Slowly, over the past week, I have found a set of filter settings that damp the violin modes. In the tables below I identify the mode frequencies that are matched to each test mass; the matching was done based on which lines were suppressed or excited using bandpass filters in the L2_DAMP filter banks for each test mass. I also indicate which filter damps that particular line.
The filter settings are given at the bottom of each table. For all the L2_DAMP filter modules, FM1 is the bandpass filter (with +120dB gain in the pass band), FM2 and 3 are phase shifters (+/-60deg respectively), and FM4 is a 100dB gain. FM1 and FM4 are always on. FM2 and FM3 are used as indicated. The gain settings are included in the Guardian - the filters shouldn't change in the locking process, but I haven't updated the safe.snap files for the suspensions!
| ITMX | |
| f (Hz) | damped using... |
| 500.053 | MODE3 |
| 500.210 | MODE3 |
| 501.091 | MODE6 (still too high) |
| 501.253 | MODE3 |
| 501.450 | MODE3 |
| 502.620 | MODE3 (still too high) |
| 502.743 | MODE3 |
| MODE3 | 0deg, -200 |
| MODE6 | -60deg, +400 |
| ITMY | |
| f (Hz) | damped using... |
| 501.680 | MODE5 |
| 501.747 | MODE6 |
| 503.007 | MODE3 |
| 504.857 | MODE2 |
| MODE2 | 0deg, -100 |
| MODE3 | +60deg, |
| MODE5 | -60deg |
| MODE6 | +60deg |
| ETMX | |
| f (Hz) | damped using... |
| 504.870 | MODE6 |
| 505.585 | MODE6 |
| 505.708 | MODE6 (still too high) |
| 505.805 | MODE4 (still too high) |
| 506.921 | MODE6 |
| 507.157 | MODE6 |
| 507.389 | MODE6 (still too high) |
| MODE4 | -60deg, -300 |
| MODE6 | -60deg, +100 |
| ETMY | |
| f (Hz) | damped using... |
| 508.008 | MODE5 |
| 508.145 | MODE5 |
| 508.204 | MODE5 |
| 508.219 | MODE5 (still too high) |
| 508.583 | MODE5 |
| 508.659 | MODE5 |
| 1008.49 | MODE3 |
| 1009.03 | MODE3 |
| 1009.44 | MODE3 |
| 1009.49 | MODE3 |
| ~1484.5 | MODE6? |
| MODE3 | +60deg, +100 |
| MODE5 | -60deg, -100 |
| MODE6 | -60deg, +10k (?) |
| Unaccounted for: | |
| f (Hz) | best guess |
| 501.606 | ITMY |
| 501.810 | ITMY |
| 503.119 | |
| 504.803 | |
| 507.192 | ETMX |
| 507.991 | |
| 508.288 | ETMY |
| 508.659 | ETMY |
The attached figure compares the noise spectrum from Friday and today. The first harmonics of the violin modes are now the dominant feature in the spectrum, along with 60Hz and the 2.5kHz BS butterfly mode.
I forgot to note the gains for the ITMY filters. They are: