40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 294 of 344  Not logged in ELOG logo
ID Date Author Typeup Category Subject
  14075   Tue Jul 17 01:07:40 2018 gautamUpdateSUSETMY EQ stops

For the heater setup on EY table, I EQ-stopped ETMY. Only the face EQ stops (3 on HR face, 2 on AR face) were engaged. The EY Oplev HeNe was also shutdown during this procedure. 

  14076   Tue Jul 17 12:46:28 2018 ranaUpdateGeneralsome notes from yesterday

For the EY, instead of balancing the table, I just moved the weight approximately so that the ETMY OSEMS were at half light, but didn't check the level since ETMY is the only optic.


Some notes on OMC/AS work (Aaron/Gautam can amend/correct):

- Beam is now well centered in OMC MMT. Hits input coupling mirror and cleanly exits the vacuum to the AS table.

- Didn't see much on OMC trans, but PDs are good based on flashlight test.

- just before closing, re-aligned beam in yaw so that it gets close to the east screw on the input coupler. Aaron and I think we maybe saw a flash there with the OMC length PZT being driven at full range by a triangle wave.

- with OMC Undulators (aka tip/tilt PZT mirrors) energized, the beam was low on PZT1 mirror. We pitched ITMY by ~150 micro-rad and that centered the beam on PZT1 mirror. ITMY-OL is probably not better than 100 urad as a DC reference?

- We checked the range of Undulator 1 and we were getting ~5 mrad of yaw of the beam for the full range, and perhaps half of that in pitch. Rob Ward emailed us from Oz to say that the range is robably 2.7 mrad, so that checks out.

Even if the ITMY has to be in the wrong position to get the beam to the OMC, we can still do the heater tests in one position and then do the OMC checkout stuff in the other position.

Gautam suspects that there is a possible hysterical behaviour in the Undulators which is related to the MC3 glitching and the slow machine hangups and also possibly the illuminati.


-We noticed a ghost beam that from MC REFL (MMT2) that should be dumped during the next vent--it travels parallel to the OMC's long axis and nearly hits one of the steering mirrors for OMC refl.

-We measured the level of the table and found it ~3 divisions off from level, with the south end tilted up

-Gautam rotated and slightly translated OM5 to realign the optic, as expected. No additional optics were added.

-Gautam and I tested the TT piezo driver. We found that 3.6V on the driver's input gave 75V (of 150V) at the output, at least for yaw on piezo 1. However, as Gautam mentioned, during testing it seemed that the other outputs may have different (nonzero) offset voltages, or some hysterisis.

  14081   Wed Jul 18 03:14:48 2018 AnnalisaUpdateGeneralVent 80 recovery

[Gautam, Johannes, Koji, Annalisa]

Tonight we increased the power of the PSL laser and we achieved the lock of both arms with high power.

The AUX beam alignment to the Y arm was recovered and the PLL restored (using the Marconi as LO).

We made a quick measurement of the phase noise and the results will be posted tomorrow.

The beam on the PSL has been blocked, as well as the AUX beam on the AS table. The Marconi has been switched off.


  1. Before turning up PSL power, I placed a block in front of MC refl to avoid any PD burning. Replaced HR Y1 2" optic with the usual 10% reflective BS to direct MC REFL to the locking PD.
  2. Waveplate was rotated back to 180 deg (original position before the vent). After optimizing PMC transmission, I measured 1.05 W going into the IMC (pre-vent value was 1.07 W, prolly within power meter absolute accuracy).
  3. IMC autolocker restored to usual high power version on megatron.
  4. There seems to be some kind of vacuum interlock in effect that prevents me from opening the PSL shutter via EPICS - I had to toggle the position on the shutter controller under the table. After tonight's work, I returned the controller to the NC state, to avoid any further interference with this interlock code that may prevent pumping in the AM.
  5. PLL gain was re-adjusted to achieve maximum stability (judged by eye) of the beat-note in lock triggered on the Marconi LO signal. Alignment onto the NF beatPD was also tweaked to squeeze out as much beat as possible.
  6. The main objective tonight was to send AUX beam in, recover transmission beat, scan the AUX frequency, and resolve some peaks (MAX HOLD scanning technique, magnitude only for now, no phase info). Thanks to JE's expert fiber alignment and beatnote maximization, we achieved this yes. Annalisa will post a plot tmr. 
  7. For unknown reasons, the Y arm ASS does not maximize TRY. So we are in the unfortunate situation of neither arm having a working ASS servo. To be worked on later.
  14084   Wed Jul 18 23:43:50 2018 KojiUpdateGeneralVent 80 recovery

Is the reflector too close to the beam and causing clipping?


For unknown reasons, the Y arm ASS does not maximize TRY. So we are in the unfortunate situation of neither arm having a working ASS servo. To be worked on later.

Attachment 1: IMG_5868.JPG
Attachment 2: IMG_5382.JPG
  14089   Thu Jul 19 18:09:17 2018 poojaUpdateCamerasUpdate in developing neural networks

Aim: To develop a neural network that resolves mirror motion from video.

Case 1:

Input : Simulated video of beam spot motion in pitch by applying 4 sine  waves of frquencies 0.2, 0.4, 0.1, 0.3 Hz  and amplitude ratios to frame size to be 0.1, 0.04, 0.05, 0.08

The data has been split into train, validation and test datasets and I tried training on neural network with the same model topology & parameters as in my previous elog (https://nodus.ligo.caltech.edu:8081/40m/14070)

The output of NN and residual error have been shown in Attachment 1. This NN model gives a large error for this. So I think we have to increase the number of nodes and learning rate so that we get a lower error value with a single sine wave simulated video ( but not overfitting) and then try training on linear combination of sine waves.

Case 2 :

Normalized the target sine signal of NN so that it ranges from -1 to 1 and then trained on the same neural network as in my previous elog with simulated video created using single sine wave. This gave comparatively lower error (shown in Attachment 2). But if we train using this network, we can get only the frequency of test mass motion but we can't resolve the amount by which test mass moves. So I'm unclear about whether we can use this.

Attachment 1: nn_simulation_mlt_sine_nodes4_lr0p00001_beta1_0p8_beta2_0p85_marked.pdf
Attachment 2: nn_simulation_2_nodes4_target-1to1_marked.pdf
  14092   Fri Jul 20 22:51:28 2018 KojiUpdateIOOIMC WFS path alignment

IMC WFS tuning

- IMC was aligned manually to have maximum output and also spot at the center of the end QPD.
- The IMC WFS spots were aligned to be the center of the WFS QPDs.
- With the good alignment, WFS RF offset and MC2 QPD offsets were tuned via the scripts.

  14093   Fri Jul 20 22:53:15 2018 KojiUpdateASSAttempt to resurrect Yarm ASS

[Koji Gautam]

We managed to realize stable ASS configuration for Yarm. The transmission of 1.06~1.07 was recovered by introducing intentional beam spot offset in the horizontal direction towards the opposite side of the elliptic reflector. The end table optics were adjusted to have the spots about the center of the mirrors, lenses, and PDs/QPDs.


