Gabriele and I talked for a while on Wednesday afternoon about ideas for transitioning to IR control, from ALS.
I think one of the baseline ideas was to use the sqrt(transmission) as an error signal. Gabriele pointed out to me that to have a linear signal, really what we need is sqrt( [max transmission] - [current transmission] ), and this requires good knowledge of the maximum transmission that we expect. However, we can't really measure this max transmission, since we aren't yet able to hold the arms that close to resonance. If we get this number wrong, the error signal close to the resonance won't be very good.
Gabriele suggested maybe using just the raw transmission signal. When we're near the half-resonance point, the transmission gives us an approximately linear signal, although it becomes totally non-linear as we get close to resonance. Using this technique, however, requires lowering the finesse of PRCL by putting in a medium-large MICH offset, so that the PRC is lossy. This lowering of the PRC finesse prevents the coupled-cavity linewidth of the arm to get too tiny. Apparently this trick was very handy for Virgo when locking the PRFPMI, but it's not so clear that it will work for the DRFPMI, because the signal recycling cavity complicates things.
I need to look at, and meditate over, some Optickle simulations before I say much else about this stuff.
I made some small edits to the LSC screen.
* When I added columns for the new AS110 PD, I had forgotten to make the Trigger matrix and Power Normalization matrix icons on the screen bigger, so we weren't seeing the last 2 columns in the overview screen.
* I added "show if not zero" oscillator icons to the Sensing Matrix part of the LSC overview screen, so that it's easier at a glance to see that there is an oscillator on.
I think Steve is trying to align the end transmission QPDs, since the arms are locked nicely right now. I noticed that the QPDX pitch and yaw signals were digital zeros. A quick look determined that the QPDX matrix to go from 4 quadrants to 3 degrees of freedom had been filled in for the POS row, but not pitch and yaw. So, I copied the QPDY matrix over to QPDX (so the ordering of the rows and columns is assumed to be the same).
Hopefully this will get us close to centered, but I suppose we ought to check really which quadrant is which, by shining a laser pointer at each quad at each end.
Steve has promised to add another row of fuses to the LSC rack first thing in the morning. Then, during Wednesday Chores, we can move the wires from the power supply to the fused power.
STEVE: NEVER MIND about doing this in the morning. Let's chat at the lunch meeting about what needs to be done to power things down, then back up again, in a nice order, and we can do it after lunch.
So, please do not do anything to the LSC rack tomorrow! Thank you.
We looked at the time series for all the oplevs except the BS, from last Tuesday night, during a time when we were building up the power in the arms. We conclude from a 400 second stretch of data that there is not discernible difference in the amount of motion of any optic, when the cavities are at medium power, and when they're at low power. Note however, that we don't have such a nice stretch of data for the really high powers, so the maximum arm power in these plots is around 5. Both the TRX and TRY signals look fairly stationary up to powers of 1 or 2, but once you get to 4 or 5, the power fluctuations are much more significant. So, since this isn't caused by any optic moving more, perhaps it's just that we're more sensitive to optic motion when we're closer to resonance in the arms.
However, from this plot, it looks like the ETMY is moving much more than any other optic. On the other hand, ETMY has not ever been calibrated (there's an arbitrary 300 in there for the calibration numbers on the ETMY oplev screen). So, perhaps it's not actually moving any more than other optics. We should calibrate the ETM oplevs nicely, so we have some real numbers in there. ETMX also only is roughly calibrated, relative to the OSEMs. We should either do the move-the-QPD calibration, or a Kakeru-style pitch and yaw some mirrors and look at transmitted power.
Traces on this xml file have been filtered with DTT, using zpk(,[0.03],1,"n").
Something funny is going on with the framebuilder's communication with the LSC machine.
This is a different failure mode / error than I have seen before. It's not the type of problem that is solved by restarting the mxstreams (that is indicated by also the 2 blocks on top of one another, that are green on the lsc machine right now, being red), although I did try that, before I looked closer and realized that that wasn't the problem.
ssh-ing to c1lsc, and doing a "rtcds restart all" seems to be fixing the problem. Both c1oaf and c1cal needed another round of restarting, because they needed their BURT buttons pressed manually. All of the models on the lsc machine are running fine now, though.
Here's a screenshot of the CDS overview screen, with the error lights:
We have decided that, rather than replacing the power source for the amplifiers that are on the rack, and leaving the Thorlabs PD as POP22/110, we will remove all of the temporary elements, and put in something more permanent.
So, I have taken the broadband PDs from Zach's Gyro experiment in the ATF. We will figure out what needs to be done to modify these to notch out unwanted frequencies, and amplify the signal nicely. We will also create a pair of cables - one for power from the LSC rack, and one for signal back to the LSC rack. Then we'll swap out the currently installed Thorlabs PD and replace it with a broadband PD.
Between the 40m meeting, and chatting with Gabriele, there was lots of talking yesterday about our 40m Lock Acquisition game plan.
From those talks, here is my current understanding of the plan, in a Ward-style cartoon:
(This is a 2 page document - description of steps is on 2nd page)
If you look closely, you will notice that there are several places that I have used "?" rather than numbers, to indicate what RFPD signal we should be using. To fill these in, I need to look at some more simulations, and think more carefully about what signals exist at what ports, and what SNR we have at each of those ports.
Also, while the overall scale of the arm power plot is correct, the power level at each step is totally arbitrary right now, and should just be taken to mean places (in time) where the CARM offset is reduced a little more.
There are several things at this point that we know we need to look into:
* POP 22/110 PD and filtering electronics should be switched to a broadband PD, rather than the Thorlabs PD + Miniciruits filters. (Hardware)
* Whitening for the transmission QPDs needs to be thought about more carefully. (Calculation, then hardware)
* Chose a good SNR REFL DC signal, which may or may not be from the PD we are currently using (I think it's the DC of REFL11, but I'll have to check). (Calculation)
* For DRMI locking, what is the size of the SRCL error signal at AS55, AS165, and the REFL ports? Do we need to lock with AS port, and then switch over to a REFL 3f port, to make acquisition easier? (Simulation)
* Similarly, I want to make the equivalent of Figure 3 of T1000294, with our 40m parameters. (Simulation)
* To set the phase of AS110, simulate the demod phase of AS110 in both DRMI and SRMI cases. If no (significant) change, maybe we can set the phase in the real system by misaligning the PRM, and watching the SRMI flash. (Simulation)
* Simulate an arm sweep, up to many orders of the sidebands, to see how close to the carrier resonance any sideband resonances might be. If something like the 4th order sideband resonates, and then beats with a 1st order sideband, is that signal big enough to disturb our 3f locking of the PRMI / DRMI? We want to be holding the arms off resonance with ALS closer to the carrier than any "important" sideband resonances (where the definition of "important" is still undetermined). (Simulation)
* Check if we can hand DARM from the DC transmission signals to the final RF signal while we still have a large CARM offset. Is there a point where the CARM offset is too large, and we must be still using the DC signals? (Simulation)
* At what arm power level can we transition from ALS to IR DC transmission signals for the individual arms? (Simulation)
* Still need to finish calculating what could be causing our big arm power fluctuations (Test mass angular motion? PRM angular motion? ALS noise?) (Calculation)
Replys, and comments are welcome, particularly to help me understand where I may have (likely did) go wrong in drawing my cartoon.
Here is a photo of the board inside the broadband photodiode (one of them) that I took from the Gyro experiment:
This PD is Serial Number S1200271.
We need to have a look at the schematic, figure out what's in here now, and then modify this to be useful (appropriate resonances / notches, as well as amplification) for POP 22/110.
I have done a sweep of CARM, while looking at the fields inside of one arm (I've chosen the Xarm), to see where any resonances might be, that could be causing us trouble in keeping the PRMI locked as we bring the arms into resonance.
Since Gabriele pointed out to me that we're using the 3x55MHz signal for locking, we should be most concerned about resonances of the higher orders of 55, and not of 11. So, on this plot, I have up to the 6th order 55 MHz sidebands, which are 332 MHz. Although the Matlab default color chart has wrapped around, it's clear that the carrier is the carrier, and the +4f2, which is the same blue, is not the giant central peak. So, it's kind of clear which trace is which, even though the legend colors are degenerate. Also, the main point that I want to show here is that there is nothing going on near the carrier, with any relevant amplitude. The nearest things are the plus and minus 55 MHz sidebands themselves, and they're more than 50 nm away from the carrier.
Recalling from elog 9122, the PRFPMI and DRFPMI linewidths are about 40pm. 50pm away from the resonant point is ~1/10 the power, and 100pm away from the resonant point is ~1/100 the power. So, 50 nm is a looooong ways away.
Just for kicks, here is a plot of all the resonances of the 1f and 2f modulation frequencies, up to 30*f1, which is the same 6*f2:
The resonances which are "close" to the carrier are the 9th order 11 MHz sidebands, and they're 280pm from the carrier, so twice as far as we need to be, to get our arm powers to ~1/100 of the maximum, and, they're a factor of ~1e4 smaller than the carrier.
I have the X end transmission QPD, as well as the whitening board, out on the electronics bench. Since the Thorlabs high-gain TRX PD also goes through this whitening board, we have no transmission signal for the Xarm at this time. The whitening board was in the left-most slot, of the top crate in the Xend rack. The only cables that exist for it (like the Yend), are the ribbon from the QPD, the 4-pin lemo from the Thorlabs PD, and the ribbon going to the ADC.
I have taken photos, and want to make sure that I know what is going on on the circuits, before I put them back in.
The whitening board:
I think that our problem of seeing significant arm power fluctuations while we bring the arms into resonance during PRMI+arms tests is coming from PRM motion. I've done 3 calculations, so I will describe below why I think the first two are not the culprit, and then why I think the PRM motion is our dominant problem.
ALS length fluctuations
Arm length fluctuations seem not to be a huge problem for us right now, in terms of what is causing our arm power fluctuations.
What I have done is to calculate the derivative of the power in the arm cavity, using the power buildup that optickle gives me. The interferometer configuration I'm using is PRFPMI, and I'm doing a CARM sweep. Then, I look at the power in one arm cavity. The derivative gives me Watts buildup per meter CARM motion, at various CARM offsets. Then, I multiply the derivative by 60 nm, which is my memory of the latest good rms motion of the ALS system here at the 40m. I finally divide by the carrier buildup in the arm at each offset, to give me an approximation of the RIN at any CARM offset.
I don't know exactly what the calibration is for our ALS offset counts, but since we are not seeing maximum arm cavity buildup yet, we aren't very close to zero CARM offset.
From this plot, I conclude that we have to be quite close to zero offset for arm length fluctuations to explain the large arm power fluctuations we have been seeing.
AS port contrast defect from ETM motion
For this calculation, I considered how much AS port contrast defect we might expect to see given some ETM motion. From that, I considered what the effect would be on the power recycling buildup.
Rather than doing the integrals out, I ended up doing a numerical analysis. I created 2 Gaussian beams, subtracted the fields, then calculated the total power left. I did this for several separations of the beams to get a plot of contrast defect vs. separation. My simulated Gaussian beams have a FWHM of 1 unit, so the x-axis of the plot below is in units of spot motion normalized by spot size.
Unfortunately, my normalization isn't perfect, so 2 perfectly constructively interfering beams have a total power of 0.3, so my y-axis should all be divided by 0.3.
The actual beam separation that we might expect at the AS port from some ETM motion (of order 1e-6 radians) causing some beam axis shift is of the order 1e-5 meters, while the beam spot size is of the order 1e-3 meters. So, in normalized units, that's about 1e-2. I probably should change the x-axis to log as well, but you can see that the contrast defect for that size beam separation is very small. To make a significant difference in the power recycling cavity gain, the contrast defect, which is the Michelson transmission, should be close to the transmission of the PRM. Since that's not true, I conclude that ETM angular motion leading to PRC losses is not an issue.
I still haven't calculated the effect of ITM motion, nor have I calculated either test mass' angular effect directly on arm cavity power loss, so those are yet to be done, although I suspect that they aren't our problem either.
I think that the PRM moving around, thus causing a loss in recycling gain, is our major problem.
