I used existing BNC cables running from the PSL table to the PSL rack and reassigned them to the PSL Shutter and PMC transmission PD channels.
The PSL shutter turned out to be a sinking channel. Jordan reconnected the PSL shutter wires to a sinking BIO Acromag. Channel list is updated.
Both channels have been tested to be working as expected.
gautam add on about EPICS:
P.S - there is a problem we noticed - if the modbus process is started with the local subnet not having a fixed IP address, then all the EPICS channels will not be responsive. The way to fix this is to run the following sequence of commands:
Jordan and I removed another 10 kg of cabling from 1X2. The c1iool0 crate now has all cabling to it disconnected - but it remains in the rack because I can't think of a good way to remove it without disturbing a bunch of cabling to the fast c1iool0 machine. We can remove it the next time the vertex FEs crash. Cross connects have NOT been removed - we will identify which cross connects are not connected to the fast system and trash those.
Do we want to preserve the ability to use the PZT driver in 1X2?
Updated noise budget curves, now computed using the latest version of pygwinc. This resolves the inconsistency between the gwinc quantum noise curves and Gautam's analytic calculations. As before, the key configuration parameters are listed in the figure titles.
Attachment 1: Phase quadrature
Attachment 2: Amplitude quadrature
Attachment 3: Comparison to aLIGO design (phase quadrature)
The quantum noise curves here are not correct. c.f. amplitude quadrature noise budget.
Had to reboot both end machines and the c1rfm model to get the TRX and TRY signals to the LSC models. Now both arms can be locked using POX/POY respectively.
Channel list with test status
== Test Status ==
[done] Lock PMC and IMC
[done] IMC Servo board test
[done] IMC LO Det Mon channel check
[0th order] WFS quadrant DC mon
[none] WFS I/F monitors
[0th order] WFS attenuators
[none] IOO QPD channels
[done] FSS readbacks
[done] PMC readbacks
Some more detailed elogs about the individual tests will follow.
Basically, I have characterized the IMC Servo board in detail. The summary finding is that the IN2 (=AO gain) slider needs to be investigated.
All other channels need to be verified in a more thorough fashion than my basic checks which were just to guarantee the core interferometer functionality, which is important to me.
[JV, JWR, YD, GV]
$TARGET_DIR = /cvs/cds/caltech/target
It remains to (Jon is taking care of these)
On Monday, we will remove the old c1psl and c1iool0 machines from the electronics rack and install the Acromag crate in a more permanent way. We will also clean up some of the old cabling and cross connects, althoug the situation seems so complicated (some cross connects are also used by the rtcds c1ioo expansion chassis) that I am inclined not to remove any cables.
The area around 1X1/1X2 has a lot of dangling cables and general detritus. Be careful if you are walking around there. We will clean up on monday.
There are several problems evident already.
For now, I've returned the old c1psl connections, the PMC and IMC are both locked. Need to do some debugging on the bench.
And so it begins.
Barring objections, tomorrow (Friday 28 Feb 2020) morning I will commence the switch
There was some UNELOGGED work at EX today. The DFD outputs were also hijacked for loss measurement. Unclear who the culprit was, but there is now a broad noise bump centered around ~180 Hz in the ALS X noise curve, which certainly wasn't there yesterday. Maybe let's keep the few working systems working, it is annoying to have to deal with these auxiliary issues every night. I'll push ahead with locking, hopefully the ALS noise is "good enough".
While my checks of the AO signal path have thrown up some unanswered questions, I don't think there's any evidence in those measurements to suggest the AO crossover can't be realized. Thinking about it today though - I was wondering if it could be that the IN1 gain slider of the CM board is configured optimally. Looking back at some data, when the ALS CARM offset is zeroed, the CM_SLOW digitized data has a peak-to-peak range of ~200 cts. This is paltry. One possibility is that as I am upping the AO path gain, I'm simply injecting the electronics noise of the CM board into the IMC error point. I'd say it is safe to up the IN2 gain by 20dB to -12 dB, in which case the peak-to-peak would be ~2000 cts, still only 10% of the ADC range. It'll be straightforward to re-scale the CARM_B loop gain to account for this. Let's see if this helps.
