I think we've seen this in simulations, but it's a little disheartening to see in real life.  AS55Q looks like it flattens out pretty significantly right around the DARM=0 point. 

Right now I have the arms held on ALS (CARM=-1*MC2, DARM=2*ETMY, as Q used last night), and the PRFPMI is on REFL165I&Q.  I have set CARM to be as close to zero offset as I can (so I get all the usual buzzing), and then I'm sweeping the DARM offset between +3 and -3 counts (roughly +/-3nm) with a 3 second ramp and looking at normalized AS55Q.  The channel called "DARM_B_ERR" is 0.006*AS55Q/(TRX + TRY).  The arm transmissions, as well as the ASDC are plotted as well - ASDC is scaled to fit on the same axes as the transmissions.

Anyhow, here's the time series of the DARM sweeps.  AS55 demod phase of -55 degrees seems to give the cleanest signal (within 5deg steps); this is the same phase that we've been using all week.

DARM_TimeSeries_5March2015.pdf

This has been done before:

http://nodus.ligo.caltech.edu:8080/40m/6938

Arm length measurements and g-factor estimates in 2012, but only with an accuracy of ~30 cm. However, Yuta was able to get many FSRs somehow.

[Jenne, Ranah]

We played around tonight with different possible ways of transitioning DARM to normalized AS55Q.  Before each try, we would use ezcaservo (or just eyeball it) to make sure that the normalized RF signals had a mean of zero, so that we knew we were pretty close to zero offset in both CARM and DARM.

We tried something that is similar in flavor to Kiwamu's self-locking technique - we summed in some normalized AS55Q to the DARM error point (using the DoF selector matrix that I created a few weeks ago), and then tried to engage a little low frequency boost.  We tried several times, but we never successfully made the transition.

In the end, we just did a direct transition over to normalized AS55Q, and lost lock after several seconds.  The buzzing that we hear didn't change noticeably after the transition, which indicates that most of the noise is due to CARM (which makes since, since it has a much smaller linewidth).  The problem with holding DARM is that occassionally we will have a CARM fluctuation that lets the arm power dip too low, and DARM's error signal isn't valid at low arm powers. So, we need to work on getting CARM stabilized before we will have a hope of holding on to DARM. 

Here's the lockloss plot from that last lock:

Also this evening, I scanned back and forth over the CARM zero crossing while locked on ALS, to see what the RF error signals looked like.  Normalized REFL55 seems to have much more high frequency noise near the edges of the linear range than does REFL11.  Also, the REFL 11 signal is much larger.  So, what I think I want to try to do is use ALS fool to lower the CARM noise by a bit, then make the DARM transition.  Then, we can come back to CARM and ramp up the gain. 

With these CARM sweeps, I think that I know the relative gain and sign between ALScomm and the normalized REFL signals, and the REFL signals versus the normalized versions.  I think that 100*REFL11I/(TRX+TRY) gives the same slope at the zero crossing as just plain REFL11I.  Same factor of 100 is true for REFL55I.  The REFL11 slope is 20,000 times larger than the ALS slope, while the REFL55 slope is -500 times the ALS slope (note that REFL55 has a minus sign).  We can probably trigger the Fool on when the arm powers are above 50, and trigger off when they're below 20.  For the zero crossings, the REFL55 threshold should be about 20, and the REFL11 threshold should be about 500. 

I also need to re-think the triggering logic for ALSfool.  We probably don't want the zero crossing logic to be able to un-trigger the lock, just in case we get an extra noise blip.  So, we want to trigger on with an AND, but only trigger off if the arm powers go too low.  Also, the zero crossing logic should look at the normalized error signals, not the plain signals.

We need to modify the ALSwatch logic so that it doesn't look at EPICS values for the thresholding.  There may be an updated filter module that includes a saturation monitor, but otherwise we can use the saturation monitor part that is in the OSC section of CDS_PARTS.  We'll set the threshold on this to match the limiter in the filter bank.  Then, if the filterbank output is constantly hitting the limiter, we should run the down scripts.

This is work that I did yesterday but didn't have time to elog.  Since it seems non-trivial to give ourselves ramping matrices, but we only really needed the ramping in the DoF selector matrices, I've replaced the separate _A and _B parts with full filterbanks.  Recall from elog 10910 that I had given each degree of freedom's _A and _B input options an offset, an epics monitor and a test point.  Now those are removed, and handled inside of the filter banks.  The outputs of the filter banks sum together.

This required some screen modifications, but everything should work the same way that it did before this change.  I've also changed the DAQ channels from the _A_ERR and _B_ERRs that I had hand-created to now be the _A_OUT and _B_OUT test points from the filter banks (acquired at 2048Hz). 

I have not yet modified the burt snapshots for the ifo configure screen.  The arms will work the same as always, since they didn't have any selector matrix stuff ever, but the rest still need tweaking.

More work from yesterday. 

Rana and I had discussed on Thursday night that we probably want to be able to use the zero crossing of an error signal to trigger a servo on, but not to un-trigger it.  So, now the zero crossing trigger is latched, using the power trigger to reset the latch. 

Also, the input to the zero crossing trigger is the input to the MC servo, before the triggered switch.  This allows us to look at the normalized error signals rather than just the non-normalized ones, if that's what we're trying to lock on.  This signal is taken before the triggered switch, so that it's looking at whatever is coming out of the input matrix (including normalization).

So.  If the absolute value of the MC error signal goes below the threshold, it outputs a 1, no matter what the arm power is.  If the arm power is high, the power trigger also outputs a 1.  These are AND-ed together, so only if both are 1 do you actually trigger the MC filter bank.  If the zero crossing trigger has been set to 1, it will stay at 1 until the arm power goes low enough to untrigger the power trigger.  So, even if you have a little bit of noise on the error signal and it pops above the threshold momentarily, this won't cause the servo to un-trigger.

This is implemented using a "set-reset latch".  The output of the latch is the zero crossing trigger, which is AND-ed with the power trigger.  This final AND-ing, in addition to doing what we want, solves the ambiguity that is inherent in SR-latches for one combination of inputs. 

The trigger screen has been modified to reflect these model changes.

Here's a screenshot of the model, which includes some notes for anyone who opens the model since it's a bit confusing:

Last report on model change / screen work from yesterday.

The ALSwatch script has always been just looking at the EPICS output of the CARM and DARM filter banks, and if it saw a single saturation, it would run the down script.  This was non-ideal because (a) the EPICS channels aren't the real signals, and (b) sometimes we'll hit the rails briefly and that's okay - we want to shut things down only when we're constantly saturating.

It turns out that there was a pre-existing saturation monitor part in CDS_PARTS, which I have used.  There is one each looking at the output of the CARM and DARM filter banks.  The threshold for what saturation means is set as an epics input.  The part outputs a running count (number of saturations since the last time it was not saturated, resets each time it goes non-saturating) and a total number since the last reset (also an epics input). 

(To be continued... still writing)

[Jenne, with Matt and Fujimi as witnesses]

It might be about time to throw that champagne in the fridge.  Nice. Not quite close enough to talk about popping it open, but we'll want it chilled just in case... 

I still haven't logged yesterday's work, and I'm still working now, so no details, but I just handed both CARM and DARM over to non-normalized RF signals, and had the arms stable at powers of about 105.  I was workinig on the ETM alignment, and the power was increasing, so I think that's where the extra power will come from. I was lowering the DARM gain as I improved the alignment, because the optical gain was increasing so much.  I probably just didn't do that fast enough for the last aligning, which is why I lost lock.

Anyhow, here's a plot, because I'm excited:

Exciting! How long was it?

I have in my notebook that at 9:49pm CARM was no longer using ALS as an error signal, and at 9:50pm, DARM was no longer using ALS as an error signal.  It looks like I was locked for 3+ minutes after getting to RF-only signals.

The increase in power near the end of the lock stretch was me trying to improve the dark port contrast by touching the ETMX alignment.  DARM was definitely oscillating as I improved the dark port contrast, so I was trying to hand-lower the gain as I worked on the alignment.

This elog will be about work that happened yesterday.  I will write a reply to this with work from this evening's success.

[Rana, Jenne]

Work started with the plan of trying ALS fool, using the new triggering scheme (elog 11114).

The PRMI was having a bit of trouble holding lock with REFL165, so we checked its demod phase.  On Monday (elog 11095) we rotated the REFL165 phase from -91 deg to -48 deg while in PRFPMI configuration (I think the -91 was from PRMI-only phase setting).  However, Friday night we saw that MICH was super noisy, especially when the CARM and DARM offsets were near zero.  Rana rotated REFL165's phase until the MICH noise seemed to get lower (by at least an order of magnitude in the control signal), while we were at zero offset everywhere. We were not driving and looking at any lines/peaks, just the overall spectra.  The final REFL165 demod phase is -80. 

We tried engaging the fool path with no success. 

