Noise plot for tonight.
The decrease around 1Hz is real, probably partly due to VCO noise, and partly due to alignment.
The increase above 100Hz is due to the loop shape - I am running with a higher UGF tonight.
Some relaxing filtering work brought the >100Hz contribution down a bit. We get 5Hz RMS across the whole band.
Also, the 0.5Hz-2Hz suspension stuff is likely an artefact of using the transmitted DC light. It improved significantly with alignment. And it is about the same order of magnitude when we sit exactly on fringe (with 500cts), and should have significantly reduced frequency coupling.
Again left it running, starting at 02:26 (July 8 2013).
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joshua.smith@LIGO.ORG - 21:20, Sunday 07 July 2013 (7001)
HI Stefan,
I think turning off the pump near HAM3 has removed a sharp line at 65.5Hz, but the rest of the structure around 60-70Hz was unchanged.
The plots below show:
1) A coherence plot between ASC-Y_TR_A_NSUM_OUT_DQ and ISI-HAM3_BLND_GS13X_IN1_DQ from one of your early locks last week (June 29) and from this weekend's lock (July 7). The major difference is that the big coherence peak at 65.5Hz is gone. The coherence at 3.5, 5, and 41.5 looks a tad higher, but maybe just due to differing seismic conditions at the time (will check some more times).
2) Uncalibrated spectra of ASC-Y_TR_A_NSUM_OUT_DQ for the same two times. Here you can see that the 65.5Hz peak is gone.
We'll keep searching in other places for stronger coherence in the 60-70Hz range.
Josh
FWIW, while Michael Coughlin and I were searching in coherence we found two more ASC-Y_TR_A_NSUM_OUT_DQ peaks that are coherent with HAM motion. The peak at 58.5Hz is coherent with HAM2 ISI and the peak at 41.5 with HAM3 and HAM2 (also in CS MICs). These don't have much contribution to your RMS though. The first plot shows the coherence peaks, the second plot shows which peaks in the ASC-Y_TR spectrum these correspond to.