First, how do I conclude that, then some thoughts on why the PRM is moving at all.
theta = 12e-6 radians (ref: oplev plot from elog 9338 last week)
L = 6.781 meters
g = 0.94
a = theta * L /(1-g) = 0.0014 meters axis displacement
w0 = 3e-3 meters = spot size at ITM
a^2/w0^2 = 0.204 ==>> 20% power loss into higher order modes due to PRM motion.
That means 20% less power circulating, hitting the ITMs, so less power going into the arm cavities, so less power buildup. This isn't 50%, but it is fairly substantial, using angular fluctuation numbers that we saw during our PRMI+arms test last week. If you look at the oplev plot from that test, you will notice that when the arm power is high (as is POP), the PRM moves significantly more than when the carrier buildup in the cavities was low. The rms motion is not 12 urad, but the peak-to-peak motion can occasionally be that large.
So, why is that? Rana and I had a look, and it is clear that there is a difference in PRM motion when the IFO is aligned and flashing, versus aligned, but PSL shutter is closed. Written the cavities flash, the PRM gets a kick. Our current theory is that some scattered light in the PRC or the BS chamber is getting into the PRM's OSEMs, causing a spike in their error signal, and this causes the damping loops to push on the optic.
We should think a little more on why the PRM is moving so much more that any other optic while the power is building up, and if there is anything we can do about the situation without venting. If we have to, we should consider putting aluminum foil beam blocks to protect the PRM's OSEMs.
The restore scripts from the IFO config screen half-failed, with this error:
Warning: "Virtual circuit disconnect"
Source File: ../cac.cpp line 1214
Current Time: Wed Nov 13 2013 17:24:00.389261330
Jamie, do you know what this might be? When requested, ETMY was not misaligned or restored, but we got these errors. So, somehow we're not talking properly to EY, but other things seem fine (the models are running okay, the suspension is damped, etc, etc.)
Nic and Evan put the ISS together (elog 9376), and we used an injection into the error point (?) to modulate the laser power before the PMC (The AOM had a bias offset, but there is no loop). This gives us some RIN, that we can try to correlate with the PRM OSEM sensors.
We injected several lines, around 100, 200, 500 and 800 Hz. For 100, 200 and 800 Hz lines, we see a ratio between POPDC and the OSEM sensors of 1e-4, but at 500 Hz, the ratio was more like 1e-3. We're not sure why this ratio difference exists, but it does. These ratios were true for the 4 face OSEMs. The side OSEM saw a slightly smaller signal.
For these measurements, the PRMI was sideband locked, and we were driving the AOM with an amplitude of 10,000 counts (I don't know what the calibration is between counts and actual drive, which is why we're looking at the POPDC to sensor *ratio*).
To get a more precise number, we may want to consider locking the PRMI on carrier, so we have more power in the cavity, and so more signal in the OSEMs.
These ratios look, by eye, similar to the ratios we see from the time back on 30 Oct when we were doing the PRMI+2arms test, and the arms were resonating about 50 units. So, that is nice to see some consistency.
This time series is from 1067163395 + 27 seconds, from 30 Oct 2013 when we did the PRMI+2arms.
Ideas to go forward:
We should think about chopping the OSEM LEDs, and demodulating the PD sensors.
We should also take a look in the chamber with a camera from the viewport on the north side of the BS chamber, to see if we see any flashes in the chamber that could be going into the OSEMs, to see where we should maybe put aluminum foil shields.
AOM driving from DAC:
I found that the DAC channels for TT3 and TT4 are connected up in the simulink model, but we aren't using them, since we don't actually have those tip tilts installed. So, we hooked up the TT4 LR DAC output, which is channel 8 on the 2nd set of SMA outputs. We put our AOM excitations into TT4_LR_EXC.
In the process of figuring out what we can do to fix our PRM motion problem, I am looking at the PRM oplev.
Eventually (as in, tomorrow), I'd like to be able to simulate some optic motion as a result of an impulse, and see what the oplev loops do to that motion. (For starters, I'll take the impulse response of the OSEM loop as my time series that the oplev loop sees).
One thing that I have done is look at the oplev model that Rana put together, which is now in the noisebudget svn: /ligo/svncommon/NbSVN/aligonoisebudget/trunk/OpLev/C1
This script plots the open loop gain of the modeled oplev:
This should be compared to the pitch and yaw measured transfer functions:
In the YAW plot, there are 2 transfer functions. The first time around, the UGF was ~2.5Hz, which is too low, so I increased the gain in the C1:SUS-PRM_OLYAW filter bank from -3 to -9.
The shapes of the measured and modeled transfer functions look reasonably similar, but I haven't done a plot overlay. I suspect that the reason I don't see the same height peak as in the model is just that I'm not taking a huge number of points. However, if the other parts of the TF line up, I'll assume that that's okay.
I want to make sure that the modeled transfer function matches the measured ones, so that I know I can trust the model. Then, I'll figure out how to use the time series data with the simulated loop. Ideally, I'd like to see that the oplev loop can fully squish the motion from the OSEM kicks. Once I get something that looks good (by hand-tweaking the filter shape), I'll give it a try in the actual system. We should, as soon as I get the optimal stuff working, redo this in a more optimal way. Both now, and after I get an optimal design, I'll look at the actual step and impulse responses of the loop, to make sure there aren't any hidden instabilities.
Other thoughts for the night:
Rana suggests increasing the gain in some of the oplev QPD heads (including PRM), so that we're getting more than a few hundred counts of power on each quadrant. Since our ADCs go to 32,000 counts, a few hundred is very small, and keeping us close to our noise limits.
Also, just an observation, but when I watch the REFL camera along with POP and AS, it's clear that the PRM is getting kicked, and I don't have the ETMs aligned right now, so this is just PRMI flashes. There is also a lot of glow in the BS chamber during flashes (as seen on the PRM face video camera).
Warning: "Virtual circuit disconnect"
Source File: ../cac.cpp line 1214
Current Time: Wed Nov 13 2013 17:24:00.389261330
This problem is now worse - the sliders on IFO_ALIGN for ETMY are white. I can't telnet to the machine either, although auxex works okay. Rather, it looks like maybe I'm getting to auxey, but then I'm immediately booted. I can ping both c1auxex and c1auxey with no problem.