First, Rana moved the low frequency boost in the MC filter bank from 20:1 to 0.3:0.03.  This gave the whole loop at least 20 or 30 degrees of phase at all frequencies below the design UGF (a few hundred Hz?  Don't quite remember).  To check this, we put in a "plant" filter, and turned on the locking filter (3:3000^2) and the low freq boost and the plant, and the phase never touched 180 at any low freq.  This is so that we can ramp on this filter bank's gain without having an unstable unity gain crossing anywhere.  Also, I added two +10dB filters to the first two filter modules, so that we could ramp on the gain at the input rather than the output.

Last night we were actuating CARM on MC2 and DARM on the ETMs, and the MC filter bank was set to actuate on MC2.  Even with super duper low gain in the MC filter bank, so that the control signal was much less than one (1) count, it would make CARM unhappy.  The CARM filter bank's output was doing +/- a hundred or more counts, so why a few tenths of a count mattered, we couldn't figure out.  We were using the power trigger for the MC filter bank, but not the zero-crossing trigger.  Since the fool tuning was checked while actuating on the ETMs, we wonder if maybe the tuning isn't valid for MC2 actuation?  Maybe there's enough of a difference between them that the fool needs to be re-tuned for MC2 actuation?  Fool had the complex pair of poles at 1Hz, the "comp1" filter to give phase lag, and a gain of 22. 

I think that at some point we even turned off the fool path, but left the MC path on with a little bit of gain, and the audible noise over the speakers didn't seem to change in character at all. Weird. 

We ended up leaving the fool path for another time, and started working on error signal blending at the CARM filter bank input.  This is pretty similar to Kiwamu's self-locking principle.

Our goal was to ramp up the gain of the RF error signal at low frequency, while letting ALS keep hold of things at higher frequencies. 

CARM and DARM sweeps from earlier seemed to indicate that the RF signals are valid without normalization above transmitted powers of 50 or so, so we thought we'd give those a whirl for this error signal blending.

From doing a CARM sweep through resonance, we guessed roughly that the REFL11 (non-normalized) slope was about a factor of 10,000 larger than the ALS slope.  We put a 1e-4 into the input matrix element REFL11I -> CARM_B.  For some reason, REFL11 seemed to be centered around -250 counts, so we put an offset of +0.025 ( = 250*1e-4) into the CARM_B filter module to compensate for this. 

Since we thought that a gain of 1 in the CARM_B filter bank would make it equal to ALS, we tried some lower gains to start with.  0.3 kicked it out of lock, so we ended up liking and using 0.15.  With this low gain on, we tried turning on a low frequency boost, 20:1, but that didn't do very much.  We turned that off, and instead turned on an integrator, 20:0, which totally made things better.  The transmitted arm power was staying higher more of the time.

From a DARM sweep, we thought that AS55Q (non-normalized) should also have an input matrix element of 1e-4 for DARM.  We gave DARM_B a gain of 0.1, which seemed good and not too high.  Again, trying the gentle boost didn't do much, so we went with the integrator. 

At this point, since both RF signals were being used as error signals with integrators, we declared that at least at DC we were on RF signals.  Hooray!! 

After this, we started increasing the CARM_B gain a little, and decreasing the CARM_A gain.  When Rana finally set the CARM_A element to zero, we lost lock.  We realized that this is because we didn't include a zero to compensate for the arm cavity pole, which the IR signal will see, but the ALS won't. 

We decided that the plan of attack would be to get back to where we were (DC error signals on RF), and try to start engaging the AO path. 

As I (very excitedly) reported in elog 11116, I was able to follow the error signal blending procedure from last night, and get CARM and DARM onto digital non-normalized RF signals.  The lock held for about 3 minutes after this transition (elog 11118 has plot of this).

I was then able to script what I did (in the carm_up script), and repeat the transition. Q joined me in the control room, but we have not been able to complete the transition a third time.

Here's the sequence that worked the two times:

• Go to zero CARM and DARM offsets 
  • CARM is locked on ALS comm through the CARM_A filter bank (CARM_A gain = 1)
  • DARM is locked on ALS diff through the DARM_A filter bank (DARM_A gain = 1)
• Lower CARM servo gain to 5 (from 7)
• Lower DARM servo gain to 5 (from 7)
• Lower PRCL servo gain to -0.03 (from -0.04)
• Lower MICH servo gain to 2.5 (from 3.0)
• Set up _B error signals
  • CARM_B has 1e-4*REFL11I, no normalization
  • DARM_B has -1e-4*AS55Q, no normalization
• Give CARM_B a gain of 0.15
• Turn on CARM_B FM7 (integrator)
• Give DARM_B a gain of 0.1
• Turn on DARM_B FM7 (integrator)
• Slowly increase CARM_B gain, lowering CARM_A gain when gain peaking happens
  • CARM_B to 0.3, sleep 2
  • CARM_B to 0.5, sleep 2
  • CARM_A to 0.8, sleep 2
  • CARM_B to 0.6, sleep 2
  • CARM_A to 0.6, sleep 2
  • CARM_B to 0.7, sleep 2
  • CARM_A to 0.4, sleep 2
  • CARM_A to 0.2, sleep 2
  • CARM_B to 0.8, sleep 2
  • CARM_A to 0
• Slowly increase DARM_B gain, lowering DARM_A gain when gain peaking happens
  • DARM_B to 0.2, sleep 2
  • DARM_A to 0.8, sleep 2
  • DARM_B to 0.3, sleep 2
  • DARM_A to 0.6, sleep 2
  • DARM_B to 0.4, sleep 2
  • DARM_A to 0.4, sleep 2
  • DARM_B to 0.5, sleep 2
  • DARM_A to 0
• This is where I started working on the ETMX alignment to improve dark port contrast.  DARM kept having gain peaking, so I was lowering the DARM servo gain as I worked on the ETMX alignment.  I didn't make note of what the final gain was when I lost lock, but whatever it was, it wasn't right.

After those two attempts, we ran the LSC offset script, since that hadn't been done since early yesterday.  We did a quick CARM sweep, and REFL11 seemed to be centered around 0 counts, so we removed the 0.025 count offset from the CARM_B filter bank.

For later attempts, we keep seeing oscillations in the lockloss plots around 50 Hz, as if we're seeing gain peaking at the low side of the phase bubble.  We have tried turning off various filters at various levels of RF gain, but none of the combinations seems to be excellent.  Turning off the FM6 bounce/roll filter in CARM was particularly bad (immediately lost arm transmitted power), but others weren't good either (eg turning off FM3 boost lost arm powers within a second or so).  When we lose arm powers, the RF signals aren't valid, so if you don't turn them off fast enough (and ALS is still on with enough gain), you'll lose the full IFO lock.  If you're fast though, you can turn off the CARM and DARM _B outputs and not have to start from scratch. 

There seemed to be a very fine line to walk between not enough gain (~50Hz oscillations), and too much gain (200-300Hz oscillations).  It has been pretty frustrating later in the evening.  We seem to only have about 3dB of gain margin on the low side, when all the boosts are on.  Not excellent. 

When the RF signals had a moderate amount of gain, but ALS was still holding CARM and DARM, Q checked the phases of REFL11 and AS55 with excitation lines.  He rotated AS55 from -55 deg to -30 deg (+25 deg) and REFL11 from 144 deg to 164 deg (+20 deg).

Prior to the all-digital attempts, I tried several times to turn on the AO path, without success.  I think that the best that I got was 0dB on the CM board input 1 gain, +14dB on the CM board's AO gain, and -30dB on the MC board's AO gain before the mode cleaner lost lock. 

I was hoping that I could get CARM entirely to RF signals, and that would make things more stable and less complicated, and I could try again to turn on the AO path, but we haven't been able to do this tonight.

A few times in the later attempts we tried turning on the UGF servos for CARM or DARM.  I'm not sure if the lines kicked things out of lock, or if the UGF servos went a little crazy, or what, but we never survived for more than a few seconds after turning on the excitations.

There is a problem with the optical lever servos.  I had thought I'd been seeing it ever since Q re-did the models, and now I'm pretty sure that's what's up.  Q is hot on the trail of figuring out what may have changed that shouldn't have.  We may want to revert to an old Foton file, and re-copy the old filters into the new filter banks just in case.  The watchdog damprestore scripts have been tweaked to clear the oplev filter bank histories before turning on the oplevs, and this seems to solve the symptom of kicking the optic when oplevs are engaged. 

Although we haven't been able to make the transition to RF-only a third time, I think we're getting there.  Progress has certainly been made in the last 2 days!

According to the official rules, we only need 8 seconds to declare it "locked".

I wonder if the double cavity pole compensation filter for CARM was on for all the attempts yesterday? IF it looks like it will not saturate, it would be more stable to have the whitening on for REFL11 / AS55. Since on Friday, I set the REFL165 demod phase just by minimizing the MICH control signal with the arms on resonance, we ought to check out the PRMI degeneracy with the ETMs misaligned.