- The Y arm was manually aligned with a given input axis. The transmission was ~0.8.
- Then, TT2 was moved in yaw such that it introduced the horizontal beam shift at the end. By moving the spot to the opposite side of the reflector. The transmission ~0.95 was obtained after patient alignment work.

- Went to the end table and checked the spots. The beam was not at the center of the last 1" lens for the Trans PDs. The beam steering was adjusted to have the spot nicely going through the lens and the mirrors. This made the transmission level to be ~1.05.

- The beam centering on the Trans PD was checked and adjusted.
- The beam centering on the RF BBPD for the arm scan was checked. The spot was too big for that PD. The lens was slightly moved away from the PD to make the spot on the BBPD small. Now the PD saw the plateu when the steering was scanned (i.e. the spot is small enough).

- With the Y arm locked with MC2, the servo gain needs to be 0.012 instead of nominal 0.015 with ETMY to prevent from servo oscilating.

ASS tuning

- First of all, only the bottom 4 loops out of total 8 loops were tuned. They are the servos for the beam alignment with regard to the caivty. The linearity and the zero crossings were checked with regard to the reference alignment. All of these 4 showed offsets that causes the servo running away. Don't know the reason of this offset, but it is freq dependent. Therefore the dither freqs were tuned to make the offset zeroed, and tuned the demod phases there. This kept the transmission as high as the reference (~1.05)

- This allowed us to play with the spot position a bit by tuning the caivty alignment. In the end, the transmission of ~1.08 was obtained. Using this alignment, A2L offset for ETMY Yaw was determined to be +17 (to make the error signal -17). This offset produces almost a beam radius (5mm) shifted on the end mirror towards the opposite direction of the reflector.

- The nominal servo setting made the spot servo running away. Gautam pointed out that this could be a gain hierarchy problem (i.e. the spot servos are too fast). We ended up reducing the gain of the servo from 1.0 to 0.3 to make the spot servo stable.

- All the ASS setting was stored in a new snap file "script/ASS/ASS-DITEHR_ON.snap". The previous snap was saved to "script/ASS/ASS_DITHER_ON_preVent201807.snap". This did not save the exc gains of the oscillators. Therefore "DITHER_ASS_ON.py" was modified to have the new exc gains (CLKGAIN). The old values are stored in the comments in this script.

Overall this is not an ideal situation as we don't know what is the actually cause of the offsets in the dither error signals. We expect to correct the beam clipping and the suspension sooner or later. Therefore, we will come back to the ASS again once the other issues are corrected.

Attachment 1: 02.png
  14095   Sat Jul 21 01:14:02 2018 gautamUpdateOMCPZT Jena driver board check

[Aaron, gautam]

We did a quick check of this board today. Main takeaways:

  • There are two voltages (HV pos and HV neg) that are output from this unit.
  • Presumably, these goto different piezoelectric elements, referenced to ground. Are there any spec sheets for these describing the geometry/threshold voltages?
  • The outputs are:
    • \mathrm{HV_{+}} = 10(V_{\mathrm{DAC}}+V_{\mathrm{offset}}), \mathrm{HV_{-}} = 10(-V_{\mathrm{DAC}}+V_{\mathrm{offset}})
    • So with V_{\mathrm{offset}} = 7.5 \mathrm{V}, we expect to be able to use +/- 7.5 V of DAC range.
  • The trim pot had to be adjusted to realize V_{\mathrm{offset}} = 7.5 \mathrm{V}​.
  • I assume 150V is some kind of damage threshold of the PZT, so there is no benefit to using 10V offset voltage (as this would result in 200 V at full range DAC voltages).

With the correct V_{\mathrm{offset}} = 7.5 \mathrm{V}, we expect 0V from the DAC to result in 0 actuation on the mirror, assuming that an equal 75V goes to 2 PZTs mounted diametrically opposite on the optic. Hopefully, this means we have sufficient range to scan the input pointing into the OMC and get some sort of signal in the REFL signal (while length PZT is being scanned) which indicates a resonance. 

We plan to carve out some IFO time for this work next week.

  14097   Sun Jul 22 14:01:07 2018 poojaUpdateCamerasDeveloping neural networks on simulated video

Aim: To develop a neural network that resolves mirror motion from video.

Since error was high for the same input as in my previous elog http://nodus.ligo.caltech.edu:8080/40m/14089

I modified the network topology by tuning the number of nodes, layers and learning rate so that the model fitted the sum of 4 sine waves efficiently, saved weights of the final epoch and then in a different program, loaded saved weights & tested on simulated video that's produced by moving beam spot from the centre of image by sum of 4 sine waves whose frequencies and amplitudes change with time.

Input : Simulated video of beam spot motion in pitch by applying 4 sine  waves of frquencies 0.2, 0.4, 0.1, 0.3 Hz  and amplitude ratios to frame size to be 0.1, 0.04, 0.05, 0.08. This is divided into train (0.4), validation (0.1) and test (0.5).

Model topology:

                                          Input               -->                  Hidden layer               -->                    Output layer                                  

                                                                                          8 nodes                                              1 node

Activation function:                                  selu                                             linear

Batch size = 32, Number of epochs = 128, loss function = mean squared error

Optimizer: Nadam ( learning rate = 0.00001, beta_1 = 0.8, beta_2 = 0.85)

Normalized the target sine signal of NN by dividing by its maximum value.

Plot of predicted output by neural network, applied input signal & residual error given in 1st attachment. These weights of the model in the final epoch have been saved to h5 file and then loaded & tested with simulated data of 4 sine waves with amplitudes and frequencies changing with time from their initial values by random uniform noise ranging from 0 to 0.05. Plot of predicted output by neural network, target signal of sine waves & residual error given in 2nd attachment. The actual signal can be got from predicted output of NN by multiplication with normalization constant used before. However, even though network fits training  & validation sets efficiently, it gives a comparatively large error on test data of varying amplitude & frequency.

Gautam suggested to try training on this noisy data of varying amplitudes and frequencies. The results using the same model of NN is given in Attachment 3. It was found that tuning the number of nodes, layers or learning rate didn't improve fitting much in this case.



Attachment 1: nn_simulation_2_normalized_mult_sin_nodes8_128epochs_lr0p00001_beta1_0p8_beta2_0p85_0p4train_0p1valid_marked.pdf
Attachment 2: nn_simulation_normalizedtarget_128epochs_mult_sin_load_wt_varyingtest_nodes8_lr0p00001_beta1_0p8_beta2_0p85_0p4train_0p1valid_marked.pdf
Attachment 3: nn_simulation_2_normalized_varying_mult_sin_nodes8_128epochs_lr0p00001_beta1_0p8_beta2_0p85_0p4train_0p1valid_marked.pdf
  14100   Tue Jul 24 06:11:50 2018 ranaUpdateCamerasDeveloping neural networks on simulated video

This looks like good progress. Instead of fixed sines or random noise, you should generate now a time series for the motion which is random noise but with a power spectrum similar to what we see for the ETM pitch motion in lock. You can use inverse FFT to get the time series from the open loop OL spectra (being careful about edge effects).


Aim: To develop a neural network that resolves mirror motion from video.

