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ID Date Author Type Category Subject
8877   Thu Jul 18 23:34:40 2013 gautamConfigurationendtable upgradeCoarse adjustment of PZT axes orientation in mount

I have managed to orient the PZT in the mount such that its axes are approximately aligned with the vertical and the horizontal.

In the process, I discovered that the 4 screws on the back face of the PZT correspond to the location of the piezoelectric stacks beneath the tip-tilt platform. The PZT can therefore be oriented during the mounting process itself, before the mirror is glued onto the tip-tilt platform.

In order to verify that the pitch and yaw motion of the mirror have indeed been roughly decoupled, I centred the spot on the QPD, fed to the 'pitch' input of the PZT driver board (connected to channel 1 of the PZT) a 10 Vpp, 1 Hz sine wave from the SR function generator (having turned all the other relevant electronics, HV power supply etc ON. The oscilloscope trace of the output observed on the QPD is shown. The residual fluctuation in the Y-coordinate (blue trace) is I believe due to the tilt in the QPD, and also due to the fact that the PZT isnt perfectly oriented in the mount.

It looks like moving the tip-tilt through its full range of motion takes us outside the linear regime of the QPD calibration. I may have to rethink the calibration setup to keep the spot on the QPD in the linear range if the full range is to be calibrated, possibly decrease the distance between the mirror and the QPD. Also, in the current orientation, CH1 on the PZT controls YAW motion, while CH2 controls pitch.

Oscilloscope Trace:

Yellow: X-coordinate

Blue: Y-coordinate

14444   Fri Feb 8 20:35:57 2019 gautamSummaryTip-TIltCoating spec

[Attachment #1]: Computed spectral power transmissivity (according to my model) for the coating design at a few angles of incidence. Behavior lines up well with what FNO measured, although I get a transmission that is slightly lower than measured at 45 degrees. I suspect this is because of slight changes in the dispersion relation assumed and what was used for the coating in reality.

[Attachment #2]: Similar information as Attachment #1, but with the angle of incidence as the independent parameter in a continuous sweep.

Conclusion: The coating behaves in a way that is in reasonable agreement with our model. At 41.1 degrees, which is what the PR3 angle of incidence will be, T<50 ppm, which was what we specified. The larger range of angles was included because originally, we thought of using this optic as a substitute for SR3 as well. But I claim that for the shorter SRC (signal recycling as opposed to RSE), we will not end up using the new optic, but rather go for the G&H mirror. In any case, as Koji pointed out, ~50 ppm extra loss in the RC will not severely limit the recycling gain. Such large variation was not seen in the MC analysis because we only varied the angle of incidence by +/- 0.5 degrees about the nominal design value of 41.1 degrees.

Attachment 1: specRefl.pdf
Attachment 2: AoIscan.pdf
7259   Thu Aug 23 17:17:49 2012 MashaSummaryComputersCode Folder Status

I cleaned up my directory (/users/masha) today. A lot of the files are just code that I experimented with, but the important files for training the classification neural network are in "neural_network_classification". The "EarthquakeData" subdirectory contains my entire dataset. Files of the form "GenerateRNNInput" are used to create input vector sets to the network, while files of the "*NeuralNetworkClassification* actually run the code that generates the neural network vectors for the classification code block in the c1pem model.

Also, the folder "feed_c", which can also be found in Den's directory, contains the neural network controller code we played around with.

13866   Fri May 18 19:10:48 2018 keerthanaUpdateGeneralCode for adjusting the oscillator frequency remotly

Target: Phase locking can be acheived by giving a scan to the oscilator frequency. This frequency is now controlled using the knobe on the AM/FM signal generator 2023B. But we need to control it remotely by giving the inputs of start frequency, end frequency and the steps.

The frequency oscilator and the computer is connected with the help of GPIB Ethernet converter. The IP address of the converter I used is '192.168.113.109' and its GPIB address is 10.

I could change the oscilator frequency by changing the input frequency with the help of the code I made (Inorder to check this code, I have changed the oscilator frequency multiple times. I hope it didn't create trouble to anyone). Now I am trying to make this code better by adding certain features like numpy, argument parse etc, which I will be able complete by next week. I am also considering to develop the code to have a sliding system to control the oscillatory frequency.

For record: The maximum limit of frequency which i changed upto is 100MHz.