Speaking of signal mixing: Although we weren't able to get the carrier term cancelled in the 3*f1 signals by the relative mod phase method, I wonder if we can do it by mixing the 3*f1 and 3*f2 signals in the input matrix. Might help to keep the PRMI more stable, if that's an issue.

P.S. I have done some scripts directory / SVN cleanup. Adding some directories that were not in (like lockloss) and then removing stuff from the repo using 'svn rm --keep-local  filenames' for the image and data files.

Here is a longer stretch of data, from the first RF-only lock on Saturday night.  Unfortunately daqd had died about 400 seconds before the lockloss, so I can't show the RF signals coming on.  

ALS was on the _A channels for CARM and DARM, so when those go to zero (about -300 seconds for CARM, and about -200 seconds for DARM), we're using RF signals only for the error signals.

CARM noise definitely improves, but holy smokes does DARM start to look good!  Although, right at the end it starts to look like REFL11I is getting bigger.  Not sure why, but we'll have to watch out for this.

Here's the equivalent plot for the second lock stretch. This is the one that was handled by the carm_up script. It looks like I had about 150 seconds of RF-only lock here. 

DARM error is getting bigger with time jnear the end, even though I wasn't working on alignment here.  Zooming in, DARM is oscillating at 16.4 Hz, which is the bounce frequency.  I thought I had my bounce/roll filters on, but somehow it still got a little rung up.  It just rings up to a steady state though, it's not getting huge, so I don't know that it was the cause of the lockloss.

[Q, J]

Not much luck locking tonight; we made the RF transition to CARM numerous times, but it never lasted more than a minute or so. We were able to take a couple of loop and spectrum measurements as we transistioned. 

Here are some spectra showing the noise evolution of CARM_IN1 and DARM_IN1 as we start to transition CARM to RF. We did not manage to grab spectra while CARM was RF only; we can go back in the DQ to find some data. 

As we transition, our phase bubble is shrinking, which may explain our poor stability. On the following plot, I actually mistyped the legend. The cyan trace is ALL RF. I'm not sure why we have a 1/f^2 shape from 100->200Hz. 

[

We adjusted the pole compensation frequency by looking at REFL11/ALS during a CARM swept sine measurement, the -3db/-45degree point looked more like 80Hz. Strangely, the compensated REFL11 signal appears to lag the ALS signal around the UGF. Maybe this is a loop effect? 

In terms of practical improvements, I've written a script that reliably transitions from POX/POY IR lock to ALS CARM/DARM lock already on resonance. This is saving us a bunch of time. I've svn'd the new ALS script and the new carm_cm_up that uses it. 

We looked into the odd oplev behavior as well. We had earlier seen what looked like railed values on the FM output medm screen (which seemed unexpected for an AC coupled loop), but dataviewer showed it was actually ringing/railing at some 10+Hz as the oplev beam fell off the QPD. The ringing continues even after the quadrant values stop crossing zero, so I think it may be the filters themselves misbehaving. Why there is new behavior here is still beyond me. 

We lost a fair bit of time to a fussy mode cleaner tonight; there was a good 45 minute stretch where it refused to lock for more than a minute or so, the PC drive angriliy never falling below 5. The thing I changed when it started working was using the fast C1:IOO-MC_F channel instead of the slow C1:IOO-MC_FAST_MON as a readback for the FSS input offset; oddly there is a DC difference between the two. This has resulted in a FSS offset of ~4.2, whereas it was previously ~1.8. After this change, the PC drive fell to ~1.0 levels, and the IMC has been mostly ok. 

Given our problems stabilizing the RF lock, we attempted to give the FOOL path a shot, since we now had a better idea of the neccesary REFL11 gain. In short, no luck. Every attempt to use some RF signal just disturbed the lock further. We didn't really pursue it too much after a couple of attempts showed little promise. 

I have looked at the CARM and DARM RF loops, assuming the loop shapes that we've been using, and it pretty much looks like a miracle that we were ever able to make the transition.  The CARM and DARM loops are very marginal.

The ALS CARM loop was already pretty close to marginal, but we lose an extra 12 degrees of phase with the REFL loop:

• -4 deg because REFL has analog AA, but ALS does not.
• -6 deg because FM1 is designed to have minimal phase loss at 100Hz, but the REFL integrator is not.
• -2 deg because the cavity pole compensator must have a zero at finite frequency.

However, if our cavity pole compensator's zero frequency is too low, we get all of that phase back, at the sacrifice of 2dB of gain margin at both ends of the phase bubble.

I looked at an Optical simulation to check what the cavity pole frequencies are expected to be, with the losses that we've measured.  In both cases, I assume the Xarm has about 150ppm of loss.  The DARM cavity pole is about 4.5kHz no matter what the Yarm loss is.  The CARM cavity pole is about 172 Hz if the Yarm has 500ppm of loss, or 120 Hz if the Yarm has 200ppm of loss.

In the plots below, I use a CARM cavity pole frequency of 150 Hz, to roughly split the difference.

Edit, 13Mar2015, JCD:  Rana points out to me that I was using from Foton the analog design strings, without including the fact that these are actually digital filters. This means that I am missing some phase lag.  Eeek.

The ALS loop includes:

• Actuator
  • 3 16kHz computation cycles (includes computer hops)
  • Pendulum
  • Analog anti-imaging
  • Digital anti-imaging
  • 1 64kHz computation cycle
  • Violin filters: ETM 1st, 2nd, 3rd order notches
• Plant
  • Flat, not including the cavity pole at ~17kHz
• Sensor
  • Closed loop response of phase tracker
  • Digital anti-aliasing
  • 1 64kHz computation cycle
  • 1 16kHz computation cycle
• Servo (CARM filter bank)
  • FM1
  • FM2
  • FM3
  • FM5
  • FM6
  • 1 16kHz computation cycle

The REFL loop includes:

• Actuator
  • 3 16kHz computation cycles (includes computer hops)
  • Pendulum
  • Analog anti-imaging
  • Digital anti-imaging
  • 1 64kHz computation cycle
  • Violin filters: ETM 1st, 2nd, 3rd order notches
• Plant
  • 150 Hz cavity pole
• Sensor
  • Analog anti-aliasing
  • Digital anti-aliasing
  • 1 64kHz computation cycle
• Servo (CARM_B filter bank and CARM filter bank)
  • Cavity pole compensator
  • Integrator (20:0)
  • FM2
  • FM3
  • FM5
  • FM6
  • 1 16kHz computation cycle

The first plot is the case of perfectly matched cavity pole and compensating zero (150Hz, with compensator having 3kHz pole):

This next version is the case where the compensating zero is a little too low, which is the case I think we have now:

The last plot is a DARM loop.  Everything is the same, except that the RF plant has a 4.5kHz pole, and no compensation:

I made very rough calibration of the DARM spectra before and after the transition for the second lock on Mar 8.

The cavity pole (expected to be 4.3kHz) was not compensated. Also the servo bump was not compensated.

[Error calibration]

While the DARM/CARM were controlled with ALS, the calibration of them are provided by the ALS phase tracker calibration.
i.e 1 degree = 19.23kHz

This means that the calibration factor is

DARM [deg] * 19.23e3 [Hz/deg] / c [m Hz] * lambda [m] * L_arm [m]
= DARM* 19.23e3/299792458*1064e-9*38.5 = 2.6e-9 *DARM [m]

[Feedback calibration]

Then, the feedback signal was calibrated by the suspension response (f=1Hz, Q=5)
so that the error and feedback signals can match at 100Hz.

This gave me the DC factor of 5e-8.

The spectra at 1109832200 (ALS only, even not on the resonance) and 1109832500 (after DARM/CARM transitions) were taken.
Jenne said that the whitening filters for AS55Q was not on.

No wins tonight.

I've tried playing with the shapes of the loops a little bit (mostly CARM so far), to no avail.  I think I made it to CARM RF-only only one time tonight.  I was able to turn on the REFL11 whitening, although I lost lock while about halfway through the DARM transition. 

I tried making a double integrator instead of a single integrator for CARM_B, since that would allow me to make a complex zero pair which could help win back some phase. I also tried just straight copying FM1 from CARM into CARM_B, so that it could be turned off for the ALS part of the loop, but left on for the REFL part, but that didn't work very well.  Like Rana and I saw last Friday, we really need the REFL signal to have a true integrator, to force the PDH signal toward zero, before we can complete the transition.

I moved the cavity pole compensator's zero back up to 120 Hz, since that was what had worked on Saturday night.  That helped me get farther before running into gain peaking problems at ~50Hz.  This is because, as seen in my simulation earlier tonight, I win back some gain margin by having the pole compensator more closely matched with the pole frequency.

