The LVEA has transitioned to LASER SAFE.
This is under work permit #7797.
Sheila, Terry, Haocun, Nutsinee
For the past few days we've had trouble with OPO locking stability and mystery offset in the error signal. Turned out we've been locking using the wrong compensation filter -- 40Hz/4kHz compensation on the common path instead of the 4/400 in the slow. Here's the OLG transfer function and the PZT response for each case (PZT calibration ~ 132V/um. I didn't do a quadratic fit but instead took the average of the two V/FSR. Good enough for now ) .
Wrong compensation filter
It's clear that we have very little phase margin here around the UGF. Gain peaking was visible around 2-3kHz on the PSD plot. Unable to engage the notch filter. End of story.
Correct compensation filter
This is the configuration we should be operating on until the modified TTFSS board is ready.
How did we have the wrong configuration in the first place? Same old story. Beckhoff restart, things didn't come back right, and I was following the wrong note on the configuration. I will make sure Guardian turns on what needs to be turned on if I haven't already done so.
Offset issue -- to be revisited
We noticed that when operating at relatively high green power (18mW input to the coupler) OPO doesn't want to lock at the right place. The loop does what it's supposed to do by driving the error signal to zero but that's not where the green refl and trans were minimized and maximized. An offset at the common path had to be added after the loop catches lock.
I haven't tried very hard to replicate this issue after the wrong compensation filter was fixed. We have been fine as of the end of today operating at 15mW green power into the coupler.
Why is nobody looking at SDF?
Changes also has been accepted in SDF.
The main task that we need to do before we can power up is get some of our ASC loops running with higher bandwidths.
Jenne and Patrick spent some time today measuring CHARD.
It looks like both pitch and yaw need to have large gain increases, which we would expect because we have about 47dB less gain now than we used during O2. For yaw I was able to increase the gain from 0.3 to 60, but increasing it to 100 unlocked the interferometer. For pitch increasing it from 0.3 to 6 was enough of a gain increase to cause instability.
I noticed that the ITMs were still not used for DHARD, so Craig and I manually turned them on and added them back in the guardian. We have only locked once since adding them at it was a little bit rough when DHARD came on, so we might want to increase the bandwidth of MICH.
Danny, Georgia, Sheila
We spent some more time on violin modes this afternoon.
Danny found that one of the modes which had been assigned to ITMX was actually on ITMY, 501.755, it is now in mode 8. I changed the phase for this mode to -gain, +60 deg phase.
There are 7 modes on ITMX which have settings in the guardian which seem to work. The filter for MODE2 (504.891 ) may be ring up by one of the other ITMX filters, but I am not sure which.
We also tested the guardian on ITMY, right now it seems to work for 5 of the 8 modes we have in the wiki table for ITMY. It sets the gain to zero for the doublet and for MODE3, which we are not sure about. We made a couple of the filters on iTMY narrower today to avoid ringing up nearby modes with them.
I also went through and changed the monitor filters on ITMY and ETMX so that they all are 8th order butterworths 20mHz wide. We want them all to have the same width so that we can directly compare the monitors to each other for automatically deciding when to turn the damping on and when to change the gain.
There is now a mechanical beam block in the squeezer path. So the laser should not need to be turned off at the control box tomorrow morning. This will give us more time in the afternoon as we won't have to wait for it to stabilize after it's turned back on. Peter will check and put up a sign by the laser control early tomorrow morning indicating the status of the laser (attached is the table layout and the position of the added beam dump).
I've placed a NOTICE on the table enclosure, right under the laser power supply, as agreed to with Terry yesterday.
When the spot position script is run on the triple suspensions, it works by driving in pitch and yaw, turning on the M3 stage DRIVEALIGN P2L and Y2L gains, and minimizing the coupling to length by adjusting this gain. Unfortunately, the script leaves these gains on, so all of our angle controls have been feeding to length for a while now. I turned off the M3 DRIVEALIGN angle2length gains for MC1, MC2, MC3, PR3, PR2, and PRM. We are controlling the angles on PR2, PRM, and MC2, so each of these were coupling into LSC. Maybe soon we can do this on purpose and reduce ASC -> LSC control noise.
TITLE: 08/27 Day Shift: 15:00-23:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Commissioning
INCOMING OPERATOR: None
SHIFT SUMMARY: Commissioners working on violin mode damping, etc. SQZ team working on ISCT6 all day.
LOG: See attached .txt. file.
