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Entry  Thu Apr 12 08:49:14 2012, Den, Update, SUS, local damping and WFS 6x
    Reply  Thu Apr 12 14:48:44 2012, Suresh, Update, SUS, local damping and WFS 
Message ID: 6528     Entry time: Thu Apr 12 14:48:44 2012     In reply to: 6527
Author: Suresh 
Type: Update 
Category: SUS 
Subject: local damping and WFS 

    WFS servo is moving the MC mirror angles to minimise TEM01 and TEM10 modes within the MC cavity.    This means it will compensate not only for angular noise in the mirrors but also for the PSL beam pointing fluctuations.  So the extra "noise" we see when WFS loops are on is because they are active below the WFS UGF of about 2 Hz.  Also if the HEPA airflow is above 20% (of its max), the PSL beam jitter (caused by the airflow) will add broadband noise into the WFS servo loops and this will show up in the OSEM signals.  See elog 5943 for details.





Then I compared MC1, MC2, MC3 suspos, suspit, susyaw and susside positions with WFS on (black curve) and off (red curve). WFS add noise to MC1 and MC3 measured by osems (MC2 is fine though). WFS should change osem readings but is it a correct way to do this below 0.5 Hz (?) It looks like just a flat noise. Need to think about the conclusion.






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