I'd also like to measure the spectrum of the REFL11_I signal in a few different states. I think I should be able to do this using the OUT2 of the CM servo board. These are the things to try tonight:
in prep for the install tomorrow, we did the following:
Barring objections, tomorrow (Friday 28 Feb 2020) morning I will commence the switch (I still want to work on the IFO tonight).
In 1X1, there is a box labelled "FSS REF" below a KEPCO HV supply. This box had a power cable that wasn't actually connected to any power. I removed said cable.
In the style of the KA characterization of the CM board, the AO path gain EPICS slider (IN2) of the IMC servo board was stepped by 1 dB through the full available range of -32 dB to +31 dB. For each value of the requested gain, I measured the TF from the injected signal (to IN2) to TP1A on the IMC servo board. I used the BNC connector for this test, whereas we use the LEMO connector for the AO path. The source was tee-d off at the SR785 side, with one leg going to IN2 of the IMC servo board, and the other going to CH1A of the SR785. TP1A of the IMC board was connected to CH2A of the SR785.
Attachment #1 - Measured gain vs requested gain.
Attachment #2 - Frequency dependent transfer functions
The motivation here is to try and figure out why I cannot engage the AO path smoothly in the CARM handoff part of lock acquisiton. I plan to use this information to do some loop modeling and project laser frequency noise coupling in various stages of the lock acquisition process.
Today, I did the following tests (and so was touching electronics/cables at/around 1X2):
Results to follow.
After this work, I reverted the EPICS channels to the usual values. The IMC can be locked.
To supplement the material presented during the BHD review, I've put together a projected noise budget for the 40m. Note these are the expected interferometer noises (originating in the IFO itself), not BHD readout noises. The key parameters for each case are listed in the figure title. Also attached is a tarball (attachment 4) containing the ipython notebook, data files, and rolled-back version of pygwinc which were used to generate these figures.
Attachment 1: Phase quadrature readout.
Attachment 2: Comparison to aLIGO design sensitivity (phase quadrature).
Attachment 3: Amplitude quadrature readout.
In order to measure the loss in the arm cavities in reflection, we use the DC method described in T1700117.
It was not trivial to find free channels on the LSC rack. The least intrusive way we found was to disconnect the ALS signals DSUB9 (Attachment 1) and connect a DSUB breakout board instead (Attachment 2).
The names of the channels are ALS_BEATY_FINE_I_IN1_DQ for AS reflection and ALS_BEATY_FINE_Q_IN1_DQ for MC transmission. Actually, the script that downloads the data uses these channels exactly...
We misalign the Y arm (both ITM ad ETM) and start a 30 rep measurement of the X arm loss cavity using /scripts/lossmap_scripts/armLoss/measureArmLoss.py and download the data using dlData.py.
We analyze the data. Raw data is shown in attachment 3. There is some drift in the measurement, probably due to drift of the spot on the mirror. We take the data starting from t=400s when the data seems stable (green vertical line). Attachment 5 shows the histogram of the measurement
X Arm cavity RT loss calculated to be 69.4ppm.
We repeat the same procedure for the Y Arm cavity the day after. Raw data is shown in attachment 5, the histogram in attachment 6.
Y Arm cavity RT loss calculated to be 44.8ppm. The previous measurement of Y Arm was ~ 100ppm...
Loss map measurement is in order.
We did some quick DC balancing of the MC2 coil drivers to reduce the l2a coupling. We updated the gains in the C1:SUS-MC2_UL/UR/LR/LLCOIL to be 1, -0.99, 0.937,-0.933, respectively. The previous values were 1, -1, 1, -1.
The procedures are the following:
Drive UL+LR and change the gain of LR to zero pitch.
Drive UR+LL and change the gain of LL to zero pitch.
Lastly, drive all 4 coils and change UR & LR together to zero yaw.
We used C1:SUS-MC2_LOCKIN1_OSC to create the excitations at 33 Hz w/ 30,000 cts. The angular error signals were derived from IMC WFSs.
While this time we did things by hand, in the future it should be automated as the procedure is sufficiently straightforward.
Seems that the GPS is out of sync on donatella. We could not get any data from diaggui...
The HVAC people replaced a valve and repaired the pneumatic plumbing on the roof air handler. Temperature has been stable during the day since Thursday. If anyone is in the control room during the evening, please make a note of the temperature.
to make the comparisons meaningfully
one needs to correct for the feedback changes
In order to adjust the relative phase for PDH locking, we used the Siglent SDG 1032X function generator which has two outputs whose relative phase can be adjusted.
