EQ UPDATE: Measured it wrong the first time, fixed now.
I measured the spectra of the SQRTINV channels from dark QPDs, with offsets adjusted to imitate various transmission levels. (While the dark noise stays constant in terms of, say, TRX counts, 1/sqrt(TRX) isn't linear, and so the noise coupling depends on the TRX offset).
I did some calculations to turn this into the equivalent displacement noise when using SQRTINV as an error signal. This depends on where on the fringe you are locking, since the slope of SQRTINV vs. position is not constant, and can only really be treated as linear down to about 1/3 of a line width away from full resonance. In my calculations, I assumed a coupled arm line width of 38pm, and a full transmission of 700 counts in TRX/Y.
The QPD dark noise RMS when two line widths away (TR = 40) is about 5fm, and only goes down from there.
[Jenne, Koji, Manasa, EricQ]
Today we successfully locked the ALS using the LSC system, with filters that are good for both the IR PDH and the ALS locking. We tried PRFPMI, but were unable to hold PRMI lock while the arms were held with ALS. We combined the ALS signals into common and differential signals, and successfully transitioned over to a combined set of 1/sqrt(TRANS) signals for the common mode part of the lock (differential stayed with ALS).
Locking the ALS using filters in the LSC system that are also good for IR PDH
The biggest difference between the ALS and LSC filters were the ones used for lock aquisition. At Koji's suggestion, I made FM5 of the LSC servos (for X and Y arms) the filter needed for ALS locking. Then, I made FM4 into a combination of old LSC FM4 and FM5, as well as an inverse of the new FM5, so that when both FM4 and FM5 are engaged, the servo shape is the same as the old LSC. I left the other LSC filters where they were. I replaced the FM1 +6dB with the combined integrators (really, just gentle DC boosts) for the ALS, since we were never using this +6dB filter module. The LSC resonant gain filter for the bounce mode also included a resgain for 18.5 Hz. I don't know what that was for, and it was eating into phase that I needed, so I removed it.
The other filter that changed significantly was the Boost filter. The ALS system had been using more DC gain than the LSC had. However, the current ALS boost filter (in FM10 of the old ALS servos) was eating too much phase near my UGF. So, I scooted the whole boost filter to lower frequencies, to give myself some extra phase margin. The boost was set to "zero history", "zero crossing", with 0.01 tolerance and an 8 second timeout. Setting it to zero crossing with a low tolerance, rather than just ramping it on, was the key to engaging the boost.
I had to be so careful about phase margin, since I lost ~15 degrees of phase at 200 Hz from the lag of going through the RFM network. This was pretty frustrating, but I don't have a better plan yet, save moving the c1als model and ADC to the SUS machine, which has Dolphin access to the LSC. I may back off my safety margin, and give myself some gain in the boost back at 10Hz, since we are now seeing too much noise at 10Hz in the closed-loop spectra. I also "cheated" and lowered my UGF from the ~150Hz it used to be in the ALS model, to 100Hz, where I was closer to the top of the new phase bubble.
With the new filter situation, I was able to lock the Xarm (the one I was using for design work) with both IR and ALS. To lock IR, the "restore" script still works. For the ALS, we should put in a separate "restore" script into the IFO_CONFIGURE screen.
The ALS locking procedure is as follows:
* Prepare ALS and green locking. Green locked to 00 mode, alignment all nice, etc, etc. Beatnote within 100MHz on spectrum analyzer. If doing both arms, try to get beatnotes on opposite sides of PSL, to keep crossbeatnotes at higher frequencies, and out of the way.
* Turn on Watch script.
* Set LSC parameters (this is where a new restore script will come in handy):
* Zeros in RFPD columns of input matrix (i.e. POX and POY).
* Ones in AUX input matrix elements.
* Zeros in power normalization matrix rows for arms.
* All FM triggers for arms set to "Man" for manual.
* Override main trigger, so that signals are always going through to the servo.
* Only FM5 engaged in arm servo.
* Gain of servo set to zero, output on, then engage main LSC master switch. ETM output on.
* Clear history in phase tracker.
* Check sign of gain using + or - 0.1 in the servo. You'll know if you got it wrong (the ETM will be kicked, and the beatnote will fly around). If you didn't get it wrong, you probably got it right.
* Increase gain to about 12 (with correct sign).
* Engage FM1 (gentle DC boost), FM6,7,8 (resonant gains for stack, bounce, roll)
* Wait a few seconds for filters to settle, then engage FM9 (boost).
* Run find IR resonance script.
* Move off resonance by ~36 counts (12 times the +3 script). This number comes from trying to be completely off the IR resonance, even when the PRMI was locked.
* Do whatever locking (ex. PRMI) you set out to do.
After locking both arms with ALS using the LSC system, we attempted to lock the PRMI. We were able to lock PRMI on REFL55 I&Q, REFL33 I&Q, and REFL55 I&AS55Q before the arms were locked, so we were hoping that we wouldn't have too much trouble.
We found the IR resonance for both arms, then moved off resonance. Then, restored the PRM. For REFL55, Koji coarsely turned the REFL 55 demod phase from 16 degrees to 87, while we were locked on the carrier. After this, I stepped farther and farther from the IR resonance, since at first I found that our transmitted powers were something like 4, rather than almost zero, so the demod phase may not be totally correct.
We were having trouble, so we locked the PRMI on carrier using REFL55 I and AS55 Q, with 1's in both elements in the input matrix. MICH gain was about -10, PRCL +0.010. We used this time to tweak up the alignment of the PRMI. At some point, Koji tweaked the REFL33 demod phase from 124 to 134 degrees. Then we switched back to sideband locking. After some trials with REFL55 I&Q, and REFL55/AS55, we went to REFL33 I&Q. REFL33I->PRCL was 1.556 in the input matrix, and REFL33Q->MICH was -0.487. No other elements in the input matrix. MICH gain was reduced to -6, PRCL gain to -0.020. MICH FMs 3,6,9 triggered, PRCL FMs 2,3,6,8,9 triggered. We were able to keep short locks on the order of ~10 seconds, but not longer. We played with every parameter we could think of (alignment being good is one of the most important!), but were not able to keep better lock. The POP spot is moving around a lot, so the PRCL ASC needs to be examined, hopefully tomorrow.
