At Seiji and Gautam's suggestion, we added an additional RF photodiode (NewFocus 1611) to the system so we can calibrate our transfer functions. The configuration is now laser -> BS --> lenses -> QPD and BS --> lenses -> RFPD. We added lenses to get the beams focused on the RFPD and QPD heads, and are again set up for TF measurement.
We took the following data. These parameters were consistent across all measurements:
After taking the data for segment 1, I moved the beam to segment 2. The beam didn't fit on segment 2 without partially illuminating segment 1 (tested by maximizing the signal on segment 2, then blocking the beam. If the beam is entirely on one segment, only that segment should be effected; in this case, we found that segment 1's DC signal also changed when the beam was blocked). We readjusted the telescoping lenses to get the beam a bit smaller, and now the beam fits on segment 2. We know it is entirely on segment 2 because small beam movements do not change the signal on segment 2.
We are trying to take the remaining data, but AGmeasure keeps hanging while sending the data (after taking the measurement, over 10 min). We tried restarting the network analyzer to no avail. I was able to grab the data by cancelling the measurement and running
I've uploaded the spectrum for segment 1 in the meantime. Zero model is on the way.
When I finished up the measurements on WFS2, I removed the cables from the AP table and closed the cover.
EDIT: I forgot to switch the LEMO connector to measure the other segments, so we measured the RF signal from segment 1 even when the beam was on segments 2-4. We'll have to try again tomorrow.
We are at it again. Rika is setting up the TF measurement, I'm looking into scripting the WFS sensing matrix measurement we made earlier in the week so we can return to it next week.
When we mesuring TF of SEG4, the beam leaking to SEG1 about 1%.
We finished mesurement SEG2-4 and get the figure by running PDH_calibrate.ipynb .
edit: We observed during segment 2 measurements that blocking the beam reduced the DC level of segment 1 by less than 1%, but still clearly observable. As you can see in the plots, something is suspicious about the normalization of these TFs. We took segment 1 data a few days before the other segments, so perhaps we weren't getting the full beam on the reference PD during the later measurements? When I make this measurement for WFS1, I will try to fix some of these problems by choosing different telescoping optics, and I will consider whether removing the QPD heads from their table will improve the measurement.
I'm scripting the WFS sensing matrix measurements. I haven't really scripted DTT before, so I'm trying to find documentation or existing scripts. I came across this elog where Gautam measured a sensing matrix during DRMI lock, and he pointed me to some .xml files used for these measurments.
not need to use DTT. I'm attaching some half-finished notebooks that give the gist.
That's it! Now you have the complex, single frequency TFs. Next you invert the matrix.
"# Get some ASC data - Calculate Sensing Matrix \n",
"### also make the radar plots"
We aligned optics of WFS as it was. Now auto-locker is working to lock MC.
But it still doesn't lock. We notice that the c1lsc machine doesn't work. So we run rebootCILSC.sh.
Now we reset the hardware!
After reset, auto locking didn't work well. Gautum and Aaron reboot slow c1ioo. Then it works, and Gautam returned the MC to a good alignment.
We found the beam is not in the center of the QPD, we (turned off the MC autolocker and MC loop, then) realigned to make beam to get in to the QPD center. Afterwards we start auto locking.
With the WFS on, the maximum MC transmission we observe is 14,700 counts; after the transmission level stabilizes (MC_TRANS pit and yaw brought to 0), the MC transmission is only 14,200 counts. Perhaps the MC_TRANS QPD offsets need adjustment. We relieve the WFS servo of its DC offsets. This is the configuration we'll use for WFS loop measurements this week.
I wanted to make a zero model of this circuit to get a handle on the results. I couldn't import zero on pianosa, and I tried pip installing zero, but was denied due to not finding version 3.0.3 of matplotlib. I finally got it to install using
Oddly, even though I can now import zero when I open a python3 session from the command line, when I open a jupyter notebook and switch to a python3 kernel, the zero module is still unavailable. I think I recall that conda manages the jupyter environment -- is pip managing an entirely separate environment (annoying)?
edit: Yeah, it was something like that. I reminded myself how this works with this article.
Let's not worry about C1LSC until the c1iscaux upgrade is done.
I'm using the notebooks from rana as a starting point, and making a script to measure and fill the WFS sensing matrix. It lives at /users/aaron/WFS/scripts/WFSsensingMatrix.ipynb for now. Here's what it does; what's been tested is in green, untested is goldenrod, uncoded is fire brick.
To run these on pianosa, I ran (inside the jupyter notebook)
I'm getting an error when starting the nds2 connection
conn = nds2.connection('192.168.113.201', 31200)
Failed to establish a connection[INFO: Request SASL authentication protocol]+
I didn't find anything on the elog about this error, but I'm looking at the nds user manual. The problem was, I didn't have a valid Kerberos ticket; I opened one on Pianosa with my albert.einstein (note all caps ligo.org).
I'm now able to run the scripts Rana mentions, but I haven't been able to grab the channels I want (eg C1:SUS-MC1_ASCPIT_IN1_OUT); it says the channel isn't found. When I check how many of the Caltech channels are available (conn.count_channels('C1*')), there are none. I was connecting to nds.ligo.caltech.edu, but this must be the wrong server (it has all the channels for the sites). fb and fb1 (and the IP they point to, 192.168.113.201) cannot be connected to, giving the error 'Error occurred trying to write to socket.'
I recall that in the cryo lab, we need to use port 8088 to get data from cymac1, and indeed substituting 31200 -> 8088 lets me access the C1 channels (I can count the channels), but no matter what time I request, nds tells me there is no data available (gap). Gautam came by and diagnosed that the gaps I'm seeing in the frames' data are real, fb is down (see elog).
Continuing, I'm going to modify the script to grab live data. I'm using the iterate and next methods. I noticed that the MC2_TRANS pit/yaw channels are not saved to frames, even though WFS1/2 pit/yaw are. Since I expect I'll want to lookback at these channels, I followed the instructions for adding a daq channel, uncommenting the following line in /opt/rtcds/caltech/c1/chans/daq/C1IOO.ini:
I made a backup of the old version of this .ini file, which can be found in /users/aaron/backups/190917_C1IOO.ini. I did not remake the model, as I couldn't find the c1ioo model in /opt/rtcds/caltech/c1/userapps/trunk or from the matlab command prompt. I restarted the fb via telnet, but didn't restart the model or check the svn (got an error?). The _DQ channels are now reachable on dataviewer, so things seem to be working.
I also tried importing cdsutils, so I can control awg in the same script that we read out the sensing matrix, but I'm getting the python3 error when I import cdsutils:
I tried pip upgrading cdsutils, but it's already up-to-date. I get the above error even if I switch to a python 2 kernel; cdsutils is installed in the python2.7 directory, so I don't know why pip is finding it when I'm running a python 3 kernel. I can move on from this for now, but it would be useful to be able to script the excitation along with the measurement.
Tangentially related, Rika wanted to be running some jupyter notebooks while working on donatella. I ran, on donatella:
hm, that didn't work. Also jupyter is installed when you install conda, so I'm not sure how there is a version of conda but not of jupyter. I also see that pip and pip3 are not recognized commands on donatella.
I noticed that some of the functions in the scipy signal processing toolbox were out of date on pianosa. The cheby and welch filters now accept additional kwargs (for eg, before you needed to give IIR filter methods a cutoff frequency normalized to the Nyquist rate, but now you can give it the frequencies and sampling rate separately).
I want to update this package, but I hesitate to break everyone's existing scripts.
Once stop the auto-locker and realigned to make beam to get into QPD again.
After we lock MC, we took TFs from suspension MC1/2/3 PIT/YAW to WFS1/2 PIT/YAW.
Diagnotics test tools
range: 7 Hz to 50 Hz
Column 0: WFS2_PIT 1: WFS2_YAW 2:WFS1_PIT 3: WFS1_YAW 4: TRANCE_PIT 5:TRANCE_YAW
I'm wondering weather the MC1data I saved is correct, becouse I found the channel was changed when I exported MC2 data. So I took MC1 data again.
We got all data for TFs already. Each data is devided to real part and imaginary part. Then we are arranging the datas to obtain TFs.
TF of MC2 is attachiment 1. So tomorrow, I make other TF.
In the data we got yesterday, we can see some filter's effect.
But it is not good coherence above 10Hz, so we mesured again. And this time we save the data as xml file.
And also we chaned the frequency regions broader to watch corner frequency of suspension.
Diagnotics test tools
range: 0.1 Hz to 100 Hz
but at low frequency, the mode maching cavity was unloked cause of too much shaking.
So, we saw single frequency TF, and searched the good amplitude.
First, I tried to get TF @0.1~1 Hz .
0.1 to 1 Hz
points: 61 (I think it's too much becous it takes about an hour)
The TFs and coherence of MC1/PIT to each QPD is below. [above window: coherence, below: TF]
During the mesurement, something happened @0.2-0.3Hz so I stopped it.
We found the coherence of WFS1P and WFS2Y is not good, but others are good.
we guess that it could come from alignment which made Q chainging to small.
Finaly, I also got the .xml data of MC1P 1 Hz to 10 Hz. In this time,
1 to 10 Hz
Now we took single frequency 6 TFs (MC1/2/3 PIT/YAW) @7Hz (Because this frequency has good coherence in all channel).
Aaron wrote the script using dtt to making matrics.
The custom ribbon cables piping the coil driver board outputs to the eLIGO (?) TTs (a.k.a. TT1 and TT2) are damaged. They need to be re-made. I can't find any pin-mapping for them.
While waiting for the LSC photodiode whitening switching cross-connect work to be done, I thought I'd re-align the IFO a bit. However, I was unable to find any beam making it to the REFL/AS ports despite some TT steering. I remembered that Chub had undone the TT connections at 1Y2 as well, and thought I'd check the cabling to make sure all was in order. On going to the rack, however, I found that these connections were damaged at the coil-driver end (see Attachment #1), presumably during the cable extraction. These need to be re-made...😔
While debugging this problem, c1lsc models crashed. I ran the reboot script this morning to bring the models back. There was a 0x4000 error on the DC indicators for the c1lsc models (mx_stream error which couldn't be fixed by restarting the mx service) the first time I ran the script so I did it again, now the indicator lights are in their nominal state.
False alarm - the mistake was mine. Looking at the schematic diagram, the AI/Dewhite board, D000316, accepts the inputs from the DAC on the P2 connector. While restoring the connections at 1Y2, I had plugged the outputs of the DAC interface board into the P1 connectors of the AI boards. Having rectified this problem, I am now able to move the beam on the AS camera in both PIT and YAW using TT1 or TT2. So to zero-th order, this subsystem appears to work. A more in-depth analysis of the angular stability of the TTs can only be done once we re-align the arms and lock some cavities.
I wanted to measure the RF transimpedance of the WFS heads, as outlined above.
Summary: Measurement is not done.
I set up the spectrum analyzer to make the WFS head RF transfer function measurement (V/W) on WFS1. I placed the Jenne laser on the AP table, along with the reference PD power supply, laptop, and laser power supply. The Agilent output AM modulates the laser; the reference PD is again NewFocus 1611, with its AC output sent to Agilent's R channel and DC output sent to an oscilloscope;
I closed the PSL shutter while checking for a location to place the breadboard, and opened it while writing this. Headed back to Cryo to pick up the large incandescent bulb we'd borrowed over the summer.
See trend. This is NOT symptomatic of some frozen slow machine - if I disable the WFS servo inputs, the lock holds just fine.
Turns out that the beam was almost completely missing the WFS2 QPD. WTF ðŸ˜¤. I re-aligned the beam using the steering mirror immediately before the WFS2 QPD, and re-set the dark offsets for good measure. Now the IMC remains stably locked.
Please - after you work on the interferometer, return it to the state it was in. Locking is hard enough without me having to hunt down randomly misaligned/blocked beams or unplugged cables.
I took this opportunity to do some WFS offset updates.
There is ~ 7% variation in the power seen by the MC2 trans QPD, depending on the WFS offsets applied to the MC2 PIT/YAW loops. Some more interpretation is required however, before attributing this to spot-position-dependent loss variation inside the IMC cavity.
Attachment #1: This shows a scatter plot of the MC2 transmission and IMC REFL average values after the WFS loops have converged to the set offset positions. The size of the points are proportional to the normalized variance of the quantity. The purpose of this plot is to show that there is significant variation of the transmission, much more than the variance of an individual datapoint during the course of the averaging (again, the size of the circles is only meant to be indicative, the actual variance in counts is much smaller and wouldn't be visible on this plot scale). For a critically coupled cavity, I would have expected that the TRANS/REFL to be perfectly anti-correlated, but in fact, they are, if anything, correleated. So maybe the WFS loops aren't exactly converging to optimize the inoput pointing for a given offset?
Attachment #2: Maps of the transmission/reflection as a function of the (YAW, PIT) offset applied. The radial coordinate does not yet mean anything physical - I have to figure out the calibration from offset counts to spot position motion on the optic in mm, to get an idea for how much we scanned the surface of the optic relative to the beam size. The gray circles indicate the datapoints, while the colormaps are scipy-based interpolation.
Attachment #3: After talking with Koji, I explicitly show the correlation structure between the IMC REFL DCMON and MC2 TRANS. The shaded ellipses indicate the 1, 2 and 3-sigma bounds for the 2D dataset going radially outwards. The correlation coefficient for this dataset is 0.46, which implies moderate positive correlation. 🤔
The following was implemented in a python scipt:
I am now setting the offsets to the WFS QPD loop to the place where there was maximum transmission, to see if this is repeatable. In fact it was. Looking at the QPD segment outputs, I noticed that the MC2 transmission spot was rather off-center on the photodiode. So I went to the MC2 in-air optical table and centered the beam till the output on the 4 segments were more balanced, see Attachment #4. Then I re-set the MC2 QPD offsets and re-enabled the WFS servos. The transmission is now a little lower at ~14,500 counts (but still higher than the ~14200 counts we had before), presumably because we have more of the brightest part of the beam falling on the gap between quadrants. For a more reliable measurement, we should use a single-element photodiode for the MC2 transmission.
I think this offset setting thing is not so good. People do this every few years, but putting offsets in servos means that you cannot maintain a stable alignment when there are changes in the laser power, PMC trans, etc. The better thing is to do the centering of the WFS spots with the unlcoked beam after the control offsets have been offloaded to the suspensions.
I installed nds2 on donatello with yum, but still can't import nds2.
