Alexa, Sheila, Kiwamu
ALS COMM is robust, we can easily transition from green to IR lock. We measured the noise to be about 20 Hz RMS.
Meanwhile, we had a bit of trouble with ALS DIFF. First the DIFF VCO is railed. To handle this we used an ezca servo to feedback to ETMX. The ezca command we used is: ezcaservo -r H1:ALS-C_DIFF_PLL_CTRL_OUTPUT -g 100 H1:SUS-ETMX_M0_TEST_OFFSET. We also had to set the tune voltage to 5.526V in the Y VCO. This technique would bring the DIFF VCO into range so we could engage the DARM feedback. We were able to close the loop with a lower gain (input matrix set to 0.05). We quickly leanred that the L2P in both ETMX and ETMY are bad (ETMX was worse than ETMY). We need to examine these filters again, and do something similar to what was done with the BS.
I checked the ETMX L2P filters today and found that the L2L gain in the DRIVEALIGN matrix on the L1 (UIM) stage had been set to a wrong value of 10.
This explains:
I set it back to 1. This should help us finding a neutron star merger.
It seems that the gain had been like this since 20th of last July for some reason. I set it back to 1. Then I checked the performance of the L2P decoupling by injecting a sinusoidal wave at 0.1 Hz (which is kind of the frequency of the signals that we have applied for the ALS DIFF loop) with an amplitude of 104 counts at the input of the DRIVEALIGN matrix. I was able to confirm that the correct L2L gain reduced the angle coupling significantly.
By the way, L1 stage's L2Y decoupling filter had been off by setting the gain to 0. This seems to be the right setting because I did not see a large motion in yaw when driving the longitudinal. Setting the gain to -1 seemed to just introduce a coupling. So I conclude that the L2Y should be off.