  14101   Tue Jul 24 09:47:51 2018 gautamUpdateCamerasDeveloping neural networks on simulated video

I was thinking a little more about the way we are training the network for the current topology - because the network has no recurrent layers, I guess it has no memory of past samples, and so it doesn't have any sense of the temporal axis. In fact, Keras by default shuffles the training data you give it randomly so the time ordering is lost. So the training amounts to requiring the network to identify the center of the Gaussian beam and output that. So in the training dataset, all we need is good (spatial) coverage of the area in which the spot is most likely to move? Or is the idea to develop some tools to generate video with spot motion close to that on the ETM in lock, so that we can use it with a network topology that has memory? 


This looks like good progress. Instead of fixed sines or random noise, you should generate now a time series for the motion which is random noise but with a power spectrum similar to what we see for the ETM pitch motion in lock. You can use inverse FFT to get the time series from the open loop OL spectra (being careful about edge effects)

  14105   Thu Jul 26 01:52:01 2018 terraUpdateThermal Compensationheater work update

Just a quick update: over the past few days we've taken (at least) 5 scans around each peak [carrier - HOM3] at 9.4V/0.8A, 4 scans around [carrier - HOM5] at 12V/0.9A hot state with the reflector setup. We also have (at least) 5 scans of carrier - HOM5 in cold state. I attach a rough overview of the peak magnitude shifts in the first attachment. Analysis ongoing. All data stored in annalisa/postVent/{date}

Initial shifts just based on rought peak placement in the meantime:

            [9.4V/0.8A]   [12V/0.9A]

HOM1    10 kHz         20 kHz

HOM2    18 kHz         28 kHz

HOM3     30 kHz        40 kHz

HOM4     N/A             26 kHz

HOM5     N/A             35 kHz

I also attach the heating thermal transient from today (12V/0.9A) as seen by the opLevs. We see a shorter time constant for pitch, longer for yaw, preceeded by a dip in yaw. Similar behavior yesterday for slightly less heating, though less pronounced pre-dip. The heater is offcentered on the optic horizontally; likely this is part of the induced yaw. The spikey stuff i removed is from people walking around inside during the transient.

I've left the heater and LSC off for the night. Heater off at 2:07 am local time.

Please don't touch the oplevs; we're taking a cool down measurement.

Attachment 1: OpLev_thermal_drift.pdf
Attachment 2: hotColdAll.pdf
  14106   Thu Jul 26 15:11:18 2018 SteveUpdateGeneral Viewports & coating of 2001

New optical quality BK-7 windows in 2001 [4 substrates ] AR coated R<0.75 % for 630-1064nm " Azury BLue" broadband : TRX, TRY, ITMY-Oplev &  ITMX-Oplev viewports.

The BS-Oplev and PRM-Oplev 10" CF with 5.38" diameter view was coated the same way. The window here is Corning 7056 Borosilicate

5 more BK-7 substrates were coated R <0.1% of 1064 nm "Golden Orange" Their location: IMC-IN, IFO-REF and OMC   The next vent we have to confirm optical quality window locations.

All other conflat flange viewports are 7056 Kovar sealed .

Technical notes of 2001 40m upgrade can be seen at LIGO-T010115- 00- R  ....page 14

Attachment 1: BK7window_Coatings.PDF
BK7window_Coatings.PDF BK7window_Coatings.PDF
  14107   Fri Jul 27 02:30:51 2018 gautamUpdateGeneralGlitchy MC

Kevin and I saw some weird IMC / PEM BLRMS behaviour today - see Attached screenshot. Not sure what was happening with the IMC, but MCtrans was oscillating at ~3Hz for a good 20 minutes or so. I just killed the lock, and restarted MCautolocker on megatron. There was a strange feature in the 3-10Hz BLRMS around that time as well. All seems back to normal now...

Attachment 1: 38.png
  14108   Fri Jul 27 10:48:57 2018 SteveUpdateSUSBS oplev window

Yesterday I inspected this BS oplev viewport. The heavy connector tube was shorting to table so It was moved back towards the chamber. The connection is air tight with kapton tape temporarly.

 The beam paths are well centered. The viewport is dusty on the inside.

The motivation was to improve the oplev noise.

Attachment 1: BSOw_.jpg
Attachment 2: dustInsideBSO.jpg
  14109   Fri Jul 27 17:16:14 2018 SandrineUpdateThermal CompensationCopied working scripts for mode spectroscopy into new directory (modeSpec)

The scripts: AGfast.py, make HDF5.py, plotSpec_marconi.py, and SandrineFitv3.py were copied into the new directory modeSpec.

The path is: /opt/rtcds/caltech/c1/scripts/modeSpec

These scripts can still be found under Annalisa's directory under postVent.

  14111   Sat Jul 28 22:16:49 2018 John MartynUpdate Characterization of Transimpedance Amplifier

Kevin and I meaured the transfer function of the photodiode circuit using the Jenne laser and agilent in the 40m lab. The attached figures depict our measured transfer function over the modulation frequency ranges of 30kHz-30MHz and 1kHz-30MHz when the power of the laser was set to 69 and 95 μW. These plots indicate a clear roll off frequency around 300 kHz. In addition, the plots beginning at 1kHz display unstable behavior at frequencies below 30kHz. I am not sure why there is such a sharp change in the transfer function around 30kHz, but I suspect this to be due to an issue with the agilent or photodiode. 

Attachment 1: PD_TF1.pdf
Attachment 2: PD_TF2.pdf
Attachment 3: PD_and_TIA_Transfer_Function_Measurements.zip
  14112   Sun Jul 29 00:59:54 2018 KojiUpdateElectronicsCharacterization of Transimpedance Amplifier

You have this measurement problem when the IF bandwidth is larger than the measurement frequency. I suspect the IF bandwidth is 30kHz.

  14113   Sun Jul 29 20:03:02 2018 ranaUpdatePEMSeismometer temp control

While Shruti is re-building Kira's heater circuit, I looked up how to do one of these (i.e. what does a real EE say about how to build a current source?):

It turns out that there is an Analog Devices application note (AN-968) about this (as there usually is once we get tired of playing around and try to look up the right answer).

I've linked to the note and attached the recommended schematic for high current applications. We'll go ahead as is, but we'll make a PCB according to this App Note for the v3 circuit.


Attachment 1: Screen_Shot_2018-07-29_at_8.00.27_PM.png
  14114   Sun Jul 29 23:15:34 2018 poojaUpdateCamerasDeveloping CNN

Aim: To develop a convolutional neural network that resolves mirror motion from video.

Input : Previous simulated video of beam spot motion in pitch by applying 4 sine  waves of frquencies 0.2, 0.4, 0.1, 0.3 Hz  and amplitude ratios to frame size to be 0.1, 0.04, 0.05, 0.08 where random uniform noise ranging 0.05 has been added to amplitudes and frequencies. This is divided into train (0.4), validation (0.1) and test (0.5).

