J. Kissel 

The message: I tried to improve the Bounce mode damping, I've installed some new filters; no change in the amount of damping for the bounce modes, and they haven't been cooled any more than when I got started. I've made no changes the guardian code, so in the next lock stretch my work will be erased / cleaned up (except for the new filters), and what used to be turned on turned on before today will be turned on again.

After spending an hour or so trying to get better results out of the installed bounce mode damping filters to no avail, I tried installing much more narrow band-pass filters. I did this because of Shiela's entry (LHO aLOG 18440) seemed to indicate we know the frequencies really well, and I could see what I thought was ETMX at 9.77 [Hz] interacting with what I thought was ITMX at 9.83 [Hz]. However, I found after exploring the parameter space (with gains and +/- 30 or 60 [deg] filters) with the more narrow filters, the situation got more confusing because the top mass of ETMY, ETMX, and ITMX would come in and out of showing 9.83 [Hz]. See for example the attached .pdf of the top mass vertical OSEMs for each. Yuck! After a while I convinced myself that having both IX and EX using the narrow band bp9.7-9.8 (in FM10 of IX and FM5 in EX) with a small gain of +0.1 and +0.05 and their normal -60 [deg] and +60 [deg] filters wasn't making it worse, but I couldn't get any improvement.

This mode interaction are stable / non-existent at low power, but as soon as we elevate to 23 [W], the MICH oscillation creeps in mentioned earlier today (LHO aLOG 18478) creeps in and breaks the lock.