We started losing the Xarm lock fairly regularly, I'm not sure why, but the Yarm was locked for almost 2 hours straight, held off resonance with ALS!
ALS Common and Differential, transition to IR control
We set PRMI aside for the rest of the night, and looked at using ALS to control the arms in common and differential modes.
Regular ALS locking procedures were used (see above), with the exception of the AUX input matrix:
Since the beatnotes were on opposite sides of the PSL frequency, the common and differential modes look opposite of what you'd expect.
We then used the regular find IR resonance scripts running simultaneously, which worked really well to find both arms' IR resonance points.
I put a 1 count offset in the Xarm servo (which was our proxy for common mode), although in retrospect this should have been +0.5 in ALSX, and -0.5 in ALSY, so that our signals going through the input matrix were at their zero crossings. Anyhow, this offset put us at about half fringe on both arms (transmissions were about 0.6).
Koji set the offsets in the 1/sqrt(trans) filter banks before the input matrix so that they would have zero crossings at this point (avg the IN1, put negative of that value into the offset).
We then stepped the input matrix values until our common mode (Xarm) row was:
We left the differential (YARM) row alone, so that the ALS system would still be controlling the differential degree of freedom. The values and sign for the 1/sqrt(trans) signals came from a transfer function of dividing the spectra of each error signal and noting the relative gain and sign.
After we swapped the error signals, we realized that we had to remove the offset from the XARM servo, which is why we should have put the offsets elsewhere in the first place.
Then, Koji took a spectrum, which is attached to this entry. We note that the ALS signals are strongly correlated, and mostly common.
To Do List
Going forward, we need to figure out what is going on with the PRMI, and why we're having trouble keeping lock.
We need to redo the PRCL ASC servo, with the anti-oplev trick that Rana mentioned a week or two ago.
We need to investigate the degeneracy of REFL165, now that Q's simulation doesn't justify / explain it.
We need to change several scripts for use with the new ALS-in-the-LSC paradigm:
* Watch arms (to turn off ALS if we lose the beatnote, before pushing optics too hard)
* Find IR resonance
* Offset from resonance
None of these should be difficult, just changing the filter bank names to match the new ones (ex. LSC-XARM rather than ALS-XARM, and LSC-ALSX rather than ALS-OFFSETTER1).
So far, I have changed the "find resonance" script (ALSfindIRresonance.py). I believe, in principle, to first order, that my modifications should work, however I have not yet tested the script. So. If you use it, watch the output of the script and ensure it's doing what it ought. I'll check it after the lunch meeting and update this log entry. (I changed the name of the "OFSFILT" variable, line 26, and also modified line 114. Both of those lines have comments on how to revert the changes).
I have also changed the "offset from resonance" script (ALSchangeOffset.py). Again, since I'm not locking right now, I have not tested this script either. So, pay attention if you need to use it, before I check it. (I changed the name of the OFSFILT variable, and the check which arm logic around line 37. Again, both of those lines have comments on how to revert the changes.)
Watch arms script (ALSdown.py) has been modified and now watches the LSC-$ARM filter module instead of the ALS-$ARM filter module. Threshold has been kept the same +/-5000 counts to the ETM suspensions. The script has been tested and works just fine. It exists in the same place scripts/ALS/.
Jenne's modified versions of ALSfindResonance.py and ALSchangeOffset.py were tested and work just fine.
Locked on the sideband, the MICH / PRCL angle is much less sensitive to the PRC length, and shouldn't in fact be as degenerate as we've seen in reality.
So, my simulations no longer provide any reason for the 3F signals to be so degenerate.
Koji noted oddities in the sensing matrix results I had gotten; namely that the plots showed REFL33 not changing at all, when we know for a fact that this should not be the case.
Gabriele lent his eyes to my code, and came up with the idea that the modulation depths I was using were maybe not ideal (.1 for both 11 and 55). This affects REFL33 in that it is not simply Carrier * 33Mhz + 11Mhz * -22Mhz but also 22MHz * 55MHz, etc.
I got more realistic values from Jenne (0.19 for 11MHz and .26 for 55Mhz) and re-ran the code, with more realistic results. The behavior for 165 has remained the same, but the other signals are more well behaved.
Moral of the story: the modulation depths affect the 3f signals in a complicated way.
As Koji measured the other day: MICH and PRCL seem very degenerate in the 3f REFL PDs.
I'm using this as a motivation to do some simulation in MIST and try to understand the best way to implement the 3F locking scheme. Hopefully my thinking below isn't nonsense...
First, I modeled the PRC with no arm cavities and the estimated cavity length I got with the PRM kick measurement, and looked at the REFL sensing matrix.
This agrees with the observed degeneracy. I then modeled the case of the PRC length that gives coincident SB resonance, again with no arm cavities.
Now there is good separation in REFL165. (REFL33 still looks pretty degenerate, however). This raised the question, "What does the angle between MICH and PRCL in REFL165 do as a function of macroscopic PRC length?"
To me, this implies that locking the PRC on 3F from scratch won't be simple. However, the whole point of the PRC length choice is to have coincident SB resonance when the arms are resonating.
So: even if we're not spot on, we should be relatively close to the PRC length where having arms resonant gives us simultaneously resonant upper and lower sidebands, where MICH and PRCL should be orthogonal-ish. I.e. building up a little bit of IR power in the arms may start to break the degeneracy, perhaps allowing us to switch from 1F to 3F locking, and then continue reducing the CARM offset.
So, I ultimately want to model the effect of arm power buildup on the angle between MICH and PRCL in the 3f PDs. This is what I'm currently working on.
