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ID Date Authorup Type Category Subject
  14923   Wed Oct 2 10:50:20 2019 gautamUpdateCDSAnaconda updated

The anaconda distribution used by the control room workstations is actually installed on the shared drive (/cvs/cds/ligo/apps/anaconda/) for consistency reasons. The version was 4.5.11. I ran the following commands to update it today. Now it is version 4.7.12.

conda update conda
conda update anaconda

The second command takes a while to resolve conflicts, so I've left it running inside a tmux session for now.

Recall that the bash alias for using the anaconda managed python is "apython". I recommend everyone set up a virtual environment when trying out new package installs, to avoid destroying the locking scripts.

  14924   Wed Oct 2 11:52:16 2019 gautamUpdateLSCPRMI Oplev loop checkout

I measured the OLTF of both the PRM Oplev loops. Nothing odd sticks out as odd to me in this measurement - there seems to be ~40 degrees of phase margin and >10 dB gain margin for both loops, see Attachment #1. I didn't measure down to the second UGF at ~0.2 Hz (the Oplev loops are AC coupled), so there could be something funky going on there. The problem still persists - if I misalign and realign the PRM using the ifoalign scripts, the automatic engagement of Oplev loops causes the loop to oscillate. Could be that the script doesn't wait for long enough for the alignment transient to die out.

Update 1230pm: Indeed, this was due to the integrator transient. It dies away after a couple of seconds.

Quote:

The PRMI Oplev servo needs some tuning, it is currently susceptible to oscillations in Pitch.

Attachment 1: PRM_OLTF.pdf
PRM_OLTF.pdf
  14926   Wed Oct 2 23:15:02 2019 gautamUpdateLSCFPMI locking

Summary:

I was able to lock the FPMI. The lock was quite stable. However, the fluctuations in the ASDC power suggest that it will be difficult to make a DC measurement of the contrast defect in this configuration. This problem can be circumvented in part by some electronics tuning. However, the alignment jitter couples some HOM light which is an independent effect. Can this be a good testbed for the proposed AS WFS system? 

Details:

  • First, the arm cavities were locked and TRX/TRY were maximized using ASS.
  • Next, AS55_Q-->MICH_A (MICH-->BS) matrix element was set to 1 in the LSC input (output) matrix. The trigger was set to always on.
  • AS55 digital demod phase was -37 degrees.
  • I was then able to increase the gain on the MICH servo and turn on some integrators without any problem.
  • Some guesswork had to be done to get the correct sign. Final servo gain used was -0.8. 

I didn't do any serious budgeting yet - need to think about / do some modeling on how this configuration can be made useful.

Attachment 1: FPMIlocked.png
FPMIlocked.png
  14927   Wed Oct 2 23:23:02 2019 gautamUpdateCDSc1oaf DC indicator needs to be green

Today, I found out that this type of "0x2bad" DC error is connected to the 1e+20 cts output. The solution was to bite the bullet and stop/start the c1oaf model (at the risk of crashing the vertex FEs). Today, I was lucky and the model came back online with all CDS indicators green. At which point I was able to engage length feedforward to MC2 (with some admittedly old filter). Some subtraction is happening, see Attachment #1. This was just meant to test whether the signal routing is happening - the feedforward signal goes to the "ALTPOS" input of the suspension CDS block, which AFAIK does not have a corresponding MEDM EPICS indicator. So I couldn't figure out whether the feedforward control signal was in fact making it to the suspension. On the evidence of the suppression of MCL in the 1-3 Hz band, I would conclude that it is. Useful to be able to engage these FF filters for better lockability.

Quote:

Attachment #1 - the vertex seismometer input produces 1e+20 cts at the output of the feedforward filter. Attachment #2 shows the shape of the feedforward filters - doesn't explain the saturation. Since this is a feedforward loop, a runaway loop can't be the explanation either.

Attachment 1: MCL_FF_Test.pdf
MCL_FF_Test.pdf
  14930   Thu Oct 3 12:08:47 2019 gautamUpdateGeneralMake the Jenne-laser setup fiber-coupled

I propose the following re-organization of the PDFR measurement breadboard. We have all the parts on hand, just needs ~30mins of setup work and some characterization afterwards. The fiber beamsplitter will not be PM, but for this measurement, I don't think that matters (the patch fiber from the diode laser head isn't PM anyways). We have one spare 1 GHz BW NF1611 that is fiber coupled (used to live on the ITMY in-air table, and is (conveniently) labelled "REF DET", but I'm not sure what the function of this was). In any case, we have at least 1 free-space NF1611 photodiode available as well. I suggest confirming that the FC version works as expected by calibrating against the free space PD first.

Update 245pm: Implemented, see Attachment #2. Aaron is testing it now, and will post the characterization results.

Attachment 1: PDFR_tabletop.pdf
PDFR_tabletop.pdf
Attachment 2: IMG_8014.JPG
IMG_8014.JPG
  14933   Thu Oct 3 19:40:18 2019 gautamUpdateLSCPOX/POY imbalance

Summary:

There is an imbalance between the POX and POY detector outputs reported in the CDS system. Possibilities are (i) the POX PD has a uncoated glass window whereas POY does not or (ii) there is some problem in the elctronics.

Details:

  1. Nominally, we run the POX/POY locking with +18dB whitening gain on POY and +30 dB on POX. This is a factor of 4 difference.
  2. The DC levels reported in C1:LSC-POXDC_OUT and C1:LSC-POYDC_OUT differ by a factor of 10 (24 cts for POY vs 2.4 cts for POX with 0dB whitening gain). These channels come from the P2 connector on the back of the PD Interface board into the fast CDS system.
  3. The levels reported by the Acromag system (which come out of the P1 connector) are 60mV for POY  vs 15 mV for POX.
  4. I confirmed that this imbalance is not due to clipping on the POX photodiode - I tweaked the steering mirror and observed the plateau (I did not, however, look at the beam on the PD active area with an IR viewew which would be a more conclusive test).
  5. I measured the power incident on either PD (using Ophir power meter, filter OFF). They were both ~10uW, as expected since the beam extraction for POY and POX are identical - a single HR mirror and the vacuum viewport.

Update 820pm: 

  1. I checked that there is no glass window on the PD.
  2. It is hard to see the beam on a viewer - but with the PRM aligned, I think I convinced myself that the beam is pretty well centered on the PD. 

So increasingly, it looks like the electronics are the source of the problem.

  14937   Fri Oct 4 00:30:31 2019 gautamUpdateGeneralMake the Jenne-laser setup fiber-coupled

I think the metric of interest here is the consistency of the AC transimpedance of the proposed new "Reference PD" (= fiber coupled NF1611) vs the old reference (free space NF1611), since everything will be calibrated against that.

Quote:

Something still looks very wrong -- the PD is supposed to be flat out to 1GHz, and physical units pending, need food.

  14938   Fri Oct 4 00:32:24 2019 gautamUpdateALSMore locking updates

Summary:

I managed to achieve a few transitions of control of the XARM length using the ALS error signal. The lock is sort of stable, but there are frequent "glitches" in the TRX level. Needs more noise hunting, but if the YARM ALS is also "good enough", I think we'd be well placed to try PRMI/DRMI locking with the arms held off resonance (while variable finesse remains an alternative).

Details:

Attachment #1One example of a lock stretch. 

Attachment #2ASD of the frequency noise witnessed by POX with the arm controlled by ALS. The observed RMS of ~30pm is ~3-4 times higher than the best performance I have seen, which makes me question if the calibration is off. To be checked...

Attachment 1: ALS_singleArm.png
ALS_singleArm.png
Attachment 2: ALS_OOL_20191003.pdf
ALS_OOL_20191003.pdf
  14941   Fri Oct 4 22:22:03 2019 gautamUpdateCDSFinal incarnation of latch.py

[KA, GV]

This elog is meant to be a summary of some of the many subtleties on the CM board. The latest schematic of the version used at the 40m can be found at D1500308 .