Attachment 1: frequency_set.jpg
12870   Mon Mar 6 14:47:49 2017 gautamUpdateSummary PagesCode status check script modified

For a few days now, the "code status" page has been telling us that the summary pages are DEAD, even though the pages themselves seemed to be generating plots. I logged into the 40m shared account on the cluster and checked the status of the condor job (with condor_q), and did not find anything odd there. I decided to consult Max, who pointed out that the script that checks the code status (/home/40m/DetectorChar/bin/checkstatus) was looking for a particular string in the log files ("gw_daily_summary"), while the recent change in the default output of condor_q meant that the string actually being written to the log files was "gw_daily_summa". This script has now been modified to look for instances of "gw_daily" instead, and so the code status indicator seems to be working again...

The execution of the summary page scripts has also been moved back to pcdev1 (from pcdev2, where it was moved to temporarily because of some technical problems with pcdev1).

279   Mon Jan 28 12:42:48 2008 DmassBureaucracyTMICoffee
There is tea in the coffee carafe @ the 40m. It is sitting as though it were fresh coffee. There is also nothing on the post it.
229   Wed Jan 9 20:29:47 2008 DmassAoGTMICoffee Carafe
If you have been using the coffee machine in the 40m, you may have noticed small brown flecks in your coffee mug. The carafe in the 40m has accumulated a layer of what is presumed to be old dried up coffee. When a small amount of water is swirled around in the bottom, flecks of the brown layer come off. Pictures below are of the inside of the carafe.

But does it provide adequate protection from 1064 light?
Attachment 1: DSC_0363.JPG
Attachment 2: DSC_0365.JPG
Attachment 3: DSC_0368.JPG
5810   Fri Nov 4 14:18:24 2011 MIrkoUpdateAdaptive FilteringCoherence between seismometers and MC length

Looking into the coherence between the seismometers and IMC length (MC_F):

FIrst with the seismometers only AC filtered at around 0.003 Hz and AA30Hz:

Ignore the increase in coherence at very low frequencies. That is an artefact.

Then with an additional filter single complex pole @1Hz Q=1000 (giving 20dB per decade in attenuation above 1Hz) , only for GUR1X:

5190   Thu Aug 11 13:41:36 2011 Ishwita, ManuelUpdatePEMCoherence of Guralp1 and STS2(Bacardi, Serial NR 100151)

Following is the coherence plot obtained when Guralp1 and STS2(Bacardi, Serial NR 100151) are placed very close to each other (but they aren't touching each other):

The seismometers were placed as shown in the picture below:

They are placed below the center of the mode cleaner vacuum tube.

5201   Fri Aug 12 00:18:30 2011 Ishwita, ManuelUpdatePEMCoherence of Guralp1 and STS2(Bacardi, Serial NR 100151)

We moved the seismometer STS2(Bacardi, Serial NR 100151) as we told in this Elog Entry, so the distance between Guralp1 and STS2 is 31.1m. Following is the coherence plot for this case:

then we also moved the Guralp1 under the BS and plugged it with the Guralp2 cable (at 7:35pm PDT), so now the distance between the two seismometers is 38.5m. Following is the coherence plot for this case:

11457   Wed Jul 29 10:34:42 2015 IgnacioSummaryLSCCoherence of arms and seismometers

Jessica and I took 45 mins  (GPS times from 1122099200 to 1122101950) worth of data from the following channels:

C1:IOO-MC_L_DQ (mode cleaner)
C1:LSC-XARM_IN1_DQ (X arm length)
C1:LSC-YARM_IN1_DQ (Y arm length)

and for the STS, GUR1, and GUR2 seismometer signals.

The PSD for MCL and the arm length signals is shown below,

I looked at the coherence between the arm length and each of the three seismometers, plot overload incoming below,

For the coherence between STS and XARM and YARM,

For GUR1,

Finally for GUR2,

A few remarks:

1) From the coherence plots, we can see that the arm length signals are coherent with the seismometer signals the most from 0.5 - 50 Hz. This is most evident in the coherence with STS. I think subtraction will be most useful in this range. This agrees with what we see in the PSD of the arm length signals, the magnitude of the PSD starts increasing from 1 Hz and reaches a maximum at about 30 Hz. This is indicative of which frequencies most of the noise is present.

