I examined a DARM spectrum with 0.0005Hz frequency resolution and used this to identify new second order violin modes, and more precisely determine the locations of previously identified modes. I have created both damping filters and monitor filters for the following violin modes: ETMX mode 11: 1006.439Hz ETMX mode 12: 1006.745Hz ETMX mode 13: 1010.356Hz ETMX mode 14: 1010.581Hz ETMX mode 15: 1011.063Hz ETMX mode 16: 1013.869Hz ETMX mode 17: 1014.091Hz ETMY mode 11: 1000.061Hz ETMY mode 12: 1000.423Hz ETMY mode 13: 1009.932Hz ETMY mode 14: 1017.985Hz ETMY mode 15: 1018.238Hz ETMY mode 18: 1000.294Hz ETMY mode 20: 1000.307Hz ITMX mode 11: 995.177Hz ITMX mode 12: 995.462Hz ITMX mode 13: 998.083Hz ITMX mode 14: 1001.843Hz ITMX mode 15: 1001.940Hz ITMX mode 16: 1002.859Hz ITMX mode 17: 1003.120Hz ITMX mode 19: 998.018Hz ITMY mode 11: 991.641Hz ITMY mode 12: 991.828Hz ITMY mode 13: 994.801Hz ITMY mode 14: 995.053Hz ITMY mode 15: 997.618Hz ITMY mode 16: 997.785Hz ITMY mode 17: 998.967Hz All of the damping filters are 0.1Hz wide, and all of the monitor filters are 0.02Hz wide. I have updated these modes in lscparams.py, and included the filter settings which have successfully damped the violin modes. There are a couple of damping filter settings which I have not tested as thoroughly as I would like to, and I have left these commented out in lscparams. There are also a couple of modes for which I, following Jenne's suggestion, left the maximum gain at a lower value than it could be set at, and included a higher value in a comment. I've updated the violin mode wiki to reflect these changes. The updated version can be found at: https://cdswiki.ligo-wa.caltech.edu/wiki/Violin_Mode_Table_v2 There are 32 second order violin modes, and we still do not know the corresponding test mass for 3 of them. These are at frequencies 998.825Hz, 1009.950Hz, and 1011.332Hz. ETMX, ETMY, and ITMY each have on of these modes on them. However, these 3 modes are relatively dormant, so are currently a low priority. We still have no consistently helpful settings for the damping filters on ETMY modes 18 and 20. But I have had success with mode 20 at 90 degrees, gain=2, and mode 18 at either 30 or 60 degrees, gain=2. Each of these settings seems to work individually, but not at the same time. Creating narrower damping filters might be wise for these 2 modes. We should exercise caution in damping ETMY modes 11 and 12, as these damping filters tend to very slowly drive up ETMY modes 18 and 20. I have begun to update the medm SUS_CUST_VIOLIN_OVERVIEW.adl to include the 2nd order modes, to the right of the first order modes. Attached is a spectrum of the violin modes before and after damping, taken during Friday's lock. A few modes remain undamped in the image because we lost lock before I did it.
In this lock, the damping for ETMY MODE 12 (1000.423 Hz) rang up ETMY mode 20 (1000.37 Hz). The settings that Kara suggested above worked well for damping mode 20 once I turned off the damping for mode 12. After a while I range up mode 18, (100.294 Hz), which I had a hard time damping. With acuation on pitch for mode 18, no phase shift and a gain of -2, it seems to be damping both mode 18+20. If we can use the same settings to damp both of these, that will be a much easier solution than trying to make two different filters.
ITMX mode 13 (998.083 Hz) also range up ITMX mode 19 (998.018 Hz), the settings that Kara suggested for mode 19 in the guardian (90 degrees, positive gain) damped it well, but rang up MODE 13. I made a narrower filter for MODE13 (50mHz wide instead of 100mHz). It seems to have damped well without ringing up mode 19 with a gain of 2 and -60degrees of phase, actuating on pitch. The mode19 filter probably needs to be made narrower as well.
I've set the gains for both ETMY MODE12 and ITMX MODE 13 to zero in the guardian for now.