jenne.driggers@LIGO.ORG - posted 15:30, Monday 05 November 2018 - last comment - 17:51, Monday 05 November 2018(45026)
SRC2 ASC semi-coherent with DARM
SRC2 is pretty coherent with DARM (attached .png, bottom right corner pink and cyan). I did some injections, so that Sheila can stick these into the noise budget (.xml attachments). But, we should roll this QPD loop off faster.
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After Jenne notice the problem, we put some extra LPs in SRC2 loops.
For the SRC2 P loop, we lowered it DC gain by 3dB from 200 to 140 and added a 4th order ellip filt at 10 Hz with 40 dB attenuation.
For SRC2 Y loop, we tried to put a LP as aggressive as the PIT one but it broke the lock once. So we lowered the SRC2 Y loop gain by 6 dB from 200 to 100 and used a 4th order ellip filt at 12 Hz with 30 dB attenuation.
The LPs seem to improved DARM noise below 30 Hz. See the attached figure.
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