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Entry  Fri May 21 11:56:34 2010, Alberto, Update, 40m Upgrading, 40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue. 7x
    Reply  Fri May 21 16:24:11 2010, Koji, Update, LSC, 40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue. 
    Reply  Mon May 24 10:03:14 2010, rana, Update, LSC, 40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue. 
       Reply  Mon May 24 11:32:05 2010, rana, Update, LSC, 40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue. reflRFpowerVsArmLength.png
Message ID: 2974     Entry time: Mon May 24 11:32:05 2010     In reply to: 2973
Author: rana 
Type: Update 
Category: LSC 
Subject: 40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue. 

Quote:

 

 If you have a working 40m Optickle model, put it in a common place in the SVN, not in your own folder.

I can't figure out why changing the arm length would effect the RF sidebands levels. If you are getting RF sidebands resonating in the arms, then some parameter is not set correctly.

As the RF sideband frequency gets closer to resonating in the arm, the CARM/DARM cross-coupling to the short DOFs probably gets bigger.

I uploaded the latest iscmodeling package to the SVN under /trunk. It includes my addition of the 40m Upgrade model: /trunk/iscmodeling/looptickle/config40m/opt40mUpgrade2010.m.

I don't know the causes of this supposed resonances yet. I'm working  to try to understand that. It would be interesting also to evaluate the results of absolute length measurements.

Here is what I also found:

reflRFpowerVsArmLength.png

It seems that 44, 66 and 110 are resonating.

If that is real, than 37.5m could be a better place. Although I don't have a definition of "better" yet.  All I can say is these resonances are smaller there.

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