Last month, Evan and I made several changes to the HAUX, HLTS and HSTS damping loops. These have already been recorded in other alogs, but I am summarizing them here. Evan and I specifically focused on contributions to DARM, but I went back and made plots showing the effect on MICH, PRCL and SRCL as well.
| Mirrors | Changes Made | Effect | See alogs |
| All HAUX (IMs 1-4) | L, P and Y filters updated to match Livingston design | Improvement in DARM 20-30 Hz, no effect on corner DOFs | 64007, 64017 |
| HLTS (PR3 and SR3) | L,T,V,R,P,Y updated to "level 2" damping design | Improvement in DARM 3-9 Hz, improvement in PRCL and SRCL | 64070, 64152, 64295 |
| HSTS (PR2 SR2 PRM SRM) | Retuned "ellip50" filter in pitch damping, reduced overall pitch damping gain | Improvement in MICH, PRCL, SRCL | 64093, 64194 |
We had the opportunity to put in the full level 2 HSTS damping design that Jeff developed, and we did import the filters into PRM. However, since these mirrors are used in lock acquisition, we were concerned that the new filters would cause excess ringing. More thought should be put into these new damping filters, and they could still be engaged. We concluded (based on measured coherences to DARM) that is wasn't urgent to update these filters and moved onto other projects. I have included a plot of the changes to MICH, PRCL and SRCL. MICH has improvement from 3-10 Hz. PRCL has improvement from 3-25 Hz. SRCL has improvement up to 15 Hz. SRCL improvement can also be explained by turning the AS_C whitening back on. There is some increase in PRCL from 30-80 Hz that I don't understand. The low frequency RMS of all three loops has either stayed the same or increased, likely due to the reduced damping gains.
