Naoki, Vicky, Gabriele

Recently Gabriele improved the M1/M3 crossover of PRM as reported in alog68864 and alog68899. Since the FC2 and PRM are the same HSTS suspensions, we imported his offload filter from PRM to FC2. The FC green can be locked with new filter. We will check if IR can be locked and see the long term stability.

The previous FC2 offload filter was designed by Sheila as reported in alog66092. Fig 1 shows the FC2 M1 LOCK filter bank. The previous filter was using FM1,3,4,6,10. We imported the FM5,7,8,9 filters from PRM M1. The gain of PRM M1 is -0.02 and the gain of PRM M2 is 10, so we set the gain of FC2 M1 as -0.2. Here is the summary of FC2 M1 filter.

old: FM1,3,4,6,10 ON, gain 0.5
new: FM1,5,7,8,9,10 ON, gain -0.2

Fig 2 shows the FC2 M3 LOCK filter bank. We are not sure about the FM2,9 in FC2 M3, but the CLP300 in FM9 seems imported from MC2 M3. Since we want to keep the crossover of green SUS/VCO, we kept these FC2 M3 filters.

Fig 3 shows the crossover of FC2 M1/M3 (purple: old, blue: new). The M1/M3 crossover frequency is 0.8 Hz. In the previous crossover, there was a peak at 1.3 Hz which required us for the wig1.3Hz filter for stable crossover. With the new filter, the peaks at 1.3 Hz and 3 Hz are removed and the crossover looks more reasonable. 

We also measured the FC2 actuation response when FC is down (Fig 4). The template is saved in userapps/sqz/h1/Templates/dtt/FC2/M1M3total.xml. The peak at 3 Hz with old M1+M3 is removed with new M1+M3.