A measurement of the HAM3-ISI motion was taken over the weekend [1] to compare the performance of this ISI now vs last year, following the replacement of the vertical CPS (ECR E2200301)
Thanks to the lower noise of the vertical CPS (90911), we see an improvement in the tilt dofs (p1 and 2 of the attached pdf) where the CPS noise was previously limiting. For Rx this is from 0.1Hz and above, and for Ry this is from 1Hz and above - up to a factor of 6 reduction, near 0.4Hz and 1Hz. For reference the noise budget shown on p7 of G2100779 shows the CPS noise limitation of the HAMs with the previous set of CPS.
It is interesting that Rx and Ry have different tilt amplitude between 0.1-1Hz (Ry is higher) and may indicate some noise injection from other loops. With the CRS now on the table, this will be easier to address.
Those improvements will contribute to a lower suspension point motion of MC2 and PR2. We will add those spectra to this alog once we gather the data.
[1] Status of the ISI for this test :
- SC was turned on
- Blend filters were set as shown on the screenshot attached
- The input motion is comparable between the two dates (see hepi data) - except at the microseism which is higher in the before / reference, but not relevant for this test.
MC2 suspoint motion comparison is plotted here. Improvement in the suspoint motion is between 1-10Hz, given the Ry dof is mostly contributing to this suspension. The difference at the microseism is due to a difference in input motion, and not related to this upgrade.
Projection of each ISI dofs is shown in the following pdfs for reference : before and after
The results for PR2 are identical so not shown here.
If Ry tilt motion can be matched to Rx (maybe with some tilt decoupling from Jim), the suspoint motion will be improved down to lower frequencies.
While the before/after comparison plot had to be manually edited, the script to make the projection plots is in the svn under /ligo/svncommon/SeiSVN/seismic/HAM-ISI/Common/MatlabTools/f1_projection.m