evan.hall@LIGO.ORG - posted 19:27, Friday 15 July 2016 - last comment - 11:18, Saturday 20 August 2016(28448)
Low-noise DARM loop retuning
I removed the 300 Hz and 600 Hz stopband filters in DARM, along with the 950 Hz low-pass filter.
I increased the gain from 840 ct/ct to 1400 ct/ct, giving a UGF of 55 Hz. This seems to have improved the gain peaking situation around 10 Hz (see attachment).
The new settings have been added to the guardian (in the EY transition state), but have not been tested. The calibration has not been updated.
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Tagging CAL Group. Evan Goetz has also been working on a better PUM roll-off. He'll be installing those improvements soon as well, and a full loop design comparison.
Since we spend a nontrivial amount of time commissioning at high powers (>20 W) with DARM controlled by EX, I moved the DARM gain increase so that it comes on once the PSL power reaches 20 W.