Now that both end transmission QPDs have the line filters, I aligned them.
I locked and aligned the IR using the ASS, then went to each end table and put the beam in the center of the QPD.
I have added another block to the LSC screen (and made the corresponding sub-screen) to expose the analog settings for the DC photodiodes.
Note that we have 2 open channels there, which are still called something like "PD2" and "PD3" from olden times.
If we ever chose to use those, we will probably want to change their names, in /cvs/cds/caltech/target/c1iscaux2/LSC_aux2.db and /cvs/cds/caltech/target/c1iscaux/LSC_aux.db
I added UGF servos for the DRMI DoFs, after creating a library block for the servos. I also deleted the FMs before the phase rotation, since we can just do it afterwards in other existing FMs. I've only added the MICH and PRCL buttons to the LSC screen because in the end, I feel like a dropdown is better, but I just wanted to get it running quickly tonight. The LSC model and the UGF block have been committed to the svn.
We were able to use the PRCL UGF servo successfully, as Jenne was exploring MICH offset space.
[Jenne, EricQ, Rana]
Tonight we started prepping for an attempt at variable finesse locking.
The idea is to put in a MICH offset and hold the lock with ASDC/POPDC (so that the offset can be larger than if we were just using RF signals). This reduces the PRC buildup, which reduces / removes the double cavity resonance problems while reducing the CARM offset.
MICH locked on ASDC normalized by POPDC, PRM and ETMs (and SRM) all misaligned.
MICH offset of -20
MICH input = -0.04*ASDC normalized by 0.1*POPDC.
MICH gain = +5
MICH always triggered on (no triggering for DoF), but FM8 (CLP400) triggered to come on after lock (didn't write down the values).
PRMI locked with MICH on ASDC normalized by POPDC, PRCL on REFL33I, ETMs and SRM misaligned.
MICH offset of -10
PRCL input = 1*REFL33I
PRCL gain = -0.4 (factor ten times the regular value)
MICH always on, PRCL triggered on POP22. MICH FM8 and PRCL FM1,2,6,9 triggered on.
Gives POPDC of about 20 counts, POP22 of about 12 counts, ASDC of about 500 counts.
Arms held at 3nm, MICH locked on ASDC/POPDC, PRM and SRM misaligned.
Arms held at 3nm, attempt at PRMI lock with MICH on ASDC/POPDC.
Failed. Tried mostly same MICH gains as arms+mich, and PRCL at 10* normal gain.
Arms held at 3nm, PRMI locked with REFL 33 I&Q, attempt at transition to MICH on ASDC/POPDC.
Failed. At first, I was putting in the TF line at ~375Hz, but we looked at the full transfer function between 100Hz and 1kHz, and there was a weird dip near 300Hz from PRCL-MICH loop coupling. Here we were seeing that the phase between REFL33Q and ASDC was ~90 degrees. What?
Tried putting the TF line at ~100 Hz (since MICH UGF is in the few tens of Hz anyway, so 100 is still above that), but still get weird relative phase. Here it seems to be about 45 degrees when I inject a single line, although it didn't seem like a weird phase when we did the full swept sine earlier. Maybe I was just not doing something right at that point??
Anyhow, no matter what values I tried to put into the input matrix (starting with REFL33I&Q, trying to get MICH to ASDC/POPDC), I kept losing lock. This included trying to ramp up the MICH offset simultaneously with the matrix changing, which was meant to help with the PRCL gain change. Q has since given us MICH and PRCL UGF servos.
In order to know where we should try to make the transition from REFL##Q to ASDC for MICH, I did a quick Optickle simulation to see what the error signals will look like.
The idea is to try to lock the PRMI on a single REFL diode (ex. REFL33 I&Q) with some MICH offset, and then transition over to ASDC. As soon as we have completed the transition, we can engage the normalization matrix to normalize ASDC by POPDC, and also increase the MICH offset if we want. Unfortunately, we do not as yet have the ability in our model to independently normalize different error signals, and then blend them, so we have to turn on the normalization after we've transitioned.
Here is the situation for PRMI-only:
You can see that REFL33Q has a slightly wider range than REFL165Q. It seems like we can perhaps try to make the transition around -15nm or so. Note that the error signals are not quite symmetric about 0nm, so we can use that to help determine what + and - mean. We expect that we need to add about 1nm offset to REFL33Q to get a true minimum in ASDC, so the sign of the digital offset that we need will tell us if there is a sign flip or not between the digital offset and this x-axis.
After we get this to work (hopefully in the next hour or so....), we will want to try the same thing with the arms held off resonance.
Usually we lock the PRMI at an offset of about 3nm:
However we could do it lower, perhaps around 1nm (which is where we currently are doing our CARM/DARM ALS->IR signals transitions):
At some point, we will arrive at 0nm CARM offset, when we'll want to transition back to RF signals (although probably we could jump straight to a 1f signal, not plotted):
The moral of the story here is that I'm not sure how we were ever successfully locking MICH on REFL165Q, unless my phase-setting in Optickle is way off. Certainly it looks like we should be sticking with REFL33 for PRFPMI. Also, since we have an offset in REFL33Q anyway (which we have seen and have commented on before), at 3nm CARM offset it looks like we could try to just do the jump without any extra digital offset. Here's a zoom of the 3nm situation:
For several MICH offsets, I measured the response of REFL33Q, ASDC and the ratio ASDC/POPDC to a MICH EXC. It appears that there is no frequency-dependent effect. The plots for MICH_OFFSET = 0.0 and 2.0 are slightly lower in magnitude: the reason is they were the first measurements done, and after that a little realignment of BS was necessary, so probably that is the reason.
