brina.martinez@LIGO.ORG - posted 14:43, Wednesday 14 June 2023 - last comment - 16:29, Friday 16 June 2023(70450)
Ham1 FF off test for 5 mins
Commissioning period,
The Ham1 FF was turned off for testing on 06/14/23 21:32:15. It stayed off for 5 minutes and was turned back on at 21:37:15.
My motivation for this test came from a bruco that I ran on the data from a long lock over the weekend: https://ldas-jobs.ligo-wa.caltech.edu/~elenna.capote/brucos/CAL_1370343461/
Specifically, the CHARD P, INP1 P and HAM1 TT L4C RY coherence were much higher than expected, and much higher than they had been in the past after successful HAM1 FF tuning and A2L gain adjustments.
The test first confirmed that we are still seeing decent subtraction of the HAM1 noise from the ASC loops, as seen in an OMC DCPD sum comparison with the feedforward on and off. I also grabbed spectra of each of the ASC loops with the feedforward on and off (in this plot the red, live traces are with the feedforward off, and the blue reference traces are with the feedforward on).
I used the feedforward off time to run the NonSENS training code and calculate a new feedforward for CHARD P, INP1 P and PRC2 P. The code also makes plots of the expected subtraction of the loops. I compared the expected subtraction plots (linked below) to the current subtraction plots linked above, and I conclude that:
I didn't check any yaw loops because there is already decent noise removal, and coherences are low. I don't expect to see much improvement there.
I will install the new INP1 P and PRC2 P feedforward filters, labeled with today's date. I think they should be engaged for the next lock if possible.
I don't understand why the coupling has changed, but I think this is a similar mystery change that changed like several other things in the IFO changed recently- perhaps some new alignment from the PR3 move? In other words, unless we have to make another big alignment change like that, I don't expect us to need to update this feedforward for a while.
Turning off the HAM1 feedforward made the CHARD and PRC2 noise signficantly larger, by about a factor 10. The effect on DARM is significant, and consistent with the fact that CHARD or PRC2 are coupling more now than before, and when the FF was on were just below the measured DARM. This is consistent with the measured coherence between DARM and CHARD or HAM1 sensors.
One possible reason for the higher coupling of HAM1 noise to DARM is that the beam spot might have moved on PR2 (where PRC2 is driven) and therefore the A2L we tuned some time ago might be wrong. It's worth and quick retuning the PR2 A2L and see if that improves the coupling of PRC2 to DARM and maybe even DARM noise.
The new filters have not yet been installed because I am getting errors from foton when I try to copy them in. I will try again tomorrow.
I have installed the new feedforward filters for INP1 and PRC2. They are labeled with "0616" for today's date. They are currently not in use, but can be quickly tested during a commissioning period. A thermalized IFO is best for the test, but they can be tried at any time.