jenne.driggers@LIGO.ORG - posted 10:42, Wednesday 04 March 2020 - last comment - 10:47, Thursday 05 March 2020(55434)
Started slow moves of SRC spot positions
[Sheila, Jenne]
We took a few tens of minutes this morning to check how far and fast we can move the SRC spot by changing the AS_C offset. Once we had those numbers, we started a script to slowly move the offsets while we're Observing. The script started at 18:21 UTC.
This measurement is now over. We lost lock during the second to last move that this script makes (going from -0.6 P 0.6 Y offsets to -0.3 P 0.3 Y). Perhaps those last moves were too large to take at once.
The pdf attachment shows the median of the kappa c value reported by the front end in the last 60 seconds of each measurement time. (Jenne's script moved the offset, waited 300 seconds, I'm grabing the last 60 seconds of the 300 seconds.). There is about a 0.5% change in kappa_c over the scan. When we are servoing the power on the DCPDs to 20mA and changning the amount of junk light photocurrent, the optical gain would be proportional to sqrt(20mA -junk light photocurrent). If we use 1.3mA of junk light estimated in 55287 then we are reducing the junk light from 1.3 to 1.1mA, or by about 15%.
While there is some noise in the data, the optical gain does seem higher for offsets in the negative pitch direction (as the beam moves up on AS_C). Our nominal position is pit -0.16 and yaw -0.06.
The second attached png is a plot of the time that we changed the modulation depth and changed the darm offset in 55405. In this offset test we are moving AS_C, SR2 and SRM much further for a smaller change in the apparent junk light compared to the modulation depth change test.