Heeeeelllp please. Is this just a "shut off, then turn back on" problem? I'm wary of hard rebooting things, with all the warnings and threats in the elog lately. I've sent an email to Jamie to ping him.
There are some vague instructions in the wiki, but they begin at doing the burt restores, not actually restarting the computers: wiki Back in July, elog 8858 was written, from which the wiki instructions seem to be based. But in the elog it says "...went to the /cvs/cds/caltech/target/ area and started to (one by one) inspect all of the targets to see if they were alive.", but I don't know what "inspected" means in this case. I probably should, since I've been here for something like a millennia, but I don't.
controls@rossa:~ 0$ telnet c1auxey
Connected to c1auxey.martian.
Escape character is '^]'.
Connection closed by foreign host.
controls@rossa:~ 1$ telnet c1auxex
Connected to c1auxex.martian.
Escape character is '^]'.
controls@rossa:~ 0$ telnet c1auxey
Connected to c1auxey.martian.
Escape character is '^]'.
Connection closed by foreign host.
Please just try rebooting the vxworks machine. I think there is a key on the card or create that will reset the device. These machines are "embeded" so they're designed to be hard reset, so don't worry, just restart the damn thing and see if that fixes the problem.
This is what I remember doing all the time when Rob was around, but with all the new computers, I forgot whether or not this was allowed for the slow computers.
Anyhow, I went down there and keyed the crate, but auxey isn't coming back. I'll give it a few more minutes and check again, but then I might go and power cycle it again. If that doesn't work, we may have a much bigger problem.
I went and keyed the crate again, and this time the computer came back. I burt restored to Nov 10th. ETMY is damping again.
It crossed my mind that, from these pictures, it could be glow from the oplev scattered light that is causing the problem. However, that seems not possible, since the power fluctuations that we see depend on the presence of the IR light - if it were the oplev light, then when I close the PSL shutter, I should see the same amount of kick, which I don't. Also, the amount of fluctuation increases with increased stored power in the cavities. Also, also, Steve reminds me that some of the MC mirrors see similar kicks in their OSEM signals, but they don't have oplevs.
So, I don't believe that the oplev light is causing the problem, but I wanted to write down why I don't think that's it.
Investigations into OSEM and oplev loops to get rid of the kicks are continuing.
I have created a new filter for the PRM oplev damping loops. The biggest change is an increase in the gain between 0.4 - 7 Hz.
Here is a plot of the old, and my new modelled open loop gain:
When I look at my step and impulse response time series, the notches for the bounce and roll were causing some ringing, so for now they are turned off, both in the model and in the real time system. Also, the "OLG orig" trace has a 4th order elliptic lowpass at 75 Hz, but the real system had a 4th order elliptic low pass at 35 Hz. When we use 35 Hz in the model, we get lots of ringing. So, we have moved both model and real system to 55 Hz 4th order elliptic low passes. Also, also, we haven't been using the 3.3 Hz resonant gain, so I removed that from the modelled loop.
I have put the "boost" for the .4-7 Hz emphasis into FM 7 of the PRM oplev filters. I also removed several old filters that are never used. So, for now, the PRM oplevs should have engaged: FM 1, 7, 9. Pitch gain is +5, yaw gain is -9. We can consider re-implementing the bounce-roll notches, and the stack resgain if it looks like those are getting rung up, and causing trouble.
Here is a set of spectra, showing the improvement. It's unclear why yaw is worse than pitch below 4Hz, and why pitch is so much worse than yaw between 4-15 Hz, however for each of pitch and yaw, the before (reference pink and cyan traces) is higher than the improved (dark red, dark blue traces) between a few tenths of a Hz up to 3ish Hz. And, we're not causing more noise elsewhere. We do want to monitor to make sure we're not ringing up the bounce and roll modes, but for now they seem fine.
The auxey machine is back, in that I can interact with the IFO_ALIGN sliders, and they actually make the optic move, but I still can't read and write to and from the EPICs channels:
controls@rossa:/opt/rtcds/caltech/c1/medm/MISC/ifoalign/burt 0$ cdsutils read C1:SUS-ETMY_PIT_COMM
Warning: "Virtual circuit disconnect"
Source File: ../cac.cpp line 1214
Current Time: Mon Nov 18 2013 21:13:52.044973819
Could not connect to channel (timeout=2s): C1:SUS-ETMY_PIT_COMM
controls@rossa:/opt/rtcds/caltech/c1/medm/MISC/ifoalign/burt 1$ cdsutils read C1:SUS-ETMY_YAW_COMM
Warning: "Virtual circuit disconnect"
Source File: ../cac.cpp line 1214
Current Time: Mon Nov 18 2013 21:14:07.040168660
Could not connect to channel (timeout=2s): C1:SUS-ETMY_YAW_COMM
This is also causing trouble for the BURT save and BURT restore scripts, that are called from the IFO_ALIGN screen. If I look at the log that is written from an attempted 'save' of the slider values, I see:
**** READ BURT LOGFILE
--- Start processing files
preprocessing ... done
pv >C1:SUS-ETMY_PIT_COMM< nreq=-1
pv >C1:SUS-ETMY_YAW_COMM< nreq=-1
--- End processing files
--- Start searches
C1:SUS-ETMY_PIT_COMM ... ca_search_and_connect() ... OK
C1:SUS-ETMY_YAW_COMM ... ca_search_and_connect() ... OK
--- End searches
Waiting for 2 outstanding search(es) ...
Waiting for 2 outstanding search(es) ...
did not find 2
--- Start reads
C1:SUS-ETMY_PIT_COMM ... not connected so no ca_array_get_callback()
C1:SUS-ETMY_YAW_COMM ... not connected so no ca_array_get_callback()
--- End reads
--- Start wait for pending reads
-- End wait for pending reads 0 outstanding read(s)
**** END BURT LOGFILE
The burt save file has no values in it. Even if I copy over the ETMX save file and put in the correct channel names and values, a burt restore is unsuccessful.