I've been turning off both FM1 and FM2 in CARM and DARM.  I think this is helping a lot, when I can get far enough to do so.  I don't want to turn off the second boost until after I'm about 50/50 on REFL.  (When  I have that much REFL, with the true integrator, the PDH signal sticks to zero).

I tried once turning off the bounce/roll filters for CARM and DARM, rather than the FM1 boost, since the bounce roll filters eat lots of phase, but I got pushed off resonance.  I think not having that focused boost may have made my overall RMS larger, which caused me to randomly jump too far outside of the good PDH range.

Early on in the evening, I turned off the MC2 violin filters in the ETM LSC-SUS filter banks, since I am actuating on only the ETMs tonight. However, I saw a violin mode ring up at ~642, which showed up in POX but not POY.  This was causing up-conversion, beating against the 40-50Hz buzzing from the IR resonance.   The MC2vio1,2 filter covers this frequency (because it's an absurdly wide notch), but the EXYvio1 filter does not.  There seems to be some confusion on the wiki as to what the ETMX violin mode frequency is - it says 631 (638??).  The notch that is in the EXYvio1 filter is for 631 Hz, but this is not correct.  DAYTIME self: Make the MC2 violin filter smaller than 40Hz(!) wide, and move the ETMX notch up to the correct frequency.  For tonight, I just turned back on the MC2 filter, and the mode has rung down.

Idea:  MICH offset, or ETM misalignment, enough to keep the power recycling low-ish, so that the CARM cavity pole doesn't come down too far in frequency?  Daytime brain should think about this.

Q doesn't like elogging, but he sent me this nice detailed email, so I'm copying it into the log:

I’ve locked the power recycled Y arm numerous times today, to try and find a usable AO recipe for the full locking.

Much more success tonight.  I only started my tally after I got the CARM transition to work entirely by script, and I have 6 tally marks, so I probably made the CARM to RF-only transition 7 or maybe 8 times tonight in total.  Unfortunately, I only successfully made the DARM transition to AS55 once.    From the wall striptool, counting the number of times the transmitted power went high, I had about 40 lock trials total. 

The one RF-only lock ended around 1:27am.

I think 2 things were most important in their contributions to tonight's success.  I modified the bounceRoll filters in the CARM and DARM filter banks to eat less phase.  Also, using Q's recipe as inspiration, I started engaging the AO path partway through the CARM transition which makes it much less delicate. 

Bounce roll filter

Koji and I added a ~29Hz resonant gain in the bounce roll filter several months ago, to squish some noise that we were seeing in the CARM and DARM ALS error signals.  This does a lot of the phase-eating.  I'm assuming / hoping that that peak won't be present in the CARM and DARM RF error signals.  But even if it is, we can deal with it later.  For now, that peak is not causing so much motion that I require it.  So, it's gone. 

This allowed me to move the complex zero pair from 30 Hz down to 26 Hz.  Overall I think this gained me about 10 degrees of phase at 100Hz, and moved the low end of the phase bubble down by about 10Hz. 

Prep for REFL 11 I through the CM board and CM_SLOW

In order to use Q's recipe (elog 11138), I wanted to be able to lock CARM on REFL11 using the CM_SLOW filter bank. 

I did a few sweeps through CARM resonance while holding on ALS, and determined that the REFL1 input to the CM board needed a gain of -20dB in order to match the slope of CM_SLOW_OUT to CARM_IN (ALS), leaving all of Q's other settings alone.  Q had been using a REFL1 gain of 0dB for the PRY earlier today.

I needed to flip the sign in the input matrix relative to what Q had (he was using +1 in the CM_SLOW -> CARM_B, I used -1 there).  To match this in the fast path, I flipped the polarity of the CM board (Q was using minus polarity, I am using positive).

The CM_SLOW filter bank had a gain of 0.000189733.  I assume that Q did this so that the input matrix element could be unity.  I left this number alone.  It is of the same order as the plain REFL11I->CARM input matrix element of 1e-4 from Saturday night, so it seemed fine.

During my sweeps through CARM resonance, I also saw that I needed an offset to make CM_SLOW's average about 0.  With the crazy gain number, I needed an offest of -475 in the CM_SLOW filter bank.  As I type this though, it occurs to me that I should have put this in the CM board, since the fast path will have an offset that isn't handled.  Ooops. 

Trying Q's recipe for engaging AO path

I am able to get the MC2 AO gain slider up to -10dB (-7 is also okay).  If I increase the digital CARM gain too much, I see gain peaking at about 800Hz, so something good is happening.  (That was with a CARM_B gain of 2.0 and CARM_A gain of 0.  Don't go to 2.0)

I tried once without engaging his 300:80 1/f^2 filter in the CM_SLOW filter banks to start stepping up the CM REFL1 and MC AO gains together, but I only made it 2 steps of 1dB each before I lost lock. 

I tried once or twice turning on that 300:80 filter that Q said over the phone really helped his PRY locking, but it causes loop oscillations in CARM.  Also, I forgot to turn it off for ~45 minutes, and it caused several locklosses.  Ooops.  Anyhow, this isn't the right filter for this situation.

AS55 whitening problem

Twice I tried turning on the AS55 whitening.  Once, I was only partly transitioned from ALSdiff to AS55, the other time was the one time I made the full transition.  It caused the lockloss from the only RF-only lock I had tonight :(

Unfortunately I don't have the time series before the whitening filters (not _DQ-ed), but you can see a giant jump in the _ERR signals when I turn on the whitening, just before the arm power dies:

AS55whitening_lockloss_12March2015.pdf

The AS55 phase is -30, I has an offset of 28.2 and Q has an offset of 6.4.  Both have a gain of 1.  This should give us enough info to back out what the _IN1 signals looked like before I turned on the whitening if that's useful.

Other random notes

Ramp times for CARM_A, CARM_B, DARM_A and DARM_B are all 5 seconds.  This is set in the carm_cm_up script.

carm_cm_up script freezes the arm ASS before it starts the IR->ALS transition, to make it more convenient to run the ASS each lockloss.

carm_cm_up script no longer has a bunch of stuff at the bottom that we're not using.  It's all archived in the svn, but the remnants from things like variable finesse aren't actively  useful.

carm_cm_down script turns off the CM_SLOW whitening (which gets set in the up script)

carm_cm_down script clears the history of the ETM oplevs, in case they went bad (from some near divide-by-zero action?), but the watchdog isn't tripped. This clears away all the high freq crap and lets them do their job.

FSS Slow has been larger than 0.55 all night, larger than 0.6 most of the night, and larger than 0.7 for the last bit of the night.  MC seems happy.

both carm_cm_up and carm_cm_down are checked into the svn.  The up script is rev 45336 and the down script is 45337.

Some offset (maybe the fact that the fast AO path had an un-compensated offset?) is pulling the arm powers down as I make the transitions:

Recipe overview

• Lock PRMI with arms held on ALS at 3nm CARM offset.  Bring CARM offset to 0.
• Turn on CARM_B and DARM_B a little bit, then turn on their integrators
• Lower the PRCL and MICH gains a little.
• Increase the CARM_B gain a bit, then turn off FM1 for both CARM and DARM.
• Increase CARM_B gain, lowering CARM_A gain.
• Increase DARM_B gain, lowering DARM_A gain.  Now the power should definitely be stable (usually ends up around 80).
• Partly engage AO path.
  • CM board REFL1 gain = -20dB
  • CM board AO gain = 0dB
  • MC2 board AO gain starts at -32dB, stepped up to -20dB
• Increase CARM_B gain a bit
• More AO path:  MC2 board AO gain steps from -20dB to -10dB
• Increase CARM_B gain to 1.5, turn CARM_A gain to zero
• CM_SLOW whitening on

After that, I by-hand made the DARM transition on the 6th successful scripted CARM transition, and tried to script what I did, although I was never able to complete the DARM transition again.  So, starting where the recipe left off above,

• Turn off DARM's FM2 boost to win some more phase margin.
• Increase DARM_B gain to 0.5, lower DARM_A gain to 0.

Since DARM doesn't have an analog fast path, it is stuck in the delicate filter situation.  I think that I should probably start using the UGF servo once the arm power is stable so that DARM stays in the middle of its phase bubble.

Rather than typing out the details of the recipe, I am attaching the up script.

Since the DARM_OUT signal is only 500 counts_peak, I don't see why AS55 whitening needs to be switched on. Maybe in a couple weeks after the lock is robust. In any case, its much better to do the switching BEFORE you're using AS55, not after.

[Jenne, Koji, Rana]

Thanks to turning off the AS55 analog whitening as well as the 1k:6k lead filter that Koji put into Darm's FM7, the DARM transition was more stable early in the evening.

The AS55 gain and offset did not change noticeably when we switched the AA on or off (switching happened while *not* using AS for any feedback).  Earlier in the evening, we did also check what happened with PRMI and REFL33 AA on vs. off, and REFL33 did have a many tens of counts offset on both the I and Q input channels.  I have turned the AA filters back on, but run LSCoffsets before trying to lock.

