Short version: The new shutter seems to be closing harder than before the vent. This is causing the ISI to trip. So far we have gotten around this by running the ISI in a low gain state, but this makes the table motion much worse above 1 hz.

After the shutter work, we started having problems with trips of the HAM6 ISI when the new shutter trips. This morning we put the ISI in the "Robust" isolated state, which uses low gain isolation loops with UGFs around 10hz. The normal loops have UGFs around 30-40 hz. For now this seems to have eliminated the tripping of the ISI, but the performance of the ISI is much reduced above 1 hz. First plot shows a comparison Y GS13s and ground STS for HAM6 for the two configurations. Red traces are with the high gain loops, blue traces are with the low gain loops. Below 1 hz they look roughly the same (low frequency diffs seem to be mostly in the ground for blue), but at 1 hz the high gain loop is doing ~100x better. Not surprising.

I've looked the GS13s in Z at shutter triggers before and after the vent and the shutter seems to be moving the table a lot more now. Attached plot shows a trigger from today with the 10hz loops (blue), yesterday with 30hz loops ( orange/ spiced cider) and Aug 1st with 30hz loops (red). I've looked over at least 3 events in each configuration and they look remarkably consistent, with respect to ISI configuration. Shutter triggers before the vent seem to have kicked the table less than they do now. Maybe this will reduce as the shutter breaks in?

We have some medium gain loops installed with slightly less gain that the high gain loops, tomorrow during maintenance I'll try testing those, but I doubt they'll be enough. Otherwise, we can come up with some loops with some better compromises between UGF and high frequency roll-off than the low gain loops. But the best option would be to figure out  what can be done to reduce the kick from the shutter.