This Siglent function generator was borrowed from Yehonathan's setup near the PSL table and can be found at the X end disconnected from our setup after our use.
Initially, we used the Siglent at 231.250 kHz and 5 Vpp from each output with zero relative phase to lock the green arm cavity. By moving the phase at intervals of 5deg and looking at the PDH error signals when the cavity was unlocked we concluded that 0deg probably looked like it had the largest linear region (~1.9 V on the yaxis. Refer elog 15218 for more information) as expected.
Then we tried the same for 225.642 kHz, 5 Vpp, and found the optimal demod phase to be -55deg, with linear region of ~3 V (Ref. Attachment 2). A 'bad' frequency 180 kHz was optimized to 10deg and linear region of ~1.5 V.
The error signals at higher frequencies appeared to be quite low (not sure why at the moment) and tuning the phase did not seem to help this much.
For the noise measurement, the IFO arms were locked to IR and green, but even after optimizing the transmission with dither, we couldn't achieve best locking (green transmission was around ~0.2). Further, the IMC went out of lock during the experiment after which Koji helped us by adjusting the gains a locking point of the PMC servo. Attachment 1 contains some noise curves for the 3 frequencies with a reference from an earlier 'good' time.
Check out this elog: ELOG 4354
If this summing box is still used as is, it is probably giving the demod phase adjustment.
Once we adjust the phase we may be able to increase the servo gain for optimal locking. Unless it may be a good idea to increase the gain without optimizing the phase?
Could you please put physical units on the Y-axis and also put labels in the legend which give a physical description of what each trace is?
It would also be good to a separate plot which has the IR locking signal and the green locking signal along with this out of loop noise, all in the same units so that w can see what the ratio is.
We proceeded with the trying to measure the ALS out-of-loop noise of the X arm when the X arm cavity is green-locked using different PDH sideband frequencies.
Before doing the experiment, Koji helped us with getting the arm cavities locked in IR using LSC (length) and ASC (angular).
With the arms locked in IR and green, we repeated the same measurements as before at different sideband frequencies (Refer Attachment 1 - label in Hz). We did not optimize the phase nor did we look at the PDH error signal today which is possibvly why we did not see an improvement in the noise. We will look into this possibly tomorrow.
We measure the IMC transfer function using SR785.
We hook up the AOM driver to the SOURCE OUT, Input PD to CHANNEL ONE and the IMC transmission PD to CHANNEL TWO.
We use the frequency response measurement feature in the SR785. A swept sine from 100KHz to 100Hz is excited with an amplitude of 10mV.
Attachment 1 shows the data with a fit to a low pass filter frequency response.
IMC pole frequency is measured to be 3.795KHz, while the ringdowns predict a pole frequency 3.638KHz, a 4% difference.
The closeness of the results discourages me from calibrating the PDs' transfer functions.
I tend to believe the pole frequency measurement a bit more since it coincides with a linewidth measurement done awhile ago Gautam was telling me about.
I think of trying to try another zero-order ringdown but with much smaller excitation than what used before (500mV) and than move on to the first-order beam.
Also, it seems like the reflection signal in zero-order ringdown (Attachment 2, green trace) has only one time constant similar to the full extinction ringdown. The reason is that due to the fact the IMC is critically coupled there is no DC term in the electric field even when the extinction of light is partial. The intensity of light, therefore, has only one time constant.
Fitting this curve (Attachment 3) gives a time constant of 18us, a bit too small (gives a pole of 4.3KHz). I think a smaller extinction ringdown will give a cleaner result.
Unlikely, the alignment was probably just not good. I restored the alignment and now the arms can be locked to IR frequency.
Even though we were not able to lock the the IR beat (by enabling LSC) during the day possibly because of increased seismic activity
Even though we were not able to lock the the IR beat (by enabling LSC) during the day possibly because of increased seismic activity, we tried to the measure the ALS beat frequency noise by changing the PDH side-band frequency to different values.
I tried choosing values that corresponded to the peaks in the PM/AM as found in elog:15206 but for some reason unknown to us the cavity did not lock between 700-800 kHz.