Looked into more of the green power fluctuations coming out from SHG, and found something interesting:
At the Jeff K's request, we have changed the amplitudes of the low frequency calibration lines running on EndY PCal for use by commissioners.
| Line frequency (Hz) | Previous Value | New Value |
| 36.7 | 500 | 1000 |
| 331.9 | 5000 | 20000 |
All other values were unchanged.
Also, OSC3 (1083.7 Hz line) was turned off by setting H1CAL-PCALY_OSC_SUM_MATRIX_1_3 to 0 on the CAL_PCAL_OSC_SUM_MATRIX.adl MEDM screen.
Fire-pump operation immediately sends cell phone alarms. To quickly show their status, I've added them to the FMCS top overview screen
11am local
Turned cleanroom ON that is over ion pumps # 1,2 in preparation for tomorrow's maintenance activities.
Attached plot, data and code for a high resolution (0.2 mHz) PSD around the violin modes. Here's how it was computed:
Additionally, I adapted some code from the C.Ri.Me. lab code library to identify peaks and measure the frequencies (code in the attached notebook). Here's a list of the main peak identified in this way and a plot
Freq. [Hz] SNR 501.5549 216 501.6304 22387449 501.6934 2208 501.7563 1016510 502.7843 5148 502.9086 3800670 503.0852 62183 503.1976 9143441 503.6788 1360642 503.7344 8771479 504.1450 10496208 504.1786 3180409 504.6066 451 504.8855 63210 504.8906 195549 504.9527 3884 505.0795 15773030 507.3577 1366 507.4948 40605 508.8452 2856 508.9412 5231498 510.7134 975575 511.1883 210 511.2993 327 513.5110 265289 516.6803 536 516.6822 59
The attached script can be used to generate the output above from any GPS times.
Syntax:
python violin_psd.py start_gps end_gps [resolution]
where the optional parameter is the frequency resolution in Hz (default to 2e-4 Hz).
The output are four files:
violin_modes_0.2mHz_resolution_*.png plot of the PSD
violin_modes_0.2mHz_resolution_*.txt full data for the PSD (in a range centered at 507 Hz)
violin_modes_0.2mHz_resolution_peaks_*.png same lot aa above, but with the identified peaks highlighted
violin_modes_0.2mHz_resolution_peaks_*.txt list of the identified peaks, same as what is printed on screen
A new PSD from the lock that is going on right now.
Freq [Hz] SNR
501.5550 459101
501.6305 61232190
501.6937 455339
501.7564 867059
502.7844 103124
502.9087 783689
503.0851 4840352
503.1974 2751967
503.6788 69546
503.7344 23972
504.1449 127328
504.1784 1989882
504.6069 31477
504.7199 964331
504.8523 1286321
504.8907 472099
504.9520 417818
505.0795 610232
505.1885 962338
507.3616 2042637
508.8460 4356110
508.9411 155619
510.7133 601203
511.1812 5551906
513.4049 1859193
516.6799 11926450
516.7792 8724
Quick conclusion: Not so good.
Details:
Here's a plot showing OPO length noise out-of-loop, in-loop, and OPO length noise without FSS engaged (pump laser not locked to PSL, out-of-loop). The OPO length noise with FSS engaged has a broad hump around 2kHz that was higher than the free-running laser noise. This hump was clearly visible in FSS fast path error signal. Once the FSS disengaged (but OPO was still locked) we get 1/f laser frequency noise with 232Hz harmonics on top of it. This harmonics disappeared when FSS engaged (at least that's what I saw today. Sometimes I do see harmonics at different frequency during OPO length noise measurement with FSS engaged). An investigation is on-going.
The high frequency part of length noise is likely to be limited by shot noise+dark noise combined but I would have to retake the dark noise measurement again to be sure. Hence those traces are not plotted here.
The OPO length noise was measured out of the I-MON of the demod box.
The loop UGF is at ~800Hz. During this particular measurement I forgot to turn the notch filter (6kHz) on. So, the UGF could be pushed a bit further but not by much.
Here's a screenshot of the configuration used for this measurement.
J. Kissel
Using the lock stretch that Sheila called out in LHO aLOG 43263, I gathered data that shows the new violin mode forest after we've replaced ETMX, ETMY, and ITMX (with ITMY been exposed to air for ~9 months, which undoubtedly also changes the violin mode frequencies). Attached are comparisons of the Fundamental (~500 Hz), 1st Harmonic (~1000 Hz), and 2nd Harmonic (~1500 Hz) DARM ASDs from O2 (after the July 2017 EQ) and this most recent lock stretch.