[Jenne, Diego, EricQ]
Hopefully there will be more later, but Chiara just went down (network? other? Q is in there right now looking at it), so this is a so-far-tonight elog.
We have successfully transitioned MICH over from REFL33Q to ASDC in both the PRMI and PRFPMI configurations. Next up is to start reducing the CARM offset.
Resetting the REFL demod phases
I have been unable to lock the PRMI for more than teeny blips since Thursday. So, tonight I finally got it to lock with MICH on AS55Q and PRCL on REFL33I, and used that to set the demod phases.
Setting the demod phases, I used an oscillation of 100 cts to PRM, at 400.123 Hz.
REFL 33 demod phase started at 148deg, now 133.2deg.
REFL165 phase started at -105.53, now -172.
No signal in REFL55???? Time series and spectra both look just like noise. Need to check alignment of beam on PD, or if cables unplugged!!
REFL11 phase started at 16.75, now 18.9deg.
Was then able to lock on REFL 33 I&Q, like normal.
Transitioning PRMI from REFL33Q to ASDC
With the PRMI locked on REFL33 I&Q, I found that a MICH offset of -5 counts gives a minimum in ASDC. From my earlier elog this evening (http://nodus.ligo.caltech.edu:8080/40m/10887), I expect the minimum to be at +1.4nm. This is only one point though, so I don't know the calibration of the MICH offset yet (we should get this calib during the day by looking at MICH-only). Anyhow, this informed which side was positive and negative relative to my Optickle plots, so I know that I wanted positive offset in the MICH servo.
I was able to comfortably hold lock at +20 counts. Looking at a calibration line at 143.125 Hz, I determined that I wanted the matrix element for ASDC to be -0.05. After I made that transition using ezcastep, I put the POPDC normalization in. At the time, POPDC was about 151counts, so I put 1/151 in the POPDC->Mich matrix element.
So, here were the final lock parameters. Note that in PRMI-only, you can acquire lock like this, and with a variety of MICH offsets:
Locking PRMI part of PRFPMI
Since the PRMI has been fussy, I'm including a brief note on the PRMI settings when the arms are held with ALS off by roughly 3nm. To get to this point, we just ran the usual carm_cm_up script, and didn't let it run anymore when it asked for confirmation that PRMI was locked.
With MICH offset of -30 counts, AS port is pretty bright. ASDC dark offset is set to -475.4 by the LSCoffsets script. with MICH offset = 0, ASDC_OUT is around 300counts. But, with MICH offset = -30, ASDC_OUT is about 525 counts. So, I put that 525 counts into the ASDC filterbank offset (so it is now the dark offset + this extra offset), so the ASDC offset is currently around -1,000. This makes the ASDC signal roughly zero when I am ready to transition MICH over to it. In principle I should probably set it so the average is the same as the MICH offset, but the noise is so high relative to that offset, that it doesn't matter.
After this, we engaged the CARM and DARM UGF servos. MICH was gain peaking, so I think we might want to turn that one on too, rather than my by-hand turning down the gain.
The transition has been successful 4 or 5 times with the arms held off resonance at 3nm. Once, we reduced the CARM offset as low as 1.7 (and had to lower the MICH gain to 1.5), but we were still hearing a woomp-woomp sound. Not sure what that was from. At this point, Chiara died, so we lost lock. After that, we re-acquired lock a few more times, but MC keeps losing it. We are still able to make the MICH to ASDC transition though, which is good.
The transition won't work if the PRCL UGF servo is not on. The gain multiplier goes from about 1.1 up to 2.4, so the PRCL gain is certainly changing through the transition.
Diego has written up scripts for the individual UGF servos (look for an elog from him separately), so now the carm_cm_up script goes as far as locking the PRMI on REFL33 I&Q, and then it starts to transition. PRCL UGF is engaged, MICH offset is set to -30 counts, MICH is transitioned to ASDC, POP normalization engaged, CARM UGF servo turned on, and DARM UGF servo turned on. There are "read"s in the script before each step, so you can stop whenever you like.
Here's the final configuration for the PRFPMI while the arms are held at 3nm, with MICH on ASDC (so after the transition):
The transition for MICH to ASDC has been successful with the arms held off resonance several times tonight. It's all part of the carm_cm_up script now. I think that if we hadn't lost about an hour of time and our momentum, we would have gotten farther. I have high hopes for tomorrow night!
These are the parameters of the UGF servos we used last night:
Some tweaking of such parameters and the commissioning of the MICH servo will be done soon; an elog post about the UGF scripts/medm screens also will be done soon.
We tried locking with the variable finesse MICH offset technique again today.
A daytime task tomorrow will be to figure out where we are in MICH and CARM offset spaces. This will require some thinking, and perhaps some modelling.
We were using the UGF servos and checking out their step resonses, and had the realization that we don't want the gain multiplication to happen before the offsets are applied, in the case of MICH and CARM. Otherwise, as the UGF servo adjusts the gain, the offset is changed. I think this is what ChrisW and I saw earlier on in the evening, when it seemed like the CARM offset spontaneously zoomed toward zero even though I didn't think I was touching any buttons or parameters. Anyhow, we no longer used the MICH and CARM UGF servos for the rest of the night. We need to think about where we want the offset to happen, and where we want the UGF servo multiplication to happen (maybe at the control point, with a very low bandwidth?) such that this is not an issue.