So far, I have reproduced some of the RC modeling results on the wiki to make sure I model the arms correctly. (I get 37.7949 m as the ideal arm length for a modulation freq of 11.066134 MHz vs. 37.7974m for 11.065399 MHz as stated on the wiki). Next, I will confirm the desired PRC length that accounts for the arms, and then look at the MICH vs PRCL angle in the REFL PDs as a function of arm power or detuning.
All 40m laser safety glasses are cleaned and measured this morning. Bring your own safety glasses if you have to enter the 40m IFO room.
Glasses were washed in 1% Liquinox water solution and their transmission measured at 165 mW, 2 mm OD beam of 1064 nm
No more progress tonight. I am still unable to lock the ALS using the regular LSC filters. I went back to putting the ALS filters into the LSC filter banks, and locked both arms with ALS, and found their IR resonances. I then held them off resonance, and tried to lock PRMI with REFL 55 I&Q, with no success. Just before locking the arms, I had redone the whole IFO alignment (lock arms in IR, ASS, lock and align MICH, lock and align PRMI), and the PRMI was flashing very nicely. I'm not sure why I wasn't able to catch lock, except that perhaps 3 or 6 ALS offset counts isn't far enough away from the IR resonance to make the 1f signals happy. The MC lost lock, which I then took as a sign that it's time to go home. (I was hoping to do a quick PRMI + 2arms, and see that we don't lose PRMI lock. I was going to catch lock with REFL55, then transition to REFL33, although if I had thought about it before the MC lost lock, I would have tried just catching lock with REFL33).
I restored the regular LSC filters for the X and Y arms, and locked the arms in IR just to make sure it's all honkey-dory. Which, it's not quite. I don't know why, but right now, neither arm wants its boost (FM9) enabled. It's part of the restore script that FM9 is triggered along with the rest of the filters, but even if I turn on the filters manually, I can turn on all but FM9, and then when I turn on the boost, the arm falls out of lock. Same behavior for both arms. Anyhow, they lock, and they seem okay modulo the boost not being able to engage.
I am also not able to lock the ALS using the 'regular' LSC filters. To figure out what filters were doing what, I made several comparison plots from Foton.
The first one is the progression of ALS locking, using the filters from ALS-XARM. FM5 is always engaged, then FMs 2, 3, 6, 7, and 8, and finally FM 10 (the low frequency boost) is engaged.
The next plot is a comparison between the ALS version of the filters, and the LSC-XARM equivalents.
Finally, just so I remember which LSC filters do what, I made an equivalent of the first plot, but for the LSC filters.
When I try to lock the Xarm ALS using the regular LSC filters, I'm getting an oscillation somewhere, that grows and eventually knocks me out of lock. It looks from dataviewer to be in the ~few Hz range, but it's hard to see it in DTT, since I don't stay locked all that long once the oscillation starts. (If I catch it, I can back off the gain and turn off the servo without losing lock, but if I don't turn off the servo, I inevitably push the ETM too hard and lose green lock to the arm.) I tried engaging the 3.2 Hz resonant gain filter, and it just makes things oscillate sooner, so that's not a solution with the current filter designs.
Also, I'm not able to lock the IR using the ALS version of the XARM filters. I'll have to meditate more on the situation, but the filters seem to be different enough that there's no crossover at this point.
Great. I indeed disabled all of the triggers and the normalization during my trial but in vain.
So I'm curious this is actually because of the filter shape or not.
I'm really excited, so I'm posting this, even though I'm still working:
I currently have ALS locked using the LSC system, and have (by hand, coarsely) found IR resonance! Hooray!
I looked at my error signals, as well as LSC-XARM_IN1 with dataviewer, and noticed that the XARM_IN1 signal was crazy when I was using the ALS signal as the error. I soon realized that this is because there was a non-zero element in the power normalization matrix, and I'm overriding the trigger. So, I was trying to divide by zero, and was getting crazy numbers. After zeroing the power normalization matrix element for the Xarm, the XARM_IN1 signal matched the ALSX_OUT, and I was easily able to acquire lock.
I had already re-transferred over the ALS versions of the filters, so that's what I'm using right now. Next up (on a 5 minute time-scale) is trying to acquire lock using the regular LSC filters.
Oh, also, something I hadn't thought of before dinner: I am setting the offset of the ALSX filter bank such that the output is centered around zero, so that I can lock, since these are not AC coupled servos.
It looks like its somehow a discrepancy between the TFs of each error signal, because features are similar, and present, in both error signals.
Hmm. Wierd. Can you look at the TFs between ETMX-EXC and the error signals so that we can identify which one has these structures.
Koji mentioned to me (and elogged) that he was unsuccessful locking the ALS using the LSC servos. He suggested I look into this.
So, rather than just looking at the transfer function between POX or POY and the green beatnotes at a single frequency, I did a whole transfer function. The point was to see if the TF is flat, and if we get any significant phase lag in the transfer from c1als to c1lsc. (c1als is running on the IOO machine, so an RFM connection is involved in getting it over to the LSC machine.)
In the first figure, I have plotted POX vs. Beatnote_PHASE_OUT (ALS error signal, still in the c1als model), and POX vs. ALSX_IN1 (the ALS error signal, after transfer over to the c1lsc model). You can see that we have a little phase lead in the blue transfer function, and fairly significant phase lag in the red (red is after transfer over to the lsc model). In the grand scheme of things, the magnitude is fairly flat, however that is not perfectly true - the peaks seen near 50 Hz and 300Hz are repeatable. The relative phase lag between the "BEATX" version of the signal in the ALS model, and the "ALSX" version of the signal in the LSC model is 15 degrees at 200 Hz, which corresponds to 33 usec.
The second figure is the same as the first, except for the Yarm. The relative phase lag between the ALS version of the error signal and the LSC version is 16 degrees at 200 Hz, which is about 35 usec.