So, I can do locking tonight by restoring and misaligning by hand, but this sucks, and needs to be fixed. Other optics (at least PRM, SRM, ETMX) seem to be working just fine. It's just ETMY that has a problem.
After I aligned the IR interferometer (no ASS - we still need to figure out what's going on with that), I am trying to find the green beatnotes for each arm.
First, I locked the green lasers to each arm.
I then went out to the PSL table and aligned the Green Yarm path by overlapping the near-field and far-field of the yarm transmission and the PSL green pickoff. I then turned on the power for the Beat PDs, since it was off (I confirmed that the outputs were plugged into the beatbox, so they are seeing 50 ohms). I assume that the beat PDs were off since Manasa pulled the Beatbox last week, but there is no elog reference!! Anyhow, after seeing a real signal, I maximized the DC power on the beat PD for the Yarm. I then maximized the light on the DC transmission PD for the Yarm.
I looked at the Xarm, and the near-field alignment looks okay, but I haven't checked the far-field.
I started looking for the beatnotes from the control room:
I am changing the SLOW_SERVO2_OFFSETs by 30 counts, and then unlocking and relocking the arms, and checking to see if I see a peak on the RF spectrum analyser.
The Y offset started at -10320, and I found a beatnote at -11230 (beatnote is about 26MHz). The X offset started at 4500. Going larger seemed to get me to a less bright TEM00 mode, so I switched and have been searching by going down in offset, but haven't yet found the beatnote. I suspect that I actually need to align the X path on the PSL table. The Y beatnote is very small, about -30dBm, so I also need to tweak the alignment by maximizing the peak value.
EricQ said that he's going to start hanging out at the 40m a bit, and I was thinking about what I can have him help me with. This lead to me writing up a wishlist for things that have to do with the ALS system and green lasers. Some of these are very small tasks, while others are pretty big. They are certainly not all high priority. But, they're on my wishlist.
Automation / script writing
I am able to lock the Yarm ALS, but not at the full gain that I should be. I attribute this to my mediocre alignment of the path on the PSL table. EDIT: Manasa pointed out that I forgot to set the PSL FSS slow adjust to ~zero, so the PSL temperature was off, so there wasn't really any hope for me last night.
However, I decided that I should write down the ALS locking procedure, as shown to me by Masayuki on 29Oct2013, that is written in one of the Control Room notebooks. So, here it is. I will write channel names and DTT template names for the Y arm, but the procedure is the same for both arms.
I forgot how we could turn on the PRM oplev servo and the PRM ASC servo at the same time without conflict.
It seems that this new oplev servo covers 0.04 to 8Hz. It's pretty broadband. Do we inject the ASC signal to the oplev error?
Right now all 3 servos that control PRM angle (OSEM damping, Oplev, and ASC) run in parallel, and they're all AC coupled.
The ETMY sliders on IFO_ALIGN were white again this morning, so I went down to the Yend and pushed the RESET button on auxey. I then did a burt restore to 00:07am this morning for both auxey and auxex (since the stickers on the machines are still the old naming convention, I wonder if the autoburt is also backwards, so I did both). Now the 'save' and 'restore' scripts for ETMY are working again.
Hopefully it's all better now, but I'll keep an eye on it.
So far this afternoon, I have redone the IFO alignment, locked both arms with ALS, moved both arms off resonance, locked PRMI, and started bringing one arm back to resonance.
The alignment was really not good, which I knew yesterday, but the ASS wasn't working yesterday. I hand-did the alignment, and tried locking, which was easier with the slightly better alignment.
I locked both arms with ALS, found the resonances, and then moved them off resonance using Masayuki's scripts.
I then restored the PRM alignment, and locked the PRMI.
I started bringing the Yarm back, but I kept losing lock when I got to about 0.1 transmission.
After losing lock several times, I switched over to looking at the ASS. I have figured out the problem, and fixed it. The ASS for the arms now works again.
Looking at the StripTool plots of the lockin outputs for each arm, it was clear that the "L" traces were their usual size, but the "T" traces, which are demodulated versions of the transmission DC PDs, were tiny. I investigated in the model, and the answer is obvious: both the LSC and the ASS get the transmission information directly from the end sus computers. Since we recently moved the normalization gain for the transmission diodes into the SUS models from the LSC model, this means that the ASS was seeing a differently sized signal than it had in the past.
To fix this, I put a gain into the T_DEMOD_SIG filter banks for all 8 lockins that use info from the transmission DC PDs. I used 1/g , where g is the gain that is in the C1:SUS-ETM#_TR#_GAIN channels. For TRX, that number is -0.003, and for TRY that number is 0.002 . So, in the .snap file that is used when turning on the ASS, I have given the Xarm lockins a gain of -333, and the Yarm lockins a gain of 500. I chose this place, because the only thing that has happened to the signal until this point is a bandpass, so the rest of the servo gains can remain the same.
I tested the ASS, and it works just like it used to. I let it run, and align all of the optics, then I misaligned by a small amount each of the ETMs, saw that the lockin output values changed, and then were servoed back to zero. So, it seems all good.
I have increased the gain of the MICH loop to -100, and set FMs 2,3,7 to be triggered. I have also increased the PRCL gain to 2. The PRCL ASC pitch and yaw gains used to be -0.004, but I have increased them both to -0.01.
Now, I'm seeing power fluctuations in POPDC of ~200 pk-pk, at an average value of 2650. That's a RIN of 7.5% . If I turn off all OSEM damping for the PRM (after the cavities are already locked), I get POP DC fluctuations of 100 pk-pk at the same average value, so a RIN of 4%.
Back on October 30th (elog 9338), we had an average POPDC of 400, with fluctuations of 200 pk-pk, so a RIN of 50%.
So, I am pleased that, with the carrier locking, I have lower power fluctuations. And, since there is more overall power in the PRC right now than we had 3 weeks ago, I'm hopeful that a PRMI+arms test will have lower power fluctuation.