2) Eric did not remember which of  GUR1 and GUR2 corresponded to the ends of XARM and YARM. So, I went to the end of XARM, and jumped for a couple seconds to disturb whatever Gurald was in there. Using dataviewer I determined it was GUR1. Anyways, my point is, why is GUR1 less coherent with both arms and not just XARM?  Since it is at the end of XARM, I was expecting GUR1 to be more coherent with XARM. Is it because, though different arms, the PSD's of both arms are roughly the same?

3) Similarly, GUR2 shows about the same levels of coherence for both arms, but it is more coherent. Is GUR2 noisier because of its location?

Code: ARMS_COH.m.zip

Attachment 1: PSD_ARMS_MCL.png
Attachment 2: XARM_STS_COH.png
Attachment 3: YARM_STS_COH.png
Attachment 4: XARM_GUR1_COH.png
Attachment 5: YARM_GUR1_COH.png
Attachment 6: XARM_GUR2_COH.png
Attachment 7: YARM_GUR2_COH.png
Attachment 8: ARMS_COH.m.zip
1723   Wed Jul 8 12:36:15 2009 ClaraUpdatePEMCoherences and things

After setting up the microphones last week, I modified the Wiener filtering programs so as to include the microphone signals. They didn't seem to do much of anything to reduce the MC_L signal, so I looked at coherences. The microphones don't seem to have much coherence with the MC_L signal at all. I tried moving Bonnie to near the optical table next to the PSL (which isn't in a vacuum, and thus would, presumably, be more affected by acoustic noise), but that didn't seem to make much of a difference. Eventually, I'd like to put a mic in the PSL itself, but I need to work out how to mount it first.

Bonnie's new location.

You can see in bonnie_butch.pdf that none of the mic signals are giving very good coherence, although they all seem to have a peak at 24 Hz. (In fact, everything seems to have a peak there. Must be a resonant frequency of something in the mode cleaner.)

I've also attached plots of the coherences for all six accelerometers and the three Guralp seismometer axes. I plotted the most coherent traces together in the last pdf: the y-axes of the MC2 accelerometer and the two seismometers (the Ranger measures ONLY y) and, interestingly, the z-axis of the MC2 accelerometer. Unsurprisingly, the seismometers are most coherent at the low frequencies, and the MC2-Y accelerometer seems to be coherent at very similar frequencies. The MC2-Z accelerometer, on the other hand, seems to be coherent at the higher frequencies, and is highly complementary to the others. I am not really sure why this would be...

Finally, I was curious about how the noise varies throughout the day, because I didn't want to mistakenly decide that some particular configuration of accelerometers/seismometers/whatever was better than another b/c I picked the wrong time of day to collect the data. So, here is a plot of Wiener filters (using only accelerometer data) taken over 2-hour intervals throughout the entirety of July 6, 2009 (midnight-midnight local).

It's a little bit confusing, and I should probably try to select some representative curves and eliminate the rest to simplify things, but I don't have time to do that before the meeting, so this will have to suffice for now.

Attachment 2: bonnie_butch.pdf
Attachment 3: Gseis_100.pdf
Attachment 4: mc1_xyz.pdf
Attachment 5: mc2_xyz.pdf
Attachment 6: most_coherent.pdf
2863   Sun May 2 13:04:51 2010 KojiSummarySUSCoil Actuator Balancing and Spot Position

I liked to know quantitatively where the spot is on a mirror.

With an interferometer and A2L scripts, one can make the balance of the coil actuators
so that the angle actuation does not couple to the longitudinal motion.
i.e. node of the rotation is on the spot

Suppose you have actuator balancing (1+α) f and (1-α) f.

=> d = 0.016 x α [m]

Full Imbalance   α = 1      -> d = 15 [mm]
10% Imbalance α = 0.1   -> d = 1.5 [mm]
1% Imbalance   α = 0.01 -> d = 0.15 [mm]

Eq of Motion:

I ω2 θ =  2 R f
(correction) - I ω2 θ =  D f cos(arctan(L/2/D))
(re-correction on Sep 26, 2017) - I ω2 θ =  D f

m ω2 x = 2 α f ,
(correction) - m ω2 x = 2 α f ,

where R is the radius of the mirror, and D is the distance of the magnets. (kinda D=sqrt(2) R)

d, position of the node distant from the center, is given by

d = x/θ = α I / (m R) = 2 α β / D,

where β is the ratio of I and m. Putting R=37.5 [mm], L=25 [mm], β = 4.04 10-4 [m2], D~R Sqrt(2)

i.e. d = 0.015 α [m]

Attachment 1: coil_balance.png
2865   Sun May 2 15:38:12 2010 ranaSummarySUSCoil Actuator Balancing and Spot Position

Oh, but it gets even better: in order to trust the A2L script in this regard you have to know that the coil driver - coil - magnet gain is the same for each channel. Which you can't.

But we have these handy f2pRatio scripts that Vuk and Dan Busby worked on. They use the optical levers to balance the actuators at high frequency so that the A2L gives you a true spot readout.

But wait! We have 4 coils and the optical lever only gives us 2 signal readouts...

2866   Sun May 2 16:52:44 2010 KojiSummarySUSCoil Actuator Balancing and Spot Position

Yes, of course. But so far I am trusting that the coils are inheretly balanced.
Probably you are talking about the dependence of the nodal position on the frequency...I need to check if 18Hz is sufficiently high or not for 0.1mm precision.

Also I am practicing myself to understand how I can adjust them by which screws as we probably have to do this adjustement many times.
(i.e. removal of the MZ, move of the table, PSL renewal and so on)

For the actuator calibration, we may be able to calibrate actuator responses by shaking them one by one while reading the OPLEV P/Y signals.

 Quote: Oh, but it gets even better: in order to trust the A2L script in this regard you have to know that the coil driver - coil - magnet gain is the same for each channel. Which you can't. But we have these handy f2pRatio scripts that Vuk and Dan Busby worked on. They use the optical levers to balance the actuators at high frequency so that the A2L gives you a true spot readout. But wait! We have 4 coils and the optical lever only gives us 2 signal readouts...

15907   Fri Mar 12 03:08:23 2021 KojiSummarySUSCoil Rs & Ls for PRM/BS/SRM

Summary

Per Gautam's request, I've checked the coil resistances and inductances.

• PRM/BS/SRM coils were tested.
• All the PRM coils look well-matched in terms of the inductance. Also, I didn't find a significant difference from BS coils.
• Pin 1 of the feedthru connectors is shorted to the vacuum chamber.
• A discovery was that: The SRM DSUB pinouts are mirrored compared to the other suspensions.

Method

A DSUB25 breakout was directly connected to the flange (Attachment 1).
The impedance meter was nulled every time the measurement range and type (R or L) were changed.

Result

 Feedthru connector: PRM1 Pin1 - flange: R = 0.8Ω Pin11-23 / R = 1.79Ω / L=3.21mH Pin 7-19 / R = 1.82Ω / L=3.22mH Pin 3-15 / R = 1.71Ω / L=3.20mH Feedthru connector: BS1 Pin1 - flange: R = 0.5Ω Pin11-23 / R = 1.78Ω / L=3.26mH Pin 7-19 / R = 1.63Ω / L=3.30mH Pin 3-15 / R = 1.61Ω / L=3.29mH Feedthru connector: SRM1 Pin1 - flange: R = 0.5Ω Pin11-24 / R = 18.1Ω / L=3.22mH Pin 7-20 / R = 18.8Ω / L=3.25mH Pin 3-16 / R = 20.3Ω / L=3.25mH Feedthru connector: PRM2 Pin1 - flange: R = 0.6Ω Pin11-23 / R = 1.82Ω / L=3.20mH Pin 7-19 / R = 1.53Ω / L=3.20mH Pin 3-15 / R = N/A Feedthru connector: BS2 Pin1 - flange: R = 0.6Ω Pin11-23 / R = 1.46Ω / L=3.27mH Pin 7-19 / R = 1.54Ω / L=3.24mH Pin 3-15 / R = N/A Feedthru connector: SRM2 Pin1 - flange: R = 0.7Ω Pin11-24 / R = N/A Pin 7-20 / R = 18.5Ω / L=3.21mH Pin 3-16 / R = 19.1Ω / L=3.25mH

Observation

The SRM pinouts seem mirrored compared to the others. In fact, these two connectors are equipped with mirror cables (although they are unshielded ribbons) (Attachment 2).

The SRM sus is located on the ITMY table. There is a long in vacuum DSUB25 cable between the ITMY and BS tables. I suspect that the cable mirrors the pinout and this needs to be corrected by the in-air mirror cables.

