Alexa, Sheila, Stefan

Our goal today was to get a good diff readout going. For this we
- Commissioned the IMTY and ETMY optical levers, See snapshot.
- Recommissioned the x-arm dither - turns out the phases were tuned up for a different suspension setting - we need configuration control on all the suspension settings. Also see the snaphot.
- With that we got fairly stable arm locking - at least for a while - see below.

- Next we tweaked up the DIFF beat note on ISCT1. We got -20dB signal out of the PD.
- Th PLL locked for short stretches, but essentially always runs out of range after a few seconds.

- Thus we decided to work on top-mass slow feed-back: There was a lot of confusion, but once everything was done right, it sort of worked.
- One thing we noticed along the way, is that our 1-3Hz BLRM traces pick up increases in noise with an roughly hourly periodicity. This noise somehow translates into extra length motion at 0.05Hz. 
- We also fine-tuned the ETMY top mass L2P filter - see Arnaud's log
- The slow feed-back gain was however limited by our main suspension resonance, which meant that we couldn't suppress the DIFF motion enough.
- We thus decided to work on the L2L filters, which should give us the ability to increase the UGF of that loop and get more suppression.
- We got a simple L2L measurement going, but more work is needed.