Also, a note, when my MICH gain was still low, I had lots of power fluctuation at the AS port, which was coherent with my POPDC power fluctuations (which makes sense). At that time, my overall RIN was higher than it is now (although I neglected to write down the numbers), but more significantly, I saw occasional 'kicks', where the ASDC and POPDC powers would ring for 1 or 2 seconds, with power fluctuations of order 40%. I have not seen any of those kicks since increasing the MICH gain.
We locked the PRMI on carrier again today, after lunch. Following a suggestion from the 40m meeting, we wanted to compare the PRMI carrier fluctuations with the new vs. old OpLev servo for the PRM.
To do change between the servo shapes, I put in an elliptic lowpass at 35Hz, since I overwrote that with the 55Hz lowpass the other day. The only other change between shapes is turning on and off my boost / emphasis filter.
So, the scenarios were:
(1) New OpLev servo
(2) Old OpLev servo (no boost, but 3.2Hz res gain and bounce roll notches on), with 55Hz lowpass
(3) Old OpLev servo with 35Hz lowpass
For scenario (1), like last night, there were small power fluctuations. For scenario (2), most of the time there were small power fluctuations, but occasionally there would be a kick somewhere, and the power would dip down by ~50%, and the fluctuations would continue like a ringdown for a few seconds, and then we'd be back to small fluctuations until the next kick. For scenario (3), even with trying different LSC servo gains, we could not get the PRMI to lock on carrier for more than a few tenths of a second. During that time, the power fluctuations were very large.
So, the old oplev servo was kind of okay, but the lowpass at 35 Hz was bad, bad, bad. It seems that the new OpLev servo is doing good things for us.
We have put the Xend QPD back in place, and centered it. The whitening board was replaced by me a few days ago.
We also went down to the Yend and centered the Yend QPD.
I used the offset.py script that Masayuki wrote to zero the offsets of the individual quadrants when the PSL shutter was closed, and then I averaged the output of the SUM filter banks, and made the gains 1/AvgSum, so that both the Thorlabs PD and the QPD are normalized to 1 at single-arm resonance, for each arm.
I don't know what the gain is of the QPD head off the top of my head, relative to the Thorlabs PD, but eventually we want them to be the same, so that 1=1 and 700=700 on each PD.
There is definitely a timing distribution malfunction at the c1iscex IO chassis. There is no timing link between the "Master Timer Sequencer D050239" at the 1X6 and the c1iscex IO chassis. Link lights at both ends are dead. No timing, no running models.
It does not appear to be a problem with the Master Timer Sequencer. I moved the c1iscey link to the J15 port on the sequencer and it worked fine. This means its either a problem with the fiber or the timing card in the IO chassis. The IO timing card is powered and does have what appear to be normal status lights on (except for the fiber link lights). It's getting what I think is the nominal 4V power. The connection to the IO chassis backplane board look ok. So maybe it's just a dead fiber issue?
I do not know what could have been the problem with c1auxex, or if it's related to the fast timing issue.
Steve and Koji looked around, and called around, and there seem to be no spare fibers that are long enough to reach the end, so Steve has ordered
"Tripp Lite N520-30M 100' Multimode Duplex 50/125 Fiber Optic Patch Cable LC/LC"
and it should be here tomorrow.
The new fiber arrived today, and we tried it out. No luck. We think it is the timing card, so we'll need to get one, since we can't find a spare.
Order of operations:
* Lay new fiber on floor, plugged it in at both ends, saw no fiber link lights.
* From control room, killed all models running on c1iscex, shutdown computer. Still no link lights.
* Power cycled computer and IO chassis.
* Tried plugging new fiber into different port on Master Timing Sequencer, with other end still plugged in to c1iscex. Still no link lights.
* Looked around with flashlight at Xend IO chassis. The board that the fiber is connected to does not have a power light, although the board next to it has 2. We compared with the SUS IO chassis, and the board there with the fiber has one power light, plus the fiber link lights, as well as 2 on the board next to the fiber. So, perhaps there's a problem with power distribution on the timing board at the Xend?
* Unplugged and replugged the power connector to the timing board, inside the IO chassis, board next to the fiber's board got lights back, but the fiber's board did not. However, power must be going through the board with the fiber attached, to the next board, so there's power at least on some part of the timing board, just not the whole thing.
From this, we conclude that the blue fiber that was in place is probably fine (or is not found guilty), and that we need a replacement timing board. Koji didn't find one in the "CDS stuff" boxes underneath the Jenne Laser, and I feel like I recall Jamie saying that we would have to get a spare from somewhere else. We rolled up the new spare fiber, and put it in the box with other "CDS Stuff" under the Jenne Laser table.
I was trying to lock the Yarm, and saw that I was not getting signals to go between the LSC and SCY models. I had digital zeros for TRY, and when I overrode the trigger and tried to force signal to ETMY, I had digital zeros at the SUS-ETMY_LSC input. The corresponding filter bank in the rfm model was receiving signals, so the Dolphin connection between LSC and SUS was okay, it was just the RFM connection going to the end station that wasn't succeeding.
Koji restarted the c1scy model, and then went inside the IFO room, and found that the SUS IO chassis power was off. We must have accidentally turned it off while we were in there earlier. Koji turned on the power, and also restarted the rfm model, and we now have real signals going back and forth.
Yarm is locked, ASS worked nicely, etc, etc, so things seem normal again (with the Yarm....ETMX stuff is still out of order).
Steve was trying to do something to it this morning, but I'm not exactly clear on what it was. Maybe that helped? Steve, can you tell us what you were trying to do this morning?
1) c1auxex - fixed
Tried telnet c1auxex => rejected by the host
Went down to the south end. Power cycled the target. Came back to the control room.
=> Confirmed the epics read/write is back.
Burtrestored the epics vars for the target to the snapshot on 31th Oct at 5:07.
When I came in this morning, in addition to the fb being unhappy [elog 9436] (which Koji later fixed [elog 9437] ), c1auxex was down / not talking to the world nicely.
I tried telnet-ing, but was rejected, so EricQ and I went down to the Xend and pushed the reset button on the computer. The computer came back up just fine, and I did a burt restore to 03:07 on Nov 30th.
2 weeks ago I took some data, and remembered today at the 40m meeting that I hadn't posted it. Bad grad student.