I installed nds2 again, this time successfully with
conda install -c conda-forge python-nds2-client
[Mirko / Kiwamu]
The resonant box has been installed together with a 3 dB attenuator.
The demodulation phase of the MC lock was readjusted and the MC is now happily locked.
We needed more modulation depth on each modulation frequency and so for the reason we installed the resonant box to amplify the signal levels.
Since the resonant box isn't impedance matched well, the box creates some amount of the RF reflections (#5339).
In order to reduce somewhat of the RF reflection we decided to put a 3 dB attenuator in between the generation box and the resonant box.
(what we did)
+ attached the resonant box directly to the EOM input with a short SMA connector.
+ put stacked black plates underneath the resonant box to support the wight of the box and to relief the strain on the cable between the EOM and the box.
+ put a 3 dB attenuator just after the RF power combiner to reduce RF reflections.
+ readjusted the demodulation phase of the MC lock.
(Adjustment of MC demodulation phase)
The demodulation phase was readjusted by adding more cable length in the local oscillator line.
After some iterations an additional cable length of about 30 cm was inserted to maximize the Q-phase signal.
So for the MC lock we are using the Q signal, which is the same as it had been before.
Before the installation of the resonant box, the amplitude of the MC PDH signal was measured in the demodulation board's monitor pins.
The amplitude was about 500 mV in peak-peak (see the attached pictures of the I-Q projection in an oscilloscope). Then after the installation the amplitude decreased to 400 mV in peak-peak.
Therefore the amplitude of the PDH signal decreased by 20 %, which is not as bad as I expected since the previous measurement indicated 40 % reduction (#2586).
Gautam and I were talking about some modulation and demodulation and wondered what is the power combining situation for the triple resonant EOM installed 8 years ago. And we noticed that the current setup has additional ~5dB loss associated with the 3-to-1 power combiner. (Figure a)
N-to-1 broadband power combiners have an intrinsic loss of 10 log10(N). You can think about a reciprocal process (power splitting) (Figure b). The 2W input coming to the 2-port power splitter gives us two 1W outputs. The opposite process is power combining as shown in Figure c. This case, the two identical signals are the constructively added in the combiner, but the output is not 20Vpk but 14Vpk. Considering thge linearity, when one of the port is terminated, the output is going to be a half. So we expect 27dBm output for a 30dBm input (Figure d). This fact is frequently oversight particularly when one combines the signals at multiple frequencies (Figrue e). We can avoid this kind of loss by using a frequency-dependent power combiner like a diplexer or a triplexer.
With all of the shaking (man-made and divine), it was a hard to debug this problem. Summary of fixes:
At least the DC indicators are telling me that the IMC locking is back to a somewhat stable state. I have not yet checked the frequency noise / RIN.
I resume my IMC ringdown activities now that the IMC is aligned again.
To avoid any accidental misalignments Gautam turned off all the inputs to the WFS servo.
I set up a PD and a lens as in attachment 1 (following Gautam's setup).
I connect the REFL, TRANS and INPut PDs to the oscilloscope.
I connect a Siglent function generator to the AOM driver. I try to shut off the light to the IMC using 1V DC waveform and pressing the output button manually. However, it produced heavily distorted step function in the PMC trans PD.
I use a square wave with a frequency of 20mHz instead with an amplitude of 0.5V offset of 0.25V and dutycycle of 1% so there will be minimal wasted time in the off state. I get nice ringdowns (attachment 2) - forgot to take pictures. The autolocker slightly misaligns the M2 every time it is acting, so I manually align it everytime the IMC gets unlocked.
Data analysis will come later.
I remove the PD and lens and reenable the WFS servo inputs. The IMC locks easily. The WFS outputs are very different than 0 now though.
I analyze the IMC ringdown data from last night.
Attachment 1 shows the normalized raw data. Oscillations come in much later than in Gautam's measurement. Probably because the IMC stays locked.
Attachment 2 shows fits of the transmitted PD to unconstrained double exponential and the Zucker model.
Zucker model gives time constant of 21.6us
Unconstrained exponentials give time constants of 23.99us and 46.7us which is nice because it converges close to the Zucker model.
One factor which hampers locking efforts is the apparent drift of the input beam into the IFO. Over timescales of ~1 hour, I have noticed that the spot on the AS camera drifts significantly (~1 spot size) in pitch. The IPPOS QPD bears out this observation, see Attachment #1. The IMC WFS control signals do not show a correlated drift, hence my claim that the TTs are to blame.
I am able to correct this misalignment by moving TT1 in pitch (see Attachment #2, which shows some signals from a ~1 hour PRMI lock, during which time the pointing drifted, and I corrected it by moving TT1 pitch). Assuming the problem is purely TT1 pitch drifting, this corresponds to 3mm / 6m ~500urad of shift in 1 hour - seems very large. The fact that the drift is only present in pitch and doesn't really show up in yaw makes me think the problem is likely mechanical (unless the voltage to the top two coils is drifting relative to the bottom, but no LR drift, which would be very coincidental). At the moment, this is just an annoyance, but it'd be good for this problem to be fixed.
