Sheila, Robert
When LLO was down Sheila and I tried adjusting IMC WFS offsets to see the effect on jitter coupling into DARM. We monitored jitter coupling with 2 injected IOO piezo peaks (290 Hz in pitch, 400 Hz in yaw), the permanent peaks around 300 Hz, and peaks from table shaking. We adjusted 3 DOFs and the best settings we found for them were:
DOF2_P : 200
DOF1_Y: 0
DOF2_Y: -1200
The first plot shows that we reduced the 2 big jitter peaks just above 300 Hz by a little more than a factor of 2. In addition, peaks in the 100-200 Hz region and just below 600 Hz were reduced. On the other hand, there seems to have been an increase in noise in the 40-80 Hz region and the 400-500 Hz region. But the coherence with jitter monitors did not seem to increase in these regions, so we interpret these increases as other noise, such as scattering, that increased by chance due to the alignment differences between the two states.
In addition to the IOO Piezo jitter lines at 290 (pitch) and 400 (yaw), we used a shaker to shake the PSL table (see second figure, bottom plot). As we adjusted the pitch offset, we found no improvement in the broad band coupling of the shaker injection or the permanent peaks above 300 Hz (although we did reduce the pitch piezo peak, which had been made very large relative to yaw in order to show in DARM), by 10. In contrast, the yaw adjustment reduced the peaks that were normally in the spectrum, and the peaks from shaking, by a factor of a little over 2, as well as the piezo yaw line at 400 Hz. We conclude that the interferometer alignment is such that yaw jitter coupling dominates. Also, the piezo injections are a good representation of general table shaking (second figure).
The adjustments didn’t change the inspiral range by much. But we would argue that changing to the settings we found is an improvement because the loudest part of our binary black hole mergers have been in the100-400 Hz region, which was improved, especially in the 300 Hz region.
We would like to try putting in the new settings and adjusting the interferometer alignment to minimize the low frequency noise that increased (and inject at BS HEPI), and we would like to try moving the spot positions to where they ended up, but without the IMC WFS offsets.
The offsets were in and the interferometer undisturbed: Feb. 16 23:09:00 - 23:19:30
