stefan.ballmer@LIGO.ORG - posted 11:30, Monday 24 November 2014 - last comment - 11:55, Monday 24 November 2014(15260)
Dealing with ETMX L1 L2P trouble
Since the ETMX L1 L2P filters gave us a unstable x-arm lock once ALS-DIFF was engaged, we switched to a DC-only strategy:
- Instead of the the L2P/L2Y filters we simply used flat gains, and tuned them at 0.1 Hz:
Pitch: -60dB (FM10) * gain of 5.3
Yaw: -60dB (FM10) * gain of -0.7
- We also tweaked the ESD L2P/L2Y's at 2Hz:
Pitch: gain of 0.021
Yaw: gain of 0.007
- This left some AC pitch fluctuations on ETMX. The OPLEV took care of that. We now have a stable ALS DIFF and COMM running in this configuration.
For reference:
The previous ETMX L1 filters were as follows: L2Y gain of 0. L2P FM1, FM2 ON with gain of -1.0. Nothing had been installed in L3.
With these new L2P/L2Y settings and pitch oplev damping on L2, and the arms locked on HEPI slow ALS DIFF has been stably locked (with no build up drifts) for 20 minutes.