aLIGO LHO Logbook

H1 PSL

sheila.dwyer@LIGO.ORG - posted 19:13, Thursday 25 August 2016 - last comment - 11:41, Friday 26 August 2016(29319)

ISS diffracted power adjusted

We had a couple locklosses when the ISS saturated, both with the third loop on and off. We just increased the ref signal to -1.52 V to move the diffracted power to around 4%. Was some setting incorect after a reboot this morning? SDF indicated that everythind is OK.

Comments related to this report

jeffrey.kissel@LIGO.ORG - 11:27, Friday 26 August 2016 (29330)

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The 1st loop's reference offset voltage (H1:PSL-ISS_REFSIGNAL) is not monitored in the SDF system. During O1, because of the alignment drift in the PSL and or interactions with the 2nd loop, the operators would often adjust the diffracted power with this offset.

I've now re-monitored the channel, for now, because we don't have any restriction of SDF difference to do science.

Keita restarted the PSL ISS model again this morning, and we had begun relocking too quickly (!!) after that reboot, so we had to adjust the offset on the fly, when it was have too late. This resulted in a close, but not the same, value of -1.602.


Also had to restore the "AOM Offset" H1:PSL-ISS_CTRL_OFFSET, which should be 3.85 (it had come up as 2.5).

I've accepted both the -1.602 offset voltage and 3.85 AOM offset in the SDF's safe.snap and down.snap for the PSLISS front-end.

jenne.driggers@LIGO.ORG - 11:41, Friday 26 August 2016 (29331)

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Note that the H1:PSL-ISS_CTRL_OFFSET used to be 2.5, but yesterday Keita and I changed it to 3.85. Thank you Jason & Jeff for pointing out that I forgot to write an alog.

We made this adjustment with the ISS first loop off, and set the offset such that the diffracted power was a little over 3%. Before doing this, the diffracted power was 1.7% with the first loop off, and we kept hitting the bottom rail, which would send the first loop into oscillation and cause it to unlock. We were able to close the 1st loop, and everything looked okay. So, 3.85 is the new best value.

With all that said, we've had a few times over the last 3 days of hitting the bottom rail of the ISS when we've got the IFO locked, and it changes the power injected into the vacuum and the IFO oscillates a bit although usually retains lock. We may need to consider increasing the first loop offset even more, so that we're a teeny bit farther away from that rail.