Also, I'm no longer sure that the sqrt(I^2 + Q^2) instead of the usual demodulation is going to work for the UGF servos (Q made this change the other day, after we had talked about it). When the numbers going into the I and Q servo banks are small (around 1e-5), the total UGF servo gets the answer wrong by a factor of 10 or so. If I made the "sin gain" and "cos gain" 1000 instead of the usual 1, the numbers were of the order 1e-2, and the servo worked like normal. So, I think we were perhaps running into some kind of numerical error somehow. We first noticed this when we lowered the DARM excitation by a factor of 10, and the servo no longer functioned. We should take out this non-linear math and go back to linear math tomorrow.
During the evening tomorrow, we should try locking the PRMI with a large MICH offset, and then leaving CARM and DARM on ALS, and seeing how far we can get. Is it possible to just jump over to RF signals, since we won't have to worry about the detuned cavity pole?
Tonight, the locking procedure was the same as usual, but stopping the carm_up script before it starts to lower the CARM offset at all. Only difference was that MICH triggered FMs were 2,3,7 rather than the usual 2,6,8.
So, assuming you have the IFO with CARM and DARM on ALS held at +3 CARM offset counts (which we think is about 3nm), and the PRMI is locked on REFL33I&Q with no offsets, here's what we did:
Something else to think about: Should we normalize our DC transmission signals by POPDC, so that the arm powers will change when we change the MICH offset (for a constant CARM offset)?
The best we got was holding for a few minutes at arm powers of 7.5, but since the MICH offset was large and the power recycling was low, this was perhaps pretty far. This is why we need some calibration action.
Also, earlier today I copied the CARM and DARM "slide" filter module screens so that we have the same thing for MICH. Now all 3 of these degrees of freedom have slider versions of the filter module screens, which are called from the ctrl_compact screen.
The UGF servos have been moved to the control point, are are once again totally linear!
The UGF servos were recommissioned today:
Our idea is that we need with some thinking about these servos and most of all try to figure out all this phase thing before we can start to trust the servos to be used for locking.
Life would be easier with the UGF servos working. As Diego already elogged, we aren't sure why the demod phases are changing, but that is certainly causing the I-signals to dip below zero, which the log function can't handle (there is a limiter before the log, so that the signal can't go below 1e-3). Anyhow, this is causing the UGF servos to freak out, so we have not been using them for tonight's locking.
Our goal tonight was to see if we could introduce a nice big MICH offset, and then lower the CARM offset while keeping the arms locked on ALS. We hope to see some kind of sign of a PDH signal in some RF PD.
In the end, the highest we got to was -460 MICH offset counts, which we think is about 29nm (if our rough calibration is accurate). The MICH half fringe should be 188nm. With this offset, we got down to 0.3 CARM offset counts while locked on ALS. We think that this is around 300pm, plus or minus a lot. Note that while yesterday I had a pretty easy time getting to -660 counts of MICH offset, tonight I struggled to get past -200. The only way we ended up getting farther was by lowering the CARM offset. Although, as I type this, I realized that last night's work already had a lower CARM offset, so maybe that's key to being able to increase the MICH offset.
We watched REFL11I and REFL11I/(TRX+TRY) on striptool, but we didn't see any evidence of a PDH signal. We lost lock when I tried to transition CARM over to REFLDC, but I wasn't careful about my offset-setting, so I am not convinced that REFLDC is hopeless.
So. Tonight, we didn't make any major locking progress (the MC started being fussy for about an hour, right after I ran the LSC offsets script, just before we started locking in earnest). However, we have some ideas from talking with Rana about directions to go:
* Can we transition CARM over to REFL11I, and then engage the AO path?
* Then, while the MICH offset is still large, can we transition DARM over to POX or POY, actuating on a single arm? If CARM is totally suppressed, this is DARM-y. If CARM doesn't have the AO path yet, this is halfsy-halfsy, but maybe we don't care.
* Then, can we lower the MICH offset and transition back to a REFLQ signal?
* Separately, it seemed like we kept losing PRC lock due to PRC motion. If the MICH offset is very large, are we sideband-limited at the POP port, such that we can use the POP DC QPD? Is it even worth it?
A single mirror (ITM) moving by lambda/2, in the MICH-only situation is the full range, from bright to dark fringe. So, half fringe should be lambda/4, or about 133nm. If we are thinking about pushing on the BS, there's an extra factor of sqrt(2), so I think the half fringe should be at 188nm of BS motion.
When we had MICH locked on ASDC/POPDC, we put in a line at 143.125Hz, at 20 counts to (0.5*BS-0.2625*PRM), so a total of 10 counts to the BS at 143Hz. Given the BS calibration in http://nodus.ligo.caltech.edu:8080/40m/8242, this is 10.1pm of actuation. We saw a line in the error signal of 0.1 counts, so we infer that the MICH error signal of ASDC/POPDC has a calibration of 94pm/count. This number was invariant over a few different MICH offsets, although the ones I measured at were all below about 100 counts of MICH offset, so maybe this number changes as we start to get farther from the MICH dark fringe.
IFO left flashing (all mirrors aligned except SRM) in case anyone wants fresh data for that.
Something that kind of drives me crazy with our current LSC model setup is that I can't make "finished" error signals before blending them. The blending happens before the normalization matrix, and there is no place to put an offset to help match a new error signal to the current offset. So. While I'm sure this is not going to be immediately popular, here's a cartoon of a proposed model change to the LSC.
