When the modecleaner is kicked out of lock, the FSS oscillates and prevents relocking.
I've reduced the FSS common gain from 30 dB to 24 dB. Now the modecleaner relocks without issue.
I noticed that ALS-Y_REFL_B_DC does not seemed to be aligned. The error threshold has been lowered so that the flag does not go off and we can still lock. I am not sure when this misalignment happened or if this was intentional (I can't remember). Whoever goes down to EY first, can he/she align it?
(Elli, Daniel)
Went to EY to center the green beams on the WFSs. They were too far out for the PZT mirrors. Auto-centering enaged and working again.
Since the ETMX L1 L2P filters gave us a unstable x-arm lock once ALS-DIFF was engaged, we switched to a DC-only strategy:
- Instead of the the L2P/L2Y filters we simply used flat gains, and tuned them at 0.1 Hz:
Pitch: -60dB (FM10) * gain of 5.3
Yaw: -60dB (FM10) * gain of -0.7
- We also tweaked the ESD L2P/L2Y's at 2Hz:
Pitch: gain of 0.021
Yaw: gain of 0.007
- This left some AC pitch fluctuations on ETMX. The OPLEV took care of that. We now have a stable ALS DIFF and COMM running in this configuration.
For reference:
The previous ETMX L1 filters were as follows: L2Y gain of 0. L2P FM1, FM2 ON with gain of -1.0. Nothing had been installed in L3.
With these new L2P/L2Y settings and pitch oplev damping on L2, and the arms locked on HEPI slow ALS DIFF has been stably locked (with no build up drifts) for 20 minutes.
model restarts logged for Sun 23/Nov/2014
2014_11_23 02:27 h1fw1
one unexpected restart. Conlog frequently changing channels log attached.
On the way to better initial alignment automation, there are some new scripts for TMS alignment in:
/opt/rtcds/userapps/release/asc/h1/scripts
they are alignTmsxDither.py and alignTmsyDither.py which use baffleAlign.py. These are still a work in progress. After testing is done, we will need to incorporate them into the IAS guardians.
The usual scripts (e.g., alignDitherFull.py) should be as before, and backup copies are in old_2014-11-24 just in case.
Matt, Dan
After Alexa gave us a quick alignment tutorial, we started by fiddling with the dither alignment of the X-arm. The PD thresholds for dithering across the baffle PDs were set to very small values, so small that the dither would declare victory before it even started. Matt has been working on the initial alignment, I'll let him say more about it.
We noticed that the green spot on the TMS-Y mirror, visible through ETMY, is very low. There are large offsets in the EY green QPDs that steer the beam to what looks like a bad place on the mirror. Zeroing these offsets (which is where they were for most of the last six months) would have forced us to begin a painful realignment procedure, so we left them as we found them. Historically it looks like people have set these values to maximize the buildup in the arms, but it's hard to believe that the optimal beam position is so far off-center.
With the arms well-aligned for green we aligned the corner optics - IM4, PR2, PRM, BS, SRM. The scripts for this went quickly, about five minutes.
Then we locked the DRMI, with the arms misaligned. Locking tonight was fast and robust; the DRMI would lock within a few minutes (rarely more than 5 minutes), and would remain locked for tens of minutes. There were many unexplained lock losses, so things are not as stable as we'd like, but we didn't see any mode hopping and the sideband buildup was consistently good. Over three hours of DRMI locking we didn't observe a significant drift in the alignment.
We went through the DRMI guardian and commented out lots of gain/switch settings that weren't needed, mostly for the DC centering. The script is now pretty fast, it goes from lock acquisition to ASC loops on in less than 30 seconds. We did not observe any unexpected long pauses. The duration of the script is dominated by ramping the SRM and PRM M2 gains, this takes 9 seconds total (4.5sec each).
We re-enabled the PRM and SRM2 offloading to M2. We found the SRM offloading was a little flaky and sometimes broke the lock. To make this a little gentler, we reduced the initial gain ramp to 1, and ramped the rest of the way (to 4.5) after the WFS turned on.