Latch logic:

  • There are several Binary Outputs and one Binary Input to the CM board.
  • The outputs control ENABLE/DISABLE switches and gains of amplifier stages, while the input reports whenever the limiter has been reached.
  • The variable gain feature is implemented by enabling/bypassing several cascaded fixed gain stages. So in order to change the gain of a single composite amplifier stage, multiple individual amplifier stages have to be switched.
  • This is implemented by the user interacting with the hardware via a "control word", consisting of a number of bits depending on the number of cascaded stages that have to be switched. 
  • This control word is sent to the device via modbus EPICS, which is an asynchronous communication protocol. Hence, it may be that the individual bits composing the control word get switched asynchronously. This would be disastrous, as there can be transient glitches in the gain of the stage being controlled. 
  • To protect against such problems, there is a latch IC in the hardware between the Binary Inputs to the board (= Binary Outputs from Acromags), and the actual switches (= MAX333) that enable/bypass the cascaded gain stages. The latch IC used is a SN74ALS573. This device acts as a bus, which transmits/blocks changes for multiple bits (= our control word) from propagating, depending on the state of a single bit (= the LATCH ENABLE bit). Thus, by controlling a single bit, we can guarantee that multiple bits get switched synchronously
  • In order to use this latch capability, we need some software logic that sets/disables the LATCH ENABLE bit. For our system, this logic is implemented in the form of a continuously running python 🐍 script, located at /cvs/cds/caltech/target/c1iscaux/latch.py. It is implemented as a systemctl service on the c1iscaux Supermicro. The logic implemented in this script is shown in Attachment #1. While the channels referred to in that attachment are for REFL1_GAIN, the same logic is implemented for REFL2_GAIN, AO_GAIN, and the SuperBoosts.
  • Some FAQ:
    1. Q: Why do we need the soft channels C1:LSC-REFL1_SET_LSB and C1:LSC-REFL1_SET_MSB?
      A: These soft channels are what is physically linked to the Acromag Binary Outputs. In order for our latch logic to be effective, we need to detect when the user asks for a change, and then disable the LATCH ENABLE bit (which is on by default, see FAQ #3) before changing the physical acromag channels. The soft channels form the protective layer between the user and the hardware, allowing latch.py to function.
    2. Q: Why is there an "_MSB" and "_LSB" soft channel? 
      A: This has to do with the mbboDirect EPICS channel type, which is used to control the multiple bits in our control word using a single input (= an MEDM gain slider). The mbboDirect data-type requires the bits it controls to have consecutive hardware addresses. However, the Acromag hardware addressing scheme is not always compatible with this requirement (see pg 33 of the manual for why this is the case). Hence, we have to artifically break up the control word into two separate control words compatible with the Acromag addressing scheme. This functionality is implemented in latch.py.
    3. Q: Why is the default state of LATCH ENABLE set to ON? 
      A: This has to do with the fact that all Binary Inputs, not just the multi-bit ones, to the CM board are propagated to the control hardware via a latch IC. For the single-bit channels, there is no requirement that the switching be synchronous. Hence, rather than setting up ~10 more single-bit soft channels and detecting changes before propagating them, we decided to leave the LATCH ENABLE ON by default, and only disable it when changing the multi-bit gain channels. This is the same way the logic was implemented in the VME state code, and we think that there are no logic reasons why it would fail. But if someone comes up with something, we can change the logic.

Acromag BIO testing:

During my bench testing of the Acromag chassis, I had not yet figured out mbboDirect and the latch logic, so I did not fully verify the channel mapping (= wiring inside the Acromag box), and whether the sitching behavior was consistent with what we expect. Koji and I verified (using the LED tester breakout board) that all the channels have the expected behavior 👏. Note that this is only a certification at the front-panel DB37 connectors of the Acromag chassis  testing of the integrated electronics chain including the CM board is in progress...

Attachment 1: LatchLogic.pdf
LatchLogic.pdf
  14943   Sat Oct 5 21:26:34 2019 gautamUpdateALSY-end green alignment tweaked

Summary:

I improved the alignment of the green beam into the Y arm cavity.

  • GTRY went from ~0.2 to ~0.25, see Attachment #1.
  • This resulted in improvement of the Y arm ALS noise above 💯Hz by a factor of ~5, see Attachment #2.
  • I tried controlling the two arm cavities in the CARM/DARM basis using ALS error signals - but didn't manage to successfully execute this transition today - this will be the commissioning goal for the upcoming week.

Details:

  • I had to do the alignment by tweaking the steering mirrors at EY - the PZTs didn't give me anywhere near enough range.
  • While I was at EY, I tried moving the two MM lenses mounted on translation stages to try and improve the mode-matching into the arm cavity - wasn't successful, still see a bunch of bullseye modes when I toggle the shutter.
  • They EY green layout would benefit from a do-over (basically just copy the EX layout), but this isn't the priority right now, the ALS noise RMS is dominated by low frequency noise (as usual). 
  • There is a ~5% leakage of the GTRX beam onto the GTRY photodiode.
  • One thing to try would be to revive the MCL loop to reduce the <1 Hz laser frequency noise and see if that helps - basically testing this hypothesis.
  • I had done some careful noise-budgeting of the EX green PDH system, the EY system would benefit from the same, but not critical.
  • The improvement of the high-frequency noise is clear, and now we are consistent with the "known good reference" level from the time the DRFPMI locking was working back in early 2016.

Other changes made today:

  1. /opt/rtcds/caltech/c1/scripts/general/videoscripts/videoswitch was modified to be python3 compatible - for some reason, there were many syntax errors being thrown (even though I was using python2.7) and I wasn't able to change the displays in the VEA using the MEDM screen, but now it works again 👍.
  2. The LSC overview and several daughter MEDM screens were edited to remove references to channels that no longer exist. All screens I edited have a backup stored in the MEDM directory with today's date as a suffix.
  3. Input pointing into the PMC was tweaked.
  4. Noted that some pump is noisy at pumpspool - also noted that the annuli are no longer pumped. Some event seems to have triggered an interlock condition that closed off the annular volume from TP3, needs investigation...
Attachment 1: ALSY_alignment.png
ALSY_alignment.png
Attachment 2: ALSY_OOL.pdf
ALSY_OOL.pdf
  14944   Sun Oct 6 15:23:27 2019 gautamUpdateALSArm control using error signals achieved

Summary:

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.

Details:

  1. Locking laser frequency to Y arm cavity length using MC2 as a frequency actuator
    • This is the usual diagnostic done to check the single-arm ALS noise using POY as an out of loop sensor.
    • The procedure is now scripted - I had to guess the sign and optimize the gains a few times, but this works deterministically now. 
    • Script lives at /opt/rtcds/caltech/c1/scripts/YARM/Lock_ALS_YARM.py.
    • Attachment #1 shows the result. If we believe the POY sensor calibration, the RMS displacement noise is ~6 pm
  2. Encouraged by the good performance of the Y arm, I decided to try the overall transition from the POX/POY basis to the CARM/DARM basis using ALS error signals.
    • The procedure starts with the arm cavities locked with POX/POY, and the respective green frequencies locked to the arm cavity length by the end PDH servos.
    • The DFD outputs serve as the ALS error signals - the PSL frequency is adjusted to the average value of DFD_X_OUT and DFD_Y_OUT.
    • I changed the LSC output matrix element for DARM-->ETMX from -1 to -5, to make it symmetric in actuation force w.r.t. ETMY (since the series resistane on ETMX is x5 that on ETMY).
    • After some guesswork, I fould the right signs for the gains. After enabling the boosts etc, I was able to keep both arms (approximately) on resonance for several minutes. See Attachment #2 for the time series of the transition process - the whole thing takes ~ 1 minute. 
    • A script to automate this procedure lives at /opt/rtcds/caltech/c1/scripts/ALS/Transition_IR_ALS.py.
    • The transition isn't entirely robust when executed by script - the main problem seems to be that in the few seconds between ramping off the IR servos and enabling the CARM/DARM integrators/boosts, the DARM error-point offset can become rather large. Consequently, when the integrator is engaged, ETMX/ETMY get a large kick that misalign the cavity substantially, degrade the green lock, and destroy the CARM lock as well. The problem doesn't seem to exist for the CARM loop. 
    • Anyways, I think this is easily fixed, just need to optimize sleep times and handoff gains etc a bit. For now, I just engage the DARM boosts by hand, putting in a DARM offset if necessary to avoid any kicking of the optic.
    • Attachment #3 shows the length noise witnessed by POX/POY when the arm cavities are under ALS control. If we believe the sensor calibration, the RMS displacement noise is ~15 (20) pm for the Y (X) arm.
    • This is rather larger than I was hoping would be the case, and the RMS is dominated by the <1 Hz "mystery noise".
    • Nevertheless, for a first pass, it's good to know that we can achieve this sort of ALS performance with the new IR ALS system.