The most important difference between this and the ramping matrix that is used at the sites is that you can put in offsets before the blend. Also useful is the fact that the normalization can happen before the blend. This proposal would make the LSC input matrix and the normalization matrix have twice as many rows, and add an extra "selector matrix" just before the triggering at the error point of the loops.
I've only drawn one degree of freedom in my cartoon, but assume that they all have the same capability (maybe we don't have to do XARM, YARM and MC this way). One row is currently being used for the error signal, while the other row is just used to prep a new singal. For a first transition (say, ALS to DC transmission), maybe the ALS signals are on row 1, and the DC trans is on row 2. Once the transition is complete, row 1 is available to prep for the next transition (such as AS55Q).
Thoughts? Is there a better way to achieve what I'm going for here?
Okay, it has taken me almost exactly 12 hours (with a dinner break), but I have implemented this change.
Everything was svn-ed before I did things, and then again afterward.
Here is the "before" screenshot of the LSC model:
And here is afterward:
If you look extra carefully, you will see that it matches my proposal from http://nodus.ligo.caltech.edu:8080/40m/10904 . I have made the change for DARM, MICH, PRCL, SRCL and CARM. I did not alter XARM, YARM or MC. Also, the CESAR stuff was taken out of the CARM area, since this is now a more generalized version of the same thing.
I have also checked and modified all of the scripts that I could think of, as well as all of the ifoconfig burt .req and .snap files that I could think of. I also ran the carm_cm_up.sh script once, and it seems to work fine. All of the transition scripts that are listed below (which are the only ones used currently in the sequence) now use the new error signal blending scheme.
Burts (listed are the .req files, but I also checked the .snap files, hand-editing the matrix element numbers where needed if I wasn't in the right config to do a save):
I also modified the screens for the input matrix and for the normalization matrix. I created a new screen for the final blending matrices (which are all 2x1's), and I also modified the LSC_OVERVIEW screen.
The input matrix and normalization matrix screens have colored bars that tell you whether a row is in use or not. If the background to the row is the blue of the whole screen, that row is not being used.
The LSC screen has new hand-modified Kissel Buttons. I wanted to show the total PD error signal that is being used, regardless of what row (A or B) it is on at that time. So, I have collapsed the rows so that DARM_A and DARM_B are overlapped, even though they are actually rows 1 and 2 of the matrix. The PD should only show up green on the LSC screen if that row is in use (so, if you are prepping a row, but aren't using it yet, you won't see those elements in the matrix). Anyhow, the point is that the LSC overview part of things shouldn't look any different than before.
Brain not working anymore now that it's ~4am, but I need to rethink and recheck to make sure that the PD whitening triggering is still okay and working. Or maybe we can remove it, and just include that in the scripts, as Rana has been suggesting for ages. Thoughts for tomorrow.
UGF Servos' commissioning still going on, updates of today:
Was the screen modified directly on LSC_OVERVIEW.adl?
Even if so, that's OK. I'll incorporate the change to the screen making script once I'm back.
Nope, I used the script.
Yesterday's changes were mostly to the generateLSCscreen/C1LSC_OVERVIEW_INPUT_MATRIX.adl sub-screen. The UGF servos were added earlier in the week to the LSC screen in the generateLSCscreen/C1LSC_OVERVIEW_SERVOS.adl sub-screen.
I found an error in the model of the UGF servos, I have now corrected it; for future reference, now the division between TEST2 and TEST1 is properly done with complex math: given
we have that TEST3:
TEST3 is the actual signal that is now phase rotated to select only the I signal while rejecting the Q one.
All the updates to the model, the screens and the script have been SVNed.
I have been playing with the IFO tonight. Mostly, I wanted to make sure that all of the scripts for the carm_cm_up sequence were working, and they seem to all be fine.
I also turned on all 4 UGF servos. My big ah-ha moment for the night is that the excitation is multiplied by the gain multiplier. This means that if the UGF servo is multiplying by a small number (less than 1), the excitation will get smaller, and could get small enough that it is lost in the noise. Now the error signal for the UGF servo is very noisy, and can dip to zero. Since we can't take the log of zero, there are limiters in the model, but they end up giving -80dB to the error point of the UGF servo. This makes it all freak out, and often lose lock, although sometimes you just get a weird step in the UGF servo output.
Anyhow, we need to be mindful of this, and offload the UGF servos regularly. I think the better thing to do though will be to divide the excitation amplitude by the gain multiplier. This will undo the fact that it is multiplied by that number, so that the number of counts that we put into the excitation amplitude box is what we expect.
LSC whitening triggering was not working, because of the implementation of the double-rows for the input matrix. I have modified the c-code that looks at the input matrix and triggers, and decides when to turn on the PD whitening, so that it now works.
The Xarm ALS has been a little funky today.
First, the green and the arm-axis would not stay co-aligned. I'm not sure which was moving (although neither ITMX nor ETMX seemed to be moving very much according to their oplevs and OSEMs). I went to the Xend table and jiggled the mounts for the steering optics, in case one was loose or something. None were. However, the transmission quit jumping around by a factor of 2 after that. The beatnote alignment on the PSL table was also bad, so I tweaked that alignment up for the Xarm. There were some not connected cables and fibers blocking the access to the X beatnote area, so those are up on top of the PSL table.
Anyhow, I haven't locked the individual arms, but I cannot hold the lock with CARM/DARM. The CARM output keeps hitting the threshold for the locking watchdog, which turns off the lock. Obviously I could just increase this threshold, but the right thing to do is figure out why the Xarm ALS is so noisy today, and why it wants to output such a large control signal to maintain the lock.
