Georgia, Craig, Peter, Stefan Tonight we worked on increasing the input power to 28W. - Along the way we found MICH marginally stable at 5-ish Hz - we increased the final MICH gain from 1.7 to 2.5. - Initially we increased the power by AC-coupling the ISS 2nd loop in low-noise, and manually stepping the power up using the POWER guardian. That method actually increased the light level on the DCPDs (as the DARM offset is not reduced to compensate). Interestingly, that seemed to slightly improve the the low-frequency noise too - we don't really understand why. We believe thee effect is there if we only use the DARM offset. - We tried going to 30W input, but started seeing increasing recycling gain fluctuations, followed by what seems to be a lock-loss due to CARM. So we left Guardian at 28W. We directly go there in the regular power-up step. - Initially, at 25W, we tried to increase Hang's radiation pressure compensation by stepping up the RPC gains by a factor of 1.5, as designed for 25W. (see Hang's alog 44709). That actually led to an instability. We were successfully able to increase it by a factor of 1.2 using z step H1:ASC-RPC_DHARD_P_GAIN *1.2 H1:ASC-RPC_DHARD_Y_GAIN *1.2 H1:ASC-RPC_CHARD_P_GAIN *1.2 H1:ASC-RPC_CHARD_Y_GAIN *1.2 However, in the end we did not need to do that to go to 30W, so that is not in the Guardian. - We ran an A2L at 28Watt. - At 28Watt input we noticed a significant decrease in the CARM gain - an we had to compensate by adding 11dB of gain in the CM board. After roughly 30min we lost lock due to ASC: CHARD_Y, PRC2_Y and SRC1_Y started running away. Attached is a DARM spectrum of the best we saw today - H1:CDS-SENSMON_CAL_SNSW_EFFECTIVE_RANGE_MPC called it at 93Mpc.
A couple of notes on locking tonight:
We updated the NLN power to 27 W (i.e. 25 W requested).
With locklosses from 28 W the fast shutter lockloss guardian asks for the user to check that the fast shutter closed. Today we have been running this guardian through the INIT state by hand to fix the problem, otherwise ISC_LOCK gets stuck in DOWN.
For most of today with the new set power the CO2X power did not get turned down by the guardian during the lock. I updated the CO2 power guardian "PSL_TARGET_POWER" to 25 W (but I haven't updated the set powers, so for now CO2X still delivers 100 mW at NLN), to fix this.
During our several 28-30W locks tonight the noise in REFL_A_LF gradually increased over the course of ~20 minutes until we lost lock. See attached screenshot of one of the 30 W locks today for an idea of the scale (REFL_A_LF is bottom left). During the last lock this evening (at 27W, CO2X power at nominal level, after an initial alignment) the noise increase on REFL_A_LF is slower.
I noticed a couple of ETMY violin modes getting rung up with their default guardian settings, have lowered the gains of MODE1 and MODE5 in the guardian. MODE1 is worth keeping an eye on.
Attaching a noise budget plot (now with giant dots) taken during our 27W lock.
Excellent. Congratulations.