I'm not sure what was up, but somehow I couldn't lock the PRMI for about half an hour or so.  Very frustrating.  Eventually after futzing around, I was able to get it to lock with REFL33 in PRMI-only, and after that it worked again in PRFPMI with REFL165. 

With FSS slow around 0.5, MC has been a bit fussy the last hour.  Also frustrating.

Later on in the evening, I started taking out a bunch of the "sleep" commands from the up script, and many of the "press enter to continue" spots, but I think it might be moving too fast.  That, or I'm just not catching where I have too much gain.  Anyhow, near the middle/end of the CARM transition I am getting severe gain peaking at several hundred Hz.  I think I need to use a lower final gain.

So, progress on DARM, but maybe a little more fine-tuning of CARM needed.

Here's a DARM loop measurement, taken after both CARM and DARM were RF-only:

DARM_RF-only_13Mar2015.pdf

I have modified the DARM model from elog 11133, to include the fact that these are digital filters.

I have also extracted the data from elog 11143, and it together with the model.

The modeled loop has an arbitrary gain factor, to make it have the same 234Hz UGF as the measured data.

The modeled loop includes:

• Actuators
  • Pendulum (1Hz, Q of 4)
  • Violin filters
    • ETMs 1st, 2nd, 3rd order
    • MC2 1st, 2nd order
  • 3 16kHz delays for computation on the rfm model, transfer to the end sus models, and computation on end sus models.
  • Digital anti-imaging to get up to the IOP model
  • Delay of 64kHz for computation on IOP model
  • Analog anti-imaging
• Plant
  • Single 4.5kHz pole
• Sensor
  • Analog anti-aliasing
  • 64kHz delay for computation on IOP model
  • Digital anti-aliasing to get to LSC model rate
• Loop Shape (digital filters extracted from Foton file using FotonFilter.m)
  • DARM B's integrator (FM7)
  • DARM's low freq boost (FM3)
  • DARM's locking filter (FM5)
  • DARM's bounceRoll filter (FM6)
  • DARM's new lead filter (FM7)
  • Delay of 16kHz for computation on LSC model (includes Dolphin hop to c1sus rfm model)

There is a 1.5 degree phase discrepancy at 100Hz, and an 11 degree phase discrepancy at 900Hz, but other than that, the modeled and measured loops match pretty well.

For the measured frequencies, here are the residuals:

[Jenne, Den]

The problem with the ASS turned out to be a mode that was rung up at 1326Hz in ETMX.  It was rung up when the Xarm's overall gain was too high.  So, by turning down the digital gain we were able to prevent it ringing up, and then the ASS worked.  To circumvent this, we added a notch to the violin filter bank.  It turned out that, upon trying to check if this existed also for the Yarm by turning up the digital gain, the ETMY frequency was almost identical.  So, the same single notch is in both ETMs, and it covers the modes for both ETMs.

After that, we got back to locking.  We have made at least 9 transitions to all-RF (both CARM and DARM) tonight (I have lost track of how many Den has done while I've been writing this - maybe we're up to 10 or so.). We have changed the order of things a little bit, but they're mostly similar to last week.  There are some new notches in the CARM_B filter bank, as well as a 700Hz low pass.  We have not been using the lead filter in DARM from last week.  Script is checked in, and also zipped and attached.  At first CARM was actuating on ETMs, but the last half of the locks we've been using MC2.  The script is optimized for MC2 actuation.

While locked all RF, we phased REFL55 in preparation for transitioning PRMI over from REFL165. REFL55 phase was +125, now is +80, give or take 5 deg.  We have tried measuring the relative gain and sign between REFL55 and REFL165, but we keep losing lock, perhaps as a result of the TFs Den is taking.  He's being gentle though. 

Up next:

Transition PRMI

Measure CARM loop (why was SRmeasure not working?? is it plugged in??)

Turn on AO boosts, etc.

[J, Q]

Terse tonight, more verbose tomorrow. 

We have succesfully achieved multiple kHz bandwidth using the CARM AO path. The CM board super boosts are at too high of a frequency to use effectively, given the flattening of the AO TF. 

Jenne's totally, completely, and in all possible ways uncalibrated plot.  Calibration lines are in here (numbers in control room notebook).  I'm going to export and replot the data tomorrow, in real units.

CARM_DARM_AOengaged_23March2015.pdf

For increased flatness of the AO response, and thus less gain peaking in the CARM loop, I reccomend turning down the MC servo VCO gain to 22dB, -6dB of the current setting. 

From there, we should be able to up the overall CARM gain by another 10dB, and turn on a super boost. 

I measured the IN1/IN2 response of the IMC loop with the aglient analyzer providing the IN2 excitation, to see the transfer function of the AO acutation. The hump in the TF explains the flattening out of the CARM OLTF we saw last night. Turning down the gain by 6dB flattens this bump, and more importantly, has around 10dB less gain when the phase goes through -180, meaning more gain margin for the CARM loop. 

Oddly, when I back out the MC OLG from these measurements, the loop shape is different than what Koji and Rana measured in December (ELOG 10841). Specifically, there is some new flattening of the loop shape around 300-400kHz that lowers the frequency where the phase hits -180. What could have caused this???

The -6dB that I mentioned was determined by putting the MC UGF at about 100kHz, at the peak of the phase bubble. This should allow us to safely have a CARM UGF of 40kHz since the MC loop has around +10dB loop gain there, which Rana once quoted as a rule of thumb for these loops. At that UGF, at least one CM board super boost should be fine, based on the loop shapes measured last night. 

Lastly, I also checked out whether the 3 MC super boosts were limiting the AO shape; I did not observe any diffrence of the AO TF when turning off one super boost. It's likely totally fine. 

Jenne has more detailed notes about how things went down last night, but I figure I should write about how we got the AO path stably up. 

As the carm_cm_up script stood after Jenne and Den's work last week, the CARM loop looked like the gold trace in the loop shape plot I posted in the previous elog. The phase bubble was clearly enlarged by the AO path, but there was some bad crossover instability brewing at 400 Hz. This was evident as a large noise peak, and would lead to lock loss if we tried to increase the overall CARM gain.

As with our single arm CM board locking adventures, it was useful to have a filter that made the digital loop shape steeper around the crossover region, so that the 1/f AO+cavity pole shape played nice with the digital slope. As in the single arm trials, this effectively meant undoing the cavity pole compensating zero with a corresponding pole, letting the physical cavity pole do the steepening. This is only possible once the AO path has bestowed some phase upon you. A zero at a somewhat higher frequency (500Hz) gives the digital loop back some phase, which is neccesary to stay locked when the loop has only a few hundred Hz UGF, and the digital phase still matters. This gives us the purple trace. 

This provided us with a loop shape that could smoothly be ramped up in overall gain towards UGFs of multiple kHz (red trace). At this point we could reliably turn on the first boost, which will help in transitioning the PRMI to 1f signals (green trace). We didn't want to ramp it up too much, as we saw that the phase bubble likely ended not much higher than 100kHz, and the OLG magnitude was flattening pretty clearly around 40kHz. While we could turn on a super boost, it didn't look too nice, as we would have to stay at low phase margin to avoid bad gain peaking (blue trace).

As could be seen in the noise spectra that Jenne showed, you can see the violin notches in the CARM noise. This means we are injecting the digital loop noise all over the place. We attempted rolling off the digital loop (by undoing the zero at 500Hz), but found this made the gain at ~200Hz crash down, almost becoming unstable. We likely haven't positioned the crossover frequency in the ideal place for doing this. 

We didn't really give the interferometer any time to see how the long term stability was, since we wanted to poke around and measure as much as we could. While not every attempt would get us all the way there, the current carm_cm_up's success rate at achieving multi-kHz CARM bandwidth was pretty good (probably more than 50%) and the whole thing is still pretty snappy. 

[Jenne, Den]

Overall a "meh" night for locking I think.  The script to all-RF worked several times earlier in the evening, although it was delicate and failed at least 50% of the time.  Later in the evening, we couldn't get even ~10% of the lock attempts all the way to RF-only. 

Den looked into angular things tonight.  With the HEPA bench at the Xend on (which it was found to be), the ETMX oplevs were injecting almost a factor of 10 noise (around 10ish Hz?) into the cavity axis motion (as seen by the trans QPD) as compared to oplevs off.  Turning off the HEPA removed this noise injection.

Den retuned the QPD trans loops so that they only push on the ETMs, so that we can turn off the ETM oplevs, and leave the ITMs and their oplevs alone. 