All I'm trying to show here is that we see flashes in the arms that are larger than the ~50 units that we see saturate the Thorlabs transmission PDs. For arm power values below ~50, the QPD sum and Thorlabs PDs give approximately the same values. So, 1 unit on the Thorlabs PDs is equivalent to 1 unit on the QPD sum, and 50 units on the Thorlabs diode is equivalent to 50 units on the QPD sum.
The situation was arms held on resonance with ALS, and the PRMI was flashing.
Arm powers of ~140 imply a power recycling gain of ~7.
Last week, Koji cleaned up the LSC model to make it much more readable, while he was working on piping the ALS signals to the LSC model. However, somehow the DAQ Channels block got deleted before the model was committed to the svn. Since there were 2 months between svn checkins for c1lsc.mdl, it's possible that someone had the model open just to look at, and the block got deleted, and that's the version that Koji started with.
Anyhow, thankfully we have the svn, so Koji and I found that the DAQ Channels block was (as expected) in the previously checked-in version of the LSC model. I put a copy of the old model onto my desktop, opened it up, copied the DAQ Channels block, and then pasted it into the new cleaned-up version of the model. (Jamie - is there a way to conveniently download a previous version through the web interface?)
I have checked it in, compiled and restarted the lsc model. The _DQ channels are back now.
We still have c1mcs having regularly time-over. Can I remove the WFS->OAF connections temporarily?
Yes. I think that's a good idea, since we're not using them at this time, and we want c1mcs to behave. Maybe make an elog note of which version is the first without them, so that we can conveniently find the model(s) in the svn?
I *finally* figured out how to bend Matlab to my will, and close a very simple oplev loop using LQR technology.
This is super, super simple, but it's a step in the right direction. There is no noise, just a simple pendulum with a resonant frequency of 0.75Hz, and a Q of 10. The LQR tries to keep the position of the pendulum at a minimum, and does not care at all about the velocity. You cannot (with Matlab's LQR, at least that I can find) make it care "0" about the control output, so it cares about the control output a factor of 1e-4 as much as the position.
Here are some plots:
The first plot has the open loop system (just the pendulum, no control at all), as well as the closed loop system (the pendulum under control).
Plot 2 is the open loop gain of the controller that the LQR designed.
Plots 3 and 4 are the step and impulse responses of the open loop (pendulum with no control), and closed loop (pendulum with feedback) systems.
The conclusion from the plots (if this were an interesting system) is that it doesn't take much to damp an ideal pendulum. The real conclusion here is that I think I now know how to use the Matlab LQR function, and can make a loop with some noise now.
The ITM oplevs were pretty close to the edge of their ranges, and none of the oplevs have been centered in a while, so I centered ITMX, ITMY, BS, PRM after having done alignment (arms, then PRMI).
Tonight we worked on tweaking up the PRCL new ASC, and then PRMI+1 arm locking. We were unable to get the Xarm to stay locked on a TEM00 mode for very long, and after an hour or two of using the PZTs to try to align the beam to the cavity, we gave up and just used Yarm green.
NB: We haven't done anything to MCL, although it is not in use. Den is still going to get around to elogging what servo shaping he changed on that last night.
I wrote a script that will handle the transitions between the new PRCL ASC and the PRM oplev and local damping. The script is accessible from the PRC ASC screen, and will detect when the PRMI is locked or not. When it is locked, it will turn down the PRM oplev gains and turn on the ASC, and then it will turn off the local shadow sensor damping for PRM pitch and yaw. When the PRMI unlocks, the script will turn off the ASC and restore oplev and local shadow sensor damping.
We saw that the bounce mode of the PRM was getting rung up with our new ASC, so we included a band stop in the ASC, and also turned on the triggering for the PRCL LSC FM6, which has the resonant gain for the bounce mode (as well as roll, and the stack mode). This made the PRMI spot very stable.
We then moved on to green arm locking. The Yarm is behaving perfectly nicely (as nice as it has been lately - it's alignment and mode matching could also use some work), but Xarm was giving us a bit of trouble. As always (since the PZTs were installed?), the mode matching isn't excellent for the green to the arm, so it can be hard to catch a TEM00 mode. Also, even if we did catch a good mode, it would often not stay locked for more than a few tens of seconds. We tried several alignment tweakings, and several different end laser temperatures (within the confines of seeing the beatnote under 100MHz), and didn't have a lot of success. It looks like Eric had the slow servo engaged for the Xend laser, so the temperature offset was something like +300,000, which seemed totally crazy. I turned that off, and found the beatnote somewhere around output of -10,300. So, I haven't gone to the end to look at the temperature, but it's going to be different than when Eric was taking measurements this afternoon. It seems like the main problem with the Xarm is poor mode matching - the maximized input pointing for TEM00, when you unlock and relock the cavity, is just as likely to give you a TEM_9_0 mode, as TEM00.
So, we gave up on the Xarm for the evening, and tried PRMI+1arm, with the new PRCL ASC. This was successful! The Yarm beatnote was around laser slow servo output of +4450. Beatnote at 46.0MHz, -26dBm. We found the IR resonance, moved off, locked the PRMI, transitioned to the new ASC, and brought the Yarm back to IR resonance. What we see is that the power fluctuations in the PRC are much smaller than they were back around Halloween (elog 9338), however the arm power fluctuations still seem very, very large. This is certainly partly due to the fact that we haven't done a thorough Yarm alignment since before messing with the greens, so we will have drifted somewhat. Also, the ALS beatnote sensor isn't perfect, so won't be perfect at holding us near resonance.
Den is thinking about whether we can use the arm transmission QPD signals to feed back to the ETM ASC servos, to try to reduce the RIN in the arms. I feel like we should also see if this amount of power fluctuation can be explained by our ALS noise, because maybe we'll be fine once we transition to IR and turn off the ALS system. Attached is a plot showing that the arm's RIN is coherent with the spot motion seen by the transmission QPD, so we need to check the alignment of the cavity, as well as consider using the trans QPD in an ASC feedback loop.
Here is a plot of the PRC sideband power, as well as the Yarm transmission. The GPS time for this plot is approximately 1070963372.