I haven't yet figured out how to make ndscope export these plots to SVG preserving the dark color theme, hence the weird light axes...
I extended the ringdown data analysis to the reflected beam following Isogai et al.
The idea is that measuring the cavity's reflected light one can use known relationships to extract the transmission of the cavity mirrors and not only the finesse.
The finesse calculated from the transmission ringdown shown in the previous elog is 1520 according to the Zucker model, 1680 according to the first exponential and 1728 according to the second exponential.
Attachment 1 shows the measured reflected light during an IMC ringdown in and out of resonance and the values that are read off it to compute the transmission.
The equations for m1 and m3 are the same as in Isogai's paper because they describe a steady-state that doesn't care about the extinction ratio of the light.
The equation for m2, however, is modified due to the finite extinction present in our zeroth-order ringdown.
Modelling the IMC as a critically coupled 2 mirror cavity one can verify that:
Where is the coupled light power
is the power rejected from the cavity (higher-order modes, sidebands)
is the cavity gain.
and are the power reflectivity and transmissivity per mirror, respectively.
is the power attenuation factor. For perfect extinction, this is 0.
Solving the equations (m1 and m3 + modified m2), using Zucker model's finesse, gives the following information:
Loss per mirror = 84.99 ppm
Transmission per mirror = 1980.77 ppm
Coupling efficiency (to TEM00) = 97.94%
I translate the results obtained in the previous elog to the IMC 3 mirror cavity. I assume the loss in each mirror in the IMC is equal and that M2 has a negligible transmission.
I find that to a very good approximation the loss per IMC mirror is 2/3 the loss per mirror in the 2 mirror cavity model. That is the loss per mirror in the IMC is 56 ppm. The transmission per mirror in the IMC is the same as in the 2 mirror model, which is 1980 ppm.
The total transmission is the same as in the 2 mirror model and is given by:
where is the coupling efficiency to the TEM00 mode.
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.
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.
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.
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.
Sometime between 1PM and 6PM on Tuesday, excess laser frequency noise shows up in MCF at around 800 Hz, as shown in Attachment #1. Sigh.
While I show the MCF spectrum here, I confirmed that this noise is not injected by the IMC loop (with the PSL shutter closed, and the IMC servo board disconnected from the feedback path to the NPRO, the PMC error and control points still show the elevated noise, see Attachment #2). I don't think the problem is from the PMC loop - see Attachment #3 which is the ALS beat out-of-loop noise with the PMC unlocked (the PSL beam doesn't see the cavity before it gets to the ALS setup, and we only actuate on the cavity length for that loop, so this wasn't even really necessary).
Was there some work on the PSL table on Tuesday afternoon that can explain this?
I did some preliminary debugging of this, and have localized the problem to the output path (after MC slow) on the IMC Servo card. Basically, I monitored the spectrum of the ALS beat frequency fluctuations under a few different conditions:
Toggling C1:IOO-MC_FASTSW, which supposedly isolates the post-MC slow (a.k.a. MCL) part of the servo, I see no difference. I am also reasonably confident this switch itself works, because I can break the IMC lock by toggling it. So pending a more detailed investigation, I am forced to conclude that the problem originates in the part of the IMC servo board after the MCL pickoff. Some cabling was removed at 1X2 on Tuesday between the times when there was no excess and when it showed up, but it's hard to imagine how this could have created this particular problem.
My old scheme was flawed as I used pitch as the readback. The pitch signal could not distinguish the cross-coupling due to coil imbalance and that due to the natural suspension L2P. A new scheme based on yaw alone has been developed and will be integrated into ifo_test. For now we revert the C1:SUS-MC2_UL/UR/LR/LLCOIL gains back to 1, -1, 1, -1.
I lowered the (FAST) PZT gain on the IMC/FSS servo today.
I noticed that the MC locks looked unstable a lot of the day, and during lock the PCDRIVE channel is above 1 Vrms (which means the loop is oscillating, ttypically at the PZT/EOM crossover frequency).
I changed the default setting from 22 to 20 19 dB in the PSL Settings screen so the mcup script will use this for now. Feel free to revert if this turns out to be a Fluke (which you would think is a terrible name for a company, but...)
since the summary pages are working again, I was clicking through and noticed that there's a wandering peak in the whitened IMC spectrogram that goes from 10-30 Hz over the course of a day.
anyone know what this is ?
There was an abrupt change in the MC_F spectrum between August 4 and August 5, judging by the summary pages - the 1 and 3 Hz resonances are no longer visible in the spectrum. Possibly, this indicates some electronics failure on the MC servo board / whitening board, the CDS settings don't seem to have changed. There is no record of any activity in the elog around those dates that would explain such a change. I'll poke around at 1X2 to see if anything looks different.
