Evan, Sheila, Dan, Lisa
We made it to 34 Mpc by managing to do at the same time all of the things we have tried before (low noise ESD on ETMY, low noise coil drivers for all the optics, POPAIR for vertex length DOF, more aggressive SRCL cut-off), plus some more ASC cut-offs. Implementing all of these things at the same time happened to be more challenging that expected because of a few problems that slowed us down today:
Some more details
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The improvement below 20 Hz in the sensitivity is entirely due to the cut-offs we added to the CHARD loops;
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Even after transitioning the BS M2 coil driver to low noise, and moving to POPAIR, we still have some coherence with MICH below 100 Hz. We tried to engage the MICH subtraction path, but we unlocked in doing so. Since unlocking from low noise costs us a trip to the end station, we didn't try harder..
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We closed the OMC REFL beam diverted;
Final IFO & Guardian state
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We promoted the SRCL 20 Hz UGF + cut-off in the Guardian, as it seems to work well;
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The transition to ETMY ESD low noise + DARM boost is still done by hand (it is written in the Guardian; we are just not brave to try it)
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The transition to BS low noise is also done by hand, and since it has failed at least once in the past, we decided not to engage it in this last lock
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Stage 2 ISI on BS is tripped..
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Sheila prepared some more cut-offs for the ASC DHARD loops, but we haven't tried those yet.
We leave the interferometer locked at 34 Mpc, starting at March 27 9:00 UTC
Spectrum attached.
Note that ISI Stage2 was a State3 trip meaning that the Damping Loops were still functional. It would be nice to know when/why the stage tripped. But I'd guess that the Guardian was set to fully isolated before the ~0700utc short lock and was untripped during the short lock, likely triggering during acquisition and then triggering again at the trip. That is what I first thought.
See attached--It looks like the stage2 when isolated survived the IFO lock loss but not the MICH reacquisition. This means, we can use the Guardian to transition the ISI between Isolated Damped and Fully Isolated with tripping nor requiring operator intervention.
This is a 50 minute stretch so the IFO lock Loss is only a couple minutes before the St2 WD trigger but there may be enough time to deisolate stage2. Looking at a zoomed in full data, looks like a full 70+ seconds after lock loss based on this CAL_DELTAL channel. The second lock loss had even more time so I don't think it is tied to the lock loss but more to the reacquisition.
Noise budget attached, with new the anticipated ETMY ESD noise. We have many other traces to add here: intensity coupling, frequency coupling, auxiliary dofs, etc.
I believe the 10 W quantum noise and the DAC→ESD noise alone limit us to no more than 60 Mpc, although based on the previous performance of the ETMX ESD, the ESD trace here may be an overestimate.