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.

Attachment 1: ALSY_20191006.pdf
ALSY_20191006.pdf
Attachment 2: transitionIRALS.png
transitionIRALS.png
Attachment 3: arms_ALS.pdf
arms_ALS.pdf
  14946   Mon Oct 7 19:50:33 2019 gautamUpdateIOOIMC locking not working after this work

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 😤. 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.

  • First I let the WFS servo settle to some operating point, and then offloaded the DC offsets to the IMC suspensions.
  • Then I disabled the WFS servo.
  • I hand-tweaked MC1 and MC3 PIT/YAW (while leaving MC2 untouched) to minimize IMC REFL (a more sensitive indicator of the optimal cavity alignment than the transmission).
  • Once I felt the IMC REFL was minimized (~1-2% improvement), I set the RF offsets for the WFS while the IMC remained locked. I chose this way of setting the RF offsets as opposed to unlocking the cavity and having the high-power TEM00 mode incident on the WFS QPDs.
  • Overnight, I'm going to run the MC2 spot position scanning code (in a tmux session on pianosa, started ~945pm) to see if we can find a place where the transmission is higher, looking at Kruthi's code now to see it makes sense...
  • The convergence time of the MC2 spot position loop is pretty slow, so the scan is expected to take a while... Should be done by tomorrow morning though, and I expect no work with the IFO tonight.
  • Does this loop have to be so slow? Why can't the gain be higher?
Attachment 1: IMCflaky.png
IMCflaky.png
Attachment 2: IMG_8015.JPG
IMG_8015.JPG
  14949   Tue Oct 8 08:08:18 2019 gautamUpdatePEMPEM BLRMS anomaly

Yesterday, Koji and I noticed (from the wall StripTool traces) that the vertex seismometer RMS between 0.1-0.3 Hz in the X-direction increased abruptly around 6pm PDT. This morning, when I came in, I noticed that the level had settled back to the normal level. Trending the BLRMS channels over the last 24 hours, I  see that the 0.3-1 Hz band in the Z direction shows some anomalous behaviour almost in the exact same time-band. Hard to believe that any physical noise was so well aligned to the seismometer axes, I'm inclined to think this is indicative of some electronics issues with the Trillium interface unit, which has been known to be flaky in the past.

Attachment 1: PEManomaly.png
PEManomaly.png
  14950   Tue Oct 8 10:29:19 2019 gautamUpdateIOOMC Transmission scan

Summary:

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.

Analysis:

Attachment #1This 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 #2Maps 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 #3After 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. 🤔 

Scan algorithm:

The following was implemented in a python scipt:

  1. Choose 2 independent random numbers from the uniform distribution in the interval [-0.5, 0.5] (in uncalibrated counts).
  2. One of these numebrs is set as the error point offset for the QPD spot-centering PITCH WFS loop, while the other is the YAW offset.
  3. Wait for 600 seconds - this long wait is required because the step-response time for these loops is long. 
  4. If there is an MC unlock event - wait till the MC relocks, and then another 600 seconds, to give the WFS loops sufficient time to converge.
  5. Once the WFS loops have converged, average a few data channels (MC TRANS, REFL, WFS loop error points etc) for 10 seconds, and write these to a file.

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.

Quote:
  • Overnight, I'm going to run the MC2 spot position scanning code (in a tmux session on pianosa, started ~945pm) to see if we can find a place where the transmission is higher,
Attachment 1: MC2_transmission_scatter.pdf
MC2_transmission_scatter.pdf
Attachment 2: transmissionMaps.pdf
transmissionMaps.pdf
Attachment 3: correlStructure.pdf
correlStructure.pdf
  14954   Tue Oct 8 18:35:09 2019 gautamUpdateLSCLocking prep

In preparation for some locking work tonight, I did the following at the POP in air table with the PRMI locked on carrier:

  1. Raised the POP camera by ~5mm. The POP spot is now well centered on the CCD view.
  2. Tweaked alignment onto the PDA10CF photodiode that serves as (i) POP22, (ii) POP110, and (iii) POP DC. In lock the POPDC level went from ~800 cts to ~1200 cts.
  3. Moved the QPD that witnesses part of the POP beam such that the spot was centered on the photodiode. This may be useful for collecting some FF data or if we want to try feedback to stabilize the PRMI.

TBC...

  14956   Tue Oct 8 20:23:03 2019 gautamUpdateCDSc1iscaux testing

Looking at the old latch.st code, looks like this is just a heartbeat signal to indicate the code is alive. I'll implement this. Aesthetically, it'd be also nice to have the hex representation of the "*_SET" channels visible on the MEDM screen.

 

Quote:

Latch logic works. But latch alive signal is missing.

  14960   Wed Oct 9 18:15:26 2019 gautamUpdateLSCPRMI 3f locking

After making sure the beams were hitting the 3f photodiodes on the "AP" table, I was able to lock the PRMI with the sidebands resonant inside the RC using 3f error signals. This would be the config we run in when trying to lock some more complicated configuration, such as the PRFPMI (i.e. start with the arms controlled by ALS, held off resonance). Tonight, I will try this (even though obviously I am not ready for the CARM transition step). The 3f lock is pretty robust, I was able to stay locked for minutes at a time and re-acquisition was also pretty quick. See Attachment #1. Not sure how significant it is, but I set the offsets to the 3f paths by averaging the REFL33_I and REFL33_Q signals when the PRMI was locked with the 1f error signals.

As usual, there's a lot of angular motion of the POP spot on the CCD monitor, but the lock seems to be able to ride it out.

Lock-settings (I modified the .snap file accordingly):

REFL33_I --> PRCL, loop gain = -0.019, Trigger on POP22, ON @ 20cts, OFF@0.5cts.

REFL33_Q --> MICH, loop gain = +1.4, Trigger on POP22, ON @ 20cts, OFF@0.5 cts.

Attachment 1: PRMI_1f.png
PRMI_1f.png
  14961   Wed Oct 9 22:02:58 2019 gautamUpdateLSCREFL55 whitening issue

This problem has re-surfaced. Is this indicative of some problem with the on-board VGA? Even with 0dB of whitening gain, I see PDH horns that are 10,000 ADC counts in amplitude, whereas the nominal whitening gain for this channel is +18dB. I'll look at it in the daytime, not planning to use REFL55 for any locking tonight.

  14962   Thu Oct 10 01:12:56 2019 gautamUpdateLSCLocking studies

Summary:

  1. ALS control of arms in the CARM/DARM basis seems pretty robust - I was able to hold lock for >40mins tonight. The scripted transition from POX/POY control to ALS control is pretty deterministic now.
  2. The PRMI could be locked with the arms detuned from resonance by applying an offset to the CARM loop error point.
  3. Much daytime work remains to be done before attempting any sort of reliable locking.