I noticed that we have not been saving the 1/sqrt(TRX) and 1/sqrt(TRY) data, so I modified the c1lsc model and added them to the DAQ channels block. I restarted the c1lsc model, and the _DQ channels are now archived.
Den just plugged an output from the common mode board into an LSC whitening board (the spare channel that used to be called "PD_XXX_I" in the LSC model). I have modified the LSC model to reflect the new name of the new signal ("CM_SLOW"), and have added this channel to the LSC input matrix. Koji is, I believe, adding this channel to the LSC screen in the auxiliary error signals section. I am also adding the _OUT of the filter bank to the DAQ channels block.
I have looked at the photo of the Xend QPD from elog 9367, as well as the schematic for the board (D990272).
Things that will need swapping out:
I have ordered from digikey via techmart 10 each of the MAX333A's and the OPA140's. (4 per QPD times 2 QPDs plus 2 spares = 10). Both of these new chips have the same footprint and pinout as the part that they are replacing, so it'll be a fairly easy task.
Next up, I need to make a LISO model for the circuit for one of the quadrants, to see what shape it'll turn out to be. Part of this will include deciding what resistors and capacitors to put in the OPA140 gain stage.
Right now, the AD797s say on the schematic that the gain options are different by a factor of 5, but the actual QPD has a different resistor than is on the schematic, and there is also a capacitor in parallel with each resistor, so I need to just pull those out, and pick some values that make sense to me.
Rana and I have discussed ignoring the 2nd and 3rd gain switching options on each quadrant, as that is getting to be more fine control than we need.
Other things on the board:
For now, I will probably just work on the QPD head, and not the whitening board. For now, we can run with 1 stage of whitening, and if we need lower noise, we can revisit the whitening board (including replacing the thick film resistors with thin film).
When thinking about what gains I want on my gain stages, I want to have my full arm power (~700 TRX units) be ~20,000 counts from the ADC. So, I want my single arm power (1 TRX unit) to be ~30 counts from the ADC. This is not such a big number, so this may also require more thinking.
Somehow the POP22 and POP110 demod phases weren't correct anymore. I guess Den saw this after he changed the setup for the REFL165 PD at the LSC rack, but didn't elog it.
I went out to the LSC rack, and found that the power supply that is supplying the amplifiers for both POP22/110 and REFL165 was set to ~16V each channel. I put it back to 15V for each channel. I don't know what Den intended for the 165 amplifier (more volts is more gain), but the POP22/110 amplifier usually runs with 15V.
I also reset the POP22 and POP110 demod phases. Since I'm not able to lock PRMI on sideband this morning (why?!?!), I locked on the carrier, and moved the phases around until POP22 and POP110 were both maximally negative. The phases are/were:
This is a ~60 degree change for both PDs.
I am not sure if Den ever checked the demod phase of REFL165 after he put in the new SMA cable (there's no mention of it in the elog!), so I'm going to check that to see if it helps get PRMI locking back. I know that Den had also been using REFL11 for PRMI locking, but the parameters he used for that aren't in the log either.
I checked out the REFL165 demod phase, and it looks like it was okay. it was -20.9 degrees. I turned on my sensing matrix oscillators, and maximized the PRCL signal in the REFL165_I_ERR channel, and got a pretty good maximization at +155 degrees. I used this to lock the PRMI on sidebands, with MICH gain of +0.3, and PRCL gain of +0.1 .
Since this is working, I'm leaving the REFL 165 phase here, at +155 degrees, although this is almost exactly 180 degrees from what Den left it at, so I'm not sure why I was not able to lock with a demod phase of -20.9. (I tried all 4 permutations of signs, with gain values of the same magnitude (0.3 for MICH, 0.1 for PRCL), and wasn't able to lock. I'll try to figure this out tomorrow, but it was time for the meeting, then the IFO has been busy doing more important things the rest of the afternoon.
Plan for checking: Lock with demod phase of 155, measure TF to one of the other REFL diodes (11, 33 or 55), lock on that other REFL diode. Then, change the REFL 165 demod phase back to -20.9, and measure the transfer function again. Hopefully the answer is just that I was doing something dumb, and it works easily. This test/measurement should only take a few minutes, but it'll make me happier knowing that things still work as they should.
My hunch is that the PRC is SHORT by a few cm, not long.
In my Optickle simulation, the sidebands are not perfectly co-resonating in the PRMI when the arms are not locked. See Fig 1, which is the fields in the PRMI using the design PRC length. If I add 5cm to the PRC length, I get Fig 2, where the peaks are about the same separation, but the upper and lower sidebands have swapped sides of the 0 mark. However, if I remove 5cm from the PRC length, I get Fig 3, where the peaks are much farther apart than in Fig 1. This case looks more similar to the data that Gabriele plotted in his elog entry, where the peaks are separated by at least a linewidth. This is not at all conclusive, but it's a guess for which direction we need to move. Obviously doing an actual measurement will be better.
My tummy feelings also agree with this simulation: When we flipped PR3 (the only optic change in the PRC since Gabriele and I measured the 55MHz peak separation in April), since the HR side of the optic is now at the back, we had to push the whole suspension cage forward to get the beam aligned to the Yarm. Conversely, however, transmitting through the glass substrate adds to the optical path length. So, my tummy feelings may be wrong.
Figure 1, PRC at design length, PRMI sweep:
Figure 2, PRC 5cm longer than design length:
Figure 3, PRC 5cm shorter than design length:
I'm not sure which pointing Rana wanted to fix today, but here's a measurement of the MC spots. They actually look pretty good. There is some room for improvement, but not a lot, so I'm leaving it alone for now, while I play with other things in the IFO.
spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
[0.63368182839757914, 1.3004245778952557, 0.33621668795755993, -1.5585578137597658, -3.1344594013487286, -1.0533063060089816]
When I got in this morning at 9-something (9:45 maybe?), Steve was taking dust photos on the AS table, of the MC Refl path. Other than that, I don't have any information.
Also, Tuesday is our traditional janitor day, so I'm hesitant to put our blame there. (I think we've kept Tuesdays, even though we're on a less-often schedule....Steve will have to correct me if I'm wrong on this).