I had a quick look at the range integrand tonight, at a time last night when both L1 and H1 had fairly good ranges according to sensmon (L1 was nearly 140Mpc, H1 was nearly 100Mpc). I used some code that gives an approximation of the range integrand, the absolute scale is wrong so that the total ranges I calculate are underestimated. The first attachment shows the sensitivity of L1 compared to H1 and in the lower plot the range integrand. The second plot shows the cumulative range for both interferometers and the difference.
From the second attachment you can see that we can gain ~20 Mpc by improving our noise from 40-20Hz. In the first attachment you can see that the shoulders on the 60Hz lines are costing us.
Last night I posted an incomplete ASC noise budget that shows that DHARD P+Y are both making large contributions to the DARM noise in this band. 47176 Since this is the band that we need to improve I started to look at why this noise is worse. The third attachment shows a comparison of the DHARD P control signals from October 25th and last night, you can see that the control signal is about a factor of 10 larger in the band where it limits DARM than it was in October. The RPC output is not included in this plot or in the noise budget that I posted last night, but it is too small to matter. The 4th attachment shows a comparison of the filters we were using in October; in addition to the filter change we are now using a gain of -42 instead of -30 in October.
The last attachment shows a comparison of the coupling (DARM uncalibrated ASD/DHARD out ASD), you can see that the coupling hasn't changed much since October and most of the difference in noise is due to the loop shaping. We have had many problems with the stability of the DHARD loop, which have been written about in several alogs, which is why the gain of this loop has increased, and the cut offs have become less aggressive. It has been a while since we measured DHARD, so we were planning to try to get a good measurement before the earthquake hit.
I ran a linear noise subtraction (T1800552T1800552) using all ASC signals, MICH/SRCL/PRCL and ISS signals. I used 600 seconds starting from GPS 1235390418. The first plot shows that the noise subtraction is effective at low frequencies, and improves the range from 93.8 MPc to 96.7 MPc (estimated using gwpy and GDS-CALIB_STRAIN). So 2.9 MPc more, no quite O(10 MPc) as Sheila expected.
The second plot shows the main contributions.
