robert.lane@LIGO.ORG - posted 10:39, Monday 15 August 2011 - last comment - 11:49, Monday 15 August 2011(1217)
H2 SUS ITMY Reaction Chain Post Cabling
After the Reaction Chain was cabled up Friday, August 12 (the UIM and PUM cables were routed down through the masses of the R0), we took another series of R0 TFs. Not all of the OSEMs have been connected to their respective cables. The results look promising, but after reviewing the results with J. Kissel, we came up with a few comments: The Pitch modes are stiffer (see page 5 of the all quads pdf), but seems to be similar to Brett's T1000569 early results (primarily of interest is the peak that moved from 1.514Hz to 1.655 Hz). The second Roll and second Trans modes have bifurcated. This could either be a physical change in the dynamics or it may be that the Q has increased such that the pendulum is swinging outside of the OSEM range, reducing the linear response. See page 2 and page 4 of the all quads pdf and 201108121552dtth2itmyr0rtf.pdf. A few of the lower frequency modes are also a little bit stiffer. One peak of interest, is the little coupling peak between modes 3 and 4 of Longitudinal (moved from 1.498Hz to 1.639Hz).
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J. Kissel, R. Lane Investigating the Transverse Mode Bifurcation a little further, we attempted to rule out the "QUAD swings out of OSEM range, but is still free" theory mentioned above by taking the same transverse TOP to TOP transfer function, but with half the drive amplitude. Attached are the results which show identical response (albeit a little noisier of course). So, we conclude that this mode splitting is physical and coherently measured. We also made sure to look at the time series of relevant channels during the measurement (ITMY_R0_OSEMOUTF_SD for drive -- plenty of head room, ITMY_R0_DAMP_T -- no saturations) and saw completely normal time series.
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