We are worried again about REFL55.  There is much more light on REFL55 than there is on REFL11 (a 90/10 beam splitter divides the light between them), and we see this in the DC output of the PDs, but there seems to be very little actual signal in REFL55.  Den drove a line (in PRCL?) while we had the PRMI locked with the arms held off resonance, and REFL55 saw the line a factor of 1,000 less than REFL 11 or REFL165.  The analog whitening gain for REFL11 is +18dB, and for REFL55 is +21dB, so it's not that we have significantly less analog gain (that we think).  We need to look into this tomorrow.  As of now, we don't think there's much hope for transitioning PRMI to REFL55 without a health checkup. 

  I turned on the HEPA at the south end during the LSC. Sorry I ment to turn it off.

After discussions during the meeting today, I removed the PBS from the REFL path, which gives much more light to REFL11, REFL33 and REFL55.  Also, the ND1.5 in front of REFL165 was replaced with ND1.1, so that REFL165 now gets 50mW of light.  REFL11 gets about 1.3mW, REFL33 gets about 13mW and REFL55 gets about 12mW. 

No locking, and importantly no re-phasing of any PDs has been done yet. 

Here is an updated diagram of the REFL branching ratios.

[Koji Den EricG]

We inspected the {REFL, AS, POP}55 demodulators.

Short in short, we did the following changes:

- The REFL55 PD RF signal is connected to the POP55 demodulator now.
Thus, the POP55 signals should be used at the input matrix of the LSC screens for PRMI tests.

- The POP55 PD RF signal is connected to the REFL55 demodulator now.

- We jiggled the whitening gains and the whitening triggers. Whitening gains for the AS, REFL, POP PDs are set to be 9, 21, 30dB as before.
However, the signal gain may be changed. The optimal gains should be checked through the locking with the interferometer.

- Test 1

Inject 55.3MHz signal to the demodulators. Check the amplitude in the demodulated signal with DTT.
The peak height in the spectrum was calibrated to counts (i.e. it is not counts/rtHz)
We check the amplitude at the input of the input filters (e.g. C1:LSC-REFL55_I_IN1). The whitening gains are set to 0dB.
And the whitening filters were turned off.

REFL55
f_inj = 55.32961MHz -10dBm
REFL55I @999Hz  22.14 [cnt]
REFL55Q @999Hz  26.21 [cnt]

f_inj = 55.33051MHz -10dBm
REFL55I @ 99Hz  20.26 [cnt]  ~200mVpk at the analog I monitor
REFL55Q @ 99Hz  24.03 [cnt]

f_inj = 55.33060MHz -10dBm
REFL55I @8.5Hz  22.14 [cnt]
REFL55Q @8.5Hz  26.21 [cnt]

----
f_inj = 55.33051MHz -10dBm
AS55I   @ 99Hz 585.4 [cnt]
AS55Q   @ 99Hz 590.5 [cnt]   ~600mVpk at the analog Q monitor

f_inj = 55.33051MHz -10dBm
POP55I  @ 99Hz 613.9 [cnt]   ~600mVpk at the analog I monitor
POP55Q  @ 99Hz 602.2 [cnt]

We wondered why the REFL55 has such a small response. The other demodulators seems to have some daughter board. (Sigg amp?)
This maybe causing this difference.

-----

- Test 2

We injected 1kHz 1Vpk AF signal into whitening board. The peak height at 1kHz was measured.
The whitening filters/gains were set to be the same condition above.

f_inj = 1kHz 1Vpk
REFL55I 2403 cnt
REFL55Q 2374 cnt
AS55I   2374 cnt
AS55Q   2396 cnt
POP55I  2365 cnt
POP55Q  2350 cnt

So, they look identical. => The difference between REFL55 and others are in the demodulator.

[Koji, Den]

- Aligned the arms with ASS. It had alot of offset accumulated. We offloaded it to the suspension.

- We could lock the PRMIsb with the new setup.
PRCL: REFL165I (-14deg, analog +9dB)) -0.1, Locking FM4/5, Triggered FM 2
MICH: REFL165Q (-14deg, analog +9dB) -1.5, Locking FM4/5, Triggered FM2/6/9

- Demod phases at REFL were adjusted such that PRCL in Q signals were minimized :
REFL165 -80deg => -14deg
POP55 -63deg
REFL11 +164 => +7
REFL33 +136 => +133

Note: analog gains: REFL11: +18dB,  REFL33: +30dB, POP55: +12dB, REFL165: +9dB

- Try some transition between REFL signals to check the signal quality.
Measure TFs between the REFL signals

PRCL gain
REFL11I/REFL165I = +58
REFL33I/REFL165I = +8.5
POP55I /REFL165I = -246

MICH gain
REFL11Q/REFL165Q = +11
REFL33Q/REFL165Q = -1.5
POP55Q /REFL165Q = +280

- This resulted us to figure out the relationships of the numbers in the input matrix 

REFL55I/Q -4e-3/4e-3
REFL165I/Q 1.0/1.0 (reference)
REFL11I/Q  0.02/0.1
REFL33I/Q +0.12/-0.7

Full locking trial

Arm locked -> ALS -> Arm offset locked
PRMI locking
REFL165 phase tuned -110deg
PRCL gain -0.1 / MICH gain -2

We needed script editing.
Previous script saved in: /opt/rtcds/caltech/c1/scripts/PRFPMI/carm_cm_up_BACKUP.sh

Change:
- PRMI gain setting (input matrix & servo gain)
- CARM/DARM transition setting (see below)

The current CARM/DARM transition procedure:

== CARM TRANSITION (PART1) ==
- CM REFL1 gain is set to be -32
- CARM_B is engaged and the gain is ramped from 0 to +2.5
- Turn on FM7 (integrator)
- MC IN2 (AO path) engaged
- MC IN2 gain increased from -32 to -21

== DARM TRANSITION (PART1) ==
- DARM_B is engaged and the gain is ramped from 0 to +0.1
- Turn on FM7 (integrator)

== CARM TRANSITION (PART2) ==
- CM REFL1 Gain is increased from -32 to -18
- Ramp down CARM A gain to 0

== DARM TRANSITION (PART2) ==
- DARM_B gain is incrased to 0.37. At the same time DARM_A gain is reduced to 0

We succeeded to make the transition several times in the new setting.

- But later the transition got hard. We started to see big jump of the arm trans (TRX/Y 50->100) at the CARM transition.

- We tested the PRCL transition from 165MHz to 55MHz. 55MHz (i.e. POP55 which is REFL55PD) looks alot better now.

- ~1:30 The PMC was realigned. This  increased PMC_TRANS about 10%. This let the Y arm trans recover ~1.00 for the single arm locking

- Decided to end around 3:00AM

Some more words on yesterday's REFL path work. 

The 90/10 BS that splits the light between REFL11 and REFL55 was placed back in August 2013, to compensate for the fact that REFL11 has a much larger RF transimpedance than REFL33.  See elog 9043 for details.

We had been operating for a long time with an embarrasingly small amount of light on the REFL PDs.  REFL11 used to have 80 uW, REFL33 used to have 400 uW and REFL55 used to have 700 uW.  REFL 165 was the only sane one, with about 15 mW of light.

After yesterday's work, the situation is now:

As an aside, I was foiled for a while by S vs. P polarizations of light.  The light transmitted through the PBS was P-pol, so the optics directing the beams to REFL11, 33 and 55 were all P-pol.  At first I completely removed the PBS and the waveplate, but didn't think through the fact that now my light would all be S-pol.  P-pol beam splitters don't work for S-pol (the reflection ratios are different, and it's just a terrible idea), so in the end I used the PBS to set the half waveplate so that all of my light was P-pol, and then removed the PBS but left the waveplate.  This means that all of the old optics are fine for the beams going to the 3 gold-box REFL PDs.  We don't have many S-pol beamsplitter options, so it was easier to use the waveplate to rotate the polarization. 

Tonight I have modified transition steps from als to pdh signals. I have added 1:20 filters to CARM_A and DARM_A filter banks to make them unconditionally stable. These filters made locking more robust -- duty cycle is was ~70% tonight. I have also modified slow/ao crossover to avoid ringing up of lines above 1kHz.

Once AO is engaged with high bandwidth, REFL55 signal looks good and I transition PRCL from 165I to 55I. Optical gain compared to PRMI reduced from 55I/165I = -330 down to 55I/165I = 30 in full lock.

I worked on alignment of ETMs. Looking on the cameras I could improve arm power up to 160 and ifo visibility was 80%. POP22 fluctuated by ~50% and every few minutes we loose lock because POP22 almost touches zero.

Jenne and I interviewd Den this afternoon to make the things clear

- His "duty cycle" is not about the lengths of the lock stretch. He saids, the transition success probability is improved.

- For this improvement, the CARM transition procedure was modified to include turning on 1:20 (Z1P20) filter in CARM_A (i.e. ALS) once CARM_B (i.e. RF) dominates the loop in all frequency.

