Dhruva, Vicky, Naoki, Dan

Previously on the ring heater change saga

Back in Feb (67327) we tried a differential ring heater change to try and match the arms better, this reduced ETMY RH and increased the ETMX. At the time we had a lockloss fairly soon after which turned out to be the 10.4kHz PI. This is caused when the Y-arm mode-separation frequency increases and pushes the 2nd order modes in the Y-arm up into the 10.4kHz acoustic modes.

The following week (67497), Craig and I tried the opposite and reduced the X-arm mode-separation frequency to match the Y-arm better. The X-arm does not seem to excite any 10.4kHz PI. However, when we tried this we found that the power buildups got much worse, but the frequency noise coupling got much better suggesting the arms were becoming better matched. Eventually we ended up trying to increase the Y-arm separation frequency again to improve buildups but eventually lost lock to the 10.4kHz PI.

Today

Today we finally got around to trying to increase the Y-arm mode separation frequency again but this time we had the PI damping on our side. I set the Y-arm RH to 1.4->0.4W. The good news is it worked great (black before, blue after), the Y-arm modes moved through 10.4kHz with little issue. Vicky+Naoki needed to adjust the excitation phase a bit, but the PI never got out of control, the DCPD min/max monitor barely changed.

Increasing the Y-arm mode separation frequency from 10350Hz upto 10500Hz brought it closer to the X-arm modes which are currently around 10750Hz. This helped the build ups, with the PRG and arm powers trending higher. We did however run into a reasonably fast ASC lock loss. I think it looks like CHARD Yaw at 1.3Hz.

I still need to demodulate the lines to make some estimate of how the frequency/intensity/jjitter coupling was changing which I will do tomorrow.

New AWG jitter coupling lines

I added three jitter coupling lines (H1:IMC-PZT_YAW_EXC) to AWG_LINES at 111.3 Hz, 167.1 Hz, 387.4 Hz