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.
Batteries replaced after 3.5 years with Amstron AP-1250F2, 8x 12V 6Ah
APC Smart -UPS 2200 model: SUA2200RM2U batteries were replaced by compatible RBC43, 8x 12V5A
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.
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.
Can we plot the arm power trend for multiple locks to see if it is associated with any thermal phenomenan in the IFO?
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?
Before locking for the evening, I wanted to try again implementing the Wiener filters that I had designed back in Jaunary (elog 10959).
The problem then was that the newer version of Quack that I was using was doing weird things to me (elog 10993). But, tonight I used the old quack3andahalf that we used to use for Wiener-related things, and that worked (for up to order 20 filters). Actually, the pitch z-axis Wiener filter, when I copy the command string into Foton, says "Error" in the alternate box (the lower one). I also get this error message if I try to put in filters that were greater than order 20, and have been split into several filters. I'm not sure what's wrong, so for tonight I'm leaving out the pitch z-axis seismometer feed forward, and only using 20th order filters for all the rest.
So, pitch has feed forward signals from the T-240's x and y axes, and yaw has feed forward signals from all 3 seismometer channels.
At first, I just had the calculated Wiener filters, and a 10Hz lowpass, but the POP beam spot on the camera was getting slowly pushed away from the starting location. So, I added a 0.01Hz cheby1 highpass filter, and that seems to have fixed that problem. I need to go back to the simulations though, and see if this is going to cause extra noise to be injected (because of incorrect phase in the feed forward signal) at very low frequencies. All 5 Wiener filter banks have a gain of -1.
I'm getting a factor of 4-5ish between 2Hz and 3Hz in both pitch and yaw. What's interesting is that despite no direct angular suppression (as measured by the QPD) at higher frequencies, both POP22 and POPDC see improvement over a much broader range of frequencies. I'll have to think about how to predict this RIN coupling in my budgets.
The time series data for these filters was collected 2 months ago, on the 29th of January. So, it's nice to see that they work now too (although we have already seen that length feed forward signals are good over a many-month period).
In uncalibrated units (I need to calibrate the QPD to microrad, and should probably quote the PD signals in RIN), here is the plot. Blue trace (taken first) was with the feed forward on. Red trace (taken immediately afterward) was with feed forward off. This data is all PRMI-only, locked on REFL165 using Koji's recipe from elog 11174, including changing REFL165 phase to -14deg (from the -110 I found it at) for the no-arms case.
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.
The 40m fenced area will start storing this large ~ 8000 lbs chamber on April 14. The asphalt will be cut, jack hammered the next 2-3 days in order to lay concrete.
Their schedule is from 8 to 5 starting tomorrow. We are asking them to work from 6 to 3pm
ETMX is about 12-15 ft away
Since none of us here are experts in pearl, I have put together a python script for a simple PID controller. This can be imported into any main scripts that will run the actual PID loop. The script, PID.py, exists in /scripts/general/
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.
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.
Have you tried a different set of laser temperatures?
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.
ITMX, ETMY, BS and SRM are oscillating ?
The BS oplev has been misbehaving and kicking the optic from time to time since noon. The kicks are not strong enough to trip the watchdogs (current watchdog max counts for the sensors is 135).
I took a look at the spectrum of the BS oplev error in pit and yaw with both loops enabled while the optic was stable. There is nothing alarmingly big except for some additional noise above 4Hz.
I have turned the BS oplev servo OFF for now.
I saw this kicking before
I think that this happens when the beam gets too close to the edge of the QPD. We see this regularly in the ETMs, if they've been kicked a bit, but not enough to trip the watchdogs. I think it might be the step/impulse response of the RES3.3 filter, which rings for almost 20 seconds.
Anyhow, I've just recentered the BS oplev. It was at -21urad in pitch, and had more than 400 counts on the top two quadrants, but only about 100 counts on the bottom two. Now it's around 300 counts on all 4 quadrants.
As a totally unrelated aside, I have installed texlive on Donatella, so that I could run pdflatex.
This is a very cool result. I'm surprised that it can work so good. Please post what frequency dependent weighting you used on the target before running the Wiener code.
I think its important to tune it to keep the low frequencies from getting amplified by a factor of 10 (as they are in your plots). The seismometers are all just noise acting like thermometers and tilt sensors below 0.1 Hz. Temperature and tilt do not couple to our interferometer very much.
It also seems weird that you would need 20th order filters to make it work good. In any case, you can always split the SOS up into pieces before making the digital filters. For LLO, we used 3 buttons in some cases.
The 40m fenced area will start storing this large chamber on April 14. The asphalt will be cut, jack hammered the next 2-3 days in order to lay concrete.
Jackhammering was happening around 7:30am
It looks like it did no harm. It is too early to say what may have moved. Rana's worrisome email was late.
The ground preparation is completed.
Unfortunately, this kind of trend plot is not detailed enough to know if something has gone bad in a quantitative way. But at least we can tell that the suspension wire didn't break.
Q is writing the locking elog for the night, but just to reply to this thread: The IFO worked well tonight, so things are at least not broken.