I went around the lab and did not find any other suspensions which have the mirror cable.

WIth the BHD configuration, we will move the feedthru for the SRM to the one on the ITMY chamber. So I believe the situation is going to be improved.

Attachment 1: P_20210311_224651.jpg
Attachment 2: P_20210311_225359.jpg
15913   Fri Mar 12 12:32:54 2021 gautamSummarySUSCoil Rs & Ls for PRM/BS/SRM

For consistency, today, I measured both the BS and PRM actuator balancing using the same technique and don't find as serious an imbalance for the BS as in the PRM case. The Oplev laser source is common for both BS and PRM, but the QPDs are of course distinct.

BTW, I thought the expected resistance of the coil windings of the OSEM is ~13 ohms, while the BS/PRM OSEMs report ~1-2 ohms. Is this okay?

 Quote: All the PRM coils look well-matched in terms of the inductance. Also, I didn't find a significant difference from BS coils.
Attachment 1: BS_actuator.pdf
Attachment 2: PRMact.pdf
15914   Fri Mar 12 13:01:43 2021 ranaSummarySUSCoil Rs & Ls for PRM/BS/SRM

ugh. sounds bad - maybe a short. I suggest measuring the inductance; thats usually a clearer measurement of coil health

15915   Fri Mar 12 13:48:53 2021 gautamSummarySUSCoil Rs & Ls for PRM/BS/SRM

I didn't repeat Koji's measurement, but he reports the expected ~3.2mH per coil on all the BS and PRM coils.

 Quote: ugh. sounds bad - maybe a short. I suggest measuring the inductance; thats usually a clearer measurement of coil health
13300   Wed Sep 6 23:06:30 2017 gautamUpdateLSCCoil de-whitening switching investigation

## Rana suggested checking if the coil de-whitening switching is actually happening in the analog path. I repeated the test detailed here. Attachments #1 and #2 suggest that all the coils for the BS and ITMs are indeed switching.

### Details:

• The motivation behind this test was the following - the analog path switching is done by applying some logic voltage to a switch, but if this voltage is common among many switches, the hypothesis was that perhaps individual switches were not getting the required voltage to engage the switching.
• This time FM9 (simulated de-whitening) and FM10 (inverse de-whitening) in the coil output filter modules turned off, so as to maintain a flat TF in the digital domain, but engage the de-whitened analog path (turning off FM9 is supposed to do this).
• There is poor coherence in the measurement above 40Hz so the data there should be neglected. It is hard to get a good measurement at higher frequencies because of the pendulum TF + heavy low pass filtering from the analog de-whitening path.
• But between 10-40Hz, we already see the analog de-whitening TF in the measurement.
• For comparison, I have plotted the measured pendulum TFs for one of the coils from an earlier test (all the coils were roughly at the same level).

So it would seem that there is some other noise which has a 1/f^2 shape and is at the same level we expected the DAC noise to be at. Rana suggested checking coherence with MC transmission to see if this could be laser intensity noise.

I also want to re-do the actuator calibrations for the vertex optics again before re-posting the revised noise budget.

Attachment 1: BScoils.pdf
Attachment 2: ITMcoils.pdf
13314   Fri Sep 15 17:08:58 2017 gautamUpdateLSCCoil de-whitening switching investigation

I downloaded a segment of data from the time when the DRMI was locked with the BS and ITM coil driver de-whitening switched on, and looked at coherence between MC transmission and the MICH error signal. Attachment #1 doesn't show any broadband high coherence between 60-300Hz, so it cannot explain the noise in the full range between 60-300Hz.

The DQ channel for the MC transmission is recorded at 1024 kHz, so to calculate the coherence, I had to decimate the 16K MICH data.

Since we have the AOM installed, I suppose we can actually measure the intensity noise coupling to MICH by driving a line in the AOM.

I also checked for coherence in the 60-300Hz band between MICH/PRCL and MICH/SRCL, and didn't see any appreciable coherence. Need to think about this more.

 Quote: Rana suggested checking coherence with MC transmission to see if this could be laser intensity noise.
Attachment 1: DRMI_IntensityNoise.pdf
13315   Sat Sep 16 10:56:19 2017 ranaUpdateLSCCoil de-whitening switching investigation

The absence of evidence is not evidence of absence.

