M. Ball, S. Dwyer

Before lock was lost during maintenance this morning, we turned on our L2A rerouting as originally tested in LHO alog 51604. This time, we activated a boost (below 0.2Hz gain in the L1 L2L filter) and still maintained lock. With the rerouted L2A signals, we saw an increase in the actuator control signals between 3 and 5 Hz. With the boost on, we saw a decrease in these actuator signals below 0.3Hz.

We then tested a "new" (modified) L2 length to L3 pitch decoupling filter that included a cutoff above 2Hz to reduce the 3-5Hz signal increase. Little else was changed by this filter.

Attached are time series of the L1, L2, and L3 actuator control signals at the time the boost was activated. The L1 signal is largely unchanged, but some spikes appear larger. The L2 signal shows a net decrease in amplitude (this may help with locklosses triggered by saturation of these signals, such as this one from 9/3). The L3 signal remains largely unchanged.

Also attached are spectra of one of these signals before turning on the L2A rerouting and boost (dotted lines), between turning on the boost and loading the new filter (dashed lines), and after loading this filter (solid lines). Timestamps are as follows:

Rerouting turned on at 15:37:43 UTC.

Boost activated at 15:38:28 UTC.

L2P filter loaded at 15:51:30 UTC.

This has not been implemented yet, but we plan to do calibration measurements for it tomorrow.