As a side note, before trying any ALS locking, I took a spectrum of the beatnote (in the ALS model) while the arms were locked with IR:
To check things, I made sure that I could lock the Xarm ALS using the old ALS system - I was able to do so. (Has someone put the "watch" script as a constantly-on thing? It's kind of nice not to have to turn it on, although we'll need to change it to turn off the LSC versions of the servos eventually).
Then, I tried locking the Xarm using the LSC system (using only FM5 of the regular LSC-XARM filter bank). Like Koji, I was not able to acquire lock. As a next step, I copied all of the LSC-XARM filters into an empty filter module, LSC-XXXDC (the first one on the list underneath LSC-XARM), and copied over the ALS Xarm filters to the LSC Xarm filter bank. I then tried to acquire lock, but am unable to get it to stay. Using the ALS system, when you put in a small gain, the beatnote starts to settle down, and as you increase the gain, the beatnote stops moving (as seen on the spectrum analyzer) almost completely. However, using the LSC system, the beatnote never really stops moving or settles down. And if I increase the gain, I push the ETM hard enough that I lose green lock. I have put the regular LSC filters back for now.
Here is a plot from Foton comparing the FM5 filter modules from the LSC-XARM (regular IR locking) and the ALS-XARM servo. They are pretty different, and have 10 degrees of phase difference at 200 Hz, because 2 of the 3 poles are complex in the LSC version, while the ALS version is just a single real pole.
Anyhow, I am declaring it to be dinnertime, and I plan to return in a few hours. Since I put the regular LSC filters back (since I'm going to have to realign after dinner anyway), the IFO should be in its nominal state if anyone wants to come in and play with it.
As we've been seeing a bit lately, the MC will be locked happily for several hours, but then it will start misbehaving.
Today, I measured the spots on the MC mirrors, and found that the MC2 spot was quite far off in yaw (about -3.5 cm). I recentered the MC2 spot, and then (with the MCWFS on), moved MC1 and 3 until their WFS outputs were close to zero (they had gone up to 100+). In the ~15 minutes since doing that, the MC refl signal is not oscillating like it was, the transmission is up, and the MC has not unlocked.
To reiterate, I did not touch any settings of anything, except the alignment of the MC mirrors to center the MC2 spot, and then offload the WFS. Next time the MC starts acting up, we should measure the spots, and roughly center them, before messing with any other settings. Note however, that this is a ~10 minute procedure (including the fact that one spot measurement takes a little less than 5 minutes). This need not be a several hour endeavour.
The floor was cleaned under the east arm tube with hand held wet towel. We moved staff around and mopped. I did at the bottom of rack 1Y1, 2 and 3.
Last week we did the south arm tube floor.
Next week we 'd like to clean under rack 1X1,2,3, 4, 5, 6 and 7
1Y4, 1X1,2,3,4 & 5 instrument racks floor space were cleaned.
My apologies for all of that crap I left at the Y-end... I cleaned the rest of it up today.
I took transfer functions of the four ETMY QPD whitening channels today. (Attempted the ETMX ones too, but had troubles driving the board; detailed below). I've attached a zip with the DTT xml files for the cases of no whitening / 1 whitening stage / both whitening stages engaged. Here's a plot of both whitening stages engaged.
Given the way I measured, the DAC output anti-imaging is in the TFs as well. ( This is a D000186 board; with something like a 4th order elliptic LP, but I need to look at the board / fit the TF to see the parameters, there are different revisions with different filter shapes.)
The c1scy model had excitation blocks on some of the unused DAC channels (C1:SCY-XXX_CHAN9 etc.), but these were in the second DAC output connection, and not cabled up. However, the 8th channel on the DAC had no connection in the simulink model, so I added another excitation block there (C1:SCY-XXX_CHAN8), and used the anti-imaging front panel lemo connector to drive the input of the whitening board.
I also added a similar channel to the SCX model, but no data would show up in the channel as viewed by data viewer (though the channel name was black), or in analog world. There's the additional weirdness that the SCY excitation channels show up under SCX in DTT and awggui... I'm not entirely sure what's going on here.
I still need to look at the noise, and peek inside the boards, to check for homemade modifications and see if there are bad things like thick film resistors that may be spoiling the noise performance...
I wanted to try common/differential ALS Friday evening. I tried ALS using the LSC servo but this was not successfull.
The usual ALS servo in the ALS model works without problem. So this might be coming from the shape of the servo filter.
The ALS one has 1:1000 filter but the LSC one has 10:3000. Or is there any problem in the signal transfer between
ALS and LSC???
Slow offset -0.302V
TRX=1.18 / TRY=1.14, XARM Servo gain = 0.25 / YARM Servo gain = 0.10
- Green Xarm:
GTRX without PSL green 0.562 / with PSL green 0.652 -> improved upto 0.78 by ASX and tweaking of PZTs
Beat note found at SLOW OFFSET +15525
Set the beat note as +SLOW OFFSET gives +BEAT FREQ
- Green Yarm:
GTRY without PSL green 0.717 / with PSL green 1.340
Beat note found at SLOW OFFSET -10415
Set the beat note as +SLOW OFFSET gives -BEAT FREQ
- BEAT X -10dBm on the RF firstname.lastname@example.orgMHz / Phase tracker Qout = 2300 => Phase tracking loop gain 80 (Theoretical UGF = 2300/180*Pi*80 = 3.2kHz)
- BEAT Y -22dBm on the RF email@example.comMHz / Phase tracker Qout = 400 => Phase tracking loop gain 300 (Theoretical UGF = 2.1kHz)
Transfer function between ALSX/Y and POX/Y11I @560Hz excitation of ETMX
POX11I/ALSX = 54.7dB (~0deg)
POY11I/ALSY = 64.5dB (~180deg)
ALSX[cnt]*19230[Hz/cnt] = POX11I[cnt]/10^(54.7/20)*19230[Hz/cnt]
= 35.4 [Hz/cnt] POX11I [cnt] (Hz in green frequency)
35.4 [Hz/cnt]/(2.99792458e8/532e-9 [Hz]) * 37.8 [m] = 2.37e-12 [m/cnt] => 4.2e11 [cnt/m] (c.f. Ayaka's number in ELOG #7738 6.7e11 cnt/m)
ALSY[cnt]*19230[Hz/cnt] = POY11I[cnt]/10^(64.5/20)*19230[Hz/cnt]
= 11.5 [Hz/cnt] POX11I [cnt] (Hz in green frequency)
11.5 [Hz/cnt]/(2.99792458e8/532e-9 [Hz]) * 37.8 [m] = 7.71e-13 [m/cnt] => 1.3e12 [cnt/m] (c.f. Ayaka's number in ELOG #7738 9.5e11 cnt/m)
As I didn't have the green laser PZT feedback for the laser temp control, I went to the yend to check out what's the situation.