After some brainstorming with Jenne and Q, both the model and the medm screen have been modified: the entire block "Test1 - injection of the excitation - Test2" has been moved after the servo output. In this way we avoid completely the multiplication problem without having to perform divisions that could lead to division-by-zero problems. Because of how the logic is done now, one UnitDelay block had to be inserted before each one of Test1 and Test2.
Since the UGF Servo has been heavily modified lately, I'll post the current status of the model (as an attachment, as inpage images lose too much quality).
This problem with the CARM loop last night was the fault of a bug that I had put into the LSC model last week. When I gave the input matrix and normalization matrix double rows, I had put the goto tags for the CARM normalization matrix rows backwards. So, even though I thought I was not normalizing CARM, in fact I was normalizing by POPDC, which was near zero since the PRM was misaligned.
Anyhow, found, fixed, currently locking, and all seems well.
Tonight we worked on the acquisition sequence (including re-re-re-commissioning the UGF servos, hopefully for the last time...) for the PRFPMI with large MICH offsets.
The procedure is all in the carm_up script, as far as things work.
We had some locklosses, but they were mostly due to non-carefulness on my part during the transitions between error signals, or the UGF servos getting upset because the oscillator peaks had gotten lost in the noise. The one that I show here is our very last one of the night, where we are hitting the rails for the MICH signal, which is then causing the other loops to have to do weird things to try to compensate, and they lose lock.
Here also is a StripTool shot during that lock stretch. I was in the middle of increasing the MICH offset to 75% of the fringe. The yellow trace (called MICH_B_MON) is ASDC/POPDC normalized so that it always goes 0-1. I was pleased to see that perhaps REFL11I and AS55Q are turning over, although as Q will tell us in a more detailed elog tomorrow, having a large MICH offset does weird things and moves the DARM zero-point. So, maybe we aren't actually anywhere awesome yet.
After some MICH offset, the maximum arm power is always going to be about 50, so arm powers of 8 or 10 equates to 100 pm. We didn't get there tonight while on IR signals.
The locking sequence is now something like this:
After this, we tried a few times to lower the CARM offset, but kept losing lock, I think because the UGF servos went crazy. The final lock, shown above, we lost because the MICH output was hitting the rails.
The problem with the MICH servo right now is the low SNR of the POPDC being used to normalize ASDC. The control output is enormous, even if we have the 400Hz lowpass on. We need to rethink our MICH servo, starting with a lower UGF, so that we're not injecting all this sensing noise all over the place.
One of tonight's goals was to tweak the CARM filters, so that we could engage the lowpass filter, to avoid the detuned double cavity pole resonance disturbing the CARM loop.
I increased the Q of the zeros in the FM3 boost so that it eats fewer than the original 18 degrees of phase at 100 Hz. We kept losing lock though, so for each lock I backed off on the Q a little bit. In the end, the filter eats 9 degrees of phase at 100 Hz. I also moved the lowpass from 700 Hz to 1kHz, although that doesn't change the phase at 100 Hz very much.
We modified the carm_up script re: PRMI locking a little bit. The PRMI is not so enthusiastic about locking immediately at 25% MICH fringe, so I backed that off. It now acquires lock at a few percent, and then ramps up the offset. Also, the MICH FM6 bounce roll filter is now turned on after lock is acquired, effectively giving it an extra second or two of delay beyond the rest of the filters.
We were able several times to get to some MICH offset and turn on the lowpass filter, but starting to reduce the CARM offset makes us lose lock. I think the problem is that the UGF servo demod phase is changing as we are changing offsets, filters and error signals. We see that the I-phase is servoed successfully to 0dB, but that the Q-phase is starting to move around by 30 degrees or more. We either need to monitor this much more closely, and add the changing demod phases to the carm_up script, or we need to go back to the sum-of-squares situation that we had last week. Note that we saw failures with that method for a completely separate reason: we were getting too close to the limiters, which cause the UGF servos to glitch and the outputs jump by a significant amount. So, the issues that we were seeing last week when we had the sum-of-squares were a different thing, that we noticed and understood later.
Anyhow, nothing too exciting and glorious tonight, but progress has been made.
Also, from some Mist simulations that Q did, Diego made a sweet plot that is now posted in the control room, so we can translate arm power to CARM offset, at various MICH offsets.
We also took some CARM loop measurements with the new filters. We have a little more phase than we used to, which is nice. These traces don't have the lowpass engaged, since I was trying to see how far we could get without it. We lost lock right after the second measurement, but I think that was to do with the UGF servos.
A small change, but now the carm_up script supports both sides of the CARM offset. After the arms are locked with ALS it asks for a "+" or a "-", which indicates which sign of digital CARM offset will be added. In the past, we have been primarily using the "+" sign.
We did a series of small things that may have helped with the locking, although we didn't actually get anywhere closer in CARM offset.
The UGF Servo medm page has been updated to reflect the last changes, namely the return of the sum of squares and the disappearance of Test3.
Tonight we were able to transition DARM from DC transmission signals to AS55Q/(TRX+TRY). That's about as far as we've gotten though.
Here are the details:
The carm_cm_up script now should get all the way to this point by itself, although occasionally the PRMI part will lose lock (but not the arms), so you have to go back to the 3nm CARM offset and relock the central part. I have written a little "relockPRMI.sh" script that lives in ..../scripts/PRFPMI/ that will take care of this for you.
We were able to transition DARM to AS55Q a total of 3 or so times tonight. The first time was with the + MICH gain, and the rest of the times were with - MICH gain. The carm_up script now asks for a sign for the MICH gain just after asking for a CARM offset sign.