I've begun to update the LHO violin mode table (Violin_Mode_Table_v2) in prep for identification of this new forest. I've used the in-air data from LHO aLOGs 40525, 42180, 38857.
So far, I can identify 29 of the fundamental 32 modes, with a 2 mHz resolution. They're tabulated below (and not yet in the table), since I've not yet associated them with a test mass (though some appear to be "obvious" given the large separation).
In hopes to identify the mode Sheila calls out as the worst, I've pushed a 503.085 Hz filter to all new test masses, on MODE 1. This way when we do get a decent lock stretch, we can identify the mass "passively" by turning on the filter with some small gain, to see on which test mass we get action. As before, we'll started by assuming the mode is controllable by driving in Pitch.
| Frequency | Potential Match w/ in-air |
| 501.553 | IY |
| 501.628 | IY |
| 501.692 | IY |
| 501.755 | IY |
| 502.784 | IX |
| 502.909 | IX |
| 503.085 | EY / IY |
| 503.198 | EY / IY |
| 503.676 | EY / IY |
| 503.733 | EY / IY |
| 504.143 | EY / IY |
| 504.176 | EY / IY |
| 504.606 | EY / IY |
| 504.719 | EY / IY |
| 504.850 | EY |
| 504.889 | EY |
| 504.942 | |
| 505.077 | |
| 505.186 | |
| 507.360 | EX |
| 507.493 | EX |
| 508.844 | EX |
| 508.938 | EX |
| 510.714 | EX |
| 510.723 | EX |
| 511.180 | |
| 513.405 | |
| 516.678 | EX |
| 516.778 | EX |
In order to gather this data, I just used the standard violin mode templates from O2 (see LHO aLOG 37921), which are linked off of the VIOLIN MODE monitor MEDM screen.
Remember, we tried to separate the mode frequencies between test masses, and cluster a given test mass, to make them more easily identifiable (see E1700342, G1701332), but the reality of implementing such a system didn't work out as planned (an already minimal supply of fibers, few sets of fiber breakages, changes in frequency after welding and annealing, etc.). See some details in LHO aLOGs 41216, 40292, and 38965, but most my memory of the failure of the plan is verbal from telecons -- perhaps others can retrace the steps.
I have started adding some violin mode bandpass filters for ETMX, but have not had a change to test them out yet.
I added bandpass, +60, -60 degree phase shifts for 508.36 Hz, 508.844 Hz, 510.714 Hz and 516.678 Hz, in the filter banks under Mode2, Mode 11, Mode 12, and Mode 13 respectively.
The 503.085 Hz mode is on ITMY, and has been damped with the MODE1 filter, with -70 gain, no extra phase ( this can definitely be tuned in the future though), and feedback to pitch.
Note: This comment should have appeared after Georgia's comment below.
The link to the wiki page above isn't working. Here is a link : Violin mode table v2
504.891 Hz is on ITMX, can be damped with a gain of -3 and a phase of -60 degrees. (FM1 in ITMX mode 1 is a 50 mHz wide filter centered at 504.891, this is narrower than our other filters because there is a nearby mode at 504.953 Hz.)
Unfortunately it looks like we have two modes on ITMY that are only separated by 4 mHz. I was able to damp a mode at 501.629 Hz on ITMY with the same MODE4 filter Georgia used to damp the mode at 501.625Hz, but with a negative gain and +60 degrees of phase. I was suspicious that these could be the same mode, so I compared a spectrum with a resolution of 2 mHz from 2:42 UTC today (before Georgia damped ITMY) with the lock at 5:09 UTC, and it looks like they are actually two modes separated by about 4mHz. (Screenshot)
To deal with this, I created a filter called doublet in MODE4 which has 0dB of gain and a phase of -31 degrees at 501.624 and -3dB with -147 degrees at 501.628 Hz. A brave soul might be able to engage this filter with the bandpass that Georgia made earlier and no additional phase shift to damp both modes at once.
Edit: I got to try the doublet filter but it isn't very effective at damping the higher frequency mode which is rung up at the moment.
I also tried to damp 501.755Hz, but I don't think this is on ITMY. I copied my filter to ETMX MODE3, and tried 2 phases of pitch, but we lost lock before I could try yaw or longitudinal for ETMX.
I added a few more violin mode damping filters for ITMY. I promise I'll update the wiki table with this information soon.
The 503.198 Hz mode (MODE5) is on ITMY YAW, and was damped easily with -10 gain (haven't optimised any of the phases yet).