I found horrible and disgusting "remnants".
WHAT ARE THESE BSs AT THE Y END?
- The table enclosure was left open
- A (hacky) DB25 cable with clips was blocking the corridor and I was about to trip with the cable.
- This DB25 cable went to the table without going through the air tight feedthrough that is designed for this purpose.
- An SR560 (presumably for the openloop TF measurement) was left inserted in the loop with entangled cables connected to the servo box.
- Of course the laser PZT out mon was left unplugged.
Even after cleaning these cables (a bit), the end setups (including the X end too) are too amature.
Everything is so hacky. We should not allow ourselves to construct this level of setup everytime
we work on any system. This just adds more and more mysteries and eventually we can't handle
Facilities just came by and cleaned the smoke detector that is above Steve's desk. It's next to an air vent, so I guess it collects dust more than a "typical" smoke detector.
Although the morning MC tuning looked stable, Koji pointed out that the MC_REFL_OFFSET was changed from its nominal value.
The offset was reset and this caused drift in the MC_TRANS_SUM.
To fix this:
- disabled the WFS servo
- aligned MC using MC1 and MC3
- centered beam on the MC_REFL
- reset WFS offsets
- locked MC
MC looks happy now.
ALS is in a very different state from a couple of days ago when we could successfully lock the arms and scan.
The green alignment to the arms had drifted.
PSL green alignment on the PSL table was off. The PSL green was not even on the steering mirror. Did anyone work around the PSL table in the last couple of days?
After aligning and finding the beat note, I found the ALS servo very noisy. The error signal had 10 times more rms noise than what was achieved earlier this week and there were some new 60Hz peaks as well.
Overall, we could not do any PRMI+ALS arms today
[Quick post, will follow up with further detail later. Excuse my sleepy ELOG writing]
Goal: Check out the transmon QPD signal chain; see if whitening works. Assess noise for 1/sqrt(TRX/Y) use.
First impression: Whitening would not switch on when toggling the de-whitening. The front monitors on the whitening boards are misleading; they are taken a few stages before the real output. ADC noise was by far the limiting noise source.
I updated the binary logic in the c1scx and c1scy to actually make the binary IO module output some bits.
After consulting a secret wiring diagram on the wiki, not linked on the rack information page (here), I worked out which bits correspond to the bypass switches in the whitening board ( a fairly modified D990399, with some notes here)
Now, FM1 and FM2 (dewhitening filters on the ETM QPD quadrants) trigger the corresponding whitening in the boards. Here's a quick TF I took of the quadrant 1 board at ETMY. (I should take a whitening+dewhitening TF too, and post it here...)
Seems to roughly work. Some features may be due to non-accounted for elements in the anti-imaging of the DAC channels I used for the excitation, or such things. The board likely needs some attention, and at least a survey of what is there.
I also need to take dark noise data, and convert into the equivalent displacement noise in the 1/sqrt(TRX/Y) error signals. For the no-whitening ADC noise, I estimated ~1pm RMS noise on a 38pm linewidth of PRFPMI arms.
[Koji, Jenne, EricQ, Manasa]
We had a short discussion this evening about what our game plan should be for transitioning from using the ALS system to IR-generated error signals.
The most fundamental piece is that we want to, instead of having a completely separate ALS locking system, integrate the ALS into the LSC. Some time ago, Koji did most of the structural changes to the LSC model (elog 9430), and exposed those changes on the LSC screen (elog 9449). Tonight, I have thrown together a new ALS screen, which should eventually replace our current ALS screen. My goal is to retain all the functionality of the old screen, but instead use the LSC-version of the error signals, so that it's smoother for our transition to IR. Here is a screenshot of my new screen:
You will notice that there are several white blocks in the center of the screen. From our discussion this evening, it sounds like we may want to add 4 more locking servo paths to the LSC (ALS for each individual arm, and then ALS for CARM and DARM signals). The reason these should be separate is that the ALS and the "regular" PDH signals have different noise characteristics, so we will want different servo shapes. I am proposing to add these 4 new servo blocks to the c1lsc model. If I don't hear an objection, I'll do this on Monday during the day, unless someone else beats me to it. The names for these filter modules should be C1:LSC-ALS_XARM, C1:LSC-ALS_YARM, C1:LSC-ALS_DARM and C1:LSC_ALS_CARM. This will add new rows to the input matrix, and new columns to the output matrix, so the LSC screen will need to be modified to reflect all of these changes. The new ALS screen should automatically work, although the icons for the input and output matrices will need to be updated.
The other major difference between this new paradigm and the old, is the place of the offset in the path. Formerly, we had auxiliary filter banks, and the summation was done by entering multiple values in the ALS input matrix. Now, since there is a filter bank in the c1lsc model for each of the ALS signals precisely where we want to add our offsets, and I don't expect us to need to put any filters into those filter modules, I have used the offset and TRAMP of those filter banks for the offsets. Also, you can access the offset value, and the ramp time, as well as the "clear history" button for the phase tracker, all from the main screen, which should help reduce the number of different screens we need to have open at once when locking with ALS. Anyhow, the actual point where the offset is added has not changed, just the way it happens has.