Model topology:

  • Number of filters = 2
  • Kernel size = 2
  • Size of pooling windows = 2
  •                                        ----->         Dense layer of 4 nodes  ---->    Output layer of 1 node 

         Activation:                      selu                                                  linear

Batch size = 32, Number of epochs = 128, loss function = mean squared error

Optimizer: Nadam ( learning rate = 0.00001, beta_1 = 0.8, beta_2 = 0.85)

Plots of CNN output & applied signal given in Attachment 1. The variation in loss value with epochs given in Attachment 2.

This needs to be further analysed with increasing random uniform noise over the pixels and by training CNN on simulated data of varying ampltides and frequencies for sine waves.

Attachment 1: conv_nn_varying_freq_amp_1.pdf
Attachment 2: conv_nn_varying_freq_amp_2.pdf
  14115   Mon Jul 30 11:05:44 2018 gautamUpdateSUSIFO SUS wonky

When I came in this morning:

  • PMC was unlocked.
  • Seis BLRMS were off scale.
  • ITMX OSEM LEDs were dark on the CRT monitor even though Sat Box was plugged in.

Checking status of slow machines, it looked like c1sus, c1aux, and c1iscaux needed reboots, which I did. Still PMC would not lock. So I did a burtrestore, and then PMC was locked. But there seemed to be waaaaay to much motion of MCREFL, so I checked the suspension. The shadow sensor EPICS channels are reporting ~10,000 cts, while they used to be ~1000cts. No unusual red flags on the CDS side. Everything looked nominal when I briefly came in at 6:30pm PT yesterday, not sure if anything was done with the IFO last night.

Pending further investigation, I'm leaving all watchdogs shutdown and the PSL shutter closed.

A quick look at the Sorensens in 1X6 revealed that the +/- 20V DC power supplies were current overloaded (see Attachment #1). So I set those two units to zero until we figure out what's going on. Possibly something is shorted inside the ITMX satellite box and a fuse is blown somewhere. I'll look into it more once Steve is back.

Attachment 1: IMG_7102.JPG
  14117   Mon Jul 30 16:11:54 2018 gautamUpdateSUSTrillium interface box is broken

[koji, steve, gautam]

We debugged this in the following way:

  1. Disconnect all fuses in the terminal blocks coming from the +/- 20 VDC Sorensens.
  2. Check that they are indeed isolated using DMM.
  3. Test blocks of fuses in order to identify where the problem is happening (i.e. plug fuses in, turn up Sorensen voltage knobs, look for current overload). We did things in the following order:
    • MC suspensions
    • BS, PRM and SRM
    • ITMY
    • ITMX
    • Trillium interface box.
  4. Turns out that the Trillium box is the culprit.
  5. Confirmed that the problem is in the trillium interface box and not in the seismometer itself by unplugging all cables leading out of the interface box, and checking that the problem persists when the box is powered on.

So for now, the power cable to the box is disconnected on the back end. We have to pull it out and debug it at some point.

Apart from this, megatron was un-sshable so I had to hard reboot it, and restart the MCautolocker, FSSslowPy and nds2 processes on it. I also restarted the modbusIOC processes for the PSL channels on c1auxex (for which the physical Acromag units sit in 1X5 and hence were affected by our work), mainly so that the FSS_RMTEMP channel worked again. Now, IMC autolocker is working fine, arms are locked (we can recover TRX and TRY~1.0), and everything seems to be back to a nominal state. Phew.

  14118   Mon Jul 30 18:19:03 2018 KojiUpdateSUSTrillium interface box was fixed and reinstalled

The trillium interface box was removed from the rack.

The problem was the incorrect use of an under-spec TVS (Transient Voltage Suppression) diodes (~ semiconductor fuse) for the protection circuit.
The TVS diodes we had had the breakdown voltages lower than the supplied voltages of +/-20V. This over-voltage eventually caused the catastrophic breakdown of one of the diodes.

I don't find any particular reason to have these diodes during the laboratory use of the interface. Therefore, I've removed the TVS diodes and left them unreplaced. The circuit was tested on the bench and returned to the rack. All the cables are hooked up, and now the BRLMs look as usual.


- The board version was found to be D1000749-v2

- There was an obvious sign of burning or thermal history around the components D17 and D14. The solder of the D17 was so brittle that just a finger touch was enough to remove the component.

- These D components are TVS diodes (Transient Voltage Suppression Diodes) manufactured by Littelfuse Inc. It is sort of a surge/overvoltage protector to protect rest of the circuit to be exposed to excess voltage. The specified component for D17/D14 was 5.0SMMDJ20A with reverse standoff voltage (~operating voltage) of 20V and the breakdown voltage of 22.20V(min)~24.50V(max). However, the spec sheet told that the marking of the proper component must be "5BEW" rather than "DEM," which is visible on the component. Some search revealed that the used component was SMDJ15A, which has the breakdown voltage of 16.70V~18.50V. This spec is way too low compared to the supplied voltage of +/-20V.

Attachment 1: P_20180730_173134.jpg
Attachment 2: P_20180730_180151.jpg
  14119   Tue Jul 31 08:17:55 2018 SteveUpdateSUSTrillium interface box was fixed,reinstalled & working



Attachment 1: all_OK.png
  14120   Tue Jul 31 22:50:18 2018 aaronUpdateOMCOMC Expected Refl Signal

I learned a lot about lasers this week from Siegman. Here are some plots that show the expected reflectivity off of the OMC for various mode matching cases.

The main equation to know is 11.29 in Siegman, the total reflection coefficient going into the cavity:


Where r is the mirror reflectivity (assumed all mirrors have the same reflectivity), t is the transmissivity, and g is the complex round-trip gain, eq 11.18


The second exponential is the loss; in Siegman the \alpha_0 is some absorption coecfficient and p is the total round trip length, so the product is just the total loss in a round trip, which I take to be 4*the loss on a single optic (50ppm each). \phi is the total round trip phase accumulation, which is 2\pi*detuning(Hz)/FSR. The parameters for the cavity can be found on the wiki.

I've added the ipynb to my personal git, but I can put it elsewhere if there is somewhere more appropriate. I think this is all OK, but let me know if something is not quite right.

Attachment 1: omcRefl.pdf
  14124   Thu Aug 2 16:30:08 2018 SteveUpdateTreasuretime capsule location

I 've just found this time capsule note from Nov. 26, 2000 by Kip Thorne:  LIGO will discover gravitational waves by Dec.31, 2007


   Beautifully Done


  what is next?

Atm 3, Ron Drever could not celebrate with us because of health issues.



Attachment 1: time_capsule.JPG
  14129   Fri Aug 3 15:53:25 2018 gautamUpdateSUSLow noise bias path idea


The idea we are going with to push the coil driver noise contribution down is to simply increase the series resistance between the coil driver board output and the OSEM coil. But there are two paths, one for fast actuation and one that provides a DC current for global alignment. I think the simplest way to reduce the noise contribution of the latter, while preserving reasonable actuation range, is to implement a precision DC high-voltage source. A candidate that I pulled off an LT application note is shown in Attachment #1.


