We took the data for the new absolute length measurement of both arms, after the latest vent and move. We will analyze soonly. We had done a round of analysis, but then Koji pointed out that our data wasn't so clean because the whitening filters were on (and saturated the ADC). We now have the data (but not the analysis) for the better data with the WF off.
So our dirty-data preliminary number for the X arm is 37.73meters, which is 14cm different from our old length. We were supposed to move by ~20cm, so....either this measurement is bad because the data sucked (which it did), or we are 6cm off. Or both.
I'll do another analysis with the clean data for both arms later today/tomorrow.
After analyzing the cleaner data, I get the following:
Y_Length_long = 37.757 meters
X_Length_long = 37.772 meters
As stated in the wiki, the goal arm length was L = 37.7974 m for each arm.
So we're within 2cm for X, and within 4cm for Y.
According to Kiwamu's awesome tolerance calculation, we need to be within 2cm for each arm. Given that we started out 20cm wrong for X and 25cm wrong for Y, we're a lot closer now, even though we aren't meeting our Yarm requirement yet.
Probably some Optickle action is in order, to see what these new lengths give us in terms of sideband phase and other stuff.
If you want more digits on my calculated numbers (which are probably meaningless, but I haven't done a careful error analysis), in my directory ...../users/jenne/Xarm and ..../users/jenne/Yarm run Xarm_find_peaks_and_length.m and Yarm_find_peaks_and_length.m respectively. These will output the lengths.
The second sideband is resonant in the arms for a cavity length of 37.9299m.
The nearest antiresonant arm lengths for f2 (55MHz) are 36.5753m and 39.2845m.
If we don't touch the ITMs, and we use the room we still have now on the end tables, we can get to 37.5m.
This is how the power spectrum at REFL would look like for perfect antiresonance:
And this is how it looks like for 37.5m:
Or, god forbid, we change the modulation frequencies...
Last night (Oct 07), I ran armLoss script in order to obtain the latest numbers for the arm cavity loss.
Here is the summary
Measured arm reflectivity R_cav: 0.875 +/- 0.005
Estimated round trip loss L_RT: 157ppm +/- 8ppm
Estimated finesse F: 1213+/-2
Data Points: 34
Measured arm reflectivity R_cav: 0.869 +/- 0.006
Estimated round trip loss L_RT: 166ppm +/- 8ppm
Estimated finesse F: 1211+/-2
Data Points: 26
TE=10ppm, LE=L_RT/2, RE=1-TE-LE
TF=0.005, LF=L_RT/2, RF=1-TF-LF
rcav = -rF +(tF^2 rE)/(1-rF rE)
R_cav = rcav^2
F = pi Sqrt(rF rE)/(1-rF rE)
I like to ask someone to review the calculation on the wiki.
Yesterday evening Nic and me were in the lab. The Mode Cleaner was unlocked, but after many attempt we could fix it and we did many scans of the Y arm cavity.
Today I was not able to keep the MC locked. Koji helped me remotely, and eventually the MC locked back, but after half an hour of measurements I had to stop.
I made some more scan of the Y arm though. I also tried to do the same for the X arm, but the MC unlocked before the measurement was finished. I'll try to come back in the night.
I see no evidence of anything radically different from my PSL table optical characterization in the IMC transmitted beam, see Attachment #1. The lines are just a quick indicator of what's what and no sophisticated peak fitting has been done yet (so the apparent offset between the transmission peaks and some of the vertical lines are just artefacts of my rough calibration I believe). The modulation depths recovered from this scan are in good agreement with what I report in the linked elog, ~0.19 for f1 and ~0.24 for f2. On the bright side, the ALS just worked and didn't require any electronics fudgery from me. So the mystery continues.
I managed to execute the first few transitions of locking the arm lengths to the laser frequency in the CARM/DARM basis using the IR ALS system 🎉 🎊 . The performance is not quite optimized yet, but at the very least, we are back where we were in the green days.