Hardware issues that need addressing:

  1. Both EX and EY Trans QPDs need a look. I believe the one at EY is simply blocked (on account of the mode spectroscopy project), while the one at EX shows a weird discontinuity between the Thorlabs PD and the QPD. Could be just a gain/normalization issue I guess. See Attachment #1.
  2. While the PRMI stayed locked, I don't think I was using anywhere close to optimal settings. Need to run some sensing lines, measure transfer functions etc, to make the PRMI + arms lock more robust. The PRMI always lost lock when I brought the CARM offset to 0. Could also benefit from some finesse modeling I guess. I could not get a reliable estimate of what the PRG is tonight, because the PRMI didn't stay locked as I approached 0 CARM offset.
  3. REFL 55 whitening board needs a checkup.
Attachment 1: PRFPMIstudies.png
PRFPMIstudies.png
  14963   Thu Oct 10 22:11:53 2019 gautamUpdateLSCTrans QPD checkout
  1. I removed the flip-mount that was installed on the EY in-air table for the mode-spectroscopy project (see Attachment #1). The Transmon QPD at EY sees IR light again.
  2. Dark noise checkout - see Attachment #2.
  3. Light-level expectations:
    • For the current config, let's say 0.8 W reaches the PRM, and we will have a PRG of 50. 
    • This implies ~5.5 kW circulating power in the arms.
    • This implies ~70mW will get transmitted through the ETM, of which at most half makes it to the QPD. 
    • In the nominal operating condition, we expect more like 6 W circulating in the arm cavity. So something like 30uW is expected to make it out onto the Trans QPDs.
    • But in this condition, we expect to run with the high-gain Thorlabs PD.
    • In reality the number is likely to be somewhat smaller. But we should set the transimpedance gain of this photodiode accordingly. Currently, there are a bunch of ND filters installed on this photodiode, which probably should be removed.
  4. Angular control
    • The other purpose these QPDs are expected to serve is to stabilize the angular motion of the cavities when locked with high circulating power.
    • Need to calculate what the sensing noise requirement is.
Attachment 1: EY_table_20191010.jpeg
EY_table_20191010.jpeg
Attachment 2: darkNoise.pdf
darkNoise.pdf
  14969   Mon Oct 14 17:24:28 2019 gautamUpdateGeneralWorkstation computers taken off UPS (temporarily)

The UPS is now incessantly beeping. I cannot handle this constant sound so I shut down all the control room workstations and moved the power strip hosting the 4 CPUs to a wall socket for tonight. Chub and I will replace the UPS batteries tomorrow.

  14972   Tue Oct 15 17:22:26 2019 gautamUpdateGeneralWorkstation computers back on UPS

Batteries + power cables replaced, and computers back on UPS from today ~3pm.

Quote:

The UPS is now incessantly beeping. I cannot handle this constant sound so I shut down all the control room workstations and moved the power strip hosting the 4 CPUs to a wall socket for tonight. Chub and I will replace the UPS batteries tomorrow.

  14973   Wed Oct 16 11:42:17 2019 gautamUpdateLSCPoor separation of PRCL/MICH in 3f signals

Summary:

There is poor separation of the PRCL and MICH length error signals as sensed in the 3f photodiodes. I don't know why this is so - one possibility is that the MICH-->PRM matrix element in the LSC output matrix needs to be tuned to minimize the MICH -->PRCL coupling.

Details:

Over the last few days, I've been trying to make the 3f locking of the PRMI more reliable. Turns out that while I was able to lock the PRMI on 3f error signals, it was just a fluke. So I set about trying to be more systematic. Here are the steps I followed:

  1. Lock the PRMI (i.e. ETMs misaligned) using REFL11 for PRCL, AS55 for MICH.
    • This is the so-called 1f scheme.
    • The servo signs are chosen such that the carrier field is resonant in the PRC.
    • Run the dither alignment to maximize POPDC, minimize ASDC. This is the main purpose of locking in this config.
    • Measure some loop TFs, make sure the servo gains are giving us ~100 Hz UGF on these loops.
  2. Change the sign of the servo loops to make the sidebands resonant in the PRC.
    • The error signals are still sourced from the 1f photodiodes.
    • Measure loop TFs, and also the TF between the 1f and 3f error signals. 
    • This allowed me to determine how the servo gains (and signs) that would be appropriate when using the 3f signals in place of the 1f.
    • Determine the offsets in the 3f error signals when the PRMI is locked on 1f error signals. This allows me to set the error point offsets for the PRCL_B and MICH_B paths, which are what is used for the 3f locking.
  3. Change the error signals from 1f to 3f. 
    • After much trial and error, I finally managed to get a stable (>10 mins) lock going.
    • Measured some loop TFs.
    • Turned on the notch filters in the control filter bank at the sensMat oscillator frequencies, and ran some sensing lines.

Attachment #1 is the result. I don't know what is the reason for such poor separation of the MICH and PRCL error signals in REFL165. The situation seems very different from when I had the DRMI locked in Nov last year.

After this exercise, I tried for some hours to get the 3f PRMI locking going with the arm cavities held off resonance under ALS control, but had no success. The angular motion of the PRC isn't helping, but I feel this shouldn't be a show stopper.

Attachment 1: sensMat.pdf
sensMat.pdf
  14974   Thu Oct 17 11:19:28 2019 gautamUpdateLSCLocking activity last night
  1. Tuning the MICH-->PRM output matrix element
    • Locked the PRMI with the carrier field resonant in the PRC.
    • REFL11 used to control PRCL, AS55 for MICH.
    • Turned on the sensing notches in the control filter bank. Drove a line in MICH at 311.10 Hz.
    • Tweaked the MICH-->PRM matrix element to minimize the coupling witnessed.
    • As shown in Attachment #1, the minimum coupling was found to be at the value -0.34 (the old value was -0.2655).
    • The minimum was very sharp. A 1% change from the optimum value increased the peak height by > x2. Is this reasonable?
  2. Some sensing matrix measurements: After tuning the output matrix element, I locked the PRMI (ETMs misaligned) in four configurations:
    • PRMI locked with carrier resonant. REFL11_I used for PRCL control, AS55_Q used for MICH control.
    • PRMI locked with sidebands resonant. REFL11_I used for PRCL control, AS55_Q used for MICH control.
    • PRMI locked with sidebands resonant. REFL11_I used for PRCL control, REFL165_I used for MICH control (based on sensing matrix measurement and offsets from previous config).
    • PRMI locked with sidebands resonant. REFL33_I used for PRCL control, AS55_Q used for MICH control.
    • The attached GIF shows the evolution of the demodulated sensing lines as we move through configurations.
       
    • The actual PDFs are attached as a zip, Attachment #2.
  3. PRMI locking with arms under ALS control
    • The arm cavity lengths were controlled as usual with ALS. This system needs some noise budgeting.
    • I set the CARM offset to -8 (arbitrarily chosen, approximately equal to 20nm, but anyways well above the cavity linewidth).
    • Then I re-aligned the PRM, and attemped to lock the PRMI using the 3f settings determined with no arm cavities --> no success.
    • Tried locking using the 1f error signals instead - in this config, the lock could be established.
    • However, I saw that there was significant light on the AS camera, and I had to put in an offset into the MICH loop to make ASDC go as low as possible.
    • I guess it is possible that the ALS control wasn't precise enough and the leaked light to the dark port was because of differential reflectivity of the arm cavities?
    • Anyways, I ran a sensing matrix measurement with the interferometer in this configuration, and I found that the MICH signal in REFL165 had rotated significantly.
    • I also found that the 3f DC offsets in this configuration were ~5x greater than what was the case for the lock with no arm cavities.

This is as far as I got last night. The first step is to see how reliable the settings determined last night are, today. I don't understand how changing the output matrix element can have brought about such a significant change in the MICH/PRCL separation in all the RF photodiodes.

Attachment 1: MICH2PRCLnulling.pdf
MICH2PRCLnulling.pdf
Attachment 2: consolidatedSensingMatrices.pdf.zip
  14975   Thu Oct 17 12:34:51 2019 gautamUpdateGeneralDaytime wishlist

Some ideas that would help increase the locking duty-cycle in the short term. 

  1. Seismometer investigation - something is not quite right with the vertex seismometer. This is the one that is primarily used for feedforward, and can be really helpful.
  2. Drifting TTs - it is really annoying to have to re-set the input pointing into the interferometer every ~ hour. See Attachment #1.
  3. FSS - this isn't a scientific statement, but there were ~20-30 minute periods last night where the PC drive RMS was displaying sharp spikes repeating every 2-3 seconds, first with increasing and then decreasing height. This is a new feature to me in the long standing PC drive saga but it doesn't tell me exactly what is going on as I don't know in what frequency band the glitch is actually happening. See Attachment #2.
  4. ALS noise - while it is possible now to routinely transition the arm length control from the POX/POY to CARM/DARM basis, I see some sharp (<0.1 s) dives in the TRX/TRY levels when the arms are under ALS control. This wasn't present a week ago. Needs to be investigated - I defer this to the daytime tomorrow.
Attachment 1: DriftingTTs.png
DriftingTTs.png
Attachment 2: FSSweirdness.png
FSSweirdness.png
  14976   Thu Oct 17 16:49:53 2019 gautamUpdateASCPRMI ASC - first pass

I tried implementing a basic PRMI ASC using the POP QPD as a sensor. The POP22 buildup RMS is reduced by a factor of a few. This is just a first attempt, I think the loop shape can be made much better, but the stability of the lock is already pretty impressive. For some past work, see here.

