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Entry  Mon Sep 12 01:21:14 2011, tara, DailyProgress, BEAT, beat layout beat_2011_09_12.png
    Reply  Tue Sep 13 20:54:11 2011, tara, DailyProgress, BEAT, beat layout 
       Reply  Wed Sep 14 19:17:19 2011, frank, paul, tara, DailyProgress, BEAT, beat layout beat_2011_09_14.pngSnapshot_2011-09-14_19-39-37.png
          Reply  Tue Sep 20 00:12:46 2011, rana, DailyProgress, BEAT, seismic noise coupling 
             Reply  Tue Sep 20 01:49:44 2011, Frank, DailyProgress, BEAT, seismic noise coupling 
                Reply  Wed Sep 21 01:39:11 2011, tara, DailyProgress, BEAT, seismic noise coupling beat_2011_09_20_m.pngbeat_2011_09_20_m.fig
Message ID: 688     Entry time: Tue Sep 20 01:49:44 2011     In reply to: 687     Reply to this: 690
Author: Frank 
Type: DailyProgress 
Category: BEAT 
Subject: seismic noise coupling 

Tara showed me a quick plot which showed the spectrum taken with the new (current) setup and the one taken when we removed the springs from the wire suspension. They look pretty identical between 10Hz and 100Hz or so. So it is likely that we see a lot of vertical seismic. I've measured a little bit at low frequencies to see where we are and we are better than before now, i would guess an order of magnitude or so, without any optimized stabilization, alignment and loops. Tara will take a nice set of measurements tomorrow and make a nice plot. The peak at 6.7Hz or so is actually the horizontal motion of the two top stack plates (not only the top plate). I used our pzt-shaker to shake the table and even with a small signal i could increase it until i got scatter noise bumps around 100Hz. So we have to damp this somehow. Is there an easy way to get some more vertical isolation? what about putting the top plate on a few springs instead of rubber? How much do you typically get when floating the table? I don't have realistic numbers for that...

We also don't have a seismometer. Jenne took her's back and Jan shipped the others back to where they came from i think. i think we should get one which we can share between labs in bridge which we can keep for longer. We needed one quite often in the past couple of months and i guess once we start with the cryo cavity we will even more frequently. Any idea where to get a cheap one? We don't need an STS-2 or so... Seismic sucks anyway in bridge...

The problem with moving supports is that the spacer has pretty wide groves. But we have to think about a clever support anyways. Currently it's sitting on viton in the groves of the spacer, which, according to comsol, is very close to the optimum position but who knows in reality.

Quote:

By taking the passive transfer function between a vertical seismometer on the table and the individual cavity signals, we should be able to see which direction to move the cavity supports so as to minimize the seismic coupling.

Our first iteration probably will have a sign error, but by making a few iterations we ought to be able to home in on a better support. Also, we should compare the theoretical estimate with the measured coupling in units of strain/(m/s^2).

 

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