• 04:42 NLN and Observing
  • Accepted same SDF diffs in ETMY M0 test offsts that we have been seeing this week and TJ will look into - alog 54726

I believe I found and fixed this, see alog54773.

It's been kind of hard to find segments to compare, with moderate-high microseism, the three attached screens are the best I've found so far. But I think that by looking at the OAF Range integrand blrms, we can say that the R0 tracking has improved the 20-50hz scattering enough that we shouldn't have to change SEI_DIFF, when the microseism is higher.

3 attached plots are 5hr timeseries for different of the 20-29hz & 38-60 range blrms, the ITMY Z .1-.3hz gnd blrms and the R0 L2 drive (indicating if the R0 tracking is on).

First image is from a lock with no R0 tracking and full cps diff on. The top suplot shows a lot of glitching (20-29 hz RLP is high) throughout the 5 hour segment here. Second subplot doesn't show a lot of extra glitching. Third subplot is the microseis for this segment, average value is about 600nm/s.

Second image is for a lock segment with full diff cps on and R0 tracking. Similar microseism, but the top subplot shows a lot less activity. It's subtle, but even the 38-60hz shows less activity with the R0 tracking on.

Third image is with corner diff cps and R0 tracking. The 20-29hz glitching looks about the same as the full diff. R0 tracking was on, similar microseism again. Not a whole lot of difference from the full diff cps with R0 tracking.

I would like some data with higher microseism and FULL_DIFF_CPS on SEI_DIFF, but I think this shows that the R0 tracking has improved the microsesmic scattering.

Sorry about this---I thought I noted somewhere that I made this transition, but looks like I didn't (I blame not being able to get on the network on my laptop last night & then being busy trying to log everything I could for recovery most of the night).  I did mention it to Patrick during the hand-off this morning (this node was new to him, and I mentioned the transition, but also that it probably wans't necessary since the microseism was below the 90th percentile.  I gave him a brief summary of the node and what it does for us, but that you could also explain it better than I.).

Thanks for catching this!! 

QUESTION:  We can transition this even when we are in OBSERVING, yes?

Shoot.  This was definitely due to the guardian change on Friday. :(

I had assumed that the BS LOCK P gain was set to -1 somewhere, just as the Y gain must be.  But, since P and Y for the BS and PR3 have always been treated differently, there must have been another place that I didn't catch and fix.

We ran all weekend without any BS P offloading to the top stage.  BS still had normal angular control on, but for pitch it was entirely on the lower stage, and the low frequency pointing wasn't being offloaded up the chain.  As long as there were no BS saturations, this shouldn't affect data quality, I believe.

I will continue to look into this, including finding where the gain for P didn't get set.

I'm not seeing an obvious place where we're saturating the BS M2 stage at lownoise_ASC that would be causing these locklosses.  However, we certainly should not be running with the M1 pitch gain off.  Maybe I'll re-implement the change tomorrow, and can watch the relock after maintenance to ensure things go smoothly.

This is a good reminder of using and posting the SDF diffs.  After reverting my guardian code change, Corey had SDF diffs that he accepted that correctly put the gains back to their nominal values, so they were accepted with the incorrect values over the weekend (although the reason they were incorrect was my guardian error).  We are continuing to remove unnecessary diffs to reduce 'alarm noise', so that any diffs that do show up should be a cause for a small amount of investigation.

I have made one more modification to the ISC_DRMI guardian, so that it will clear the history of the pitch filter.  Since the line 71 was still commented, FM1 was not going to be turned off (which is what used to do the 25 min clearing).  The gain was getting set to 0 (which makes the pitch the same as yaw), but the clear history (near line 143, setting the _RSET channel equal to 2) was only being done to yaw.  This meant that when the gains were put back to their nominal values near lines 158, the BS would still have all the integrated output.  So, I fixed line 143 so that it will clear history for both pitch and yaw.  With Corey's addition of the writing the pitch gains at line 158 (this is the piece that I had forgotten on Friday), now the guardian should work as I had intended on Friday, not taking 25 min to clear the BS pitch.