Attachment 1: PRMI_ASC.pdf
PRMI_ASC.pdf
  14977   Fri Oct 18 17:35:07 2019 gautamUpdateSUSETMX sat box disconnected

Koji suggested systematic investigation of the ETMX suspension electronics. The tests to be done are:

  1. Characterization of PD whitening amplifiers - with the satellite box disconnected, we will look for glitches in the OSEM channels.
  2. Characterization of LT1125s in the PD chain of the amplifiers - with the in-vacuum OSEMs disconnected, we will look for glitches due to the on-board transimpedance amplifiers of the satellite box.
  3. Characterization using the satellite box tester - this will signal problems with the physical OSEMs.
  4. Characterization of the suspension coil driver electronics - this will happen later.

So the ETMX satellite box is unplugged now, starting 530 pm PDT.

The satellite box was reconnected and the suspension was left with watchdog off but OSEM roughly centered. We will watch for glitches over the weekend.

  14980   Mon Oct 21 11:44:19 2019 gautamUpdatesafetyInterlock reconnected to Innolight controller

We also took this opportunity to re-connect the interlock to the Innolight controller (after it was disconnected for diagnosing the mysterious NPRO self-shutdowns). The diode pump current was dialled down to 0, the interlock wires reconnected, and then the diode current was ramped back up to the nominal 2.1 A. The fan to cool the unit remains mounted in a flaky way as we couldn't locate the frame Chub had made for a more secure mounting solution. 

It seems like the pointing of the beam out of the laser head varies somewhat after the startup - I had to adjust the pointing into the PMC a couple of times by ~1 full turn of the Polaris mount screws, but the IMC has been locked (mostly) for the last ~16 hours.

Quote:

I've checked the state of the laser interlock switch and everything looked normal.

  14981   Mon Oct 21 12:25:46 2019 gautamUpdateALSDFD electronics checkout

Summary:

There are no unexpected red-flags in the performance of the DFD electronics. The calibration factors for the digital phase tracker system are 71.291 +/- 0.024 deg/MHz for the X delay line and 70.973 +/- 0.024 deg/MHz for the Y delay line, while the noise floor for the frequency noise discrimination is ~0.5 Hz/rtHz above 1 Hz (dominated by ADC noise).

Details:

  1. Attachment #1 - This observation is what motivated my investigation.
    •  found that for certain beat frequencies between the PSL + EX lasers, the frequency noise reported by the DFD system was surprisingly low.
    • The measurement condition was: EX laser frequency locked to the arm cavity length by the uPDH servo at EX, arm cavity length locked to PSL frequency via POX locking.
  2. To investigate further, I disconnected the output of the NF1611 PDs going to the ZHL-3A amplifiers on the PSL table (after first blocking the PSL light so that the PDs aren't generating any RF output).
    • An RF function generator (IFR2023B) was used to generate an RF signal to mimic the ALS beat signal.
    • I used a power splitter to divide the signal power equally between the two DFD paths.
    • The signal level on the Marconi was set to -5 dBm, to mimic the nominal power level seen by the DFD system.
    • I then performed two tests - (i) to calibrate the Phase Tracker output to deg / MHz and (ii) to measure the frequency noise reported by the DFD system for various signal frequencies.
    • Test (i): sweep the marconi frequency between 10 MHz - 200 MHz, measure the I and Q channels for each phase tracker servo, and figure out the complex argument of the signal using the arctangent. A linear polynomial was fit to the measured datapoints to extract the desired slope.
    • Test (ii): Sample frequencies uniformly distributed between 20 MHz - 80 MHz (nominal range of ALS beat frequencies expected). Reset the phase tracker servo gain, clear the output histories, wait for any transients to die out, and then collect the phase tracker servo output for 1 minute. Compute the FFT to figure out the frequency noise.
    • Attachment #2: Shows the phase tracker calibration, i.e. the results of Test (i). I took this opportunity to update the EPICS calibration fields that convert phase tracker servo output to Hz, the correction was ~7%. These numbers are consistent with what I measured previously - but the updated values weren't registered with SDF so everytime the LSC model was restarted, it reverted to the old values.
    • Attachment #3: Shows the spectra for the various measurements from Test (ii).
    • Attachment #4: Shows the gain of the phase tracker servo as a function of the RF signal frequency. This is a proxy for the signal strength, and the observed trend suggests that the signal power seen after digitization of the demodulated delay line output goes down by ~20% at 80 MHz relative to the level at 20 MHz. Seems reasonable to me, given frequency dependent losses of the intervening electronics / cabling.

Conclusion and next steps:

I still don't know what's responsible for the anomalously low noise levels reported by the ALS-X system sometimes. Next test is to check the EX PDH system, since on the evidence of these tests, the problem seems to be imprinted on the light (though I can't imagine how the noise becomes lower?).

Attachment 1: ALSnoiseAnomaly.pdf
ALSnoiseAnomaly.pdf
Attachment 2: DFDcalib.pdf
DFDcalib.pdf
Attachment 3: spectra.pdf
spectra.pdf
Attachment 4: PTgains.pdf
PTgains.pdf
  14982   Mon Oct 21 16:02:21 2019 gautamUpdateSUSETMX over the weekend

Looking at the sensor and oplev trends over the weekend, there was only one event where the optic seems to have been macroscopically misaligned, at ~11:05:00 UTC on Oct 19 (early Saturday morning PDT). I attach a plot of the 2kHz time series data that has the mean value subtracted and a 0.6-1.2 Hz notch filter applied to remove the pendulum motion for better visualization. The y-axis calibration for the top plot assumes 1 ct ~= 1 um. This "glitch" seems to have a timescale of a few seconds, which is consistent with what we see on the CCD monitors when the cavity is locked - the alignment drifts away over a few seconds.

As usual, this tells us nothing conclusive. Anyways, I am re-enabling the watchdog and pushing on with locking activity and hope the suspension cooperates.

Quote:
 

The satellite box was reconnected and the suspension was left with watchdog off but OSEM roughly centered. We will watch for glitches over the weekend.

Attachment 1: filteredData.pdf
filteredData.pdf
  14983   Tue Oct 22 00:52:27 2019 gautamUpdateLSCLocking updates
  1. Transition of arms from POX/POY to CARM/DARM was much smoother today - a change was made at the EX PDH setup, see here.
  2. Reliable settings for 3f locking with arms held off resonance seem to have been found.
  3. Took sensing matrix in this condition, measured loop TFs.
  4. Reduced CARM offset - reached arm powers ~50 at which point the PRMI lost lock. Reacquisition was quick though.
    • The POP22_I level seemed to decay as I reduced the CARM offset.
    • This would suggest that somehow the PRCL lock point is getting shifted as I reduce the CARM offset.
    • Tonight, I will investigate this more.
Attachment 1: PRMI3f_ALS_Oct21sensMat.pdf
PRMI3f_ALS_Oct21sensMat.pdf
  14984   Tue Oct 22 15:32:15 2019 gautamUpdateALSEX uPDH electronics checkout

Summary:

The EX PDH setup had what I thought was insufficient phase and gain margins. So I lowered the gain a little - the price paid was that the suppression of laser frequency noise of the end laser was reduced. I actually think an intermediate gain setting (G=7) can give us ~35 degrees of phase margin, ~10dB gain margin, and lower residual unsuppressed AUX laser noise - to be confirmed by measurement later. See here for the last activity I did - how did the gain get increased? I can't find anything in the elog.

Attachment 1: uPDH_X_OLTFs.pdf
uPDH_X_OLTFs.pdf
  14985   Tue Oct 22 17:35:30 2019 gautamUpdateASCPRMI ASC - first pass

I made a change to the c1ass model to normalize the PIT and YAW POP QPD outputs by the SUM channel. A saturation block is used to prevent divide-by-zero errors, I set the saturation limits to [1,1e5], since the SUM channel is being recorded as counts right now. Model change is shown in the attached screenshots. I compiled and installed the model. Ran the reboot script to reboot all the vertex FEs to avoid the issue of crashing c1lsc.