  • The series resistance in the bias path should be 10 k\Omega, such that the noise from this stage is dominated by the Johnson noise of said resistor, and hence, the current noise contribution is negligible compared to the series resistance in the fast actuation path (4.5 k\Omega).
  • Since we only really need this for the test masses, what actuation range do we want?
    • Currently, ETMY has a series resistance of 400\Omega and has a pitch DC bias voltage of -4 V. 
    • This corresponds to 10 mA of DC current.
    • To drive this current through 10 k\Omega, we need 100 V. 
    • I'm assuming we can manually correct for yaw misalignments such that 10mA of DC current will be sufficient for any sort of corrective alignment.
    • So +/- 120 V DC should be sufficient.
  • The current noise of this stage should be negligible at 100 Hz. 
    • The noise of the transistors and the HV supply should be suppressed by the feedback loop and so shouldn't be a significant contribution (I'll model to confirm).
    • The input noise of the LT1055 is ~20nV/rtHz at 100 Hz, while the Johnson noise of 10 k\Omega is ~13nV/rtHz so maybe the low-passing needs to be tuned, but I think if it comes to it, we can implement a passive RC network at the output to achieve additional filtering.
  • To implement this circuit, we need +/- 125V DC. 
    • At EX and EY, we have a KEPCO HV supply meant to be used for the Green Steering PZTs. 
    • I'm not sure if these can do bipolar outputs, if not, for temporary testing, we can transport the unit at EY to EX.

If all this seems reasonable, I'd like to prototype this circuit and test it with ETMX, which already has the high series resistance for the fast path. So I will ask Steve to order the OpAmp and transistors.

Attachment 1: LT1055_precOpAmp.pdf
  14130   Fri Aug 3 16:27:40 2018 ranaUpdateSUSLow noise bias path idea

Bah! Too complex.

  14131   Fri Aug 3 18:54:58 2018 gautamUpdateSUSGlitchy MC1

The wall StripTool indicated that the IMC wasn't too happy when I came in today. Specifically:

  • MC1 watchdog was tripped.
  • Even in the tripped state, MC REFL spot on the camera showed spot motion that was too large to be explained as normal seismic driven motion (i.e. with local damping supposedly disabled).
  • Strange excursions were observed in the MC1 shadow sensor signal levels as well, see Attachment #1 - negative values don't make any sense for this readout.

The last time this happened, it was due to the Sorensens not spitting out the correct voltages. This time, there were no indications on the Sorensens that anything was funky. So I just disabled the MCautolocker and figured I'd debug later in the evening.

However, around 5pm, the shadow sensor values looked nominal again, and when I re-enabled the local damping, the MC REFL spot suggested that the local damping was working just fine. I re-enabled the MCautolocker, MC re-locked almost immediately. To re-iterate, I did nothing to the electronics inside the VEA. Anyways, this enabled us to work on the X arm ASS (next elog).

Attachment 1: MC1_sensorAnomaly.png
  14132   Fri Aug 3 19:02:11 2018 gautamUpdateASSX arm ASS recovery

[koji, gautam]

After I effected the series resistance change for ETMX, the X arm ASS didn't work (i.e. IR transmission would degrade if the servo was run). Today, we succeeded in recovering a functional ASS servo yes.

So both arms have working dither alignment servos now. But remember that the Y arm ASS gains have been set for locking the Y arm with MC2 as the actuator, not ETMY.


  • Koji pointed out that the demodulated signals from the ETM dither are only used to center the spot on the ETM, and that we should first run the servo with existing settings with the ETM pitch and yaw spot centering loops disabled.
    • This improved TRX level from ~0.8 to 1.1
  • Next, we tried increasing the LO amplitudes by x5 to account for the reduced actuation of the dither on ETMX
    • We then re-enabled the two loops that were earlier disabled.
    • This resulted in TRX degrading very quickly.
  • So we decided to try going back to the nominal LO gains, and reducing the gain of the two ETM spot centering loops.
    • This did the trick, TRX went from 1.1 --> ~1.23, which is the nominal maximum pre-vent value.
  • The snap file used to recover the correct settings to run the dither alignment servos have been updated, the old one has been backed up with today's datestamp.

We then tried to maximize GTRX using the PZT mirrors, but were only successful in reaching a maximum of 0.41. The value I remember from before the vent was 0.5, and indeed, with the IR alignment not quite optimized before we began this work, I saw GTRX of 0.48. But the IR dither servo signals indicate that the cavity axis may have shifted (spot position on the ITM, which is uncontrolled, seems to have drifred significantly, the Pitch signal doesn't stay on the StripTool scale anymore). So we may have to double check that the transmitted beam isn't falling off the GTRX DC PD.

  14133   Sun Aug 5 13:28:43 2018 gautamUpdateCDSc1lsc flaky

Since the lab-wide computer shutdown last Wednesday, all the realtime models running on c1lsc have been flaky. The error is always the same:

[58477.149254] c1cal: ADC TIMEOUT 0 10963 19 11027
[58477.149254] c1daf: ADC TIMEOUT 0 10963 19 11027
[58477.149254] c1ass: ADC TIMEOUT 0 10963 19 11027
[58477.149254] c1oaf: ADC TIMEOUT 0 10963 19 11027
[58477.149254] c1lsc: ADC TIMEOUT 0 10963 19 11027
[58478.148001] c1x04: timeout 0 1000000 
[58479.148017] c1x04: timeout 1 1000000 
[58479.148017] c1x04: exiting from fe_code()

This has happened at least 4 times since Wednesday. The reboot script makes recovery easier, but doing it once in 2 days is getting annoying, especially since we are running many things (e.g. ASS) in custom configurations which have to be reloaded each time. I wonder why the problem persists even though I've power-cycled the expansion chassis? I want to try and do some IFO characterization today so I'm going to run the reboot script again but I'll get in touch with J Hanks to see if he has any insight (I don't think there are any logfiles on the FEs anyways that I'll wipe out by doing a reboot). I wonder if this problem is connected to DuoTone? But if so, why is c1lsc the only FE with this problem? c1sus also does not have the DuoTone system set up correctly...

The last time this happened, the problem apparently fixed itself so I still don't have any insight as to what is causing the problem in the first place frown. Maybe I'll try disabling c1oaf since that's the configuration we've been running in for a few weeks.

  14134   Sun Aug 5 13:45:00 2018 gautamUpdateSUSETMX tripped

Independent from the problems the vertex machine has been having (I think, unless it's something happening over the shared memory network), I noticed on Friday that the ETMX watchdog was tripped. Today, once again, the ETMX watchdog was tripped. There is no evidence of any abnormal seismic activity around that time, and anyways, none of the other watchdogs tripped. Attachment #1 shows that this happened ~838am PT today morning. Attachment #2 shows the 2k sensor data around the time of the trip. If the latter is to be believed, there was a big impulse in the UL shadow sensor signal which may have triggered the trip. I'll squish cables and see if that helps - Steve and I did work at the EX electronics rack (1X9) on Friday but this problem precedes our working there...