- I think this transition can be summarized like the attachment. At STEP4, the integration of the ALS is reduced. This actually does not change the stability of the servo as the servo stability is determined by the stability of the CARM_B loop. But this does further allow CARM_B to supress the noise. Or in other word, we can remove the noise coming from the CARM_A loop.

- The POP22 issue: Jenne has the trigger signal that is immune to this issue by adding some amount of POPDC for the trigger.
We can avoid the trigger issue by this technique. But if the issue is due to the true optical gain fluctuation, this may mean that the 11MHz optical gain is changing too much. This might be helped by PRC angular feedforward or RF 22MHz QPD at POP.

- Adjutsed the IMC WFS operating point. The IMC refl is 0.42-0.43.

- The arms are aligned with ASS

- The X arm green was aligned with ASX. PZT offsets slides were adjusted to offload the servo outputs.

- I tried the locking once and the transition was successfull. I even tried the 3f-1f transition but the lock was lost. I wasn't sure what was the real cause.

I need to go now. I leave the IFO at the state that it is waiting for the arms locked with IR for the full locking trial.

Tonight I measured seismic noise coupling to beam spot on PR2. There is coherence of 0.9 from X to PIT and Y to YAW around the stack resonances. TF was fited using vectfit and put into static matrix of oaf in the elements T240X -> PRM PIT, T240Y -> PRM YAW. I think we should actuate on the error point of the PRM OL but I decided not to go for a model change tonight. Data from seismometers and POP QPD was obtained during the UTC time 04:06:00 - 04:50:00 when PRMI was locked on sideband

Interferometer was locking rather robustly and every lock lasted on the everage of 3 minutes. During these lock periods I incresed bandwidth of optical lever servos of BS and test masses from 4Hz up to 10Hz and then closed transmission QPD loops. It seems from the camera that lock losses correspond to strong motion of the beam on pop camera. Scripts that change OPLEV bandwidth are in /users/den "increase_ol_bandwidth.sh" "decrease_ol_bandwidth.sh". Script "engage_qpd_servos" turns off ETM oplevs and turns on ETM -> trans QPD servos. These scripts can be copied to locking directrly if are useful.

Please, note that transition from 3f to 1f should still be tuned. Only PRCL was stably controlled using 1f so far

I had a handful of ~10 minute locks tonight. I intended to work on the 1f PRMI transition, but ended just familiarizing myself with the current scheme. 

Before touching anything, I committed the locking scripts to the svn. Unfortunately, the up script as I found it never worked for me tonight. I had to reintroduce the digitial crossover helper in CM_SLOW to get past the ramping up of the overall REFL11 gain. (With this is in place, there is some bad ringing around 200Hz for a time, but it goes away... or unlocks)

I did phase the PD formally known as REFL55 with an 800Hz PRM excitation while in full lock.42 to 102 degrees, ~30dB ratio between the I and Q peaks. However, come to think of it, how much does the CARM loop interfere with this?

The locklosses I had seemed to be due to a large fluctuation in all cavities' power. Maybe this will be helped by better PRC angular control, but we could maybe be helped by normalizing the digital part of the CARM loop by the arm transmissions once lock is acquired. 

Assuming the carrier mode in PRC is stable and the SB is the one moving, can we just use the POP DC QPD to control PRM?

Can we plot the arm power trend for multiple locks to see if it is associated with any thermal phenomenan in the IFO?
They should be able to fit with an exp + DC.

I'm currently more inclined to believe that the arm power trends have more to do with the arm alignments. Here's a 10 minute lock from last night, where the QPD servos were switched on about halfway through. I couldn't get Den's new servos to turn on without blowing the lock, so I reverted to my previous design, but still only actuated on the ETMs, with their oplevs still on. 

The most obvious feature is the reduction in power that seems to correspond to a ~10urad pitch deflection of ITMX when the lock begins. Is this optical spring action?

Also, it looks like the Y arm Yaw loop was badly tuned, and injecting noise. Ooops.

As of Den's QPD tuning, the QPD servos just actuate on the ETM. This next lock effectively had the QPD servos on the entire time, and we can see a similar drift in ITMX, and how ETMX then follows it to keep the QPD spot stationary. (Here, I'm plotting the QPD servo control signals, unlike above, so we can see X pitch servo output drift with the ITMX deflection)

Again, ITMX is moving in pitch by ~10urad when the interferometer starts resonating. If this is an optical spring, why does this just happen to ITMX? If it is digital shenanigans, how does it correlate with the lock, since there is nothing actuating on ITMX but oplevs and OSEM damping? Is light scattering into the ITMX OSEMs?

I got the PRMI transitioned from REFL165 over to REFL55 two times tonight.  Also, I had 2 long-ish locks, one 9 minutes, and one 6 minutes.  All the other locks were short - less than a minute or two.

I've done some shuffling around of the point in the CARM transition when the anti-boosts (1:20 filters) come on in the CARM A filter bank.  I've moved the turn-on of these filters a several gain steps earlier, but I'm not sure that they're in the best place yet.  Fiddling with the turn-on of the anti-boosts makes the big CARM oscillations last for longer or shorter - if they last too long, they blow the lock, so we don't want them to get too big.

The PRMI angular feedforward has helped a lot tonight, I think.  I've added a line to the up script to enable the output of the OAF after the PRMI is locked, and the down script turns it off again.  It's not so great when the PRM isn't aligned, since it's designed to work when the oplev is on, so it should be off unless the PRM is aligned.  I tried to get a comparison of off vs. on PRC powers with the arms resonating, but I can't hold the lock for long enough when the OAF is not on to get even one average on my 0.01Hz bandwidth spectrum. 

I've turned the arm ASC on a few times, but not every lock.  Around 12:34am, I set the offsets when CARM and DARM were on RF signals, and I had hand-aligned the ETMs to minimize the power at the AS port.  But, this wasn't a good spot for the next lock - the AS port was much darker with the ASC off for that lock.  It would be nice to think about trying some dither alignment, and then maybe resetting the setpoints every lock.  I'm using Q's original loop shapes, but as he left them yesterday, only actuating on the ETMs (with Yarm Yaw gain 0.7 rather than 0.9).

The CARM crossover might need more tuning.  There's some gain peaking around 400 Hz that goes mostly away if I turn the digital CARM gain down by 2dB.  (I'm not using any filters in the CM_SLOW filter bank).

I think that the CARM/DARM transition is more likely to be successful if the FSS slow DC is greater than 0.55ish.  So far this is pretty anecdotal, but I think I have more success when it's higher.  We should pay attention, and see if our trouble locking later in the nights correlates with smaller FSS slow DC values. 

I got the PRMI over to 1f two times, at 1:54am and at 2:25am.  I did not re-phase "POP"55 (which is the REFL55 signal), but I did check the values for the input matrix.  I needed MICH = 0.01*POP55Q and PRCL = 0.008*POP55I.  The first time I lost lock because I turned down the CARM digital gain too much.  The second time I forgot to turn down the PRCL gain (I was *actually* using 0.01*POP55I for the PRCL input matrix, but needed to lower the gain from -0.08 to -0.07, which is about the same as just using 0.008 in the input matrix).  Anyhow, I think PRCL loop oscillations were the cause of the second lockloss.

Here's a strip chart of my first lock of the night, which was the 9 minute lock.  Up until about -6 minutes, I was hand-aligning (including the dip around -7.5 minutes, where I was figuring out which direction to move the ETMs).  Around -3.5 minutes there is a significant dip down, that corrected itself.  By the time I realized that the power had gone down, and was trying to figure out why, it came back.  Maybe the same thing happened at the end of the lock, but it kept getting worse?  Self, re-look at this time (around 11:50pm) to find out why the power dips. 

My tummy feelings (without any data) make me think that this could be something with ITMX, like Q saw earlier today.  Or, maybe ETMX, like we've seen for ages.  Anyhow, my tummy feeling says this is an optic pointing problem.  I certainly think this might be the same thing we see at the end of many locks, the power going low suddenly.  So, it might give a big clue to our locklosses.  Maybe.

RXA: I've changed the above text into pink Comic Sans to lend it the appropriate level of gravitas, given its scientific justification.

I'd like to get a concrete list of measurements written down, so that it's clear what needs to be done before I graduate.

Noise couplings:

• Laser amplitude noise coupling to DARM
  • We don't have an AOM for ISS right now, but we should be able to just stick it back in the beam path, right?  I think Koji checked that the AOM was all okey-dokey recently.
  • AOM calibration should tell me how much the single-pass amplitude changes as a function of input signal.
• Laser frequency noise coupling to DARM
  • Inject signal at the CM board input, which should be calibrated by looking at response to calibrated MC2 motion.
• Marconi phase noise coupling to DARM
  • Marconi can produce internally or accept via BNC 0-10 rad of phase modulation.  Marconi spec sheet should give me rad/V for the input calibration.
• Marconi amplitude noise coupling to DARM
  • Using external input of Marconi.  Marconi spec sheet should give me input calibration.
• MICH err to DARM
  • Compare with Optickle model
• PRCL err to DARM
  • Compare with Optickle model

Noise cancellation:

• PRC angle
• MICH noise removed from DARM (compare flat gain FF vs. Wiener FF)
• PRCL noise removed from DARM (compare FF shape from model vs. Wiener FF)
• MC length noise (equiv. to laser freq noise) removed from CARM & DARM

Are there things that I'm missing?  I've never had an IFO to characterize before.