Update 1740: I found that the MCL / MCF cables were disconnected. So since August 5, these channels were NOT recording any physical quantity. Because their inputs weren't terminated, I guess this isn't a clean measurement of the whitening + AA noise, but particularly for MC_F, I guess we could use more whitening (see Attachment #1). Probably also means that the wandering ~10-30Hz line in the spectrogram is a electronics feature. The connections have now been restored and things look nominal again.
that's a very curious disconnection
the "Pentek" whitening board that carries the MC channels has jumpers to enable either 1 or 2 stages of 15:150 whitening. Looks lik MC_F has 2 and MC_L has 1.
I guess the MC_F signal is so low because of the high gain on the FSS board. We could lower the FSS common gain and increase the IMC board's VCO gain to make up for this. Maybe 6 dB would be enough. IF that is risky, we could also up the analog gain on the whitening board.
This elog suggests that there is uniformly 1 stage engaged across all channels. I didn't look at the board to see what the jumper situation is, but only 1 stage of whitening is compensated digitally for both _F and _L. The Pomona box attached to the NPRO PZT input is also compensated digitally to convert counts to frequency.
I tried the gain re-allocation between VCO gain and FSS COMM (and also compensated for the cts to Hz conversion in MCF), but it doesn't seem to have the desired effect on the MCF SNR in the 5-50Hz band. Since the IMC stays locked, and I had already made the changes to mcup, I'll keep these gains for now. We can revert to the old settings if the IMC locking duty cycle is affected. Explicitly, the changes made were:
VCO gain: +7dB ---> +13 dB
FSS COMM: +6 ddB ---> +0 dB
The mcdown script wasn't modified, so the lock acquisition gains are the same as they've been.
We wanted to track down the excess noise seen in MC_F and other places (see the previous report by Gautam)
Setup1: The IMC was locked and MC_F signal between 500 and 1500Hz was observed. The DTT template was saved as /users/Templates/MC/MCF_noise_201023.xml
- Suspected mech resonance/jitter coupled with clipping or any other imperfections. Poked the various optics and optomechanics on the table. Basically no change. If we tap the laser chassis and the optics close to the laser source, we occasionally unlocked the IMC
- When we touched (lifted) the Innolight controller box from the shelf, for the first time we saw a significant change in the shape of the noise spectrum. The peak around the 700Hz shited towards lower frequency by a few %. Other peaks have no obvious change in the shapes and the heights.
- While observing the MC_F signal on the laptop, we went to the back of the laser controller. Placing a hand close to the fan clearly changes the peak frequency lower. By temporarily disconnecting the fan from the power supply for a short moment, the 700Hz peak could be eliminated. We also tried to see the noise level with the slow thermal servo and diagnosis DB cable disconnected, but we didn't see any significant change of the noise level.
Setup 2: Using the ALS phase tracker, we can observe the relative freq noise of the PSL laser and the ETMY AUX laser without any servo involved. This way we can freely disconnect any cables from the lasers. The measurement template for DTT was saved as /users/Templates/ALS/Y_ALS_FINE_PHASE_OUT_102320.xml
- Noise spectrum before disconnecting the cable (REF0, RMS REF1)
- The Fast PZT input to the PSL was disconnected => This made all the peaks (including the 700Hz) disappeared (REF2, RMS REF3)
- The Fast PZT input was restored as before, then the chain was disconnected at the input of the HV PZT driver (Thorlabs) => Again, this made the peaks disappeared (REF4, RMS REF5)
- The chain was disconnected at the input of the TTFSS box => Again, this made the peaks disappeared (REF6, RMS REF7)
- Disconnected the demod input and the AO cables from the IMC servo board => This made the peaks came back (REF8)
- Disconnected all the input/peripheral cables from the IMC servo board except for the connection to the TTFSS box => Still the excess noise was observed (REF9)
- In addition to the above, the cable to the FSS box was disconnected but the ground was still touching the MC servo board => This made the peaks disappeared (REF10)
The conclusion is that the noise is injected from the main circuit of the IMC servo board.
Next time we will check if the backplane connection is doing something wrong. Also, we'll test if the presence of the RF signals does something bad to the IMC board via EMI and RFI.
We have reverted the connection and tested if we lock the IMC and Y arm. ==> We saw at least they were locked for a short period. The things are still stabilizing, but left them turned on so they keep trying to lock automatically for the night.
In fact, the problem was the grounding issue (presumably on the IOO racks).
A temporary differential receiver at the TTFSS side was built using an SR560 and a few ponoma cables. This removed the structures ~850Hz.
The MC Servo Output was disconnected from the TTFSS box and monitored with SR785. The 850Hz structure was kept visible no matter what cables, including all the acromag DB cables, were removed. This made me suspicious about the measurement setup. The SR785 was connected to an AC power strip under the SP table and this was too far from the IOO rack.
