Sebastien, Hugh

We investigated a little more on BSC-ITMX comb issue that we noticed yesterday (see Jeff's log).

Our guess what that the position sensors are cross talking with each other between the chambers at the corner station. To verify that, we turned off the CPSs of BSC-BS, to see if it makes the comb disappear.

In the plots attached, the red curves are the reference curve (BSC-BS ON). We can see a comb on the rotational DOFs, starting at 0.45Hz. When the CPSs of the BS are OFF (blue curves), the comb goes away. At this point, I think we can clearly assest that we have a CPS issue.

PS: the huge spike at 0.5Hz on X and Y seems unrelated with the CPS effect. We're still investigating to understand where it comes from. For now, we just installed a narrow notch at this frequency in our blend filters as a temporary solution.