[Lucia, Fabian]

In the last couple of days, we started to reduce the coupling between DOF at the IP stage, measuring the LVDTALIGN (S) matrix and ACTALIGN (D) matrix as reported in klogs 2236 and 22337. 

The updated matrices MEDM are:

S = [ 0.81120 -0.2350 -0.1399

       0.26380 0.9198 -0.00115

       0.67940 -0.2826 0.8790]

D = [ 0.87060 0.09460 0.78

      -0.0601 0.9959 -0.1171 

       -0.1342 0.03230 0.9455]

To test the broadband performance of S and D and to estimate the residual coupling between d.o.f, the transfer functions along L, T, and Yaw have been measured, while to check the residual coupling in DC the IP has been pushed.

Pic.1 shows the broadband residual coupling, as a function of the frequency, before and after changing S and D.
Pic.2, Pic.3, and Pic.4 show the comparison of the TFs before and after changing S and D.
Looking at these plots, it is possible to note that the mechanical response of the IP is not dramatically changed, but the couplings in all DOFs are reduced. It seems that the new matrices are working fine.
Concerning the DC coupling:

Y2L coupling is reduced from 0.0830 to 0.0041 (a factor of 20 lower than before)

Y2T coupling is reduced from 0.0054 to 0.0009 (a factor of 6 lower than before)

L2T, L2Y, T2L, and T2Y were already low.