Attachment 1: ETMX_tripped.png
Attachment 2: ETMX_tripped_zoom.png
  14135   Sun Aug 5 15:43:50 2018 gautamUpdateSUSAnother low noise bias path idea

OK, how about this:

  • Attachment #1 shows the proposed schematic.
    • It consists of a second order section with Gain x10 to map the +/-10V DC range of the DAC to +/- 100V DC such that we preserve roughly the same amount of DC actuation range.
    • Corner frequency of the SOS is set to ~0.7 Hz. In hindsight, maybe this is more aggressive than necessary, we can tune this.
    • DC gain is 20 dB (typo in the text where I say the DC gain is x15, though we could go with this option as well I think if we want a larger series resistance).
    • A first order passive low-pass stage is added to filter out the voltage noise of the PA91, which dominates the output voltage noise (next bullet).
  • Attachment #2 shows the transfer function from input to output
    • The two traces compare having just a single SOS filtering stage vs the current topology of having two SOS stages.
    • The passive output RC network is necessary in either case to filter the voltage noise of the PA91 OpAmp.
    • For the DAC noise, I just assumed a flat noise level of 5 \mu V / \sqrt{\mathrm{Hz}}, I don't actually know what this is for the Acromag DACs.
  • Attachments #3 shows a breakdown of the top 5 noise contributions.
    • The PA91 datasheet doesn't give current noise information so I just assumed 1 fA / \sqrt{\mathrm{Hz}}, which was what was used for the PA85 in the existing opamp.lib file.
    • The voltage noise is modelled as 4.5 \sqrt{1+\frac{80}{f}} nV / \sqrt{\mathrm{Hz}}, which seems to line up okay with the plot on Pg4 of the datasheet.
    • So the model suggests we will be dominated by the voltage noise of the PA91.
  • Attachment #4 translates the noise into current noise seen by the actuator.
    • I add the Johnson noise contribution of the series resistance for this path, which is assumed to be 10 k \Omega.
    • For comparison, I add the filtered DAC noise contribution, and Johnson noise of the proposed series resistance in the fast path.
    • For the bias path, we are dominated by the Johnson noise of the series resistor from ~60 Hz upwards.
    • It's not quite fair to say that the Johnson noise of the resistance in the fast path dominates, the quadrature sum of fast and bais paths will be ~1.2 times of the former alone. 
    • Bottom line: we will be in the regime of total current noise of ~2.2 pA/rtHz, where I think Kevin's modeling suggests we can see some squeezing.

The question still remains of how to combine the fast and bias paths in this proposed scheme. I think the following approach works for prototyping at least:

  • Remove the series resistance on the existing coil driver boards' bias path, hence isolating this from the coil.
  • Route the DB15 output connector from the coil driver board (which is now just the fast actuation signals) into a sub-sattelite box housing the bias path electronics.
  • Sum the two signals as it is done now, by simply having a conductor (PCB trace) merge the two paths after their respective series resistances.

In the longer term, perhaps the Satellite Box revamp can accommodate a bias voltage summation connector.


Bah! Too complex.

I have neglected many practical concerns. Some things that come to mind:

  1. Is it necessary to protect the upstream DAC from some potential failure of the PA91 in which the high voltage appears at the input?
  2. What is the correct OpAmp for this purpose? This chart on Apex's page suggests that PA15, PA85, PA91 and PA98 are all comparable in terms of drive capability, and the spec sheets don't suggest any dramatic differences. Some LIGO circuits use PA85, some use PA90, but I can't find any that use PA91. Perhaps Rana/Koji can comment about this.
  3. What kind of protection is necessary for the PA91 power?
  4. What is the correct way to do heat management? Presumably we need heatsinks, and in fact, there is a variant of the packaging style that has "formed" legs, which from what I can figure out, allow the heat sink plane on the PA91 to be parallel to the PCB surface. But I think the heat-sink wisdom suggests vertical fins are the most efficient (not sure if this holds if the PCB is inside a box though). What about the PCB itself? Are some kind of special traces needed?
  5. Can we use the current-limiting resistor feature on the PA91? The datasheet seems to advice against it for G>10 configurations, which is what we need, although our requirement is only at DC so I don't know if that table is applicable to this circuit.
  6. Are 3W resistors sufficient? I think we require only 10mA maximum current to preserve the current actuation range, so 100 V * 10mA = 1W, so 3W leaves some safety margin.
  7. All capacitors should be rated for 500 V per the datasheet.  
Attachment 1: HV_Bias_schematic.pdf
Attachment 2: TF.pdf
Attachment 3: bias.pdf
Attachment 4: HVbias_currentNoise.pdf
  14136   Mon Aug 6 00:26:21 2018 gautamUpdateCDSMore CDS woes

I spent most of today fighting various CDS errors.

  • I rebooted c1lsc around 3pm, my goal was to try and do some vertex locking and figure out what the implications were of having only ~30% power we used to have at the AS port.
  • Shortly afterwards (~4pm), c1lsc crashed.
  • Using the reboot script, I was able to bring everything back up. But the DC lights on c1sus models were all red, and a 0x4000 error was being reported.
  • This error is indicative of some timing issue, but all the usual tricks (reboot vertex FEs in various order, restart the mx_streams etc) didn't clear this error.
  • I checked the Tempus GPS unit, that didn't report any obvious problems (i.e. front display was showing the correct UTC time).
  • Finally, I decided to shut down all watchdogs, soft reboot all the FEs, soft reboot FB, power cycle all expansion chassis.
  • This seems to have done the trick - I'm leaving c1oaf disabled for now.
  • The remaining red indicators are due to c1dnn and c1oaf being disabled.

Let's see how stable this configuration is. Onto some locking now...

Attachment 1: CDSoverview.png
  14137   Mon Aug 6 09:34:02 2018 SteveUpdateVACRGA scan at day 20



Attachment 1: pd81d20.png
  14139   Mon Aug 6 14:38:38 2018 gautamUpdateCDSMore CDS woes

Stability was short-lived it seems. When I came in this morning, all models on c1lsc were dead already, and now c1sus is also dead (Attachment #1). Moreover, MC1 shadow sensors failed for a brief period again this afternoon (Attachment #2). I'm going to wait for some CDS experts to take a look at this since any fix I effect seems to be short-lived. For the MC1 shadow sensors, I wonder if the Trillium box (and associated Sorensen) failure somehow damaged the MC1 shadow sensor/coil driver electronics.


Let's see how stable this configuration is. Onto some locking now...

Attachment 1: CDScrash.png
Attachment 2: MC1failures.png
  14140   Mon Aug 6 19:49:09 2018 gautamUpdateCDSMore CDS woes

I've left the c1lsc frontend shutdown for now, to see if c1sus and c1ioo can survive without any problems overnight. In parallel, we are going to try and debug the MC1 OSEM Sensor problem - the idea will be to disable the bias voltage to the OSEM LEDs, and see if the readback channels still go below zero, this would be a clear indication that the problem is in the readback transimpedance stage and not the LED. Per the schematic, this can be done by simply disconnecting the two D-sub connectors going to the vacuum flange (this is the configuration in which we usually use the sat box tester kit for example). Attachment #1 shows the current setup at the PD readout board end. The dark DC count (i.e. with the OSEM LEDs off) is ~150 cts, while the nominal level is ~1000 cts, so perhaps this is already indicative of something being broken but let's observe overnight.

