I added two band stops to the CHARD loops, which have reduced the CHARD drives from 15-25 Hz by about a factor of 10. ASC noise should no longer be limiting our DARM sensitivity above 15Hz, the noise is only slightly better from 15-20 Hz.
The first attachment shows the slight improvement in the DARM noise, the difference in the drives (the cut offs I added were 2nd order elliptic bandstops), and the reduction in the coherence between the ASC drives and DARM. For CHARD Y the first screenshot shows the loop measurement before I added the bandstop, the bandstop should have reduced the phase at the upper ugf (2.5 Hz) by about 5 degrees. For CHARD P I reduced the gain by about 3dB, the third screenshot shows the before measurement in blue, a measurement after I reduced the gain but before I added the cut off in red. For CHARD the cut off only reduced the phase at the upper ugf of 3 Hz by 6 degrees, we are left with almost 50 degrees of phase margin.
I also re ran the noise budget injections for CHARD, DHARD, MICH, SRCL, PRCL and IMC PZT jitter. There only real change is that the ASC noise is lower, and there is a larger gap between the sum and the measured noise at 25 Hz. I am not able to download GDS strain from this afternoon, so I will post a noise budget when I can get data.
Was there a change to H1:ASC-CHARD_P_GAIN from -0.10 to -0.14? (This came up as an SDF Diff for the next lock.)
Yes, Corey, sorry I forgot to load the guardian.
The first attachment is the noise budget with measurements from yesterday. You can see that the broad lump that we blame on beam size jitter is worse, there is a gap between the measured noise and the sum of the predicted noises from 300-800 Hz which was not present in the noise budget from early Jan (here) Looking at the summary pages, you can see that this has happened in the last week. (April 18th compared to yesterday). Kiwamu and I had a look at some alignment sensors, and at first glance it doesn't seem like we've had an unusual alignment change this week. We asked Aidan to check the Hartmann data to see if there has been a change in absorption on ITMX.
The linear jitter is also slowly getting worse, which you can see by comparing the 350 Hz peak to January. The next two attached pngs are screenshots of the jitter transfer functions measured yesterday using the IMC PZT. You can compare these to measurements from mid Feb and see that the coupling is about 50% worse for yaw and almost a factor fo 2 worse for pit.
The 4th attachment shows a comparison of the coherence between DARM and the IMC WFS DC signals for February to earlier today. We now have broad coherence between IMC WFS B pit and darm, which I don''t think I have seen before even when we had a broad lump of noise in DARM before our pre O2 alignment change.
The last attachement shows coherences between DARM and the bullseye PD on the PSL.
