Sheila Jenne Matt Carl Jeff
Tonight we tried a repeat of what Kiwamu and I did last week, and we were able to restore a recycling gain of ~32 (according to the POP DC/ IM4 channel, which is more like 36 according to the way we calculated it durring O1) at 40 Watts. We moved PRM PIT 90 urad in the negative direction, and had to touch up SRM as we did that. We moved the spot on the POPX WFS enough that we railed the PZT and the spot was off center by 0.5. Again the spot on POP A was mostly on just the bottom 2 quadrants. The power on the baffle PDs also decreased as we moved the alingment. We also tried Yaw but this wasn't able to improve the recycling gain.
Since it seems like we might want to use pico motors on POPA, Jenne tried to repeat the PRM move at 2 Watts by moving PRM to match the witness sensors at 40 Watts, she could only go about half way before we lost lock.
Stopping for the night so I can come in for Tues maint. in the morning, but not a lot more progress.
This last lock, I engaged an extra offset of 0.4 in the PRC1 pit loop once we got to 40W. This puts the PRM in the same place as Sheila mentioned earlier, and brings up the PRC gain. I used a ramp of 100 seconds, which may have been a bit fast for the SOFT loops, but we held the lock.
I then got bold, and requested 45W (intending to stop there only momentarily on my way to 50W), but the ISS 3rd loop went unstable. Probably we need to reduce the gain, since we've got a bit more optical power, although I'm not totally sure why, since Kiwamu's measurement in alog 27940 shows that the loop is ultra stable. Probably we should measure the 3rd loop again at 40W.
Attached are some plots showing what happened as we powered up and moved PRM last night, compared to a power up from december.
In the first plot you can see that the recycling gain drops as we power up, with a similar trend in all three diodes that we use to monitor the power recycling gain. Last night's trends are in the first column, the trends from december are in the right column. Last night the ratio of IMC_PWR_IN_OUT to IM4_TRANS_SUM was pretty much constant, while in december it increased by 10%, which explains why the POP/IM4 power recycling gain monitor does not agree with the others in December. There is also an unknown overall gain change for IM4 sum between now and December.
The second row in the first attachement shows how the baffle PDs normalized to the input power (IMC_PWR_IN_OUT).
The second attachment shows pitch oplevs (you can tell that as we move PRM CSOFT P is changing) and QPDs durring this change.
