Stefan, Matt, Evan
This afternoon and this evening we made some more attempts at locking DRMI3f+arms, with the goal of implementing a handoff from ALS to sqrt(TRX+TRY).
Below are some issues that we’ve noticed.
ALS:
- When ALS DIFF locks, there is a terrible transient that appears in the ALS-X transmission (see attachment). Often the transients are enough to break the green locks. We think this is because there is still significant L2P coupling in ETMX L1, even with the new decoupling filters installed. Matt thinks this is because the alignment of the UIM actuators is especially bad compared to the other stages. Should we revisit the choice to use L1 as part of the ALS DIFF loop? Maybe use L2 instead?
- When acquiring DRMI with arms held of resonance, the modecleaner is sometimes kicked out of lock. It’s still unclear which loop is responsible for this.
- We changed the gain in the L1 locking filter for ETMX from 0.28 to 0.5. This increases the crossover, and decreases the ESD signals.
DRMI:
- The DRMI WFS are taking too long to engage (sometimes several minutes). We are occasionally losing lock because of this.
-
Tonight the
ISC_DRMIguardian seems to get stuck on theOFFLOAD_DRMIstate. It engages the M2 locking filters in PRM and SRM, but then does not move on. For the time being I’ve short-circuited therunportion of the state so that it directly returnsDRMI_1F_OFFLOADED. -
Stefan thinks that setting the SRCL gain to -60 rather than -50 makes DRMI lock more frequently with arms engaged. We’ve put this new value into the
ISC_DRMIguardian. - Stefan found that PRMI (first free-swinging, and then locked) is a good way to touch up the alignment of PRM and BS without having to misalign the ITMs or ETMs. This is useful when we are trying to lock DRMI with arms held off resonance.
Alignment:
- We need to figure out how to align the pointing into the arms so that the IR and green beams are maximally and simultaneously resonant.
Other:
- A certain fraction of the time after the mode cleaner is kicked out of lock, the FSS will oscillate and prevent the MC from relocking.
Good UTC time for DRMI3f+arms starts 2014-11-22 06:48:00
I think Evan means "2014-11-23 06:48:00". About the L2P on ETMX L1, it is not just the transient that appears to be problematic. This is a quick look at the first hour of data. ETMX gets badly misaligned once corrections are sent to L1: the green power decreases down to half its maximum level (first plot). The second plot shows corrections sent to L1, while the third plot shows the induced pitch misalignment as seen by the optical lever. Around t = 30min it looks like a realignment attempt happened.
We don't want to cut out the DRMI offloading. When we locked DRMI we only actuate on M3 of PRM and SRM, but we need to offload to M2 to avoid saturating M3. So we need to figure out why the guardian is getting stuck there (maybe there is a hidden sleep some where). Another thing we could do is engage the wfs first and then offload; maybe that would be fine.
Also there haven't been any "new" decoupling filters installed in ETMX L2P L1 stage since Arnaud installed these (alog 11832). Jeff/Sheila/I had only been investing ETMY L2P more recently because that seemed to be the bigger issue.
This is a 5 hour trend with more advanced tools.
