pep.covas@LIGO.ORG - posted 11:04, Friday 07 June 2019 - last comment - 15:28, Friday 07 June 2019(49741)
Update on bounce/roll modes in DARM
I've looked at some data comparing DARM before and after the changes we made this tuesday.
The attached images show the comparisons, where the blue line is after the changes and the red line is before the changes (the noise floor is a little bit higher due to some unrelated noise problems which were present after the maintenance). The 27.71 Hz feature looks much better, although it is not completely damped. The Q of the line seems to have increased. The line at 27.59 Hz has also decreased, but the lines at 40.87 and 26.06 Hz look very similar as they did before.
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Here's a look at a 0.002 Hz ASD of MICH, PRCL, and SRCL starting at 2019-Jun-07. Using the table of ID'd modes from LHO aLOG 49643, I went through and made a comparison to see what lives were. Here's a key to the table values: - " N " -- not visible - " Y " -- visible - " Y* " -- visible with the highest SNR of the three - (blank) -- not visible in any of the ASDs Optic Freq MICH PRCL SRCL BS 17.79 MC1 27.39 PR2 27.41 N Y* Y MC3 27.42 SRM 27.45 SR2 27.50 N N Y* PRM 27.59 Y Y* Y SR3 27.71 N N Y* MC2 27.74 PR3 28.21 N Y* Y Optic MICH PRCL SRCL BS 26.06 MC1 40.81 PRM 40.87 SRM 40.88 SR2 40.91 MC2 40.91 PR2 40.94 Y Y* Y MC3 -- SR3 45.32 N Y Y* PR3 46.09 I'm surprised how mouch *more* stuff is in these ASDs that look like SUS resonances...
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Translating into optics, using the inventory in LHO aLOG 49643, and comparing against expectations from the above cited LHO aLOG 49649: - The impact of SR3's highest vertical mode (aka "bounce" mode or V3) at 27.71 Hz in DARM has been drastically reduced after updating the band-stop filters in the top M1 OSEM damping loops. - PRM's highest vertical mode (bounce, V3) at 27.59 Hz has already been reduced, (though not as significantly as SR3) from simply turning ON the band-stop filters in the top M1 OSEM damping loops that were present but OFF. - The changes in filtering for PRM and BS highest roll (R3) modes at 40.87 and 26.06 Hz had little-to-no effect. LLO has proposed using DRMI LSC signals as error signals for new damping loops -- see LLO aLOG 45255 -- these are under investigation (see above).