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Message ID: 9742     Entry time: Fri Mar 21 01:54:32 2014
Author: ericq 
Type: Update 
Category: LSC 
Subject: Some early CARM modeling 

 I've been getting a simulation going with the eventual goal of simulating CESAR-type signals for CARM. So for I've only been using MIST, though I'm still thinking about what to do for a fully time domain approach. (For example, maybe a mixture of simulink and analytical equations? We'll see how painful that gets...)

Anyways, with the parameters I have for the 40m, I've set up a simulation, where I can do things like a "static" CARM scan.

(i.e. PRMI perfectly locked. Ask what different PDs see if the arms were just statically sitting at some CARM offset)

staticCarmSweep.pdf

PDH signals are there in the REFL diodes. The coupled line width here looks smaller than the ~40pm number I've heard before, so I should check my parameters. (Likely culprit, I'm using nominal R and T for the arm cavities)

I've also done the slightly more sophisticated thing of looking at the transfer function from CARM motion to different PDs, at different CARM offsets. For TRX and REFLDC, these seem to match up qualitatively to some plots that Kiwamu has done for aLIGO, with frequencies shifted by the relative arm length factor of 100. (Q's left, K's right, Y-axis on mine are W/m with 1W input the IFO)

carm2TRX.pdfCARM_TFs_TRXDC.pdf

 

carm2reflDC.pdf CARM_TFs_REFLDC.pdf

 

We can also look at the PDH diodes (revised from my initial post. Had an error in my code): 

 carm2refl11.pdfcarm2refl55.pdf

 

That's where I've gotten so far!

 

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