When we make the move to using the ALS in the LSC, we'll also need to make sure our "watch arm" and "scan arm" scripts are updated appropriately.
As an intermediary locking step, we want to try to use the ALS system to actuate in a CARM and DARM way, not XARM and YARM. We will transition from using each ALS signal to feed back to its own ETM, to having DARM feed back to the ETMs, and CARM feed back to MC2. We may want to break this into smaller steps, first lock the arms to the beatnotes, then find the IR resonance points. Transition to CARM and DARM feedback, but only using the ETMs. After we've done that, then we can switch to actuating on MC2. If we do this, then we'll be using the MC to reduce the CARM offset.
Once we can do this, and are able to reduce the CARM offset, we want to switch CARM over to a combination of the 1/sqrt(transmission) signals. The CARM loop has a tighter noise requirement, so we can do this, but leave DARM locked to the beatnotes for a while.
After continuing to reduce the CARM offset, we will switch CARM over to one of the RF PDs, for its final low-noise state.
We'll then do a quick swap of the DARM error signal to the AS port (maybe around the same time as CARM goes over to a PDH signal, before the CARM offset is zero?).
During all of this, we hope that the vertex has stayed locked. If our 3f sensing matrix elements are totally degenerate when the arms are out of resonance, then we may need to acquire lock using REFL 1f signals, and as we approach the delicate point in the CARM offset reduction, move to 3f signals, and then move back to 1f signals after the arm reflection has done its phase flip. Either way, we'll have to move from 3f to 1f for the final state.
I was able to get the PRMI locked on REFL33 I&Q, but it wasn't overly stable, since there is so little separation between the MICH and PRCL signals in that PD.
We have already adjusted the phase to maximize PRCL in the I-phase. Since MICH is ~45 degrees separated from PRCL, there is some projection of MICH in the I-phase, and some in the Q-phase.
To remove this MICH component, I locked the PRMI on REFL55, and drove MICH. I looked at REFL33I at the CARM filter bank input (as just a dummy location to get a signal into DTT). I then added REFL33Q to the CARM row of the input matrix, to try to get the MICH line minimized. I then used these values for PRCL, and used just REFL33Q for MICH, and re-locked the PRMI. The PRMI was much more stable and happy.
The input matrix values that I used were:
MICH: REFL33Q = -0.487, Servo Gain = -20.0
PRCL: REFL33I = 1.556, REFL33Q = 1.8, Servo Gain = -0.020
Some locking notes:
The PRMI is very sensitive to alignment, and the PRM tends to drift away from optimal alignment on a ~1 hour timescale. When the PRM was not well aligned, it looked like MICH had a locking offset (manifested as non-equally sized blobs at AS). The MICH offset seemed to go away when we realigned the PRM.
Jenne and I noticed high pitch sound from our acoustic interferometer noise diagnostic system.
The frequency of this narrow band noise was 1256Hz, which is enough close to twice of the PRM violin mode freq.
After putting notch filter at 1256+/-25Hz at the violin filters, the noise is gone. Just in case I copied the same filters to all of the test masses.
Later, I found that the 4th violin modes are excited. Additional notch filters were added to "vio3" filter bank to mitigate the oscillation.
Y arm green: Nothing much was disturbed. I touched the steering mirrors and brought GTRY from 0.2 to 0.9.
X arm green: The PDH lock was not very stable mostly because of the low power in green. I changed the oven temperature for the doubler to 36.4 corresponding to maximum green power. GTRX increased from 0.1 to 0.9
Both the X and Y arm green alignment were tuned on the PSL table to their respective beat PDs.
The PSL green shutter was not responding to the medm buttons. I found the PSL green shutter set to 'local' and 'N.O' (these are switches in the shutter controller). I do not see any elog and not sure as to why the controller was even touched in the first place. I set the shutter controls to 'remote' and 'N.C'.
ETMX green power at shutter 3.6 mW at 36.35 C doubler crystal temp. [ Innolight IR settings 2.0 A, 40.83 C, 500 mW before Faraday 1/2 plate ]
ETMY green power at shutter 0.75 mW at 35.8 C doubler crytal temp. [ NPRO IR settings 1.82A, 231 mW_ display, DT 21 C, DTEC +1V, LT 40 C, LTEC 0.1V, T +41.041 ]
The MC has been funny since yesterday. I checked the suspensions INMON channels and they seemed ok. So I went ahead and tweaked the alignment with WFS disabled (yesterday). Although the WFS PDs were cenetered at this point, the WFS servo was throwing the MC in a not-so-happy state. We worked with the WFS servo OFF all of yesterday.
* I fine tuned the MC alignment from yesterday (TRANS_SUM > 17800 counts)
* measured the spot positions
* recentered the spots on the WFS PDs (was already quite centered)
*reset the WFS filterbank offsets.
The MC has been locked happily since then with autolocker and WFS servo enabled.
We usually want to remove PRCL from the Q quadrature for each PD.
Therefore, you are not supposed to see any PRCL in Q assuming the tuning of the demod phases are perfect.
Of curse we are not perfect but close to this regime. Namely, the PRCL in Qs are JUNK.
In the condition where MICH is supressed by the servo, it is difficult to make all of the Qs line up because of the above PRCL junk.
But you shook MICH at a certain freq and the signal in each Q signal was calibrated such that the peak has the same height.
So the calibration should give you a correct sensing matrix.
If you tune the demod phases precisely and use less integrations for MICH, you might be able to see the residual MICH lines up on the Q plot.
I calibrated the REFL signals to meters from counts. The I-phase signals all line up very nicely, but the Q-phase signals do not at all. I'm not sure what the deal is.
I locked the PRMI on sidebands, and drove the PRM. I looked at the peak values at the drive frequency in the REFL signals, and used that as my "COUNTS" value for each PD.