Over the week, I'll try some noise budgeting, to improve the performance. The next step in the larger scheme of things is to see if we can lock the PRMI/DRMI with CARM detuned off resonance.
I made some attempts to measure the current length of the arm cavities by using the mass-kicking technique.
However unfortunately I am running out my energy to complete the measurement,
so I will finish the measurement at some time today.
I still have to set an appropriate kick amplitude. Right now I am injecting AWG into ETMY_LSC_EXC at 0.2 Hz with amplutde of 400 cnts.
I guess it needs a little bit more amplitude to get more psuedo-constant velocity.
Volunteers are always welcome !
The procedure was well-described in entry #555 by Dr.Stochino.
Here is just an example of the time series that I took today showing how the time series looks like.
Why not just scan the Green laser to measure the arm lengths instead? The FSR of the arm is ~3.75 MHz and so all you have to do is lock the arm green and then sweep the PZT until the resonance is found at 3.75 MHz.
As discussed at today's meeting, we would like to (re)measure the Arm cavity lengths to ~mm precision, and their g-factors. Any arm length mismatch affects the reflection phase of the sidebands in the PRMI, which might be one source of our woes. Also, as I mentioned in a previous elog, the g-factors influence whether our 2f sidebands are getting pulled into the interferometer or not.
These both can be done by scanning the arm on ALS and measuring the green beat frequency at each IR resonance. (Misaligning the input beam will enhance the TM10 Mode content, and let us measure its guoy phase shift)
I started working on this today, but I have measurements to do, since at the time of today's measurements, I was fooled by the limits of the ALS offset sliders that I could only scan through two FSRs. Looking back at Manasa's previous measurment (ELOG 9804), I see now that more FSRs are possible.
Ways I will try to improve the measurement:
Just for kicks, here are scans from today.
This has been done before:
Arm length measurements and g-factor estimates in 2012, but only with an accuracy of ~30 cm. However, Yuta was able to get many FSRs somehow.
For both sidebands to be antiresonant in the arms, the first modulation frequency has to be:
f1 = (n + 1/2) c / (2*L)
where L is the arm length and c the speed of light. For L=38m, we pick to cases: n=3, then f1a = 13.806231 MHz; n=2, then f1b = 9.861594 MHz.
If we go for f1a, then the mode cleaner half length has to change to 10.857m. If we go for f1b, the MC length goes to 15.200m. A 2 meter change from the current length either way.
And the mode cleaner would only be the first of a long list of things that would have to change. Then it would be the turn of the recycling cavities.
Kind of a big deal.
As per Ignacio's request, I restored the arm locking.
- MC WFS relief
- Slow DC restored to ~0V
- Turned off DARM/CARM
- XARM/YARM turned on
- XARM/YARM ASS& Offset offloading
There are multiple methods by which the arm loss can be measured, including, but not limited to:
We found that the second method is extremely sensitive to errors in the ITM transmissivity. The first method was not an option for a while because the AOM (which serves as a fast shutter to cut the light to the cavity and thereby allow measurement of the cavity ringdown) was not installed. Johannes and Shubham have re-installed this so we may want to consider this method.
Most of the recent efforts have relied on the 3rd method, which itself is susceptible to many problems. As Yutaro found, there is something weird going on with ASDC which makes it perhaps not so reliable a sensor for this measurement (unfortunately, no one remembered to follow up on this during the vent, something we may come to regret...). He performed some checks and found that for the Y arm, POY is a suitable alternative sensor. However, the whitening gain was at 0dB for the measurements that Johannes recently performed (Yutaro does not mention what whitening gain he used, but presumably it was not 0). As a result, the standard deviation during the 10s averaging was such that the locked and misaligned readings had their 'fuzz' overlapping significantly. The situation is worse for POX DC - today, Eric checked that the POX DC and POY DC channels are indeed reporting what they claim, but we found little to no change in the POX DC level while misaligning the ITM - even after cranking the whitening gain up to 40!