13015   Thu May 25 19:27:29 2017 gautamUpdateGeneralCoil driver board noises

[Koji, Gautam]

### Summary:

• Attachment #1 shows the measured/modeled noise of the coil driver board (labelled ITMX).
• Measurement was made with "TEST" input (which is what the DAC drives) is connected to ground via 50ohm terminator, and "BIAS" input grounded.
• The model tells us to expect a noise of the order of 5nV/rtHz - this is comparable to (or below) the input noise of the SR785, and even the SR560. So this measurement only serves to place an upper bound on the coil driver board noise.
• There is some excess noise below 40Hz, would be interesting to see if this disappears with swapping out thick-film resistors for thin film ones.
• The LISO model says that the dominant contribution is from the voltage and input current noise of the two op-amps (LT1125) in the bias LP filter path.
• But if we can indeed realize this noise level of ~10-20nV/rtHz, we are already at the ~10^-17m/rtHz displacement noise for MICH at about 200Hz. I suspect there are other noises that will prevent us from realizing this performance in displacement noise.

### Details:

This measurement has been troublesome - I was plagued by large 60Hz harmonics (see Attachment #1), the cause of which was unknown. I powered all electronics used in the measurement set up from the same power strip (one of the new surge-protecting ones Steve recently acquired for us), but these remained present. Yesterday, Koji helped me troubleshoot this issue. We did the various things, I try to put them here in the order we did them:

1. Double check that all electronics were indeed being powered from the same power strip - OK, but harmonics remained present.
2. Tried using a different DC power supply - no effect.
3. Checked the signal with an oscilloscope - got no additional insight.
4. I was using a DB25 breakout board + pomona minigrabbers to measure the output signal and pipe it to the SR785. Koji suggested using twisted ribbon wire + soldered BNC connector (recycled from some used ones lying around the lab). The idea was to minimize stray radiation pickup. We also disconnected the WiFi extender and GPIB box from the analyzer and also disconnected these from the power - this finaly had the desired effect, the large harmonics vanished.

Today, I tried to repeat the measurement, with the newly made twisted ribbon cable, but the large 60Hz harmonics were back. Then I realized we had also disconnected the WiFi extender and GPIB box yesterday.

Turns out that connecting the Prologix box to the SR785 (even with no power) is the culprit! Disconnecting the Prologix box makes these harmonics go away. I was using the box labelled "Santuzza.martian" (192.168.113.109), but I double-checked with the box labelled "vanna.martian" (192.168.113.105, also a different DC power supply adapter for the box), the effect is the same. I checked various combinations like

• GPIB box connected but not powered
• GPIB box connected with no network cable

but it looks like connecting the GPIB box to the analyzer is what causes the problem. This was reproducible on both SR785s in the lab. So to make this measurement, I had to do things the painful way - acquire the spectrum by manually pushing buttons with the GPIB box disconnected, then re-connect the box and download the data using SRmeasure --getdata. I don't fully understand what is going on, especially since if the input connector is directly terminated using a 50ohm BNC terminator, there are no harmonics, regardless of whether the GPIB box is connected or not. But it is worth keeping this problem in mind for future low-noise measurements. My elog searches did not reveal past reports of similar problems, has anyone seen something like this before?

It also looks like my previous measurement of the de-whitening board noises was plagued by the same problem (I took all those spectra with the GPIB boxes connected). I will repeat this measurement.

### Next steps:

At the meeting this week, it was decided that

• All AD797s would be removed from de-whitening boards and also coil-driver boards (as they are unused).
• Thick film resistors with the most dominant noise contributions to be replaced with thin-film ones.
• Gain of 3 on de-whitening board to be changed to gain of 1.

I also think it would be a good idea to up the 100-ohm resistors in the bias path on the ITM coil driver boards to 1kohm wire-wound. Since the dominant noise on the coil-driver boards is from the voltage noise of the Op-Amps in the bias path, this would definitely be an improvement. Looking at the current values of the bias MEDM sliders, a 10x increase in the resistance for ITMX will not be possible (the yaw bias is ~-1.5V), but perhaps we can go for a 4x increase?

The plan is to then re-install the boards, and see if we can

1. Turn on the whitening successfully (I checked with an extender board that the switching of the whitening stages works - turning OFF the "simDW" filter in the coil driver filter banks enables the analog de-whitening).
2. Relize the promised improvement in MICH displacement noise with the existing whitening configuration.