I tried to tackle the ITMY forest around 501.6 Hz but had trouble with cross coupling, accidentally ringing up neighbouring modes. I narrowed the filters and had some success damping
- The 501.625 Hz mode in pitch with a gain of 15 (filter bank MODE4)
- The 501.555 Hz mode in yaw with a gain of 20 (filter bank MODE6)
- The 501.692 Hz mode had some success with a gain of -5, before we dropped lock for other reasons. Will come back to it (filter bank MODE7).
J. Kissel
We don't yet have enough long lock stretches to get more precise than 0.005 mHz resolution, but I attach a few 1 mHz BW ASDs in the recent lock stretches that Sheila mentions (and some that I've found / reported),
- 2018-08-21 07:25 - 07:54 UTC,
- 2018-08-21 02:43 - 03:11 UTC,
- 2018-08-20 21:50 - 22:25 UTC,
- 2018-08-15 19:19 - 20:48 UTC,
where, because the last from several days ago, was 1.5 hrs, I was able to get a 0.5 mHz BW ASDs.
The message -- I can concur with Sheila's assessment that these two modes at 501.625 and 501.629 are 4 mHz apart -- however, only in 1 of the 4 measurements is the lower, 501.625 mode rung up. Thus, I think (thus far, we're not yet on DC readout) this is a weakly coupled mode that was rung up by our damping exploration attempts, so if we can design a filter that only tackles 501.629, then we might be OK. (It may not even be ITMY, but the 4 mHz mode separation does smell very much like a barely-elliptic mode splitting.)
I think Sheila and Georgia are on the right track of refining the band-pass filter to be that much more narrow. Mode frequencies for these violins are stable to temperature and test mass alignment at the ~10 microHertz level, so I think plant inversion -- or at least a very narrow (0.5 mHz) band-pass -- might be OK (see second attachment; figure 2 from G1601163 and/or G1700038).
Updated the table with some gains and phases for modes 504.606 Hz, 504.719 Hz, 504.85 Hz, all on ITMX and requiring low gains (<~5). And 504.953 Hz on ITMY (high gain, -30).
Posting this screenshot as a message to all the other v-modes out there. Blue reference is before damping, red is after.
In response to Sheila's request to compare the two following locks:
Aug 21 2018 02:42:00 UTC > Aug 21 2018 03:11:00 UTC [1218854538 > 1218856278]
Aug 21 2018 05:09:00 UTC > Aug 21 2018 05:29:00 UTC [1218863358 > 1218864558]
I ran 1mHz resolution PSDs. Results are below.
LOCK Aug 21 2018 02:42:00 UTC
Freq. [Hz] SNR
501.3750 77
501.5556 33815
501.6251 10114
501.6913 2815
501.6972 184
501.7553 181884
501.8750 76
502.7849 21376
502.9092 185016
503.0863 111095
503.1984 8470
503.6779 36286
503.7335 82344
504.1442 1609
504.1778 6259
504.6075 19039
504.7205 103589
504.8516 8474
504.8900 26733
504.9529 33514
505.0786 29540
505.1875 230981
507.3609 143884
507.4945 1342
508.8452 783438
508.9403 590
510.7142 915952
510.7255 268
511.1820 147617
513.4059 398372
513.5119 159
516.6806 693925
516.7800 5140
Lock Aug 21 2018 05:09:00 UTC
Freq. [Hz] SNR
501.5540 147
501.6293 478058
501.6925 2127
501.7553 612669
502.7849 17214
502.9091 183754
503.0860 50717
503.1984 88
503.6779 48336
503.7335 45705
504.1442 5292
504.1778 17130
504.6075 45363
504.7205 529860
504.8516 386988
504.8900 1223
504.9529 534100
505.0786 50532
505.1875 238858
507.3609 269516
507.4945 1032
508.8452 459774
508.9404 271
510.7142 492155
510.7254 108
511.1819 184454
513.4059 193424
513.5119 159
516.6806 423031
516.7799 4596
I am sorry I have just noticed these round of violin modes alog entries.
I will investigate further but as a quick comment to add to the comments above:
Jeff suggested that the frequency separation of 4mHz of the two modes may indicate frequency splitting of modes associated to the same fibre. However based on the data we have from all fibres of both LIGO detectors this is very improvable. Frequency splitting observed so far is on the order of tens to hundreds of mHz, there only one case of about 1mHz separation at LLO ITMX and it is not certain to be associated to the same fibre.