Eric then suggested deriving ASDC from the AS110 photodiode, where there is more light. This increased the SNR significantly - in a 10s averaging window, the fuzz is now about 10 ADC counts out of ~1500 (~<1%) as opposed to ~2counts out of 30 previously. We also set the gains of POX DC, POY DC and ASDC to 1 (they were 0.001,0.001 and 0.5 respectively, for reasons unknown).
I ran a quick measurement of the X arm loss with the new ASDC configuration, and got a number of 80 +/- 10 ppm (7 datapoints), which is wildly different from the ~250ppm number I got from last night's measurement with 70 datapoints. I was simultaneously recording the POX DC value, which yielded 40 +/- 10 ppm.
We also discovered another possible problem today - the spot on the AS camera has been looking rather square (clearly not round) since, I presume, closing up and realigning everything. By looking at the beam near the viewport on the AS table for various configurations of the ITM, we were able to confirm that whatever is causing this distortion is in the vacuum. By misaligning the ITM, we are able to recover a nice round spot on the AS camera. But after running the dither align script, we revert to this weirdly distorted state. While closing up, no checks were done to see how well centered we are on the OMs, and moreover, the DRMI has been locked since the vent I believe. It is not clear how much of an impact this will have on locking the IFO (we will know more after tonight). There is also the possibility of using the PZT mounted OMs to mitigate this problem, which would be ideal.
Long story short -
GV Edit 8 Oct 2016: Going through some old elogs, I came across this useful reference for loss measurement. It doesn't talk about the reflection method (Method 3 in the list at the top of this elog), but suggests that cavity ringdown with the Trans PD yields the most precise numbers, and also allows for measuring TITM
From the last plot:
- Subtracting the offset of 0.0095, the modulation depth were estimated to be 0.20 for 11MHz, 0.25 for 55MHz
- Carrier TEM00 1.0, 1st order 0.01, 2nd order 0.05, 3rd order 0.002, 4th order 0.004
==> mode matching ~93%, dominat higher order is the 2nd order (5%).
Eric: now we have the number for the mode matching. How much did the cavity round-trip loss be using this number?
Using these numbers for both arms (Modulation takes away .2*.25 = 5% power, mode matching takes away 7% after that), I get the following from my data from March:
Xarm loss is 561.19 +/- 14.57 ppm
Yarm loss is 130.67 +/- 18.97 ppm
Obviously, the Xarm number looks very fishy, but its behavior was qualitatively very different when I took the data. ASDC would change from ~0.298 to ~0.306 when the Yarm was locked vs. misaligned, whereas the xarm numbers were .240 to .275.
In any case, I'll do the measurement again tomorrow, being careful with offsets and alignment; it won't take too long.
I want to measure the transfer function of the arm cavities to extract the pole frequencies and get more insight into what is going on with the DC loss measurements.
The idea is to modulate the light using the PSL AOM. Measure the light transmitted from the arm cavities and use the light transferred from the IMC as a reference.
I tried to start measuring the X arm but the transmission PD is connected to the QPD whitening filter board with a 4 pin Lemo for which I couldn't find an adapter.
Could this be because of the PDA520 limited BWs? I tried playing with the PD gain/bandwidth switch but it seems like it was already set to high bandwidth/low gain.
In any case, the extracted pole frequency ~ 2.9kHz implies a finesse > 600 (assuming FSR = 3.9MHz) which is way above the maximal finesse (~ 450) for the arm cavities.
I disconnected the source from the AOM. But left the other two BNCs connected to the SR785. Also, TRY PD is still teed off. Long BNC cable is still on the ground.
when doing the AM sweeps of cavities
make sure to cross-calibrate the detectors
else you'll make of science much frivolities
much like the U.S. elections electors
I measured the cross-calibration of the two PDs on the PSL table.
I used the existing flip mounted BS that routes the beam into a PDA255, the same as in the IMC transmission.
I placed a PDA520, the same as the one measuring TRY_OUT on the ETMY table, on the transmission of the BS (Attachment 1).