The three attachments have data for different sideband frequencies:
Attachment 1: 819.472 kHz (peak in PM/AM, measured around noon)
Attachment 2: 225.642 kHz (peak in PM/AM, measured earlier in the morning)
Attachment 3: 693.500 kHz (not a peak in PM/AM)
We don't think these plots mean much and will do the measurement at some quieter time more systematically.
While doing the experiment, the ITMY pitch actuation was changed from -2.302 to -2.3172V because it locked better.
The ITMX, ETMX alignment was also tweaked to try to lock with different sideband frequencies and then restored to the values that were found earlier in the morning.
In the process of setting up some cabling at 1Y2, I must've bumped a cable to the c1lsc expansion chassis. Anyways, the c1lsc models crashed. I ran the reboot script around 530pm PDT. Usual locking behavior was recovered after this. The work at 1Y2 was:
The IN2 to CM board was already connected to I single ended output of the ALS X demodulator. The ~100 Hz UGF digital locking using the CM_SLOW path is straightforward but I didn't have any success with the AO path tonight. I wonder how high BW this lock can be made without injecting a ton of noise into the IMC loop, given that the EX uPDH only has ~ 10 kHz UGF.
Attachment #1 shows the spectra of the ALS signal
Attachment #2 is an OLTF measurement.
[Meenakshi, Gautam, Shruti]
- We initially aligned the arm cavities to get the green lasers locked to them. For the X arm cavity, we tweaked the ITMX and ETMX pitch and yaw and toggled the X green shutter until we saw something like a TEM00 mode on the monitor and a reasonable transmitted power.
- With the LSC servo enabled, the IR light also became resonant with the cavities.
- Then we measured the noise in different configurations. Attachment 1 shows the the ALS OOL (in the IR beat signal) noise with the arms locked inidividually via PDH.
The script for plotting the ALS beat frequency noise is:
I measured the transfer function of the AO path, and think that there are some features indicative of a problem somewhere in the IMC locking loop.
Regardless of the locking scheme used, high bandwidth control of the laser frequency relies on the fact that the laser frequency is slaved to the IMC cavity length with nearly zero error below ~50 kHz (assuming the IMC loop has a UGF > 100 kHz). In my single arm experiments, I didn't know what to make of the ripples that became apparent in the measured OLTF as the AO gain was ramped up.
Tonight, I measured the TF of the "AO path", which modifies the error point of the IMC, thereby changing the laser frequency.
Attachment #1 shows the result of the measurement.
I didn't use POX / POY as a sensor to confirm that this is real frequency noise, I will do so tomorrow. But it may be that realizing a stable crossover is difficult with so many features in the AO path.
Previous thread with a somewhat detailed characterization of the IMC loop electronics.
A few years ago, Koji and I setup a delay line phase shifter, which can be used to impart a (switchable) delay to a signal path. Since we talked about reviving the fast (= high bandwidth) ALS control scheme at the meeting, I reminded myself of the infrastructure available.
For a beat note in the regime 10-100 MHz, we should have plenty of range in this module to add a delay such that we zero one quadrature of the ALS DFD output (for a linear error signal).
I then proceeded to connect the single-ended front panel BNC corresponding to the ALS_X_I DFD channel to the IN2 input of the CM board (this would be what we use for high bandwidth ALS feedback). The conventional ALS system uses the differential output from a rear-panel D-sub, so in principle, both systems could run in parallel. I confirmed that I could see a signal when the IN2 path on the CM board was engaged (monitored using ndscope at the CM_Slow output), and that this signal stabilized when the green laser was locked to the X-arm length, which itself was slaved to the PSL frequency using the usual POX locking scheme. I have not yet routed the LO leg of the ALS_X beat through the delay line phase shifter - see next elog for details.
Update about the ALS MEDM screen slider: the trick was to change the OMSL field of the C1:LSC-BO_1_0 channel to "closed_loop" instead of "supervisory". Once this is done, the DOL value of the same channel can be set to the soft channel C1:ALS-DelayCalc, which sets the 16 bit binary string that controls the delay. Because arbitrary delays are not possible, I think it's more natural for the user to interact with this 16-bit binary string rather than the actual delay itself. So the MEDM screen has been slightly modified from what is shown in Attachment #1.