Quote:

I tried implementing a basic PRMI ASC using the POP QPD as a sensor. The POP22 buildup RMS is reduced by a factor of a few. This is just a first attempt, I think the loop shape can be made much better, but the stability of the lock is already pretty impressive. For some past work, see here.

Attachment 1: originalPOP_QPD.png
originalPOP_QPD.png
Attachment 2: POP_QPD_modified.png
POP_QPD_modified.png
  14987   Wed Oct 23 11:11:01 2019 gautamUpdateALSEX uPDH electronics checkout

The closest thing I can think of is here.

Quote:

Is there a loop model of green PDH that agrees with the measurement? I'm wondering if something can be done with a compensation network to up the bandwidth or if the phase lag is more like a non-invertible kind.

  14988   Wed Oct 23 11:14:21 2019 gautamUpdateASCPRMI ASC with QPD signals normalized.

Attachment #1 - comparison of the POP QPD PIT and YAW output signal spectra with and without them being normalized by the SUM channel. I guess the shape is different between 30-100 Hz because we have subtracted out the correlated singal due to RIN?

This did not have the effect I desired - I was hoping that by normalizing the signals, I wouldn't need to change the gain of the ASC servo as the buildup in the PRC changed, but I found that the settings that worked well for PRMI locked with the carrier resonant (no arm cavities, see Attachment #2, buildup RIN reduced by a factor of ~4) did not work for the PRMI locked with the sideband resonant. Moreover, Koji raised the point that there will be some point in the transition from arms off resonance to on resonance where the dominant field in the PRC will change from being the circulating PRC carrier to the leaking arm carrier. So the response of the actuator (PRM) to correct for the misalignment may change sign. 

In conclusion, we decided that the best approach to improve the angular stability of the PRC will be to revive the PRC angualr feedforward, which in turn requires the characterization and repair of the apparently faulty vertex seismometer.

Attachment 1: PRMI_ASC_normalization.pdf
PRMI_ASC_normalization.pdf
Attachment 2: PRMI_ASC_Oct22.pdf
PRMI_ASC_Oct22.pdf
  14989   Wed Oct 23 11:49:21 2019 gautamUpdatePEMPEM BLRMS anomaly

I looked into the seismometer situation a bit more today. Here is the story so far - I think more investigation is required:

  1. There is an abrupt change in the PEM BLRMS channels around 6pm PDT every day. This has been consistently seen for the last two weeks.
  2. The seismometer spectra look normal - see Attachment #1. The reference traces are from some months ago. There is elevated activity between 0.1-0.3 Hz, but this is seen in all the seismometers in all 3 DoFs.
  3. I looked at the minute trend of the raw seismometer outputs (before being BLRMSed) for the last 200 days and don't see any abrupt change in characteristics (the data gap is due to the issue in this thread).
  4. All the correct BLRMS filters seem to be engaged in the respective filter banks.

Attachment #2 has some spectrograms (they are rather large files). They suggest that the increase in noise in the 0.1-0.3 Hz band in the BS seismometer X channel is real - but there isn't a corresponding increase in the other two seismometers, so the problem could still be electronics related.

Quote:

Yesterday, Koji and I noticed (from the wall StripTool traces) that the vertex seismometer RMS between 0.1-0.3 Hz in the X-direction increased abruptly around 6pm PDT. This morning, when I came in, I noticed that the level had settled back to the normal level. Trending the BLRMS channels over the last 24 hours, I  see that the 0.3-1 Hz band in the Z direction shows some anomalous behaviour almost in the exact same time-band. Hard to believe that any physical noise was so well aligned to the seismometer axes, I'm inclined to think this is indicative of some electronics issues with the Trillium interface unit, which has been known to be flaky in the past.

Attachment 1: seisAll_20191021.pdf
seisAll_20191021.pdf
Attachment 2: specGrams.zip
  14990   Wed Oct 23 18:40:58 2019 gautamUpdateCDSanother round of vertex FE reboots

I wanted to restart the c1oaf model. As usual, the first time the model was restarted, it came back online with a 0x2bad error. This isn't even listed in the diagnostics manual as one of the recognized error states (unless there is a typo and they mean 0x2bad when they say 0xbad). The fix that has worked for me is to stop and start the model again, but of course, there is some chance of taking all the vertex FEs down in the process. No permutation of mxstream and daqd process restarts have cleared this error. We need some CDS/RCG support to look into this issue and fix it, it is not reasonable to go through reboots of all the vertex FEs every time we want to make a model change.

  14991   Thu Oct 24 11:58:16 2019 gautamUpdateASCPRC angular feedforward

Summary:

I'd like to revive the PRC angular feedforward system. However, it looks like the coherence between the vertex seismometer channels and the PRC angular motion witness sensor (= POP QPD) is much lower than was found in the past, and hence, the stabilization potential by implementing feedforward seems limited, especially for the Pitch DoF.

Details:

I found that the old filters don't work at all - turning on the FF just increases the angular motion, I can see both the POP and REFL spots moving around a lot more on the CRT monitors.

I first thought I'd look at the frequency-domain weiner filter subtraction to get a lower bound on how much subtraction is possible. I collected ~25 minutes of data with the PRC locked with the carrier resonant (but no arm cavities). Attachment #1 shows the result of the frequency domain subtraction (the dashed lines in the top subplot are RMS). Signal processing details:

  • Data was downloaded and downsampled to 64 Hz (from 2kHz for the POP QPD signals and from 128 Hz for the seismometer signals). The 'FIR' option of scipy decimate was used.
  • FFT time used was 16 seconds for the multi-coherence calculations

The coherence between target signal (=POP QPD) and the witness channels (=seismometer channels) are much lower now than was found in the past. What could be going on here?

Attachment 1: ffPotential.pdf
ffPotential.pdf
  14992   Thu Oct 24 18:37:15 2019 gautamUpdatePEMT240 checkout

Summary:

The Trillium T240 seismometer needs mass re-centering. Has anyone done this before, and do we have any hardware to do this?

Details:

I went to the Trillium interface box in 1X5. In this elog, Koji says it is D1000749-v2. But looking at the connector footprint on the back panel, it is more consistent with the v1 layout. Anyway I didn't open it to check. Main point is that none of the backplane data I/O ports are used. We are digitizing (using the fast CDS system) the front panel BNC outputs for the three axes. So of the various connectors available on the interface box, we are only using the front panel DB25, the front panel BNCs, and the rear panel power.

The cable connecting this interface box to the actual seismometer is a custom one I believe. It has a 19 pin military circular type hermetic connector on one end, and a DB25 on the other. Power is supplied to the seismometer from the interface box via this cable, so in order to run the test, I had to use a DB25 breakout board to act as a feedthrough and peek at the signals while the seismometer and interface boards were connected. I used Jenne's mapping of the DB25--> 19 pin connector (which also seems consistent with the schematic). Findings:

  1. We are supplying the Trillium with 39 V DC between the +PWR and -PWR pins, while the datasheet specifies 9V to 36V DC isolated. Probably this is okay?
  2. The analog (AGND) and digital (DGND) ground pins are shorted. Is this okay?
  3. I measured the DC voltages between the AGND pin and each of the mass position outputs.
    • These are supposed to indicate when the masses need re-centering.
    • The nominal output ranges for these are +/- 4 V single-ended.
    • I measured the following values (I don't know how the U,V,W basis is mapped onto the cartesian X,Y,Z coordinates):
      U_MP: 0.708 V
      V_MP: -2.151 V
      W_MP: -3.6 V
    • So at the very least, the mass needs centering in the W direction (the manual recommends doing the re-centering procedure when one of these indicators exceeds 3.5 V in absolute value).
  4. I also checked the DC voltages of the (X,Y,Z) outputs of the seismometer on the front panel BNCs, and also on the DB25 connector (so directly from the seismometer). These are rated to have a range of 40 Vpp differential between the pins. I measured ~0V on all the three axes - this is a bit confusing as I assumed a de-centered mass would lead to saturation in one of these outouts, but maybe we are measuring velocities and not positions?
  5. We probably should consider monitoring these signals long term to inform of such drifts, what is the spare channel situation in the c1sus acromag?
  6. Interestingly, today evening, there is no excess noise in the 0.1-0.3 Hz band in the X-axis of the seismometer even though it is past 6pm PDT now, which is usually the time when the excess begins to show up. The z-axis 0.3-1Hz BLRMS channel has flatlined though...