Attachment 1: IMG_7106.JPG
  14141   Mon Aug 6 20:41:10 2018 aaronUpdateDAQNew DAC for the OMC

Gautam and I tested out the DAC that he installed in the latter half of last week. We confirmed that at least one of the channels is can successfully drive a sine wave (ch10, 1-indexed). We had to measure the output directly on the SCSI connector (breakout in the FE hard drive cabinet along the Y arm), since the SCSI breakout box (D080303) seems not to be working (wiring diagram in Gautam's elog from his SURF years).

I added some DAC channels to our c1omc model:
And determined that when we go to use the ADC, we will initially want the following channels (even these are probably unnecessary for the very first scans):
DVMDC (drive voltage monitor, DC level)
DVMAC ("", AC level, only needed if we dither the length)
I attach a screenshot of the model, and a picture of where the whitening/dewhitening boards should go in the rack.
Attachment 1: OMCDACmdl.png
  14142   Tue Aug 7 11:30:46 2018 gautamUpdateCDSMore CDS woes

Overnight, all models on c1sus and c1ioo seem to have had no stability issues, supporting the hypothesis that timing issues stem from c1lsc. Moreover, the MC1 shadow sensor readouts showed no negative values over a ~12hour period. I think we should just observe this for another day, in any case I don't think there is any urgent IFO related activity scheduled.

  14143   Tue Aug 7 22:28:23 2018 gautamUpdateCDSMore CDS woes

I am starting the c1x04 model (IOP) on c1lsc to see how it behaves overnight.

Well, there was apparently an immediate reaction - all the models on c1sus and c1ioo reported an ADC timeout and crashed. I'm going to reboot them and still have c1x04 IOP running, to see what happens.

[97544.431561] c1pem: ADC TIMEOUT 3 8703 63 8767
[97544.431574] c1mcs: ADC TIMEOUT 1 8703 63 8767
[97544.431576] c1sus: ADC TIMEOUT 1 8703 63 8767
[97544.454746] c1rfm: ADC TIMEOUT 0 9033 9 8841

Overnight, all models on c1sus and c1ioo seem to have had no stability issues, supporting the hypothesis that timing issues stem from c1lsc. Moreover, the MC1 shadow sensor readouts showed no negative values over a ~12hour period. I think we should just observe this for another day, in any case I don't think there is any urgent IFO related activity scheduled.

  14144   Tue Aug 7 23:06:30 2018 KojiUpdatePSLEOM measuement preparation

I was preparing for the aLIGO EOM measuement to be carried out tomorrow afternoon.

I did a few modifications to the PLL setup.

  • The freq mixier in the PLL setup was replaced with ZP3 (level 7) from ZAD-6
  • The PLL gain was reduced from 3.10 to 2.80 to prevent servo oscillation
  • The main PSL marconi is connected to the PLL mixier and providing fixed 200MHz 8dBm.
  • The main PSL modulation is off.

Tomorrow I am going to modulate the EOM with the AUX Marconi via an amplifier (probably)

Automated scripts (AGinit.py and AGmeas.py) are in /users/koji/scripts

I will revert the setup once the measurement is done tomorrow.

  14145   Wed Aug 8 20:56:11 2018 KojiUpdatePSLEOM measuement preparation

Rich and I worked on the EOM measurement. After the measurement, the setup was reverted to the nominal state

  • AUX PLL mixer was restored to ZAD-6
  • The PLL gain was restored to 3.10
  • The main PSL marconi is connected to the freq generator again. Using the beat note, I've confirmed that the modulations are applied on the beam.
  • The PSL HEPA was reduced from 100 to 30.
  14146   Wed Aug 8 23:03:42 2018 gautamUpdateCDSc1lsc model started

As part of this slow but systematic debugging, I am turning on the c1lsc model overnight to see if the model crashes return.

  14147   Wed Aug 8 23:06:59 2018 gautamUpdateSUSAnother low noise bias path idea

Today while Rich Abbott was here, Koji and I had a brief discussion with him about the HV amplifier idea for the coil driver bias path. He gave us some useful tips, perhaps most useful being a topology that he used and tested for an aLIGO ITM ESD driver which we can adapt to our application. It uses a PA95 high voltage amplifier which differs from the PA91 mainly in the output voltage range (up to 900V for the former, "only" 400V for the former. He agrees with the overall design idea of 

  • Having a LN opamp with the HV amp inside the feedback loop for better voltage noise at low frequencies.
  • Having a passive RC network at the output of the HV amp to filter out noise at high frequencies.

He also gave some useful suggestions like 

  • Using the front panel of the box that as a heatsink for the HV amps.
  • Testing the stability of the nested opamp loop by "pinging" the output of the opamp with some pulses from a function generator and monitoring the response to this perturbation on a scope.

I am going to work on making a prototype version of this box for 5 channels that we can test with ETMX. I have been told that the coupling from side coil to longitudinal motion is of the order of 1/30, in which case maybe we only need 4 channels.

  14148   Thu Aug 9 02:12:13 2018 gautamUpdateCOCSouth East or West?


For operating the SRC in the "Signal-Recycled" tuning, the SRC macroscopic length needs to be ~4.04m (compared to the current value of ~5.399m), assuming we don't do anything fancy like change the modulation frequencies and not transmit through the IMC. We're putting together a notebook with all the calculations, but today I was thinking about what the signal extraction path should be, specifically which chamber the SRM should be in. Just noting down the thoughts I had here while they're fresh in my head, all this has to be fleshed out, maybe I'm making this out to be more of a problem than it actually is.


  • For the current modulation frequencies, if we want the reosnance conditions such that the f2 sideband is resonant in the SRC (but not f1, i.e. small Schnupp asymmetry regime) while the carrier is resonant in the arms (required for good sensing of the SRC length), the macroscopic length of the SRC needs to be changed to ~4.04m.
  • Practically, this means that the folded SRC would only have one folding mirror (SR2).
  • There is a shorter SRC length of ~1.something metres which would work, but that would involve changing the relative position between ITMs and BS (currently ~2.3m) so I reject that option for now.
  • So the SR2 would be roughly where it is right now, ~20cm from the BS.
  • The question then becomes, where do we direct the reflection from the SR2? We need an optical path length of ~1.5m from SR2. So options are 
    • ITMY table (East)
    • ITMX table (South)
    • IMC table (West)
  • Moreover, after the SRM, we have to accommodate:
    • Some kind of pickoff for in-air PDs.
    • OFI.
    • OMC MMT.
    • OMC.
  • Some kind of CBA (as of now I think going to the ITMY table is the best option):
Option Advantages Disadvantages
  • Easy to direct beam from BS/PRM chamber to the ITMY table (i.e. we don't have to worry too much about avoiding other optics in the path etc).
  • Ease of access to chamber, ease of working in there.
  • ITMY table probably has the most room to work out an OFI + OMC MMT + OMC solution.
  • AS beam extraction to air will be more complicated, possibly have to do it on ITMY optical table.
  • Not sure if the ITMY table can accommodate all of the output optics subsystems I listed above.
  • Routing the LO beam to this table would be tricky I guess.
  • Routing the LO beam for homodyne detection is probably easiest in this chamber.
  • Allows for small AoI on folding mirror, reducing the impact of astigmatism.
  • Pain to work in this chamber because of IMC tube.
  • Steering beam from SR2 to ITMX table means threading the needle between PRM and PR3 possibly.
  • Probably allows the use of (almost) the entire existing OMC chamber for the output optics (OFI, OMC MMT, OMC).
  • IMC table is crowded (2 SOS towers, several steering optics for the input beam, input faraday).
  • Not sure what is the performance of the seismic isolation stacks on these tables vs the larger optical tables.
  • Painful to work in these smaller chambers.
  14149   Thu Aug 9 12:31:13 2018 gautamUpdateCDSCDS status update