I know the PRM actuator calibration is 19.6e-9 (Hz/f)^2 m/ct , so if I plug in my drive frequency (564 Hz, with the notch in the PRC loop enabled), and multiply by my drive amplitude in counts, I know how many meters I am pushing the PRM. Then, to get a meters per count calibration, I divide this calibration number (common for every PD) by the peak value in each PD, to get each signal's calibration.
As a side note, I also drove MICH, and tried to use this technique for the Q-phase calibrations, but neither calibration (using the PRCL drive nor the MICH drive) made the Q-phase signals line up at all.
At least for the I-phase signals, it's clear that REFL33 has more noise than REFL11 or REFL165, and that REFL55 has even more noise than REFL33.
Here are the calibration values that I used:
I'm not happy with the beam position on that first lens, but since it's so crazy in the BS chamber, and the PRM oplev has something like 5 in-vac steering mirrors, I'm hesitant to suggest that we do anything about it until our next vent. But we should definitely fix it.
The input pointing of PRM oplev beam was streered just a touch to remove clipping from it's return.
The spots did not move visibly on these two lenses. The spot diameter on the qpd is ~1.5 mm, 65 micro W and 3440 counts.
Steve fixed the PRM oplev pointing. I turned on the loops and measured the OLG, then set the pitch and yaw gains such that the upper UGF was ~8Hz (motivated by Jenne's loop design in ELOG 9401)
I then measured the oplev spectra of the optics as they were aligned for PRMI. (OSEMs on, oplevs on, LSC off, and ASC off)
Next, Jenne and I need to fix the ASC loop such that it properly accounts for the oplev loop.
[Rana, Jenne, Manasa]
We looked at the I vs. Q separation in several of the Refl PDs, while driving the PRM, while the PRMI was locked on sidebands.
For REFL 55, we adjusted the demod phase to try to minimize the peak in the Q signal, and were only able to get it to be about 1/10th the size of the I peak. This is not good, since it should be more like 1/100, at least.
For both REFL 11 and REFL 165, we were able to get the Q peaks to less than 1/100 of the I peak height.
We changed the REFL55 phase from 17 to 16, and the REFL165 phase from -160.5 to -162.5.
Since we believed that we had done a good job of setting the demod phase for REFL165, we used it to also check the balance of BS/PRM for MICH locking. I drove the BS with an arbitrary number (0.5), which creates a peak in the I phase of REFL165, and then I put in a drive on the PRM and tweaked it around until that peak was minimized. I came up with the same ratio as Koji had last Friday: BS=0.5, PRM=-0.2625. (The old ratio we were using, up until ~December when we started locking MICH with the ITMs, was BS=0.5, PRM=-0.267).
Also, while we were locked using REFL55 I&Q, we noticed that the other REFL PDs had lots of broadband noise in their I signals, as if some noise in the REFL55 diode is being injected into the PRM, that we are then seeing in the other PDs.
Some checks that we need to do:
* Inject a calibration line, set all the peak heights equal, and look at the noise floors of each PD.
* Use the calibration line to calibrate the PDs (especially REFL165) into meters, so that we know that it's noise is low enough to hold the PRC through the CARM offset reduction.
* Check out the state of the transmission QPDs - what is their noise, and is it good enough to use for holding the arms after we transition from green beatnote locking? Does the whitening switching do anything? What is the state of the whitening?
Nice restoration. We eventually want to make transition of the servo part from ALS to LSC model for the further handing off to the other signals.
Please proceed to it.
The X and Y arms were locked successfully using ALS and the arms could be scanned and held to support IR resonance.
The same procedure as in elog 9219 was followed. In-loop noise was measured to be between 200-300 Hz rms for the lock.
ALS settings for the lock
X arm : FM 2, 3, 5, 6, 7, 8, 10 Gain = 11.0
Y arm : FM 2, 3, 5, 6, 7, 8, 10 Gain = 10.0
Ignoring the OSEM damping loops, the oplev servo loops make it so that the POP ASC loops do not see a simple pendulum plant, but instead see the closed loop response. Since the filter in the OL bank is proportional to f, this means that the open loop gain (OLG):
Which means that the CLG that the ASC sees is going to dip below unity in the band where the OL is on. For example, if the OL loop has a UGF of 5 Hz, it also has a lower UGF of ~0.15 Hz, which means that the ASC needs to know about this modified plant in this band.
For i/eLIGO, we dealt with this in this way: anti-OL in iLIGO
I have turned off the 3.2Hz res gains in the PRC ASC loops, since those seem to make the loops unstable.
Right now the pitch gain is -0.001, with FM1,3,9 on. Yaw gain is -0.004, with FM1,3,9 on.
Pitch gain can't increase by factor of 2 without oscillating.
I tried to take transfer functions, but I think the ASC situation is really confusing, since I have OSEM damping, oplev damping, and this POP QPD damping on the PRM. It's hard to get coherence without knocking the PRC out of lock, and it keeps looking like my gain is 0dB, with a phase of 0 degrees, from ~1 Hz to ~10 Hz. Outside that range I haven't gotten any coherence. Moral of the story is, I'm kind of puzzled.
Anyhow, as it is right now, the ASC helps a bit, but not a whole lot. I increased the trigger ON value, so that it shouldn't kick the PRM so much. I wish that I had implemented a delay in the trigger, but I'm not in the mood to mess with the simulink diagrams right now.
I have configured one of the spare Supermicro X8DTU-F chassis as a dual-CPU, 12-core CDS front end machine. This is meant to be a replacement for c1sus. The extra cores are so we can split up c1rfm and reduce the over-cycle problems we've been seeing related to RFM IPC delays.
I pulled the machine fresh out of the box, and installed the second CPU and additional memory that Steve purchased. The machine seems to be working fine. After assigning it a temporary IP address, I can boot it from the front-end boot server on the martian network. It comes up cleanly with both CPUs recognized, and /proc/cpustat showing all 12 cores, and free showing 12 GB memory.
The plan is:
Obviously the when of all this needs to be done when it won't interfere with locking work. fwiw, I am around tomorrow (Tuesday, 2/11), but will likely be leaving for LHO on Wednesday.