I am holding off on attempting any re-centering, for more experienced people to comment.

  14993   Fri Oct 25 01:04:49 2019 gautamUpdateALSALS electronics chain was saturating

[Koji, gautam]

Summary:

We think we got to the bottom of this issue today. The RF signal level going into the demod board is too high. This electronics chain needs some careful gain reallocation.

Details:

I was demonstrating to Koji a strange feature I had noticed in the ALS control, whereby when applying a CARM offset to detune the arms, the two arms seemed to respond differently (based on the transmission levels). This kind of CARM-->DARM coupling seemed strange to me. Anyway, I also noticed that the EPICS indicators on the ALS MEDM screen suggested ADC saturations were going on. I had never really looked at the fast time series of the inputs to the phase tracker servos, but these showed saturating behavior on ndscope traces. I went to the LSC rack and measured these on a scope, indeed, they were ~20V pp.

The output of the BeatMouth PDs are going to a ZHL-3A amplifier - we should consider replacing these with lower gain amplifiers, e.g. the Teledyne AP1053. This is relegated to a daytime task.

Other findings tonight:

While working on the PSL table, I somehow put the IMC FSS into a bad state, reminiscent of this behavior. Seems like this is linked to some flaky connection on the PSL table. One candidate is the unstable attachment of the Pomona box between the NPRO PZT and the FSS output - we should install a short BNC cable between these to avoid the lever arm situation we have right now.

  14995   Mon Oct 28 23:20:11 2019 gautamUpdateALSALS power budget

 

IR ALS power budget
Photodiode PSL VDC [V] PSL IDC [uA] AUX VDC [V] AUX IDC [uA] IRF [mA pk] PRF [dBm]
PSL+EX 3 300 2.5 250 ~600  ~3
PSL+EY 3 300 0.6 60 ~270 ~ -3

In calculating the above numbers, I assumed a DC transimpedance of 10 khhms and an RF Transimpedance of ~800 V/A.

[Elog14480]: per these calculations, with the NewFocus 1611 PDs, we cannot achieve shot noise limited sensing for any power below the rated maximum for linear operation (i.e. 1mW). Moreover, the noise figure of the RF amplifier we use to amplify the sensed beat note before driving the delay-line frequency discriminator is unlikely to be the limiting noise source in the current configuration. Rana suggested that we get two Gain Blocks. These can handle input powers up to ~10dBm while still giving us plenty of power to drive the delay line. This way, we can (i) not compromise on the sacred optical gain, (ii) be well below the 1dB compression point (i.e. avoid nonlinear noise effects) and (iii) achieve a better frequency discriminant

Temporary fix: While the gain blocks arrive, I inserted a 10dB (3dB) attenuator between the PSL+EX (PSL+EY) photodiode RF output and the ZHL-3A amplifiers. This way, we are well below the 1dB compression point of said RF amplifiers, and also below the 1dB compression point of the on-board Teledyne AP1053 amplifiers on the demodulator boards we use.

Nest steps: Rana is getting in touch with Rich Abbott to find out if there is any data available on the noise performance of the post-mixer IF amplifier stage in the 0.1 -30 Hz range, where the voltage and current noise of the AD829 OpAmps could be limiting the DFD performance. But in the meantime, the ALS noise seems good again, and there is no evidence of the sort of CARM/DARM coupling that motivated this investigation in the first place. Managed to execute several IR-->ALS transitions tonight in the PRFPMI locking efforts (next elog).

No new Teledyne AP1053s were harmed in this process - I'll send the 5 units back to Rich tomorrow.

  14996   Tue Oct 29 01:24:45 2019 gautamUpdateLSCMore locking updates

Summary:

  1. The two arm lengths can be controlled reliably in the CARM/DARM basis using ALS error signals.
  2. With a CARM offset to keep the arm cavitites off resonance, the PRMI can be locked using 3f error signals.
  3. On attempting to reduce the CARM offset, I see a drop in the POP22 buildup in the PRC (correlated with the arm powers increasing). Not entirely clear why this is happening.

I ran some sensing measurements at various CARM offsets to check if the PRCL-->REFL33 and MICH-->REFL165 signals were being rotated out of the sensing quadrature as I lowered the CARM offset - there was no evidence of this happening. See Attachment #2. Other possibilities:

  • CARM offset dependant offsets in the MICH/PRCL error points?
  • Check the RAM due to the EOM? Perhaps the pointing / polarization control into the EOM got degraded.
  • Angular stability of the PRC is still pretty poor, getting the angular feedforward back up and running would help the duty cycle enormously.

The IMC went into some crazy state so I'm calling it for the night, need to think about what could be happening and take a closer look at more signals during the CARM offset reduction period for some clues...

Attachment 1: POP22_feature.png
POP22_feature.png
Attachment 2: PRMI3f_ALS_Oct21sensMat.pdf
PRMI3f_ALS_Oct21sensMat.pdf
  14997   Tue Oct 29 15:13:19 2019 gautamUpdateLSCMore locking updates

I looked at some signals for a 10 second period when the PRMI was locked with at some CARM offset, just before the PRMI lost lock, to see if there are any clues. I don't see any obvious signatures in this set of signals - if anything, the PRM is picking up some pitch offset, this is seen both at the Oplev error point and also in the POP QPD spot position. But why should this be happening as I reduce the CARM offset? The arm transmission is only ~5, so it's hard to imagine that the radiation pressure is somehow torquing the PRM. There are no angular feedback loops actuating on the PRM in this state except the local damping and Oplev loops.

The 1f signals are also changing their mean DC offset values, which may be a signature of a changing offset in the 3f MICH and PRCL error points? The MICH error signal is pretty noisy (maybe I can turn on some LPF to clean this up a bit), but I don't see any DC drift in the PRCL control signal.

Attachment 1: PRMI_lockloss.png
PRMI_lockloss.png
  14998   Tue Oct 29 17:40:48 2019 gautamUpdateLSCMore locking updates

I set up a photodiode (PDA10CF) in the IFO REFL beampath and the Agilent NA is sitting on the east side of the PSL enclosure. This was meant to be just a first look, maybe the PDA10CF isn't suitable for this measurement. The measurement condition was - PRM aligned so we have a REFL beam (DC level = 8.4V measured with High-Z). Both ITMs and ETMs were macroscopically misaligned so that there isn't any cavity effects to consider. I collected noise around 11 and 55 MHz, and also a dark measurement, plots to follow. The optics were re-aligned to the nominal config but I left the NA on the east side of the PSL enclosure for now, in anticipation of us maybe wanting to tune something while minimizing a peak.

Attachment #1: Results of a coarse sweep from 5 MHz to 100 MHz. The broadband RIN level is not resolvable above the dark noise of the photodiode, but the peaks at the modulation frequencies (11 MHz, 55 MHz and 29.5 MHz) are clearly visible. Not sure what is the peak at ~44 MHz or 66 MHz. Come to think of it, why is the 29.5 MHz peak so prominent? The IMC cavity pole is ~4kHz so shouldn't the 29.5 MHz be attenuated by 80dB in transmission through the cavity?

Attachment #2: Zoomed in spectra with finer IF bandwidth around the RF modualtion frequencies. From this first measurement, it seems like the RIN/rad level is ~10^5, which I vaguely remember from discussions being the level which is best achieved in practise in the 40m in the past.

Quote:
 

Check the RAM due to the EOM? Perhaps the pointing / polarization control into the EOM got degraded.

Attachment 1: broadSweep.pdf
broadSweep.pdf
Attachment 2: zoomSweep.pdf
zoomSweep.pdf
  14999   Wed Oct 30 01:27:00 2019 gautamUpdateLSCMore locking updates

Tried a bunch of things tonight.