We can then take a call on how much to up the series resistance in the DAC signal path.

Now that I have figured out the cause of the harmonics, I will also try and measure the combined electronics noise of de-whitening board + coil driver board and compare it to the model.

 Quote: The last piece (?) in this puzzle is the coil driver noise - this needs to be modeled and measured.

Attachment 1: coilDriverNoises.pdf
13017   Mon May 29 16:47:38 2017 gautamUpdateGeneralCoil driver boards reinstalled

### Yesterday, I reinstalled the de-whitening boards + coil driver boards into their respective Eurocrate slots, and reconnected the cabling. I then roughly re-aligned the ITMs using the green beams.

I've given Steve a list of the thin-film resistors we need to implement the changes discussed in the preceeding elogs - but I figured it would be good to see if we can realize the projected improvement in MICH displacement noise just by fixing the BS Oplev loop shape and turning the existing whitening on. Before re-installing them however, I did make a few changes:

• Removed the gain of x3 on all the signal paths on the De-Whitening boards, and made them gain x1. For the De-Whitened path, this was done by changing the feedback resistor in the final op-amp (OP27) from 7.5kohm to 2.49kOhm, while for the bypass path, the feedback resistor in the LT1125 stages were changed from 3.01kohm to 1kohm.
• To recap - this gain of x3 was originally implemented because the DACs were +/- 5V, while the coil driver electronics had supply voltage of +/- 15V. Now, our DACs are +/- 10V, and even though the supply voltage to the coil driver boards is +/- 15V, in reality, the op-amps saturate at around 12V, so we aren't really losing much in terms of range.
• I also modified the de-whitening path in the BS de-whitening board to mimic the configuration on the ITM de-whitening boards. Mainly, this involved replacing the final stage AD797 with an OP27, and also implementing the passive pole-zero network at the output of the de-whitened path. I couldn't find capacitors similar to those used on the ITM de-whitening boards, so I used WIMA capacitors.
• The SRM de-whitening path was not touched for now.
• On all the boards, I replaced any AD797s that were being used with OP27s, and simply removed AD797s that were in DAQ paths.
• I removed all the potentiometers on all the boards (FAST analog path on the coil driver boards, and some offset trim Pots on the BS and SRM de-whitening boards for the AD797s, which were also removed).
• For one signal path on the coil driver board (ITMX ch1), I replaced all of the resistors with thin-film ones and re-measured the noise. However, the excess noise in the measurement below ~40Hz (relative to the model) remained.

Photos of all the boards were taken prior to re-installation, and have been uploaded to the 40m Google Photos page - I will update schematics + photos on the DCC page once other planned changes are implemented.

I also measured the transfer functions on the de-whitened signal paths on all the boards before re-installing them. I then fit everything using LISO, and updated the filter banks in Foton to match these measurements - the original filters were copied over from FM9 and FM10 to FM7 and FM8. The new filters are appended with the suffix "_0517", and live in FM9 and FM10 of the coil output filter banks. The measured TFs (for ITMs and BS) are summarized in Attachment #1, while Attachment #2 contains the data and LISO file used to do the fits (path to the .bod files in the .fil file will have to be changed appropriately). I used 2 complex pole pairs at ~10 Hz, two complex zero pairs at ~100Hz, real poles at ~15Hz and ~3kHz, and real zeros at ~100Hz and ~550Hz for the fits. The fits line up well with the measured data, and are close enough to the "expected" values (as calculated from component values) to be explained by tolerances on the installed components - I omit the plots here.

After re-installing the boards in the Eurocrate, restoring rough alignment, and updating the filter banks with the most recent measured values, I wanted to see if I could turn the whitening on for one of the optics (ITMY) smoothly before trying to do so in the full DRMI - switching off the "SimDW_0517" filter (FM9) should switch the signal path on the de-whitening board from bypass to de-whitened, and I had confirmed last week with an extender board that the voltage at the appropriate backplane connector pin does change as expected when the FM9 MEDM button is toggled (for both ITMs, BS and SRM). But today I was not able to engage this transition smoothly, the optic seems to be getting kicked around when I engage the whitening. I will need to investigate this further.