Over the last couple of days, I've been trying to see if I can measure the phase advance due to the AO path - however, I've been unable to do so for any combination of CM board IN1 gain and MC Servo board IN2 gain I've tried. Yesterday, I tried to understand the loop shapes I was measuring a little more, and already, I think I can't explain some features.
Attachment #1 shows the TF measured (using SR785, and the EXC_A bank of the CM board) when the CM Slow path has been engaged.
Attachment #2 shows error signal spectra for the in-loop PRFPMI DoFs, for a few different conditions.
I believe that a stable crossover is hopeless under these conditions.
Tried to open MATLAB on Donatella and found the error:
MATLAB is selecting SOFTWARE OPENGL rendering.
License checkout failed.
License Manager Error -9
This error may occur when:
-The hostid of this computer does not match the hostid in the license file.
-A Designated Computer installation is in use by another user.
If no other user is currently running MATLAB, you may need to activate.
Troubleshoot this issue by visiting:
License path: /home/controls/.matlab/R2015b_licenses/license_donatella_865865_R2015b.lic:/cvs/cds/caltech/apps/lin
Licensing error: -9,57.
So I used my caltech credentials to get an activation key for the computer. I could not find the option for a campus license so I used the individual single machine license.
Now it can be run by going to the location:
On opening MATLAB, there were a whole bunch of other errors including a low-level graphics error when we tried to plot something.
The results of the AM/PM measurements:
Both the AM and PM TFs were scaled to make them have the same average value. Manually adjusting the delay line offset for each measurement using the oscilloscope was probably not accurate enough and therefore resulted in different scaling which this should somewhat compensate.
The new calibration factor used: 5 MHz/V at the output of the mixer to obtain the frequency modulation and then division by the mod. freq. to obtain PM.
5 MHz/V because changing the PZT voltage by 0.01 V=> change in beat frequency by 0.1 MHz, which was seen as a 20 mV change in the delay line mixer output.
Again, the calibration is not very precise and I will probably repeat this experiment at some point more precisely.
Gautam showed me how the PMCTRANSPD signal was reading zero, and he suspected it might have to do with the acromag wiring. Disconnected the acromag box underneath the PSL table and checked the ADC wiring. Side note: When benchtesting the c1psl acromag chassis there was excess noise in the AI channels, and grounding the minus pin of the ADC channel eliminates the noise.
So I grounded the (-) pins on the ADC1 (192.168.113.122), which PMCTRANSPD is connected to and that seemed to fix the problem. As of right now PMCTRANSPD is reading ~.75 V.
See attached pictures
gautam: While this fix seems to have worked, I wonder why this became necessary only in the last month. Note that the problem was a noisy readback on the PMC transmission PD, which also made the FSS_RMTEMP channel noisy, leading me to suspect some kind of ground loop issue.
All spare channels on the PSL acromag chassis are connected with ~12in of spare wiring for future use.
Ran HDMI to the new tv mounted on the north wall of control room.
I found the PMC unlocked this morning. It was re-locked using the usual procedure. I feel like this has been happening more frequently in the last month than before. In the past, the cause seems to have been the PZT voltage drifting too close to one of the rails - however, in this case, it looks like an IMC unlock event is what triggered the PMC lockloss (admittedly the PZT voltage was somewhat close to the rail). It would be good if someone can re-connect the PMC Transmission photodiode, it was a useful diagnostic channel we had working fine before the ringdowns started.
I also tweaked the input pointing into the PMC and ran the WFS DC offset relief script.
On February 5, 2020, the Dell engineering workstation located in the 40M lab, was replaced with a newer Engineering workstation, per a request from Koji . The new workstation should perform a good deal better over the older unit. It has more cores, more memory and a better video card. Since this unit is being used by the 40M group, the Comsol s/w pkg. was also installed on the unit.
During the computer swap, Koji had a problem with a print job and it was discovered the bottom tray of the HP5550 printer was broken. The broken tray was replaced from another unit that was being disposed of.
This measurement tells you how the gain balance between the SLOW_CM and AO paths should be. Basically, what you need is to adjust the overall gain before the branch of the paths.
Except for the presence of the additional pole-zero in the optical gain because of the power recycling.
You have compensated this with a filter (z=120Hz, p=5kHz) for the CM path. However, AO path still don't know about it. Does this change the behavior of the cross over?