I think that we understand all of our locklosses from these states. Twice (including the time described above) the UGF lines got lost in the noise, and the UGF servos went crazy. Once the PRCL loop rang up, because a filter that wasn't supposed to be on was on. This was a terrible filter that I had made a long time ago, and was never supposed to be part of the locking sequence, but it was getting turned on by a restore script, and kept eating our phase. Anyhow, I have deleted this terrible boost filter so it won't happen again (it was called "boost test", which may give you an idea of how non-confident I was in its readiness for prime-time). The last time of the night I must not have been quite close enough in CARM offset, so we should probably check with a TF before making this last jump.
Diego wrote a nifty burt restoring script that will clear out all the elements of the input matrix and the normalization matrix for a row that you tell it (i.e. DARM_A will clear out all the elements in the first row of those 2 matrices). This is useful for the switches back and forth between the _A and _B signals, to make sure that everything is in order. So, I now run those clear scripts, then put in the elements that I want for the next step. For example, DARM initially locks with ALS using the A row. Then, DARM transitions to the B row for DC transmission. Then, I prepare the A row for AS55Q locking, and I don't want any elements accidentally left from the ALS signal. It lives in ..../scripts/LSC/InputMatrix/
Thoughts for tomorrow:
Daytime re-commission the Xarm ASS.
Nighttime try to get back to DARM on AS55Q and push farther forward.
Why AS55/(TRX + TRY) instead of just TRX? Isn't (TRX+TRY) controlled by CARM?
(question is secretly from Kiwamu)
Tonight, we transitioned CARM from ALS directly to REFL11 I at 25% Mich Offset.
We attempted the transition twice, the first time worked, but we lost lock ~5 seconds after full transition due to a sudden ~400Hz ringup (see attached lockloss plot). The second barfed halfway, I think because I forgot to remove the CARM B offset from the first time
The key to getting to zero CARM offset with CARM and DARM on ALS is ekeing out every bit of PRMI phase margin that you can. Neither MICH nor PRCL had their RG filters on and I tweaked the MICH LP to attenuate less and give back more phase (the HF still isn't the dominant RMS source.) PRCL had ~60 degrees phase margin at 100Hz UGF, MICH had ~50 deg at 47Hz UGF. The error signals were comparitively very noisy, but we only cared that they held on. Also important was approaching zero slooooooooowly, and having the CARM and DARM UGF servo excitations off, because they made everything go nuts. Diego stewarded the MICH and PRCL excitation amplitudes admirably.
Oddly, and worringly, the arm powers at zero CARM offset were only around 10-12. Our previous estimations already include the high Xarm loss, so I'm not sure what's going on with this. Maybe we need to measure our recycling gain?
I hooked up the SR785 by the LSC rack to the CM board after the first success. For the second trial, I also took TFs with respect to CM slow, but they looked nowhere near as clean as the normal REFL11 I channel; I didn't really check all the connections. I will be revisiting the whole AO situation soon.
In any case, I think we're getting close...
Tonight we continued following the plan of last night: perform the transition of CARM to REFL11_I while on MICH offset at -25%:
Nothing earth-shattering today.
A few things of note:
See first plot below for the PRCL->CARM coupling just before lockloss. The second plot is the corresponding lockloss, where the PRCL loop is starting to see that oscillation again, and it's just barely starting to get into CARM.
We just changed the input to the CM board from REFL11 to AS55.
Tonight we worked on the CM board and AO path:
The BLUE plot is at MC Gain = 0.10 and REFL1 Gain = 4dB; the GREEN plot is for MC Gain = 0.10 and REFL1 Gain = 3dB, which seemed a more stable configuration; after this last configuration, we increased the MC Gain to 0.15 and the AO Gain from 8dB to 9dB and took another measurement, the RED plot; this is as far as we got as of now. We also couldn't increase the REFL11 Gain because it made things unstable and more prone to unlock.
So, some little progress on the AO path procedure, but we are very low on our UGF and we have to find a way to increase our gains without breaking the lock and avoiding the gain peaking we have witnessed tonight.
I have removed REFLDC and the SR560 offsetter from the CM board IN2. Now, analog AS55 I lives there, for our single arm testing. (Analog I has more of the single arm Y PDH signal in it). REFL11 has been reconnected to IN1.
With ITMX super misaligned, Diego and I locked the Y-arm with the AO path on AS55, ultimately at 4kHz bandwidth, but with plenty of gain margin. We didn't allocate the gains too intelligently, and had the CM board input gain slider maxed out, but plenty of headroom in the digital and AO sliders, making it inconvenient to up the UGF even more, to engage the super boosts. However, since this is just a test case to make sure we still can AO lock, I'm not too worried about this.
Since LSC FMs and such had changed around, old recipies didn't neccesarily work 1:1. Diego is writing a script for the current recipe, and will post an elog with the steps.
Gains and signs are able to be tracked by loop TFs, the real sticking point is a stable crossover. We used the 1.6k:80 hardware filter in the CM board to give the AO Path a 1/f shape in the crossover region, and undid it digitally in the CM_SLOW input FM. However, we do use a 300:80 in the MC2 sus FM to make the digital loop like 1/f^2 around the crossover, once a little bit of AO has come in to pull up the digital loop's phase. We used the CARM filter bank to do this, so I think we should be able to use a similar technique to do it in the PRFPMI case, as long as the coupled cavity pole is around ~100Hz.