I have saved and svn-ed the guardian, so next time we're out of observing we should load ISC_DRMI.  (The reason to not wait until Tuesday is that I think the code as-loaded will cause relocking problems).

Something is rounding these values. Their actual values should be the higher precision ones, but I also don't think that it really matters other than from a consistency standpoint. I'll look into this.

I believe that I found this discrepancy in lscparams.py. It wasn't the code that was rounding it, but it must have been a human. The filter medm only displays the offset values to the precision of 10*-1, even though the actual value of it could be much more. Ex: offset value actual = 10.15, displayed = 10.2

Either way, the place in the code that was doing it I have changed and reloaded the appropriate nodes.

After talking to Sheila and Jim, we all agree that we can probably get rid of these wire heating decay filters, since the new BS baffle was put in pre-O3 to further protect the wires from seeing any heating.  

In the first attached figure, we lose lock around 1300 seconds from a TR_CARM lockloss (so no power buildup). Very quickly, we have a transient that get through to the BS_M2_LOCK_P output, and so gets integrated in with the M1 Lock input.  But, since we've just lost lock, the ASC output isn't sent to the coils (because the lockloss trigger is stopping the signal), but after ~100 seconds the lockloss trigger is reset in the guardian, so we allow the decaying ASC signal back to the coils, and see a jump in the BS oplev signal.  The salient point is that as the coil output filter changes over 20 min, the BS oplev is also changing.  If the decay filter were compensating for wire heating, then the oplev should be more constant and flat.  Since it's not, we're pushing unneccessarily.

In the second attached figure, we lose lock from a 2 hour long Nominal Low Noise lock around 20 seconds.  No major transient in the M2 filter that gets sent to the M1 output, although the lockloss trigger again takes away the coil output for about a minute, during which time the optic swings a bit.  But, once the ASC outputs are again sent to the coils, we see the BS move as the coil output is changed.  I suspect that we'd be okay here also without having the long decay filters.  

Since we would only even potentially need the heating decay filters when losing lock from nominal low noise, it's a bit hard to do chopping tests with and without the filter, so probably we'll just try removing it entirely, and making the pitch filter banks operate the same way the yaws do (without any decay, just normal ramp-down).

I have just changed ISC_DRMI to treat BS and PR3 pitch the same as yaw (as is done for all other suspensions) when clearing the ASC history in the DOWN state.  Next time we're out of Observing, we'll reload the ISC_DRMI guardian, so that we can (hopefully) see an improvement in some lock acqusition cases. If BS pointing is a real problem over the weekend, we can revert the DRMI guardian and reload it.

Still to be seen (fair game for an operator to look at over the weekend, otherwise I'll look next week) is whether the MICH BS ASC is in fact undoing / taking care of any leftover decay filter offset when we go through DRMI ASC, or whether this decay filter output has been causing trouble for us during the TR_CARM states.  I think that it's probably true that the MICH ASC is doing its job and pushing the BS where it needs to go (we do see improvements in buildups afterall), and that the TR_CARM locklosses are from something different. 

Even if the TR_CARM locklosses are unrelated to the BS pitch decay filters, it is still interesting that the TR_CARM locklosses seem to go away so easily after initial alignment.  Maybe something to check is where the optics were pointing when attempting and failing TR_CARM earlier in the afternoon before initial alignment, versus where the optics were pointing after initial alignment when we successfully got through TR_CARM.

I have just changed ISC_DRMI to treat BS and PR3 pitch the same as yaw (as is done for all other suspensions) when clearing the ASC history in the DOWN state.  Next time we're out of Observing, we'll reload the ISC_DRMI guardian, so that we can (hopefully) see an improvement in some lock acqusition cases. If BS pointing is a real problem over the weekend, we can revert the DRMI guardian and reload it.

Still to be seen (fair game for an operator to look at over the weekend, otherwise I'll look next week) is whether the MICH BS ASC is in fact undoing / taking care of any leftover decay filter offset when we go through DRMI ASC, or whether this decay filter output has been causing trouble for us during the TR_CARM states.  I think that it's probably true that the MICH ASC is doing its job and pushing the BS where it needs to go (we do see improvements in buildups afterall), and that the TR_CARM locklosses are from something different. 