I used the SR785 to measure the frequency response of PDA520 with reference to PDA255 (Attachment 2). Indeed, calibration is quite significant.
I calibrated the Y arm frequency response measurement.
However, the data seem to fit well to 1/sqrt(f^2+fp^2) - electric field response - but not to 1/(f^2+fp^2) - intensity response. (Attachment 3).
Also, the extracted fp is 3.8KHz (Finesse ~ 500) in the good fit -> too small.
When I did this measurement for the IMC in the past I fitted the response to 1/sqrt(f^2+fp^2) by mistake but I didn't notice it because I got a pole frequency that was consistent with ringdown measurements.
I also cross calibrated the PDs participating in the IMC measurement but found that the calibration amounted for distortions no bigger than 1db.
Ok, now I understand my foolishness. It should definitely be 1/sqrt(f^2+fp^2) .
The measured RIN of the arm cavity transmission when the PRFPMI is locked is ~10x in RMS relative to the single arm POX/POY lock. It is not yet clear to me where the excess is coming from.
Attachment #1 shows the comparison.
My speculation for the worse RIN is:
- Unoptimized alignment -> Larger linear coupling of the RIN with the misalignment
- PRC TT misalignment (~3Hz)
Don't can you check the correlation between the POP QPD and the arm RIN?
I agree, I think the PRC excess angular motion, PIT in particular, is a dominant contributor to the RIN. Attachments #1-#3 support this hypothesis. In these plots, "XARM" should really read "COMM" and "YARM" should really read "DIFF", because the error signals from the two end QPDs are mixed to generate the PIT and YAW error signals for these ASC servos - this is some channel renaming that will have to be done on the ASC model. The fact that the scatter plot between these DoFs has some ellipticity probably means the basis transformation isn't exactly right, because if they were truly orthogonal, we would expect them to be uncorrelated?
I guess what this means is that the stability of the lock could be improved by turning on some POP QPD based feedback control, I'll give it a shot.
- PRC TT misalignment (~3Hz)
Don't can you check the correlation between the POP QPD and the arm RIN
how bout corner plot with power signals and oplevs? I think that would show not just linear couplings (like your coherence), but also quadratic couplings (chesire cat grin)
X Arm: 0.875 +/- 0.005
Y Arm: 0.869 +/- 0.006
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.
The IFO is ready for 3F DRMI comissioning
Since last Friday either the arms or the PRC can't lock.
The montors show the beam flashing on the end mirrors, but the cavity can't get locked. The error signal looks fine. I suspect a computer problem.
Also PRC can't lock. SPOB is suspiciously stuck at about -95. Although that's not a fixed number, but covering the by hand the SPOB PD on the ITMY table doesn't change the number. I check the DC output of the photodetector and it is actually seen the beam.
Suspecting computer problems started after last Thursday's IP switch, I rebooted the frame builder, c1dcuepics, c1daqctrl and all the front ends. I then burtrestored to February 1st at 1:00 am.
Before I burtrestored c1iscepics, SPOB had gone back to more typical numbers around 0, as it usually read when PRC wasn't locked.
But burtrestoring c1iscepics, return it to the -95 of earlier.
Burterestoring to other times or dates didn't solve the problems.
Koji and I started poking around, trying to understand what was going on. At first, we thought it might be related to a computer error, as it seemed.
Fortunately, Rob stopped by and explained that the boost stage of the filter comes under c1lsc control, and will be turned on or off depending on the power in the arms. Although if you turn it off, it will remain off, it just if its manually selected on, it may go on or off.
Similarly, the output from the Xarm filter bank to the ETMX filter input will be turned on or off depending on the power in the arm.
Anyways, the locking trouble turns out to be due to no RF sidebands at 33 MHz. The output of the Marconi was unplugged. I don't know who, or why did it, but I've plugged it in for now, so we can lock the arms. Let us know if you need in unplugged. Thanks.
