jenne.driggers@LIGO.ORG - posted 10:51, Wednesday 23 January 2019 - last comment - 18:43, Wednesday 23 January 2019(46596)
Locking Notes
- IFO has been at 30W for ~2 hours, so I'm immediately starting LOWNOISE_ASC, stepping through.
- Waiting a few minutes between each step, so far it seems okay.
- I'm using DHARD_P FM4, the less aggressive cutoff. However, I skipped a line earlier where DHARD_P FM1, the more aggressive LP, would have been engaged. I'm not sure if this line was commented out when they were trying things in alog 46556. If not, then perhaps the 1Hz ring-up was again just due to FM1.
- After a few minutes, I noticed a 0.011 Hz ring-up starting, so I have turned off the DHARD_P cutoff. That seems to have stopped the oscillation. (Yes, a period of just under 100 sec).
- Trying CHARD_Y FM3 (less aggressive 10Hz lowpass) rather than the FM2 (sharper 10Hz cutoff) that is in the guardian. There is a note commenting out FM3 in favor of FM2, saying that FM3 killed the lock, but FM3 should be gentler around the UGF of CHARD_Y, and the same amount of isolation above 20Hz (less isolation in the 10-20Hz band is the price we pay.)
- Seems fine. May not have needed to do this, but it shouldn't hurt.
- Engaging DHARD_Y lowpass (FM2) seems to have given the arm soft Yaw dither loops a kick, which is then also seen by SRC1_Y and PRC2_Y. (Immediately before engaging DHARD_Y FM2, I had also engaged lowpasses on the SOFT_P loops, but this kick was really only in yaw, not at all in pitch, so I think it must be the DHARD_Y lowpass, not the CSOFT_P and DSOFT_P lowpasses.)
- Lowering dither line amplitudes, and ADS_DOF gains seems fine. The DEMOD_I gains (so, the amplitude of the error signals) for 2 of the yaw loops are increased to compensate for the lowering of the dither amplitudes, although the equivalent increase in all the other ADS error points is commented out. These 2 loops that still do have a gain increase on the error signal got a pretty good sized kick, but again seem to have come back fine.
- LOWNOISE_ASC state is now complete, done by hand, everything seems stable. Only differences: No DHARD_P cutoff at all right now, and CHARD_Y using a less agressive lowpass. Both of these changes are in the LOWNOISE_ASC guardian state.
- Started measuring DHARD after LOWNOISE_ASC, but lost lock during my excitation around 1Hz. (Was zeroing the ADS DOF loop gains during my noise injections).
- While reacquiring, engaging ASC for full IFO, big osc at 1.1Hz. SRC2 was hitting input limiter, which might have made situation worse?
- Not the limiter's fault. Next lock, watching state carefully, SRC2 (or MICH?) started to ring up slowly.
- Next lock, doing ENGAGE_ASC_FOR_FULL_IFO by hand, and waiting for a long time for convergence, and it seemed okay. Sheila notes that we should double check that everything is set properly in PREP_ASC, since we are now using DRMI ASC, and it has some different settings from full IFO ASC.
- Also, PR gain was reporting too small of a number when we were at full resonance.
- Looks like the value that is being used is IM4_NSUM, which is now calibrated into Watts injected into vacuum, not mW on the PD. The model is somewhat confusing though. Need to re-check what's going on in the model (which doesn't match what the screens are displaying, I think). Then need to change the calib in PR_GAIN.
- Later lock, changes to LownoiseASC seemed good, although very slowly over time (maybe 20+ minutes later) 1.1 Hz is starting to ring up. I increased the DHARD_P gain from -50 to -60, and that seems to be allowing the resonance to die down. Why are we not able to suppress this HAM2 motion before it starts to bother the ASC???
[Sheila, Jenne]
About the 1.1 Hz noise in PRCL:
Although the ISI suspoint indicates about 10 nm/rt Hz at 1.1 Hz for PR2 longitudinal, in the PRCL calibrated spectrum, we see about 100 nm/rt Hz. The residual 1.1 Hz was dominating PRCL, SRCL and MICH. The attached screenshot shows the error signal time series when we engaged the resG.
We initially tried adding this resG when we reach full lock but before the ASC is on, it made the ASC and LSC unstable, so we moved it to just before DC readout instead, which has been fine.
Other locking notes from this evening:
We have manually been increasing the DSOFT P gain to 30. We lost lock due to a fast instability this last locking attempt because we didn't do this manual increase, so I've put the factor of 2 increase in the gain in when we first engage DSOFT P.About the extra noise in today's lock: it seems to be Y2L coupling, see alog coming soon.