Even if the TR_CARM locklosses are unrelated to the BS pitch decay filters, it is still interesting that the TR_CARM locklosses seem to go away so easily after initial alignment.  Maybe something to check is where the optics were pointing when attempting and failing TR_CARM earlier in the afternoon before initial alignment, versus where the optics were pointing after initial alignment when we successfully got through TR_CARM.

When doing this work on Friday, I had forgotten to ensure that the pitch gains get set back to their nonzero values in the guardian.  Corey fixed this, see thread in alog 54746.

Here is a plot of the data taken from the DCPDs up to 4MHz.  I've removed the 20dB of gain and the poles at 265kHz and 290kHz from D1700376 in this plot.  This was measured with our usual darm offset, restuling in 10mA on each of the DCPDs (we used one of the single PD outputs from D1700376).  We tried to repeat this measurement with a diode set up in the AS air path yesterday, 54636, but the 3.125MHz peak was only 20dB above the noise level, so we weren't able to see any of the other noise apparent in this measurement.  

Thanks, this is useful for ongoing CLF work.

For reference, Koji's measurements of the transimpedance are below. You can see that the rolloff flattens a bit in the MHz, so I'm less certain how real the bump is.

https://nodus.ligo.caltech.edu:8081/OMC_Lab/236

https://nodus.ligo.caltech.edu:8081/OMC_Lab/235

does your RF equipment have the ability to make a decently long cross correlation? That is surely what we need if we can conveniently get equipment to do it. Alternatively, you may be able to take spectra simultaneously in a sum and null output configuration, and then subtract them. It won't be as clean as xcorr, but it will show excess in a way that is less succeptible to systematic errors from inverting the PD response. Sum can be picked off from the SQZ chassis, and null just needs the phase shift before an RF splitter used in reverse (depending on the phase convention of the splitter).

Update, I remembered that I had acquired the LISO model and fit it in IIRrational for just these kinds of occasions. These fits should be decent up to 10MHz where the simulation cut off.

scipy ZPK notation:

(array([-1.09367517e+06+9.16935186e+04j, -1.09367517e+06-9.16935186e+04j,
       -4.54321270e+01+3.94631525e-01j, -4.54321270e+01-3.94631525e-01j,
       -2.85835003e+07+0.00000000e+00j]), array([-1.12584306e+07+1.59926553e+07j, -1.12584306e+07-1.59926553e+07j,
       -3.11667017e+07+1.49827313e+08j, -3.11667017e+07-1.49827313e+08j,
       -4.41594538e+07+5.59042545e+07j, -4.41594538e+07-5.59042545e+07j,
       -1.51046460e+07+2.52263715e+07j, -1.51046460e+07-2.52263715e+07j,
       -1.02822684e+05+0.00000000e+00j, -9.54273138e+04+0.00000000e+00j,
       -5.08417603e+02+0.00000000e+00j, -4.91824766e+02+0.00000000e+00j]), 2.71124765615596e+56)

foton notation:
ZPK([
  -174063.80969071676 + 14593.476738924443*i; -174063.80969071676 - 14593.476738924443*i;
  -7.2307475830315395 + 0.06280755795247621*i; -7.2307475830315395 - 0.06280755795247621*i;
  -4549205.365087142;
],[
  -1791834.8749338891 + 2545310.1382306265*i; -1791834.8749338891 - 2545310.1382306265*i;
  -4960334.630691198 + 23845757.522465646*i; -4960334.630691198 - 23845757.522465646*i;
  -7028195.359231514 + 8897438.443450466*i; -7028195.359231514 - 8897438.443450466*i;
  -2403979.0673290133 + 4014901.7200727463*i; -2403979.0673290133 - 4014901.7200727463*i;
  -16364.738450407038; -15187.728699344743;
  -80.91717459920993; -78.27634271397135;
], 2.71124765615596e+56, "f")

Attached are the fits and the output of the LISO model. I think the model differs a touch from Koji's measurements on the exact 3MHz cutoff frequency.