We measured the LSC OLTFs and found that MICH and PRCL didn't have much phase margin (~25deg each). We reduced the gain for these loops so that they both have >30deg. The MICH gain is now 3 (was 5) and PRCL is 15 (was 22).
Afterwards I mucked around with the OMC, I found a set of good misaligned values for ITMX and ITMY that minimized the RIN at the dark port when the other ITM was aligned (presumably this steers ghost beams away from the OMC). Following Gabriele's instructions I used the picos to center the beam on IMC WFS A and added some offsets to the IMC ASC loops; this reduced the intensity noise measured by the ISS second loops PDs by a factor of three or so. I tried to engage the ISS second loop but failed. The script posted here did not appear to work; I tried to follow these directions but the loop was unstable.
Plots attached are MICH, PRCL, SRCL loops before we reduced the gain to get some phase back in MICH and PRCL.
FWIW the misalignment settings for ITMX/Y that inject the least amount of RIN at the dark port (with a single bounce off the other ITM) are:
| ITMX PIT | ITMX YAW | ITMY PIT | ITMY YAW | |
| Aligned | 64 | -1.7 | 222 | -140 |
| Nominal misaligned | 0 | -62 | 0 | 0 |
| Better misaligned | -10 | -380 | 282 | -450 |
I didn't observe any change in the RIN spectrum when moving the PRM, SRM, or ETMs. This doesn't solve the problem - the OMC TRANS spectrum is still a little ratty - but it seems to be dominated by RIN noise that is coming from the input beam, which is a job for the ISS.
The ISS second loop scripts are not 100% fail proof. If they fail once, try a couple of times more. Normally the switch one script works more than 50% of the times.
Well, Gabriele is right -- running the ISS secondloop script with Sudrashan this afternoon was problem-free.
For posterity, I've been using Sheila's DRMI OLTF templates for measuring loop gains: /ligo/home/sheila.dwyer/DRMI/DRMI_MICH_OLG.xml and related.
no restarts reported.
conlog frequently changing channels list attached.
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:
DRMI:
ISC_DRMI guardian seems to get stuck on the OFFLOAD_DRMI state. It engages the M2 locking filters in PRM and SRM, but then does not move on. For the time being I’ve short-circuited the run portion of the state so that it directly returns DRMI_1F_OFFLOADED.ISC_DRMI guardian.Alignment:
Other:
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.
(Alexa, Evan, Stefan, Matt)
The ETMX bounce mode has been limiting us in locking ALS DIFF, and causes us to lose lock when the ESD saturates. The first attachment shows the coil outputs of the stages, and there is a clear peak in the ESDs (note this screen shot was taken with a much lower gain in DIFF and with the boosts off; this peak causes saturation when the DIFF gain is nominal). The second attachment shows the bounce mode appearing in the oplev spectrum. You can see that this mode starts to appear Friday and gets worse into today. Thursday night the mode looks fine, which explains why we were able to lock DIFF Thursday night. At some point Friday afternoon we turned off the ETMX L2 oplev damping; however, we see this mode ringing up before this was switched off.
We managed to damp this bounce mode using the optical lever signal. This has the advantage of not needing anything to be locked, so it is very robust, which is important since it took about 2 hours to damp. The first image shows the L2_OLDAMP_P filter configuration we were using, and a time series of the resulting coil signal. The second image is a trend of the OLDAMP_P_OUT signal, which shows the damping in action (the envelope of the signal slowly decreases with time as the mode rings down, and then jumps up each time we increase the gain). After a couple of hours of damping, we were able to reduce the mode amplitude by a factor of 10, and then return to locking. Note - the bounce mode frequency is 9.775 Hz
I want to give some more detail on the filters we used for the bounce mode damping: We used the ETMX_L2_OLDAMP_P filter, and had only FM1 (0:0.5) and FM6 (Pass 9.8) engaged. The OLDAMP pitch gain was -1.
no restarts reported.
conlog frequently changing channel report attached.
Even at 24 dB, the FSS common loop will still oscillate every so often.