Someone left the arms aligned, and the LSC engaged, so the arms have been locked almost continuously for several days hours. The trend below is for 4 days hours. What is most impressive to me is that we don't see a big degredation in the transmitted power over this time.
EDIT: Okay, I got excited without paying attention to units. It was only several hours, which is not too unusual. Although the lack of transmission degredation is still unusual. However, this may be due to improved oplevs? I'm not sure why, but we're not seeing (at least in this plot) the degredation to ~0.7 after an hour or so.
[Koji, Manasa, Jenne]
The Y arm was locked in IR, and we saw flashing in the Xarm (Gautam had the Xarm for green work when we began). I checked IPANG, and the beam was beautifully unclipped, almost perfectly centered on the first out of vacuum mirror. I aligned the beam onto the QPD.
We then swapped out the MC Y1 that we use at low power, and replace the usual 10% BS, so that we wouldn't crispy-fry MC REFL. Manasa adjusted the half wave plate after the laser, to maximize the power going toward the PMC. We relocked the PMC, and see transmission of ~0.84, which is at the high side of what we usually get. The beam was aligned onto MC REFL and centered on the WFS, and the MC was locked at nominal power. Koji tweaked up the alignment of the MC, and ran the WFS offset script. I aligned beam onto POP QPD and POP110 coarsely (using a flashing PRC, not a locked PRM-ITMY cavity, so the alignment should be rechecked). The arms have both been locked and aligned in IR....the green beams need to be steered to match the current cavity axis.
The AS beam, as well as REFL and POP, are all coming out of the vacuum nicely unclipped.
Notes: When Koji was aligning the SRM to get the SRC cavity roughly aligned (the AS flashes all overlapping), we noticed that there is some major pitch-yaw coupling. Serious enough that we should be concerned that perhaps some connector is loose, or an actuator isn't working properly. This should be checked.
Moral of the story: Coarse alignment of all mirrors is complete after pump-down and we have IR locked and aligned to both arms at nominal power.
Still to do:
* Restore PRM, align beam onto the REFL PDs.
* Lock PRM-ITMY cavity, align beam onto POP PDs.
* Align AS beam onto AS55.
* Recenter all oplevs.
* Recenter IPPOS and IPPANG at nominal power.
* Start locking!!
I have a concern about the SRM suspension. The yaw alignment bias produces huge pitch coupling.
This could be a connector issue or the rubbing of the mirror on the EQ stops.
We have the photos of the magnets and they were not touching the OSEMs.
I aligned both the X and Y end green to the arms.
The day before yesterday, I was cleaning a flow bench in the clean room.
I found that one SOS was standing there. It is the SRM suspension.
I thought of the nice idea:
- The installed PRM is actually the SRM (SRMU04). It is 2nd best SRM but not so diiferent form the best one.
==> Use this as the final SRM
- The SRM tower at the clean room
==> Use this as the final PRM tower.
==> The mirror (SRMU03) will be stored in a cabinet.
- The two SOS towers will be baked soon
==> Use them for the ETMs
This reduces the unnecessary maneuver of the suspension towers.
This afternoon I epoxied the guiderod and wire standoff to the new PRM. I also epoxied the magnets that Suresh picked out to the dumbbell standoffs. We'll let them all cure over the weekend, and then I'll glue the magnets to the optic on ~Monday.
Notes about the epoxy:
Previously, we had been using the "AN-1" epoxy, which is gray, with a clear hardener. Bob recommended we switch to "30-2", which is clear with clear, and has been chosen for use in aLIGO. Both were vacuum approved, but the 30-2 has gone through ~2 months of testing at the OTF (Optics Test Facility?) over in Downs under vacuum, to check the level of outgassing (or really, non-outgassing).
The 30-2 is less viscous than the AN-1, and it takes less glue to do the same job, so we should keep that in mind when applying the epoxy. When I put the glue next to the guiderod and standoff, it got wicked along the length of each rod, which is good. I can't reach the whole length of the rod with my glue applicator because the fixture holding them in place blocks access, so the wicking is pretty handy.