Alignment is making it tough for locks to last more than 10 minutes. Many (but not all) locklosses correlate with some optic drifting away, and taking all of the light with it. The other locklosses are the quick ones that seem to pop up out of nowhere; we haven't made any headway on these. We wanted to get to a state where we could just let the interferometer sit for some minutes, to explore the data, but got caught up with alignment and PRMI things.
We're finding that both ITMs experience some DC force when entering full PRFPMI lock. I will calculate the torque expected from radiation pressure + offset beam spot, especially for ITMX, where we choose the spot position to be uncontrolled by ASS.
I set up the QPD ASC servos to act in a common/differential way on the ETMs. The C1:ASC-XARM_[PIT/YAW] filter modules act on the common alignment, whereas the C1:ASC-YARM_[PIT/YAW] filter modules act on the differential alignment. This can soon be cleaned up with some model renaming to reduce confusion.
Using DC oplev values as a guide, we are hand tuning ITM alignment once the AO path is engaged and we see the DC drift occurring. Then, we set the QPD servo offsets and engage them.
In this manner, we were able to lock the interferometer at:
We made the PRMI transition to 1f numerous times, but found that the sideband power fluctuations would get significantly worse after the transition.
We found that the gains that were previously used were too small by a factor of a few. There is a DC change visible in REFL165 before and after the transition (Also POP55, aka REFL55, is not DQ'd ). Really, it isn't certain that we've zero'd the offset in the CARM board either, so REFL55's zero crossing isn't necessarily more trustworthy that REFL165's. We can go back in the data and do some 2D histograming to see where in the error signal space the sideband power is maximized.
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.
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.
I was poking around with the PDFR hardware today.
I moved the Agilent which had its screen projected on the monitor. I have put it back...but please verify the settings before using it for tonight.
blarg. Chrome ate my elog.
112607010 is the start of five minutes on all whitened 1F PDs. REFL55 has more low frequency noise than REFL165, I think we may need more CARM supression (i.e. we need to think about the required gain). This is also supported by the difference in shape of these two histograms, taken at the same time in 3f full lock. The CARM fluctuations seem to spread REFL55 out much more.
I made some filters and scripts to do DC coupling of the ITM oplevs. This makes maintaining stable alignment in full lock much easier.
I had a few 15+ minute locks on 3f, that only broke because I did something to break it.
Here's one of the few "quick" locklosses I had. I think it really is CARM/AO action, since the IMC sees it right away, but I don't see anything ringing up; just a spontaneous freakout.
There was a period of short unexpected jackhammering this morning. I asked them to stop.
The good mood of GTRX was not changed.
Small steps tonight, but all in the forward direction.
On one of my better locks, I saw a kind of weird phenomenon with the PRMI sideband powers versus the carrier powers:
For the last 100 seconds of this plot, I'm all 1f. Alignment is being handled mostly by Q's DC coupled ITM oplevs, and the transmission QPD ASC loops, although I was trying to adjust the offsets in the ASC loops to improve transmission for a bit.
At the very end, the last 10 seconds or so, the POP110 power goes down, and sits at about half it's maximum value. POP22 isn't quite as bad, in that it still touches the max, but the RIN is about 50%. The carrier DC signals (TRX, TRY, POPDC) don't see this huge jump. I don't think I was touching anything the last few tens of seconds. I'm not sure yet how I can so significantly lose sideband power, without losing a similar amount of carrier power.
The ring-ups at about -70sec in the CARM and DARM outs are the bounce mode.
I tried looking at 2D histograms of different combinations of channels, for the time around -30 seconds where things looked pretty clean. It looks like the offsets that Q put in last night (+1 for MICH_B and -3 for PRCL_B) are still about right. The PRCL_IN1 and MICH_IN1 were centered around zero at the maximum power points. CARM and DARM had small offsets, which I put into the DARM_B and CARM_B filter banks (0.0066 for DARM_B, and 0.027 for CARM_B), although these are small enough that I don't know that they really do anything.
As a break from locking for a little while, I tried to see if I could get the TT3 and TT4 DAC channels to work for me. I had hoped it would be a quick and easy task, but I'm not seeing signal out. Since it wasn't working, I decided to go back to locking for the night, and look into the DAC in the daytime. I want to use one channel as the IN2 input of the CM board, and another as the external modulation input to the Marconi for transfer functions, so I need them to work.
As a side note on the input to the Marconi situation, it occurred to me that instead of laying a new cable, I can borrow the POP55 heliax. We don't have a POP55 diode right now, and the other end comes out across the hall from the Marconi, so it would be pretty easy to have a medium-length cable go from ITMX table to the Marconi. Objections to this?
I saw this same kind of behavior in my locklosses on Wednesday night; we should check out the 165 data, and see if the 3f PRCL error signal shows some drift away from zero.
Also, it's odd that CARM_IN1 and REFL11_I_ERR have different low frequency behavior in the plot you posted. I guess they have some difference in demodulation phase. REFL11_I's bump at -40sec coincides with the dip in arm power and a rise in REFLDC, but ASDC seems pretty smooth, so maybe it is a real CARM fluctuation.