The model seems to have run without issues overnight. Not completely related, but the MC1 shadow sensor signals also don't show any abnormal excursions to negative values in the last 48 hours. I'm thinking about re-connecting the satellite box (but preserving the breakout setup at 1X6 for a while longer) and re-locking the IMC. I'll also start c1ass on the c1lsc frontend. I would say that the other models on c1lsc (i.e. c1oaf, c1cal, c1daf) aren't really necessary for basic IFO operation.


As part of this slow but systematic debugging, I am turning on the c1lsc model overnight to see if the model crashes return.

  14150   Thu Aug 9 12:40:14 2018 gautamUpdateSUSETMX trip follow-up

A brief follow-up on this since we discussed this at the meeting yesterday: the attached DV screenshot shows the full 2k data for a period of 2 seconds starting just before the watchdog tripped. It is clear that the timescale of the glitch in the UL channel is much faster (~50 ms) compared to the (presumably mechanical) timescale seen in the other channels of ~250 ms, with the step also being much smaller (a few counts as opposed to the few thousand counts seen in the UL channel, and I guess 1 OSEM count ~ 1 um). All this supports the hypothesis that the problem is electrical and not mechanical (i.e. I think we can rule out the Acromag sending a glitchy signal to the coil and kicking the optic). The watchdog itself gets tripped because the tripping condition is the RMS of the shadow sensor outputs, which presumably exceeds the set threshold when UL glitches by a few thousand counts.

Attachment 1: ETMXglitch.png
  14151   Thu Aug 9 22:50:13 2018 gautamUpdateCDSAlignSoft script modified

After this work of increasing the series resistance on ETMX, there have been numerous occassions where the insufficient misalignment of ETMX has caused problems in locking vertex cavities. Today, I modified the script (located at /opt/rtcds/caltech/c1/medm/MISC/ifoalign/AlignSoft.py) to avoid such problems. The way the misalign script works is to write an offset value to the "TO_COIL" filter bank (accessed via "Output Filters" button on the Suspension master MEDM screen - not the most intuitive place to put an offset but okay). So I just increased the value of this offset from 250 counts to 2500 counts (for ETMX only). I checked that the script works, now when both ETMs are misaligned, the AS55Q signal shows a clean Michelson-like sine wave as it fringes instead of having the arm cavity PDH fringes as well yes.

Note that the svn doesn't seem to work on the newly upgraded SL7 machines: svn status gives me the following output.

svn: E155036: Please see the 'svn upgrade' command
svn: E155036: Working copy '/cvs/cds/rtcds/userapps/trunk/cds/c1/medm/MISC/ifoalign' is too old (format 10, created by Subversion 1.6)

 Is it safe to run 'svn upgrade'? Or is it time to migrate to git.ligo.org/40m/scripts?

Attachment 1: MichelsonFringing.png
  14152   Fri Aug 10 01:10:56 2018 gautamUpdateLSCSome vertex locking restored

For the first time after the whirlwind vent, I managed to lock the PRMI.

  • First, I did POX/POY locking, dither aligned the arms to maximize TRX and TRY.
  • Next, I misaligned the ETM and tested the Michelson locking
    • Since we've lost ~70% of power on the AS55 PD, I set the whitening gain for AS55 I and Q channels to +6dB (old value was 0dB).
    • worked alright. In this new config, the peak-to-peak Michelson fringe count is ~80 cts, while I reported ~60cts-pp a couple of months ago, so all seems good on that front.
    • But the config script in the IFOconfigure MEDM screen somehow doesn't set the AS55_Q ----> MICH_A element in the LSC input matrix anymore.
    • I edited the .snap file for this configuration to set the relevant matrix element EPICS channel to +1.0.
    • I also edited the overall loop gain for this configuration from +30 to +2 (for bright fringe, use -2 for dark fringe).
  • Feeling adventerous, I decided to try PRMI in the carrier resonant tuning (to be clear, PRCL on REFL11_I, MICH on AS55_Q).
    • Finding the REFL spot on the camera took a while since the PRM has been macroscopically misaligned for the mode-scanning
    • Went out to the table and centered the REFL beam onto REFL11 and REFL55 PDs - didn't need much tweaking, which is a good sign, since we shouldn't have screwed anything up on the symmetric side by any of the vent activities.
    • Restored PRMI locking using the IFOconfigure MEDM screen - lock caught almost immediately.
    • Ran the dither alignment servos for MICH and PRCL - BS needed a bit of encouragement to make the dark spot dark, but POP has been pretty stable over ~15mins.
    • I didn't take any loop transfer functions, to do.

I don't have the energy to make a DRMI attempt tonight - but the signs are encouraging. I'd like to use the IFO in the next few days to try and recover DRMI locking. The main concern is that the optical path on the AS beam has changed by ~0.3m I estimate. So the demod phase for AS55 may need to be adjusted, but the change due to optical path length only should be ~10degrees so the DRMI locking with the old settings should still work. Perhaps we also want to scan the PRC and SRC with the phase information from the Trans/Refl transfer functions as well.

Don't want to jinx it, but the c1lsc FE models have been stable. Tomorrow, I'd like to re-enable c1cal, since it has some useful channels for NBing. Could c1daf/c1oaf which have significant amounts of custom C code be the culprits?

Attachment 1: PRMIcarrier.png
  14156   Mon Aug 13 09:56:23 2018 SteveUpdateSUSETMX trip follow-up

Here is an other big one


A brief follow-up on this since we discussed this at the meeting yesterday: the attached DV screenshot shows the full 2k data for a period of 2 seconds starting just before the watchdog tripped. It is clear that the timescale of the glitch in the UL channel is much faster (~50 ms) compared to the (presumably mechanical) timescale seen in the other channels of ~250 ms, with the step also being much smaller (a few counts as opposed to the few thousand counts seen in the UL channel, and I guess 1 OSEM count ~ 1 um). All this supports the hypothesis that the problem is electrical and not mechanical (i.e. I think we can rule out the Acromag sending a glitchy signal to the coil and kicking the optic). The watchdog itself gets tripped because the tripping condition is the RMS of the shadow sensor outputs, which presumably exceeds the set threshold when UL glitches by a few thousand counts.


Attachment 1: ETMXglitch.png
Attachment 2: ETMXgltch.png
ELOG V3.1.3-