lot of alignment drift in BS yaw while we sit locked. I had to touch up the aligment by hand.

We stayed in PRMI for 25 minutes.

***

We struggled to lock DRMI, and eventually chose to relock PRMI and fix the alignment. After this, DRMI locked quickly. We lost lock at the 3 f transition, so Sheila went to check we were aligned to REFLAIR 3f diodes. Then, I rephased the diodes while locked in PRMI by injecting a PRCL line and maximizing the height in 27 I, and a MICH line to maximize the height in 135 Q. PRCL, MICH, SDF

With DRMI locked, we saw that the PRCL OLG looked strange, so I also checked the REFLAIR 1f phasing. I made a minimal change to reflair 9 to improve PRCL in I and a 50 deg change in 45 to reduce SRCL in 45 Q. PRCL, SRCL, SDF

Sheila's guardian changes, to improve some problems we faced when locking.

• removed srcl mode hop offset
• if PRMI ASC flags are false, the guardian returns true (doesn't check for ASC convergence), we should also do this for DRMI ASC
• changed PRMI to DRMI transition to just zero gains for MICH and PRCL

***

Jenne and I attempted to check the PRCL/SRCL decoupling in the LSC matrix, and measured a value by injecting a PRCL line into reflair 9 and 45. However, the resulting OLGs looked even worse. Both PRCL and MICH look very strange, possibly indicating cross coupling. Unfortunately I don't have images of the PRCL transfer function but here is the MICH tf.

Seems like the phasing is wrong, but the loops became more unstable when we reverted the phasing changes I made earlier.