Attached are a few OLTFs from the progression.
[Diego, Jenne, Eric]
Tonight we kept on following our current strategy for locking the PRFPMI:
both of the last two locks, the most stable ones (one transition to usual REFL11 and one transition to "CM_SLOW" REFL11) were acquired actuating on MC2;
EDITs by JCD: At least one of the times that we lost PRMI lock (although kept CARM and DARM lock on ALS), was due to MICH hitting the rail, even after we increased the limiter to 15,000 counts.
Here is the transfer function between CARM ALS (CARM_IN1) and REFL11 coming through the CM board (CARM_B), just before we transitioned over. Coherence was taken simultaneously as usual, I just printed it to another sheet.
Here is the lockloss plot for the very last lockloss. This is the time that we were sitting on REFL11 coming through the CM_SLOW path. A DTT transfer function measurement was in progress (you can see the sine wave in the CARM input and output data), but I think we actually lost lock due to whatever this glitch was near the right side of the plots. This isn't something that I've seen in our lockloss plots before. I'm not sure if it's coming from REFL11, or the CM board, or something else. We know that the CM board gives glitches when we are changing gain settings, but that was not happening at this time.
Q: Here's the SR785 TF of CARM locked through CM board, but still only digital control; nothing exciting. Excitation amplitude was only 1mV, which explains the noisy profile.
At the lunch meeting, we were thinking about the exess high frequency content of the MICH control signal, which leads to railing against the FM output limiter and lock loss. I propsed that POPDC sensor/ADC noise was the culprit.
In short, I was wrong. Just now, I locked the PRMI with a MICH offset as we normally do, and then froze the POPDC output. The MICH spectrum did not change in any noticible way.
However, increasing the analog ASDC whitening gain showed a direct improvement of the error signal noise floor, and thus a reduction in the control signal spectrum. I.e. we have been suffereing from ASDC ADC noise.
We had previously set the ASDC whitening gain so that half fringe of the PRMI would be well within the ADC range, but since we're actually only ever going to 25%, I feel fine upping this gain. Interestingly, when increasing the whitening gain by 12dB, the control signal spectrum has fallen by more like 20 dB in the 400Hz-1kHz region, which is great.
The only potential hurdle I can think of is that when we start reducing the MICH offset at zero CARM offset, we may approach ADC saturation in ASDC before we can hand off to RF signals, in which case we would have to dynamically lower the whitening gain, which introduces offsets, which could get hairy. But, since MICH railing has been directly seen to lead to lock-loss, I'd rather solve that problem first.
c1lsc had 60 full-rate (16kS/s) channels to record. This yielded the LSC to FB connection to handle 4MB/s (mega-byte) data rate.
This was almost at the data rate limit of the CDS and we had frequent halt of the diagnostic systems (i.e. DTT and/or dataviewer)
Jenne and I reviewed DAQ channel list and decided to remove some channels. We also reviewed the recording rate of them
and reduced the rate of some channels. c1lsc model was rebuilt, re-installed, and restarted. FB was also restarted. These are running as they were.
The data rate is now reduyced to ~3MB nominal.
The following is the list of the channels removed from the DQ channels:
The following is the list of the channels with the new recording rate:
Tonight was a sad night... We continued to pursue our strategy, but with very poor results:
We kept struggling with the PRMI, although it was a little better than yesterday:
So, still no exciting news, but PRMI lock seems to be improving a little.
I'm leaving the PRC aligned and locked. Feel free to unlock it, or do whatever with the IFO.
I wrote the script with the recipe we used, using the Yarm and AS55 on the IN2 of the CM board; however, the steps where the offset should be reduced are not completely deterministic, as we saw that the initial offset (and, therefore, the following ones) could change because of different states we were in. In the script I tried to "servo" the offset using C1:LSC-POY11_I_MON as the reference, but in the comments I wrote the actual values we used during our best test; the main points of the recipe are:
I tried the procedure and it seems fine, as it did during the tries Q and I made; however, since it touches many things in many places, one should be careful about which state the IFO is into, before trying it.
The script is in scripts/CM/CM_Servo_OneArm_CARM_ON.py and in the SVN.
We wanted to make the PRMI lock more stable tonight, which would hopefully allow us to hold lock much longer. Some success, but nothing out-of-this-world.
We realized late last week that we haven't been using the whitening for the ASDC and POPDC signals, which are combined to make the MICH error signal. ASDC whitening is on, and seems great. POPDC whitening (even if turned on after lock is acquired) seems to make the PRMI lock more fussy. I need to look at this tomorrow, to see if we're saturating anything when the whitening is engaged for POPDC.
One of the annoying things about losing the PRMI lock (when CARM and DARM have kept ALS lock) is that the UGF servos wander off, so you can't just reacquire the lock. I have added triggering to the UGF servo input, so that if the cavity is unlocked (really, untriggered), the UGF servo input gets a zero, and so isn't integrating up to infinity. It might need a brief "wait" in there, since any flashes allow signal through, and those can add up over time if it takes a while for the PRMI to relock. UGF screens reflect this new change.
Unfortunately, we only had one good CARM offset reduction to powers of about 25, but then my QPD loop blew it. We spent the vast majority of the night dealing with headaches and annoyances.
Things that were a pain:
I found the PSL enclosure open (about a feet wide) on the north side this morning. I am assuming that whoever did the X beatnote alignment last night forgot to close the door to the enclosure before locking attempts
Here is a lock loss from around 11 PM tonight. Might be due to poor PRC signals.