Something funky is happening with the green light locked to the X arm. The green transmitted power is drifiting around. Maybe something weird is happening with the doubler? The digital thermal feedback loop is not on. 

The green has been locked on a TM00 mode this whole time. The step in power is me closing the PSL green shutter, but I'm not doing anything during the smooth changes in power. IR power is steady, so the alignment should be ok. I can't recover full power with the end PZT alignement either. 

Have you tried a different set of laser temperatures?  I don't remember the value for the Xgreen, but whatever the value that matches PSL of 0.62ish and above seems to put the Xgreen laser at a bad temperature.  I think this is the mode-hopping region, and we sometimes lock to the wrong mode. 

So, FSS values of above 0.5ish are good, but they should be below 0.61ish. 

Yep, that is how I got back to stable powers. 

A paltry two locks tonight, but not entirely useless. I had some issues keeping the PRMI locked, which some additional boosts helped with. But, my feeling was that our crossover process is not tuned well. 

At full lock, both sub-loops have high gain around the crossover region, so the usual DTT loop transfer function measurement produces a meausrement of Gdigital/G_aopath (or minus that. I.e. I'm not currently 100% which is the bad phase in this plot, though it intuitive looks like 0 ). Thus, we can directly look at the crossover frequency and the effect of the different filters there. (I've also been working on an up-to-date CARM loop model today, so this will help inform that). 

Below, the black traces are the crossover at the end of the script when using the 120:500 "helper," and purple is without it. As we turn up the AO path gain, the trace "falls" from above, which explains why we can see instabilities around the violin filter. 

Having the helper on definitely made the probability of surviving the first overall CARM gain ramp higher, but it's not currently intuitively clear to me why that is the case. Afterwards, we can turn the helper off, to keep the shallower crossover shape. This is what I've put in to the up script for now. I also added a few seconds delay for when the script wants to switch DARM to RF only; I found it was maybe speeding too fast through this point.

DTT xml attached

Here's the comparison of last night's crossover measurement to my loop model. Not stellar, but not totally off base. All of the digital filters are read directly from the foton filter file, and translated from their SOS coefficients, so they should be accurate. I may have tallied together the wrong arrangement of FMs, though. I will recheck. 

Although I don't have a measurement to compare it with yet (as I don't know where the crossover was, the filter statesolder, etc. for the older loop measurements), here's what my current CARM loop model looks like, just for kicks. Here, only the first CM board boost is on. If we turn on some super boosting, we can probably ease up on some of the digital boosts, lower the crossover frequency, and put some lowpass that suppress the violin filters' effect on the crossover and reduces digital sensing noise injection. 

Lastly, I'll just note that my current MIST model predicts that the CARM cavity pole should be at ~170Hz, and a peak arm transmission of 180 times single arm power. I saw powers of ~120 last night. 

Whoops, I implemented the IOP downsampling filters wrong. Once I did that, it looked like just delay mismatch, so I added two more computation cycles for a total of four 16k cycles, which is maybe not so justified... Nevertheless, model and measurement now agree much better. Here are the corrected plots. 

I have 12 tick marks for times I got all the way to 1f for all 4 degrees of freedom in the PRFPMI.  The CARM / DARM transitions now succeed more than they fail, which is nice. 

At Q's suggestion, I am turning off all the violin filters in the MC2 path during the CARM transition.  This also means that I don't need any of the notches that Den and I put into the CARM_A and CARM_B filter banks last week, which were right at the edges of the violin notches.  Anyhow, this seems to make the transition much more likely to succeed.  I don't ever use the CM_SLOW FM10 "crossover helper" that Q had to use last night.  The violin filters are turned back on after the CARM transition is complete.  We don't ever need those other notches.

I checked the REFL165 vs. REFL55 transfer functions for PRCL and MICH, and they are mostly flat.  REFL55 seems like it'll give us extra phase for some reason.

I tried setting offsets for PRMI, but they seem to be strongly dependent on arm alignment.  I ended up being pretty confused, and since all the REFL signals are pretty close to zero (when CARM/DARM on RF, PRMI on 3f), I have given up on that avenue for tonight. 

I think many of my locklosses tonight (lost from the all 1f state) have been fast things, faster than the ADCs can handle.  On the lockloss plots that I've looked at, the FSS PC drive is railed at 10V about 200msec before I lose lock.  So, something (presumably in the fast CARM path) is making the MC/FSS loop unhappy.  I have plugged in the Agilent to the Out2 of the CM board, so that it looks at REFL11.  Unfortunately, this is after the input gain slider, so we don't see much until we're locked, but that seems fine.  A video camera is pointed at the screen, so that I get real time spectra.  It's hard to watch the TV at the same time as everything else, so I haven't witnessed the moment of lockloss in the fast spectrum yet.  Be careful when walking down the Yarm.  The tripod is partly in the walkway.

Q, I took a few TFs of the total CARM loop, although none of them are particularly good below a few kHz.  I can't push hard enough to get coherence, without blowing the lock.  TF data is in /users/jenne/PRFPMI/CM_TFs/CM_TFs_2Apr2015/ . 

I was worried for a while that, after I transition PRMI to 1f, I hear lots of low frequency rumbling.  However, watching the spectra (relative to references taken with CARM and DARM on RF, but PRMI on 3f), the low frequency error and control signals are staying the same for all 4 DoFs, but the high frequency for PRCL and MICH goes down significantly, so it's probably just that the low frequency stuff sounds more obvious, since it's not drowning in high frequency fuzz. 

It was only a mediocre locking night.  I was foiled for a long time by 2 things, both of which are now taken care of in the scripts, so I don't waste so much time again.

• Somehow FM4 (LP700) in the CARM_A filter bank was turned off.  It took me a long time to figure this one out. 
  • At first, I had a 2056Hz oscillation, and then if I notched that, I would have problems at the edges of my notch.
  • I turned on the LP1000 in CARM_B (which we don't usually use) to fight the 2k resonances, but then I had violin mode problems. 
  • I couldn't turn off the violin mode filters on MC2 for the transition, so the edges of these notches were causing instability.
  • Anyhow, in the end, I realized that FM4 of CARM_B wasn't on, but it usually is.
  • It is now turned on in the carm_cm_up.sh script.
• After that fiasco, I had trouble turning on the ASC loops.
  • Turns out we had left the offsets in place from last night in the ASC loops, so that when I zeroed the outputs of the transmission QPDs, the offsets in the ASC loops didn't make any sense, and they pushed the IFO severely out of alignment.
  • Now the ASC down script (which is run by the carm down script) zeros the filter bank offset values

Scripts are checked into the svn.

I used Q's handy-dandy 2D histogram plotter (..../scripts/general/dataHist, which I have taken the liberty of adding to the svn) to set the PRCL offset when I was locked on REFL165.  Here is a version of the plot, when I had an offset of +10 in the PRCL filter bank. There was so much noise on the PRCL input that I quit bothering to try and put in an excitation or ramp the offset value.  Note that I have since moved this offset to PRCL_A's offset instead, so taking this plot again should have PRCL_IN1 centered around zero.

I had trouble doing something similar for PRCL when I was locked on REFL55.  At first, the offset was so poor that POP110 was only about half the value it was when locked on REFL165, and it had a huge amount of RIN.  I tried just doing a z avg of the PRCL_B_IN1 (REFL55I) while locked on REFL165, and that said that REFL55I had an offset of +33.8 counts, so I tried an offset of -33.8 counts to get to zero.  But, that was still terrible for POP110 power.  As I increased the offset, eventually up to +30 counts, POP110 kept getting better and better.  I lost lock at that point (while trying to get 10 sec of histogram data), so I'm not sure that +30 is the final value.  I want to also get equivalent histograms with POP22 and POPDC (and maybe arm transmissions?) as the X-axis on these plots.  There's no excitation, so all of these can be collected at once.

By babysitting the ITM alignment (looking at the rough DC values of the optical lever error siganls), and doing a little adjustment of the ASC differential offset, I was able to keep lock a few times for more than 2 or 3 minutes while all 1f.  Not a whole lot longer than that though, even if I wasn't "poking" the interferometer other than maintaining alignment.

As the POP55 demod board is actually demodulating the REFL55 signal, I have connected its outputs to the REFL55 ADC inputs. Now, we can go back to using the REFL55 input matrix elements, and the data will be recorded. 

I have changed the relevant lines in the locking script to reflect this change.