I set the REFL11 analog demodulation angle (via cable length) about a year ago (ELOG 9850), with some assumption about PRCL having the same demod angle as CARM, but this was probably set with the arms misaligned. We should recheck this; maybe we're coupling some other junk into CARM.
I did a quick measurement get an idea of the ETM actuator calibration, relative to the ITMs. This will still hold if/when we revisit the ITM calibration via the Michelson.
For the test masses, I locked the arms individually using MC2 as the actuator, and took transfer functions from the SUS-[OPTIC]_LSC_EXC point to the PO[X/Y]_I_ERR error signals. There were two points with coherence less than 99% that I threw away. I then took the fraction at each point, and am using the standard deviation of those fractions as the reported random error, since the coherence was super high for all points, making the error of each point negligible relative to their spread.
With the data from ELOG 8242, this implies:
MC2 data was taken with the arms locked with the ETMs. The results are not so clean, the fractions don't line up; there is some trend with excitation frequency... The ratio is around the same as the ETMs, but I'm not going to quote any sort of precision, since I don't fully understand what's happening. Kind of a bummer, because it struck me that we could get an idea of the arm length mismatch by the difference in IMC frequency / arm FSR. I'll think about this some more...
I didn't verify that the loop gain was low enough at the excitation frequencies.
I put a 1kHz ELP in both arm servos, and got cleaner data for both. The ETM numbers are pretty much consistent with the previously posted ones, and the MC2 data now is consistent across frequencies. However, the MC2 numbers derived from each arm are not consistent.
With the data from ELOG 8242, this implies:
I've been fiddling with the mode cleaner and green beat box today, to try and get an absolute frequency calibration for MC2 motion. The AC measurements have all turned out weird, I get fractional power laws instead of the 1/f^2 that we expect from the MC2 pendulum. At DC, I get a rough number of 15 green kHz per MC2 count, but this translates to ~7e-10 m/count which is in contrast to the 6e-9 m/count from 2009. I will meditate on this a bit.
In any case, while working at the IOO rack, I tuned the 11MHz modulation frequency, as was done in ELOGs 9324 and 10314, by minimizing one of the beats of the 11MHz and 29.5MHz sidebands.
The new modulation frequency / current IMC FSR is 11.066209 +- 1 Hz, which is a only a few ppm change from the tuning from last July.
This implies a IMC round trip length of 27.090800m +- 2um.
Attached is a plot showing the beat of 55-29.5 going down as I changed the marconi frequency.
It is here.
I spent some time tonight trying to revive DRMI locking, with the arms held off on ALS. Not much news, I haven't been able to get more than a few short spurts of resonance, using 1F signals.
I did use SRY to measure the BS->SRCL coupling by exciting each mirror and looking at their relative coupling to AS55Q. I found that we should use a value of +0.28 +-0.01 in the MICH->SRM element.
CDSutlils has been updated to the newest version, 474; there are some matrix interface methods that will make our locking scripts easier to read, modify, and maintain.
I've tested the ALS and CARM down scripts, and the LSC offsets script, and they all work fine.
The SUS align/misalign scripts don't work after the new CDS utils upgrade.
I don't know if it's looking for the _SWSTAT channel to confirm that the offset has been turned on/off, or if it is trying to set that channel, to do the switching, but either way, the script is failing. Recall that our version of the RCG still has _SW1R and _SW2R, rather than the newer _SWSTAT for the filter banks.
ezca.ezca.EzcaConnectError: Could not connect to channel (timeout=2s): C1:SUS-PRM_OL_PIT_SWSTAT
Q, can you please (please, please, pretty please) undo this upgrade, and then hold off on any further changes to the system for a few weeks?
The DAC was fine. I realized tonight that the digital filter bank outputs were off, so I wasn't actually sending signals out. Oooops.
Q remotely reverted this change. Scripts seem to work again.
The IFO_overview of oplevs seems ok, The servos are working fine. The green arms are locked, but master and oplev_summary monitoring screens are not.
I'm proposing to Erick G. to postpone the oplev noise measurement.
Does anyone know where the Busby or Rai low noise pre-amp boxes are?
I think I need one in order to measure the noise of the Marconi. Right now, I am trying to measure the amplitude noise, but I'm not seeing anything on the SR785 above the analyzer's noise level.
The Rai box was in the Cryo lab, and the Busby box was in the TCS lab. Neither had been signed out. Lame. Anyhow, thanks to Evan and Zach's memories of having seen them recently, they have been returned to the 40m where they belong. (Also, I grabbed a spare Marconi while I was over there, for the phase noise measurement).
The laser below is dead. JDSU 1103P, SN P845655 lived for 3.5 years.
JDSU 1103P died after 4 years of service. It was replaced with new identical head of 2.9 mW output. The power supply was also changed.
The return spots of 0.04 mW 2.5 mm diameter on qpds are BS 3,700 counts and PRM 4,250 counts.
It was replaced by JDSU P/N 22037130,( It has a new name for 1103P Uniphase ) sn P919639 of mfg date 12-2014
Beam shape at 5 m nicely round. Output power 2.8 mW of 633 nm
BS spot size on qpd ~1 mm & 60 micro W
PRM spot size on qpd ~1 mm & 50 micro W