This is with arm powers of ~6-10. You can see that with such a large MICH offset, POP22 signal has gone done to zero. Perhaps this is why the optical gain for PRCL has also dropped by a factor of 30 .
This seems untenable . We must try this whole thing with less MICH offset so that we can have a reasonable PRCL signal.
Since we're having trouble keeping the PRC locked as we reduce the CARM offset, and we saw that the POP22 power is significantly lower in the 25% MICH offset case than without a MICH offset, Rana suggested having a look at the RF spectra of the REFL33 photodiode, to see what's going on.
The Agilent is hooked up to the RF monitor on the REFL33 demod board. The REFL33 PD has a notch at 11MHz and another at 55MHz, and a peak at 33MHz.
We took a set of spectra with MICH at 25% offset, and another set with MICH at 15% offset. Each of these sets has 4 traces, each at a different CARM offset. Out at high CARM offset, the arm power vs. CARM offset is pretty much independent of MICH offset, so the CARM offsets are roughly the same between the 2 MICH offset plots.
What we see is that for MICH offset of 25%, the REFL33 signal is getting smaller with smaller CARM offset!! This means, as Rana mentioned earlier this evening, that there's no way we can hold the PRC locked if we reduce the CARM offset any more.
However, for the MICH offset 15% case, the REFL 33 signal is getting bigger, which indicates that we should be able to hold the PRC. We are still losing PRC lock, but perhaps it's back to mundane things like actuator saturation, etc.
The moral of the story is that the 3f locking seems to not be as good with large MICH offsets. We need a quick Mist simulation to reproduce the plots below, to make sure this all jives with what we expect from simulation.
For the plots, the blue trace has the true frequency, and each successive trace is offset in frequency by a factor of 1MHz from the last, just so that it's easier to see the individual peak heights.
Here is the plot with MICH at 25% offset:
And here is the plot with MICH at 15% offset:
Note that the analyzer was in "spectrum" mode, so the peak heights are the true rms values. These spectra are from the monitor point, which is 1/10th the value that is actually used. So, these peak heights (mVrms level) times 10 is what we're sending into the mixer. These are pretty reasonable levels, and it's likely that we aren't saturating things in the PD head with these levels.
The peaks at 100MHz, 130MHz and 170MHz that do not change height with CARM offset or MICH offset, we assume are some electronics noise, and not a true optical signal.
Also, a note to Q, the new netgpib scripts didn't write data in a format that was back-compatible with the old netgpib stuff, so Rana reverted a bunch of things in that directory back to the most recent version that was working with his plotting scripts. sorry.
As the measurements have been done under feedback control, the lower RF peak height does not necessary mean
the lower optical gain although it may be the case this time.
These non-33MHz signals are embarassingly high!
We also need to check how these non-primary RF signals may cause spourious contributions in the error signals,
including the other PDs.
While meditating over what to do about the fact that we can't seem to hold PRMI lock while reducing the CARM offset, we have started to nucleate a different idea for locking.
We aren't sure if perhaps there is some obvious flaw (other than it may be tricky to implement) that we're not thinking about, so we invite comments. I'll make a cartoon and post it tomorrow, but the idea goes like this.....
Can we use ALS to hold both CARM and DARM by actuating on the ETMs, and sit at (nominally) zero offset for all degrees of freedom? PRMI would need to be stably held with 3f signals throughout this process.
1) Once we're close to zero offset, we should see some PDH signal in REFL11. With appropriate triggering (REFLDC goes low, and REFL11I crosses zero), catch the zero crossing of REFL11I, and feed it back to MC2. We may want to use REFL11 normalized by the sum of the arm transmissions to some power (1, 0.5, or somewhere in between may maximize the linear range even more, according to Kiwamu). The idea (very similar to the philosophy of CESAR) is that we're using ALS to start the stabilization, so that we can catch the REFL11 zero crossing.
2) Now, the problem with doing the above is that actuating on the mode cleaner length will change the laser frequency. But, we know how much we are actuating, so we can feed forward the control signal from the REFL11 carm loop to the ALS carm loop. The goal is to change the laser frequency to lock it to the arms, without affecting the ALS lock. This is the part where we assume we might be sleepy, and missing out on some obvious reason why this won't work.
3) Once we have CARM doubly locked (ALS pushing on ETMs, REFL11 pushing on MC/laser frequency), we can turn off the ALS system. Once we have the linear REFL11 error signal, we know that we have enough digital gain and bandwidth to hold CARM locked, and we should be able to eek out a slightly higher UGF since there won't be as many digital hops for the error signal to transverse.
4) The next step is to turn on the high bandwidth common mode servo. If ALS is still on at this point, it will get drowned out by the high gain CM servo, so it will be effectively off.
5) Somewhere in here we need to transition DARM to AS55Q. Probably that can happen after we've turned on the digital REFL11 path, but it can also probably wait until after the CM board is on.
The potential show-stoppers:
Are we double counting frequency cancellation or something somewhere? Is it actually possible to change the laser frequency without affecting the ALS system?
Can we hold PRMI lock on 3f even at zero CARM offset? Anecdotally from a few trials in the last hour or so, it seems like coming in from negative carm offset is more successful - we get to slightly higher arm powers before the PRMI loses lock. We should check if we think this will work in principle and we're just saturating something somewhere, or if 3f can't hold us to zero carm offset no matter what.
A note on technique: We should be able to get the transfer function between MC2 actuation and ALS frequency by either a direct measurement, or Wiener filtering. We need this in order to get the frequency subtraction to work in the correct units.