In an effort to stop the PRC from wiggling around so much, I recentered the POP QPD after maximizing the POPDC power when locked on carrier. The beam was basically off the QPD in yaw, and at half-range in pitch.
The PRC (locked on carrier so far today), is pretty wobbly. It'll stay locked on carrier, but it's wobbling. The ASC was over-ridden during the vent. While I was looking around for that, I noticed that the PRM oplev sum is very low.
I went into the lab, and turned off / blocked all oplev beams except the PRM beam. I can't tell what it's clipping on, but there is definitely some red glow in the BS chamber (not as much as the stuff that's coming from the ITMY or SRM oplev hitting a tip tilt suspension - that giant spot went away when I turned off the ITMY/SRM oplev laser). The beam going into the vacuum is nice and strong, but the beam coming out is very weak, and has a horizontal line of scatter through it, like it's clipped somewhere in pitch. The PRM oplev sum is currently ~150 cts, when it should be closer to 2,000.
So far, this seems to be livable, but it's definitely disappointing.
Pumpdown completed. IR shutter opened at P1 1 mTorr The block is still in the beam path.
Remember to protect MCR pd before crack up the PSL power.
The ion pump gate valves were just closed by cc1 triggered interlock
The cry pump was "regenerated" during the vent and it's outgassing rate minimized.
CC3 cold cathode gauge was replaced.
Valve configuration for week end:
1, VA6 disconnected to avoid accidental venting the IFO through the annulos
2, VC2 disconnected to insure that the cryo stays closed
3, RGA is not running, It's pressure limit 1e-5 Torr
Valve configuration: Vacuum Normal is reached in really 4 days if we do not count overnight rest of roughing.
VA6 and VC2 are reconnected. I'm turning on the RGA next
All 4 ion pumps were vented with air and pumped down to ~ 1e-4 Torr
Ion pumps gate valve control cables are connected and their pumps are disconnected.
The black relay box was tested repeatedly and it stopped misbehaiving.
We were at atmosphere for 13 days. Chamber BS, ITMX, ITMY and ETMY were opened.
Al foil "cups" were placed on the back side OSEMs of PRM.
Today, I kicked the PRM to see the sideband splitting in POP110.
First, we can qualitatively see we moved in the right direction! (See ELOG 9490)
I fit the middle three peaks to a sum of two Lorentzian profiles ( I couldn't get Airy peaks to work... but maybe this is ok since I'm just going to use the location parameter?), and looked at the sideband splitting as a fraction of the FSR, in the same way as in Gabriele's ELOG linked above.
This gave: c / (4 * f55) * (dPhi / FSR) = 0.014 +- .001
Since the PRC length with simultaneous resonance (to 1mm) is given by c / (4 * f11) = 6.773, this means our length is either 6.759m or 6.787m (+- .001). Given the measurement in ELOG 9588, I assume that we are on the short side of the simultaneous resonance. Thus
The sideband splitting observed from this kick indicates a PRC length of 6.759m +- 1mm
PRCL: 100cnt -> PRM 567.01Hz
Signal in demod Q ch were minimized
REFL11I -19.2deg demod I, Lockin I out (C1:CAL-SENSMAT_PRCL_REFL11_I_I_OUTPUT) 12.6 cnt
REFL33I +130.4deg 1.70cnt
REFL55I +17.0deg 2.30cnt
REFL165I -160.5deg 27.8cnt
MICH: 1000cnt -> ITMX(-1) & (ITMY +1.015 => Minimized the signal in REFL11I to obtain pure MICH)
REFL11I +0.0 REFL11Q +0.119
REFL33I +0.023 REFL33Q -0.012
REFL55I +0.023 REFL55Q -0.113
REFL165I +0.68 REFL165Q +0.038
It seems that REFL165 has almost completely degenerated PRCL and MICH.
ITMX(-1)/ITMY(+1.015) actuation was cancelled by BS (+0.16). This introduces PRCL in REFL11I. This was cancelled by PRM (-0.084)
REFL11I +0.0 REFL11Q +0.13
REFL33I -0.012 REFL33Q 0.025
REFL55I +0.041 REFL55Q -0.45
REFL165I +0.69 REFL165Q +/-0.02
Again, It seems that REFL165 has almost completely degenerated PRCL and MICH.
[Signal source] REFL11I (-19.2deg) x 0.16, OR REFL33I (+130.4deg) x 2.0, OR REFL55I (+17.0deg) x1.0, OR REFL165I (-160.5deg) x0.05
[Trigger] POP110I(-81deg) 100/10, FM trigger 35/2, delay 0.5sec FM2/3/6/9
[Servo] FM4/5 always on. G=-0.02, Limitter ON
[Output] PRM x+1.00
[Signal source] AS55Q (-5.5deg) x 1, OR REFL11Q x 0.25, OR REFL55Q x-0.06
[Trigger] POP110I 100/10, FM trigger 35/2, delay 5sec FM2/3/9
[Servo] FM4/5 always on. G=-10, Limitter ON
[Output] ITMX -1.0 / ITMY +1.0 (or +1.015), OR PRM -0.084 / BS +0.16
Nice work!! As with all the other RF PDs, POP110's phase likely needs tuning. You want POP110 (and POP22) I-quadratures to be maximally positive when you're locked on sidebands, and maximally negative when locked on carrier. What you can do to get close is lock PRC on carrier, then rotate the POP phases until you get maximally negative numbers. Then, when locked on sideband, you can tweak the phases a little, if need be.
Adjusted the angles as Jenne suggested:
I then used the same settings as in ELOG 9554, except I used -1s instead of +1s for the POP110I trigger matrix elements. (I'm not sure why this is different, but I noticed that the PRC would lock on carrier with positive entries here, so I figured we wanted the peaks with opposite sign).
Very good news! We should have a look at the POP110 sideband peak splitting, to see if we really got the right PRC length...