Here is a plot (and the data used to make it) of the DCPD output measured with the analyzer in noise mode.  The first set of data (in the original log above) were taken in spectrum mode.  The dark noise in this new plot was measured durring Friday's EQ in Turkey, the "squeezer blocked" trace was taken durring the commisioning time Thursday (54681).   These are calibrated using the filters in D1700376 and Lee's estimate of the OMC DCPD transimpedance above.  Both spectra were taken with 30Hz resolution bandwidth and 3Hz video bandwidth.  A potential problem with this measurement could be that the squeezer came unlocked and the beam diverter closed partway through the measurement, although that didn't seem to have an impact on the spectrum here.  

It does seem suspicous that the quadrature difference, which should represent noise coming from the interferometer light, has a spectrum so similar to the dark noise. 

This appears qualitatively a bit different than the post-demodulation measurement of the spectrum at LLO50307. There the blocked and dark noise ASD's changed by a factor of about 1.5. This appears to be substantially less than that at 3.125MHz.

Here is one more plot of the DCPD spectrum up to high frequency, again.  In the original version of the attached plot in 54753  I made two mistakes in the calibration, which are fixed here..

• The field on the DCPDs could be written as E_carrier +E_clf + E_am where E_am is am sidebands from the interferometer at audio frequencies around 3.125MHz.  The amplitude noise spectrum we measure on the DCPD is E_carrier*E_am while the term that could cause audio frequency noise by downconverting with the CLF is E_clf*E_am  The requirement for the amplitude noise around 3MHz is that the ASD of the photocurrent at 3MHz should be smaller than our audio frequency photocurrent asd*abs(E_carrier/E_clf)  In other words, the amplitude noise requirement around the CLF (and RLF) fields is less stringent than that at DC by the amplitude ratio of the clf to carrier light.
• With 20mA total on the DCPDs, our shot noise limited sensitivity on each individual diode is 6e-11A/rtHz, without squeezing. 
• We have been running with 5uW CLF injected into the OPO, and about -29dBm of RF power at the 3.125MHz demodulator since Nov 26th, before that we used -19dBm.  These powers are measured after the 20dB of gain in D1700376. This means we get 10uW of RF power out of the transimpendance amp, which is 92uA of photo current from the beat note of the 3MHz sideband with the DC power (20mA, 23mW). This means that we were using about 0.5uW of CLF on the DCPDs for the first part of O3, when we had noice from the CLF just below DARM.  Edit: The filter cavity design document T1800447 states on page 24 that there will be 10uW of CLF and RLF combined on the DCPDs OMC, which means about 0.1uW on the DCPDs, so this is similar to our current operating power. 
• This means that to determine if ampltude noise down-converted by the CLF can explain the observed CLF noise, we would need to measure the spectrum of the DCPDs a factor of a few below 1.7e-8A/rtHz on a single diode.  To allow for 20 times more CLF power reaching the DCPDs with the filter cavity, we'd need to measure noise below 3e-9A/rtHz. 

The attached plot shows, in addition to the dark noise and locked spectrum, the level of amplitude noise which I think would be needed to create downconverted noise about equal to the current shot noise limited sensitivity.  One conclusion is that the dark noise of the DCPDs at 3MHz is too high for us to measure the level of amplitude noise that we need to measure to be sure that we can turn up the CLF power to the level required for the filter cavity controls. However, the difference between the in lock and the dark noise spectrum suggests that the current level of amplitude noise is well above this level, such that it should be dominating the noise in DARM.  So something seems to be wrong either with the measurement or with my projections.

One could worry that there might be significant variation between the individual transimpednce amplifiers at 3MHz.  We have a measurement made at 3.12MHz with the installed amplifier: 47540  which is roughly consistent with the one that Koji measured and Lee's fit above.  Another worry could be that we are running with a different transimpedance than these measurements were taken with, but we are running in high Z which is 400 Ohms at DC according to D060572, My plot of Lee's fit above gives a DC transimpedance of 200 Ohms, but it is ~220 Ohms at 3.125 MHz, so I think it is close enough.