I've also added the updated version of my Status Table for the suspensions.
This morning I assembled LO3, LO4 and AS3 (all mirrors) onto polaris K1 mounts. The mounts stand as per this elog, on 4.5" posts with 0.5" Al spacers to match the beam heigth of 5.5". I also assembled ASL by adding a 0.14" Al spacer, and finally, recycled two DLC mounts (from the XEND flowbench) and posts to mount the 2 inch diameter beamsplitters BHDBS and AS2 (T=10%). I stored the previous 2" optics in the CVI and lambda optic cases and labeled appropriately.
The ETM assembly has moved forward a couple of steps. We have completed the following:
1) Positioning the guide rod and wire stand-off on both the ETMs (5 and 7)
2) The magnets had to be cleaned with an acetone wash as they had touched the plastic Petri-dish (not cleaned for vacuum).
3) The magnets and the Al dumb-bells have been glued together and left to cure in the gluing fixture.
4) The guide-rod and wire stand-offs have also been glued to the optic and left to cure for 24 hrs.
JD: As you can see in my nifty status table, we are nearing the end of the suspension story.
JD: As you can see in my nifty status table, we are nearing the end of the suspension story.
We are going to try (but can't guarantee) to get ETMX to Bob for baking by Friday at lunchtime, that way we can re-suspend it on ~Monday, and place it in the chamber. Then we could potentially begin Green arm locking next week. Steve has (hopefully!!) ordered the spring plungers for ETMY. The receiving and baking of the spring plungers is the only current delay that I can foresee, and that only is relevant for one of the optics.
We (who is going to be in charge of this?) still need to move the SRM OSEMs & cables & connectors to the ITMY chamber from the BS chamber.
We've begun assembling the new c1psl Acromag chassis based on Yehonathan's final pin assignments. So far, parts have been gathered and the chassis itself has been assembled.
Yehonathan is currently wiring up the chassis power and Ethernet feedthroughs, following my wiring diagram from previous assemblies. Once the Acromag units are powered, I will help configure them, assign IPs, etc. We will then turn the wiring over to Chub to complete the Acromag to breakout board wiring.
I began setting up the host server, but immediately hit a problem: We seem to have no more memory cards or solid-state drives, despite having two more SuperMicro servers. I ordered enough RAM cards and drives to finish both machines. They will hopefully arrive tomorrow.
RTFE. Where did the spares go?
I found them, thanks. After c1psl, there are 4 2GB DIMM cards and 1 SSD left. I moved them into the storage bins with all the other Acromag parts.
I finished pre-wiring the PSL chassis. I mounted the Acromags on the DIN rails and labeled them. I checked that they are powered up with the right voltage +24V and that the LEDs behave as expected.
I configured the Acromag channels according to the Slow Controls Wiki page.
We started testing the channels. Almost at the beginning we notice that the BIO channels are inverted. High voltage when 0. 0 Voltage when 1. We checked several things:
1. We checked the configuration of the BIOs in the windows machine but nothing pointed to the problem.
2. We isolated one of the BIOs from the DIN rail but the behavior persisted.
3. We checked that the voltages that go into the Acromags are correct.
The next step is to power up an isolated Acromag directly from the power supply. This will tell us if the problem is in the chassis or the EPICs DB.
I isolated a BIO Acromag completely from the chassis and powered it up. The inverted behavior persisted.
Turns out this is normal behavior for the XT1111 model.
For digital outputs, one should XT1121. XT1111 should be used for digital inputs.
Slow machines Wiki page was updated along with other pieces of information.
I replaced the XT1111 Acromags with XT1121 and did some rewiring since the XT1121 cannot get the excitation voltage from the DIN rail.
I added an XT1111 Acromag for the single digital input we have in this system.
I don't think this is an accurate statement. XT1111 modules have sinking digital outputs, while XT1121 modules have sourcing digital outputs. Depending on the requirement, the appropriate units should be used. I believe the XT1111 is the appropriate choice for most of our circuits.