The SR785 was connected to the AC power strip on 1X2, and now the difference becomes clear. No matter if the acromag cables are connected or not, the connection (particularly ground connection) between the MC servo module and the TTFSS box causes the MC servo output contaminated. (Comparison between Blue and Orange of Attachment #1). During the measurement, the EPICS switch for the fast path was disengaged (=no signal) and the VCO gain (...so called. It's just the MC Servo Gain) was set to be 0dB.
To test if the differential receiving of the MC Servo Output at the PSL helps to reduce this noise, I've built a simple (hacky) differential receiver using an SR560. (Attachment #2)
This kept the noise level same as the disconnected case (Comparison between Green and Orange of Attachment #1, I don't think the difference between them is not significant), while the IMC is locked as before.
Note that we can see that the 36kHz line was significantly reduced. Did we remove this annoying noise?
After talking with Gautam, we decided to leave this configuration while the SE-Diff cable was replaced with a more robust one. (See Attachment #3)
The PSL laser frequency performance was evakluated in the following two ways as we did last week:
1) Use the beat frequency of the free running PSL and the Y-end laser (Attachment #4). The PSL shutter was closed and thus the IMC was not locked.
2) Use the IMC MCF while the IMC was locked. (Attachment #5)
For both cases, the improvement was confirmed.
I also tried to check the reported issue by Gautam on this elog. He used 1Hz BW, but I cheated with 16Hz BW and 10x12.8kHz span PSDs. (Attachment #6)
For the measurement, IN1 GAIN of the IMC Servo was set to be 0dB and the OUT2 was switched to monitor the IN1 noise, while IN1 was terminated by a 50Ohm.
As I mentioned above, the AC power of SR785 was taken from a 1X2 power strip. Is this the reason for the power line forest look less severe compared to the previous case???
Anyway, I tried to use the same differential receiving technique (but with gain of x100) to see if this helps. The differential receiver helped to reduce the structure above 50kHz. The floor noise level was observed to be higher. I didn't pursue this any further, but the forest of the power line looked like a part of the measurement noise. This is indicative that the grounding condition on 1X2 is really not great and we need to review the configuration of the acromag grounding.
Apart from the questionable wiring on the Acromags, one other important difference is in the way the connections were made between the old VME crates to the Eurocrate backplanes, and how we do it now. The thick cables had their sheilds connected to the eurocrate ground (or at least, there was a dedicated ground lug on those cables which we screwed on to the ground terminals on the Eurocrate backplanes). However, in our current configuration, we interface the Acromag ADCs and DACs to the backplane via these adaptor boards. The shields of the DSUB cables are presumably NOT connected to the Eurocrate grounds. This should also be investigated as one potential cause of the grounding issue - while on some of the Eurocrate modules, the P1/P2 connectors may have either the "A" or "C" row of connectors shorted to ground, some may not, and the TTFSS may suffer from such an issue?
Note that we have this problem in all of the slow machines that were upgraded to Acromag (if this turns out to be the issue).
In fact, the problem was the grounding issue (presumably on the IOO racks).
Looking back through the elog, 1mtorr is the pressure at which it is deemed safe to send the full power beam into the IMC. After replacing the HR mirror in the MCREFL path with a 10% reflective BS, I just cranked the power back up. IMC is locked. With the increased exposure on the MC2T camera, lots of new scattered light has become visible.
While proceeding with the interferometer recovery, I noticed that there appeared to be no light on WFS2. I confirmed on the AP table that the beam was indeed hitting the QPD, but the DC quadrants are all returning 0. Looking back, it appears that the failure happened on Monday 26 October at ~6pm local time. For now, I hand-aligned the IMC and centered the beams on the WFS1 and MC2T QPDs - MCT is ~15000 cts and MC REFL DC is ~0.1, all consistent with the best numbers I've been able to obtain in the past. I don't think the servo will work without 1 sensor without some retuning of the output matrix.
It would appear that both the DC and RF outputs of WFS2 are affected - I dithered the MC2 optic in pitch (with the WFS loop disabled) at 3.33 Hz, the transmission and WFS1 sensors see the dither but not WFS2. It could be that I'm just not well centerd on the PD, but by eye, I am, so it would appear that the problem is present in both the DC and RF signal paths. I am not going into the PD head debugging today.
I checked the backplane connection for IMC WFS2 and found that the cables for IMC WFS2 and the IMC demod were swapped during my IMC noise hunting activities. I reverted it just now.
But we need to check if this damaged anything such as the WFS2 head, the WFS2 demod, etc, once the IMC locking is back.
There seems to be significant phase loss in the TTFSS path, which is limiting the IMC OLTF to <100 kHz.
See Attachment #1 and #2. The former shows the phase loss, while the latter is just to confirm that the optical gain of the error point is roughly the same, since I noticed this after working on and replacing the RF frequency distribution unit. Unfortunately there have been many other changes also (e.g. the work that Rana and Koji did at the IMC rack, swapping of backplane controls etc etc - maybe they have an OLTF measurement from the time they were working?) so I don't know which is to blame. Off the top of my head, I don't see how the RF source can change the phase lag of the IMC servo at 100 kHz. The only part of the IMC RF chain that I touched was the short cable inside the unit that routes the output of the Wenzel source to the front panel SMA feedthrough. I confirmed with a power meter that the power level of the 29.5 MHz signal at that point is the same before and after my work.
