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AOS (Beam Reducing Telescopes)
satoshi.tanioka - 21:23 Monday 23 July 2018 (5585) Print this report
Measurement of Spectra & TFs

Akutsu, Shoda, Tanioka

Today, we measured the spectra both LVDTs and Geophones.
http://klog.icrr.u-tokyo.ac.jp/osl/uploads/5585_20180723140344_spectrahandv.pnghttp://klog.icrr.u-tokyo.ac.jp/osl/uploads/5585_20180723141113_spectrageo.png

Left figure shows spectra of LVDTs and right one shows that of Geophones.
In both figure, upper graphs show the vertical and the lower one is horizontal.
We can see 3 peaks around 0.98 Hz, 1.3 Hz and 1.8 Hz.
0.98 Hz and 1.8 Hz peaks seemed coupled to horizontal spectra.

Then we measured TFs to identify the peaks.
http://klog.icrr.u-tokyo.ac.jp/osl/uploads/5585_20180723141543_20180723tfyexc.png

This shows the TFs when we inject Y direction.
The legends are shown in the graph of coherence (left lower figure).
Seeing green line and cyan line (LVDT Yaw and Geophone Yaw), we can see 2 peaks around 0.98 Hz and 1.8 Hz.
So these peaks come from some Y resonances (coupling from vertical mode? or couple to vertical mode?).

Also, the peak at 1.3 Hz seems come from horizontal direction resonance.

Some details are described here.
http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA/subgroup/AOS/TMS-VIS0/2018-07-23

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Comments to this report:
satoshi.tanioka - 21:32 Tuesday 24 July 2018 (5599) Print this report

I mistook the Geophone's spectra graph.
In the upper figure showed the spectra of vertical Geophone.
However, I plotted H3 (horizontal) spectra instead of V3 (vertical).

The correct figure is as follow.

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