  1. Modified the "ELP300" filter module in the MICH filter bank - this was really a 4th order elliptic low pass with corner at 80 Hz, which was much too low. I tried upping the corner to 500 Hz, and reducing the order, while I was able to enable the filter, there was clearly a gain-peaking feature visible after engaging this module, so the exercise of reducing the high frequency MICH actuation requires more careful (daytime) loop optimization.
  2. Tried adding some POPDC to the MICH/PRCL trigger once the PRMI was locked - I thought this would help if the problem was just with POP22 triggering turning off the MICH/PRCL loops, but the problem seems to persist with the mixed matrix trigger as well, once I reach a CARM offset where the arm powers exceed ~10, the PRMI loses lock.
  3. One strange feature I don't understand is that with the PRMI locked with the carrier field resonant, when running the dither alignment servo to minimize REFLDC (= more carrier coupled into the PRC), the POPDC level also goes down, but TRX and TRY go up slightly. I confirmed that the beam isn't falling off the POP22 photodiode (Thorlabs PDA10CF), but I don't understand why these two DC powers should fall simultaneously - if I couple more carrier into the PRC, shouldn't the POPDC level also increase?

One possibility is that the arm buildup is exerting some torque on the ITMs, which can also change the PRC cavity axis - as the buildup increases, the dominant component of the circulating field in the PRC comes from the leakage from the overcoupled arm cavity. We used to DC couple the ITM Oplev servos when locking the PRMI. The TRX level of 1 corresponds to ~5W of circulating power in the arm cavity, and the static radiation pressure force due to this circulating power is ~30 nN, rising up to 300nN as the TRX level hits 10. So for 1mm offset of the spot position on the ITM, we'd still only exert 300 pN m of torque. I don't see any transient in the Oplev error signals when locking the arm cavity as usual with POX/POY, but on timescales of several seconds, the Oplev error point shows ~3-5 urad of variation.

Attachment 1: POP_ASS.png
POP_ASS.png
  15000   Wed Oct 30 11:53:41 2019 gautamUpdateLSCMICH loop shape tuning

I changed the shape of the low pass filter to reduce high frequency sensor noise injection into the MICH control signal. The loop stability isn't adversely affected (lost ~5 degrees of phase margin but still have ~50 degrees), while the control signal RMS is reduced by ~x10. This test was done with the PRMI locked on the carrier, need to confirm that this works with the arms controlled on ALS and PRMI lcoked on sideband.

Attachment 1: MICH_ELP.pdf
MICH_ELP.pdf
Attachment 2: MICH_ELP_TFs.pdf
MICH_ELP_TFs.pdf
  15001   Wed Oct 30 17:08:40 2019 gautamUpdateLSCPOP22 investigation

The POP beam coming out of the vacuum chamber is split by a 50/50 BS and half is diverted to the POP22/POP110/POPDC photodiode (Thorlabs PDA10CF) and the other half goes to the POP QPD. This optical layout is still pretty accurate. I looked at the data of the POPDC and POP QPD SUM channels while the dither alignment was running, to see if I could figure out what's up with the weird correlated dip in REFLDC and POPDC. While the POPDC channel shows some degradation as the REFLDC level goes down (=alignment gets better), the QPD sum channel shows the expected light level increase. So it could yet be some weird clipping somewhere in the beampath - perhaps at the 50/50 BS? I will lock the PRMI (no arms) and check...

Attachment 1: POP22anomaly.pdf
POP22anomaly.pdf
  15002   Wed Oct 30 19:20:27 2019 gautamUpdateSUSPRM suspension issues

While I was trying to lock the PRMI this evening, I noticed that I couldn't move the REFL beamspot on the CCD field of view by adjusting the slow bias voltages to the PRM. Other suspensions controlled by c1susaux seem to respond okay so at first glance it isn't a problem with the Acromag. Looking at the OSEM sensor input levels, I noticed that UL is much lower than the others - see Attachment #1, seems to have happened ~100 days ago. I plugged the tester box in to check if the problem is with the electronics or if this is an actual shorting of some pins on the physical OSEM as we had in the past. So PRM watchdog is shutdown for now and there is no control of the optic available as the cables are detached. I will replace the connections later in the evening.

Update 10pm:

  1. Measured coil inductances with breakout board and LCR meter - all 5 coils returned ~3.28-3.32 mH.
  2. Measured coil resistances with breakout board and DMM - all 5 coils returned ~16-17 ohms.
  3. Checked OSEM PD capacitance (with no bias voltage) using the LCR meter - each PD returned ~1nF.
  4. Checked resistance between LED Cathode and Anode for all 5 LEDs using DMM - each returned Hi-Z.
  5. Checked resistance between PD Cathode and Anode for all 5 PDs using DMM - each returned ~430 kohms.
  6. Checked that I could change the slow bias voltages and see a response at the expected pins (with the suspension disconnected).

Since I couldn't find anything wrong, I plugged the suspension back in - and voila, the suspect UL PD voltage level came back to a level consistent with the others! See Attachment #2.

Anyway, I had some hours of data with the tester box plugged in - see Attachment #3 for a comparison of the shadow sensor readout with the tester box (all black traces) vs with the suspension plugged in, local damping loops active (coloured traces). The sensing noise re-injection will depend on the specifics of the  local damping loop shapes but I suspect it will limit feedforward subtraction possibilities at low frequencies.

However, I continue to have problems aligning the optic using the slow bias sliders (but the fast ones work just fine) - problem seems to be EPICS related. In Attachment #4, I show that even though I change the soft PITCH bias voltage adjust channel for the PRM, the linked channels which control the actual voltages to the coils take several seconds to show any response, and do so asynchronously. I tried restarting the modbus process on c1susaux, but the problem persists. Perhaps it needs a reboot of the computer and/or the acromag chassis? I note that the same problem exists for the BS and PRM suspensions, but not for ITMX or ITMY (didn't check the IMC optics). Perhaps a particular Acromag DAC unit is faulty / has issues with the internal subnet?

Attachment 1: PRMUL.pdf
PRMUL.pdf
Attachment 2: PRMnormal.pdf
PRMnormal.pdf
Attachment 3: PRM-Sensors_noise.pdf
PRM-Sensors_noise.pdf PRM-Sensors_noise.pdf
Attachment 4: PRMsuspensionWonky.png
PRMsuspensionWonky.png
  15004   Thu Oct 31 10:44:40 2019 gautamUpdatePSLPMC re-locked

PMC got unlocked at ~4am. I re-locked it. Also tweaked the input pointing into the cavity. The misalignment was mostly in pitch.

There was also a loud buzzing in the control room due to the audio cable being improperly seated in the mixer. I re-seated it.

  15009   Mon Nov 4 15:29:47 2019 gautamUpdateLSCPOP signal path

There are many versions of the POP22 signal path I found on the elog, e.g. this thread. But what I saw at the LSC rack was not quite in agreement with any of those. So here is the latest greatest version.

Since the 2f signals are mainly indicators of power buildups and are used for triggering various PDH loops, I don't know how critical some of these things are, but here are some remarks:

  1. There is no Tee + 50 ohm terminator after the minicircuits filters, whose impedance in the stopband are High-Z (I have been told but never personally verified).
  2. The RF amplifier used is a Minicircuits ZFL-1000-LN+. This has a gain of 20dB and 1dB compression output power spec of 3dBm. So to be safe, we want to have not more than -20dBm of signal at the input. On a 50-ohm scope (AC coupled), I saw a signal that has ~100mVpp amplitude (there is a mixture of many frequencies so this is not the Vpp of a pure sinusoid). This corresponds to -16dBm. Might be cutting it a bit close even after accounting for cable loss and insertion loss of the bias tee.
  3. We use a resistive power splitter to divide the power between the POP22 and POP110 paths, which automatically throws away 50% of the RF power. A better option is the ZAPD-2-252-S+.
  4. The Thorlabs PDA10CF photodiode (not this particular one) has been modelled to have a response that can be approximated by a complex pole pair with Q=1 at ~130 MHz. But we are also using this PD for measuring the 110 MHz PD which is a bit close to the band edge?
Attachment 1: POPchain.pdf
POPchain.pdf
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