The time domain demod monitor point signals appear somewhat noisier in todays measurement compared to some old data I had from 2018, but I think this isn't significant. Once the SR785 becomes available, I will measure the error point spectrum as well to confirm. One thing I noticed was that like many of our 1U/2U chassis units, the feedthrough returns are shorted to the chassis on the RF source box (and hence presumably also to the rack). The design doc for this box makes many statements about the precautions taken to avoid this, but stops short of saying if the desired behavior was realized, and I can't find anything about it in the elog. Can someone confirm that the shields of all the connectors on the box were ever properly isolated? My suspicion is that the shorting is happening where the all-metal N-feedthroughs touch the drilled surfaces on the front panel - while the front and back surfaces of the panel are insulating, the machined surfaces are not.
This is an unacceptable state but no clear ideas of how to troubleshoot quickly (without going piece by piece into the IMC servo chain) occur to me. I still don't understand how the freq source work could have resulted in this problem but I'm probably overlooking something basic. I'm also wondering why the differential receiving at the TTFSS error point did not require a gain adjustment of the IMC servo? Shouldn't the differential-receiving-single-ended-sending have resulted in an overall x0.5 gain?
Update 8 Dec 1200: To test the hypothesis, I bypassed the SR560 based differential receiving and restored the original config. I am then able to run with the original gain settings, and you see in Attachment #4 that the IMC OLTF UGF is back above 100 kHz. It is still a little lower than it was in June 2019, not sure why. There must be some saturation issues somewhere in the signal chain because I cannot preserve the differential receiving and retain 100 kHz UGF, either by raising the "VCO gain" on the MC servo board, setting the SR560 to G=2, or raising the "Common Gain Adjust" on the FSS box by 6 dB. I don't have a good explanation for why this worked for some weeks and failed now - maybe some issue with the SR560? We don't have many working units so I didn't try switching it.
So either there is a whole mess of lines or the frequency noise suppression is limited. Sigh.
The servos are almost certainly not optimal - but we have the IFO sort of working, so before we make any changes, let's make a strong case for it. Once the loop TFs and noises (e.g. the sensing noise reinjection you maybe saw) are fully characterized and a new loop is shown to perform better, then we can make the changes, but until then, let's continue using the "nominal" configuration and keep all the WFS loops on . I turned everything back on.
BTW, MC2_ASCPIT_IN1 isn't the correct channel to measure the sensing noise re-injection, you need some other sensor, e.g. is the MC transmission (de)stabilized. 0-20 Hz is where I expect the WFS is actually measuring above the sensing noise.
I spent an hour today evening checking out the remote waveplate operation. Basic remote operation was established 👍 . To run a test on the main beam (or any beam for that matter), we need to lay out some long cabling, and install the controller in a rack. I will work with Jordan in the coming days to do these things. Apart from the hardware, some EPICS channel will need to be added to the c1ioo.db file and a python script will need to be set up as a service to allow remote operation.
Satisfied that the unit works basically as expected, I decided to stop for today. My thinking was that we can have the ESP300 installed in 1X1 or 1X2 (depending on where space is more readily available). I will upload have uploaded a cartoon here so people can comment if they like/dislike my plan.
Once everything is installed, we can run some tests to see if the rotary motion disturbs the PSL in any meaningful way. I will upload some photos to the picasa later. Photos here.
I spent some time today setting up a workable user interface to control the waveplate.
So this system is ready to be installed once Jordan and I find some time to lay out cabling + install the ESP300 controller in a rack.
At the moment, there is no high power and there is minimal risk of damaging anything, but someone should double check my logic to make sure that we aren't gonna burn the precious IFO optics. We should also probably hook up a hardware interlock to this controller.
I went through some aLIGO documentation and believe that they are using a custom made potentiometer based angle sensor rather than the integrated Newport (or similar) sensor+motor. My reading of the situation was that there were several problems to do with hysterisis, the "find home" routine etc. I guess for our purposes, none of these are real problems, as long as we are careful not to randomly rotate the waveplate through a full 180 degrees and go through the full fringe in the process. Need to think of a clever way to guard against careless / accidental MEDM button presses / slider drags.
Unrelated to this work: I haven't been in the lab for ~a week so I took the opportunity today to go through the various configs (POX/POY/PRMI resonant carrier etc). I didn't make a noise budget for each config but at least they can be locked 👍 . I also re-aligned the badly misaligned PMC and offloaded the somewhat large DC WFS offsets (~100 cts, which I estimate to be ~150 nNm of torque, corresponding to ~50 urad of misalignment) to the IMC suspensions' slow bias voltages.