40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Fri May 2 03:51:29 2014, rana, Update, LSC, farther into CM MCkicked.png
    Reply  Sun May 4 22:28:54 2014, ericq, Update, LSC, farther into CM OLTF.png
       Reply  Tue May 6 03:17:15 2014, rana, Update, LSC, farther into CM 
          Reply  Tue May 6 17:58:44 2014, ericq, Update, LSC, farther into CM AOTFs.pdf
Message ID: 9917     Entry time: Tue May 6 17:58:44 2014     In reply to: 9913
Author: ericq 
Type: Update 
Category: LSC 
Subject: farther into CM 

 I took a look at the MC OLTF and AO path TFs with the fast agilent analyzer. 

I played with the relative gain of the EOM and PZT, but couldn't really change the MC OLTF shape much without making the PC Drive RMS angry. 

However, it turns out we have plenty of phase headroom to up the MC UGF from ~100kHz to ~180, with about 40 degrees of phase margin and ~7dB of gain margin. As I write this, PC drive RMS is around 1.1, and FSS Fast at 5.6, so I think the extra gain is fine for now. 

This pushes up and smoothens out the gain peaking in the AO path; see this figure:

AOTFs.pdf

(why does ELOG hate my python plots?! argggg)

Rana's rule of thumb was "We need at least +3dB MC loop gain at our CM servo UGF," so it looks like high tens of kHz bandwidth may be doable from the AO standpoint.

RXA: No, no, no, no, no, noooo. Rana said we need a gain of 3-10 at the CM UGF, not +3 dB.

ELOG V3.1.3-