If the servo is not unconditionally stable when the AO gain is set low, can we just turn on the AO path at the nominal gain? This causes some glitch but if the servo is stable, you have a chance to recover the CARM control before everything explodes, maybe?
To study the evilution of the AO path TFs a bit more, I've hooked up POY11_Q Mon to IN1 of the CM board. I will revert the usual setup later in the evening.
Update 1730: I've returned the cabling at 1Y2 to the nominal config, and also reverted all EPICS settings that I modified for this test. Y-arm POY locking works. Attachment #1 shows the summary of the results of this test - note that the AO gain was kept fixed at +5dB throughout the test. I have arbitrarily trimmed the length of the frequency vector for some of these traces so that the noisy measurement doesn't impede visual interpretation of the plots so much. At first glance, the performance is as advertised. I basically followed the settings I had here to get started, and then ramped up various gains to check if the measured OLTF evolved in the way that I expected it to. The phase lead due to the AO path is clearly visible.
Some important differences between this test and the REFL11 blending is (i) in the latter case, there will also be a parallel loop, CARM_A, which is effecting some control, and (ii) the optical gain of CARM-->REFL11_I is much higher than L_Y-->POY. So the initial gain settings will have to be different. But I hope to get some insight into what the correct settings should be from this test. I think IMC servo IN2 gain and AO gain slider on the CM board are degenerate in the effect they have, modulo subtle effects like saturation.
One possibility is that the gain allocation I used yesterday was wrong for the dynamic range of the CARM error signal. In some initial trials today, when I set the CM board IN1 gain to -32dB (as in the case of attempting the CARM RF handoff) and compensated for the reduced POY PDH fringe amplitude by increasing the digital gain for the CM_Slow path, I found that there was no phase advance visible even when I ramped up the IMC IN2 gain to +10dB. So, for the CARM handoff too, I might have to start with a higher CM board IN_1 gain, compensate by reducing the CM_Slow digital gain even more, and then try upping the IMC IN2 gain.
P.S. When the excitation input to the CM board was enabled in order to make TF measurements, I saw significant increase in the RMS of the error signal. Probably some kind of ground loop issue.
I took the metal PMC box and examined its content and find the following items:
There seem to be enough parts to build 2 PMCs + spares.
I find several problems in the metal PMCs:
PMC1 has a broken screw in one of its flat mirror mounts (Attachment 16). We need to get it out in the machine shop.
PMC2 one of the flat mirrors has a scratch on the AR coating and its ORing is failing (Attachment 17). Mirror and ORing need to be replaced.
I measure the physical dimensions of the PMC with the help of https://dcc.ligo.org/LIGO-E1400332. The roundtrip is found to be 24cm which gives an FSR of 1.25GHz.
I use Evan Hall's Python script for calculating the mode spectrum as a function of the cavity length of the metal PMC and overlay the RF sidebands (Green dashed lines) on it (Attachment 18) to check for any HOM coincidence. The width of the lines is the mode splitting due to the cavity astigmatism.
It seems like the only issue might come from a 10th order modes (green ribbon) which are hopefully small enough in reality.
I took a few AM TF measurements at the X end for which I:
I will post the data soon.
Not sure what's wrong, but the workstation desk is freezing cold again and the room temp is 18degC (64degF).
Plots + interpretation tomorrow.
Getting closer... To facilitate this work, I made some convenience scripts that can be run from the CM MEDM screen.
Today I engineered the last piece of the new c1psl system: the multi-bit binary output (mbbo) channels that control the MC servo board gains. These 6-bit channels have to be split across two 4-bit Acromag registers. To enforce synchronous switching, I adapted the latch.py script developed by Gautam to address this problem in c1iscaux. Analogously to the c1iscaux implementation, I scripted the code to automatically run as a systemd service which is launched by the main modbusIOC service. I tested this all using the DB37 LED test board and confirmed it to work.
This now completes the electronics bench testing.
There are still several DB37 connectors to be wired, which carry only spare channels for future use and are not interfaced with the EPICS IOC. Jordan and I discussed this today and he or Chub will complete it shortly. To allow time for the spare channel wiring to be completed (as well as for more locking progress before interruption), Gautam and I think Monday/Tuesday next week would be the earliest possible window to install the new system.