[JimW, Jenne]

While the IFO was down due to high microseism and high wind this afternoon, we have measured the 2 transfer functions needed for MC2's M1 stage to create the L2A decoupling feedforward filter. 

For both L2P and P2P measurements, the pre-existing flat L2P decoupling gain of -0.007 was disengaged.  So, we started from scratch since we weren't sure about that number. 

In order to get good coherence for the L2P measurement, I was driving MC2 enough that the IMC was having trouble staying locked.  So, I unlocked the IMC and just used the MC2 OSEMs as my pitch witness.  Before unlocking the mode cleaner, I saw that I was already getting better coherence with the OSEMs than MC2 Trans, so I don't think I lost out on anything by doing the measurements with the IMC unlocked. 

We fit the FF TF using vectfit, and hand-added a pair of poles at a few Hz to make the high frequency shape roll off rather than being flat.  The result looks very similar to what Arnaud and Marie got for the PRM at LLO (LLO alog 32503), which is good since they're the same type of suspension. 

The new filter is in the H1:SUS-MC2_M1_DRIVEALIGN_L2P FM3.  The IFO has started relocking though, so we are leaving the pre-existing flat L2P decoupling gain in place and our new filter off.  When we turn on the new filter, we'll need a gain of unity in the filter bank. 

Next commissioning window, I think we're ready to do an on/off test with L2P transfer functions, to show that the filter is doing good things. 

Attached are the individual L2P and P2P transfer functions (excitations done with awggui), and the measured and fit TFs that we've installed.