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Entry  Tue Feb 4 16:43:50 2014, manasa, Update, General, IFO alignment update 
    Reply  Tue Feb 4 17:40:19 2014, manasa, Update, General, Ready for pump down?? 
       Reply  Tue Feb 4 23:01:24 2014, Jenne, Update, General, Ready for pump down?? 
          Reply  Wed Feb 5 15:26:57 2014, manasa, Update, General, Ready for pump down?? 
       Reply  Mon Feb 10 16:02:12 2014, Jenne, Update, General, PRM oplev clipped in vacuum Screenshot-Untitled_Window-1.png
          Reply  Mon Feb 10 16:20:28 2014, Jenne, Update, General, PRM QPD recentered 
             Reply  Mon Feb 10 18:59:25 2014, Jenne, Update, ASC, PRM ASC better, but not great yet 
                Reply  Mon Feb 10 19:56:10 2014, rana, Update, ASC, PRM ASC better, but not great yet 
Message ID: 9620     Entry time: Mon Feb 10 19:56:10 2014     In reply to: 9619
Author: rana 
Type: Update 
Category: ASC 
Subject: PRM ASC better, but not great yet 

Ignoring the OSEM damping loops, the oplev servo loops make it so that the POP ASC loops do not see a simple pendulum plant, but instead see the closed loop response. Since the filter in the OL bank is proportional to f, this means that the open loop gain (OLG):

 

Which means that the CLG that the ASC sees is going to dip below unity in the band where the OL is on. For example, if the OL loop has a UGF of 5 Hz, it also has a lower UGF of ~0.15 Hz, which means that the ASC needs to know about this modified plant in this band.

For i/eLIGO, we dealt with this in this way: anti-OL in iLIGO

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