Jennie W, Camilla

Today Camilla and were trying to move around the IM1 and IM2 mirrors in turn and try and clip the beam going through the Faraday Isolator to see how centred we are.

Details in a log from Camilla.

As part of this we need to make a move with either IM1 or IM2 and bring the beam back onto the centre of IM4 TRANS with IM3 pitch or yaw moves.

Jenne had the idea we could use a DC centering loop to speed this up by moving IM3 for us.

We used the DC7 centering path after trending the outputs of this back to make sure it was not used during locking or in nominal low noise - checked back at least 70 days and the outputs were zero.

I checked the DC1 centering loop filters and copied over the three that are on during lock for both yaw and pitch into the DC7 foton files, putting all three filters in place of the FM2 module (previously called OFF and having a value of gain(0)) in ASC.adl DC7_P and DC7_Y.

Then we altered the ASC input and output matrices so that DC7 takes IM4 TRANS QPD as an input and moves IM3 to centre on this.

We tried different gain up to +/-50 in the yaw loop but never managed to make the yaw of IM4 TRANS converge to zero.

After talking to Sheila we realised that the DC1 loop servo will not match the plant of the IM3 suspension so to use this for IM moves we would have to put more thought into the filters.

NB: My changing and saving of the ASC.txt foton file led to some confusion with Dave B. et al. who were trying to track down a rounding error in the DHARD filter in the same fofon file. But this has been resolved.