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Entry  Wed Oct 15 20:10:29 2014, ericq, Update, LSC, Interim DARM Signal 7x
    Reply  Thu Oct 16 16:21:42 2014, ericq, Update, LSC, Interim DARM Signal dcDARMSweep-300.pdfdcDARMSweep-120.pdfdcDARMSweep-50.pdfdcDARMSweep-0.pdf
       Reply  Thu Oct 16 21:20:59 2014, rana, Update, LSC, misleading modelling 
          Reply  Fri Oct 17 03:05:00 2014, ericq, Update, LSC, DARM locked on DC Transmission difference TRdifflock.pngOct17lock.pdf
             Reply  Fri Oct 17 13:19:48 2014, Jenne, Update, LSC, POP22 ?!?! 
          Reply  Tue Oct 21 00:38:40 2014, ericq, Update, LSC, sweep + RMS as uncertainty dcCARMSweep_uncertainties.png
             Reply  Wed Oct 22 06:32:29 2014, rana, Update, LSC, sweep + RMS as uncertainty 
Message ID: 10621     Entry time: Fri Oct 17 03:05:00 2014     In reply to: 10619     Reply to this: 10622
Author: ericq 
Type: Update 
Category: LSC 
Subject: DARM locked on DC Transmission difference 

 I've been able to repeatedly get off of ALS and onto (TRY-TRX)/(TRY+TRX). Nevertheless, lock is lost between arm powers of 10 and 20. 

I do the transition at the same place as the CARM->SqrtInv transition, i.e. arm powers about 1.0 Jenne started a script for the transition, and I've modified it with settings that I found to work, and integrated it into the carm_cm_up script. I've also modified carm_cm_down to zero the DARM normalization elements. 

I was thwarted repeatedly by the frequent crashing of daqd, so I was not able to take OLTFs of CARM or DARM, which would've been nice. As it was, I tuned the DARM gain by looking for gain peaking in the error signal spectrum. I also couldn't really get a good look at the lock loss events. Once the FB is behaving properly, we can learn more. 

Turning over to difference in transmission as an error signal naturally squashes the difference in arm transmissions:

TRdifflock.png


I was able to grab spectra of the error and control signals, though I did not take the time to calibrate them... We can see the high frequency sensing noise for the transmission derived signals fall as the arm power increases. The low frequency mirror motion stays about the same. 

Oct17lock.pdf


So, it seems that DARM was not the main culprit in breaking lock, but it is still gratifying to get off of ALS completely, given its out-of-loop-noise's strong dependence on PSL-alignment. 

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