Louis and I immediately started where we left off yesterday with BS M3 commissioning. Louis copied over the LLO filter design that sets up the BS feedback with a 7 Hz crossover between M2 and M3, 82200 (thanks LLO for doing the heavy lifting here!).

I copied these filters into my matlab model so we could confirm we understand what it is doing. This plot shows the modeled feedback with the locking and drivealign filters applied. The LLO design is applied to M2 and M3, such that the crossover is roughly 7 Hz as expected. I applied our current M1 offloading scheme, and the M1/M2 crossover is still 30 mHz.

This looks good to us, so we proceeded to copy over the filters to the BS sus banks. I first locked MICH dark using the old feedback design without the lowpass filters so we had much more phase. This provides a reference for us to make sure we do the switchover correctly.

Louis and I engaged the correct filters in ISCINF M3 L, M3 lock L, M3 drivealign L2L and M2 lock L. Here is a screenshot of the old M2 filter design, and here is a screenshot of the settings we used to test the new feedback. I want to note that one difference is I found that we need a gain of -1 overall in BS M3 drivealign to get the phase correct.

I did touch up the MICH alignment before locking, since the arm team is working on aligning the arms now that gate valves are open (spoiler alert).

We successfully locked MICH dark, no issues! I measured the MICH olg again, and saw that we were almost exactly where we wanted to be in the gain, and the phase is a little different but not drastically so.

Masayuki noted in a previous alog that the MICH gain is a bit low, it would be better to have a 10 Hz UGF. Therefore, I bumped up the gain by a factor of 3 and remeasured. Looks good! This plot compares all three MICH dark olgs.

Louis has updated the ALIGN_IFO guardian with these new settings and is working through ISC_DRMI. In addition to the filters in the BS sus, we are updated the MICH dark and MICH bright gains to be 3x higher (so plus/minus 7200 instead of 2400).

As a note, ALIGN IFO does not use M1 feedback, we expect to test this when we lock PRMI/DRMI. However, I don't predict any issues, as the crossover should still be the same.

I have accepted new settings in the SDF as well, screenshot.

Below are the foton strings that we copied over:

BS_M2_LOCK_L

FM1: zpk([-4.398229715026552+i*5.654866777052986;-4.398229715026552-i*5.654866777052986], [-344.8589087698574+i*562.4185982606715;-344.8589087698574-i*562.4185982606715; -2513.274122871833],21314144.89497595)

FM2: zpk([0+i*754.0107241782374;0-i*754.0107241782374], [-114.2660735869546+i*205.9572881820654;-114.2660735869546-i*205.9572881820654], 0.09757621338967941)

FM4: zpk([],[-50.26548245743591],50.2654824574367)