Unrelated to this work: the ETMY Oplev HeNe is dead (see Attachment #3). I thought we had just replaced this laser a couple of months ago - what is the expected lifetime of these? Perhaps the power supply at the Y-end is wonky and somehow damaging the HeNe heads?

Attachment 1: deWhitening_consolidated.pdf
Attachment 2: deWhitening_measurements.zip
Attachment 3: ETMY_OL.png
13019   Tue May 30 16:02:59 2017 gautamUpdateGeneralCoil driver boards reinstalled

I think the reason I am unable to engage the de-whitening is that the OL loop is injecting a ton of control noise - see Attachment #1. With the OL loop off (i.e. just local damping loops engaged for the ITMs), the RMS control signal at 100Hz is ~6 orders of magnitude (!) lower than with the OL loop on. So turning on the whitening was just railing the DAC I guess (since the whitening has something like 60dB gain at 100Hz).

The Oplev loops for the ITMs use an "Ellip15" low-pass filter to do the roll-off (2nd order Elliptic low pass filter with 15dB stopband atten and 2dB ripple). I confirmed that if I disable the OL loops, I was able to turn on the whitening for ITMY smoothly.

Now that the ETMY OL HeNe has been replaced, I restored alignment of the IFO. Both arms lock fine (I was also able to engage the ITMY Coil Driver whitening smoothly with the arm locked). However, something funny is going on with ASS - running the dither seems to inject huge offsets into the ITMY pit and yaw such that it almost immediately breaks the lock. This probably has to do with some EPICS values not being reset correctly since the recent slow-machine restarts (for instance, the c1iscaux restart caused all the LSC RFPD whitening gains to be reset to random values, I had to burt-restore the POX11 and POY11 values before I could get the arms to lock), I will have to investigate further.

GV edit 2pm 31 May: After talking to Koji at the meeting, I realized I did not specify what channel the attached spectra are for - it is  C1:SUS-ITMY_ULCOIL_OUT.

 Quote: But today I was not able to engage this transition smoothly, the optic seems to be getting kicked around when I engage the whitening. I will need to investigate this further.  Unrelated to this work: the ETMY Oplev HeNe is dead (see Attachment #3). I thought we had just replaced this laser a couple of months ago - what is the expected lifetime of these? Perhaps the power supply at the Y-end is wonky and somehow damaging the HeNe heads?

Attachment 1: OL_noiseInjection.pdf
13026   Thu Jun 1 00:10:15 2017 gautamUpdateGeneralCoil driver boards reinstalled

[Koji, Gautam]

We tried to debug the mysterious sudden failure of ASS - here is a summary of what we did tonight. These are just notes for now, so I don't forget tomorrow.

What are the problems/symptoms?

• After re-installing the coil driver electronics, the ASS loops do not appear to converge - one or more loops seem to run away to the point we lose the lock.
• For the Y-arm dithers, the previously nominal ITM PIT and YAW oscillator amplitudes (of ~1000cts each) now appears far too large (the fuzz on the Y arm transmission increases by x3 as viewed on StripTool).
• The convergence problem exists for the X arm alignment servos too.

What are the (known) changes since the servos were last working?

• Gain of x3 on the de-whitening boards for ITMX, ITMY, BS and SRM have been replaced with gain x1. But I had measurements for all transfer functions (De-White board input to De-White Board outputs) before and after this change, so I compensated by adding a filter of gain ~x3 to all the coil filter banks for these optics (the exact value was the ratio of the DC gain of the transfer functions before/after).
• The ETMY Oplev has been replaced. I walked over to the endtable and there doesn't seem to be any obvious clipping of either the Oplev beam or the IR transmission.

Hypotheses plus checks (indented bullets) to test them:

1. The actuation on the ITMs are ~x10 times stronger now (for reasons unknown).
• I locked the Y-arm and drove a line in the channels C1:SUS-ETMY_LSC_EXC and C1:SUS-ITMY_LSC_EXC at ~100Hz and ~30Hz, (one optic at one frequency at a time), and looked at the response in the LSC control signal. The peaks at both frequencies for the ITMs and ETMs were within a factor of ~2. Seems reasonable.
• We further checked by driving lines in C1:SUS-ETMY_ASCPIT_EXC and C1:SUS-ITMY_ASCPIT_EXC (and also the corresponding YAW channels), and looked at peak heights at the drive frequencies in the OL control signal spectra - the peak heights matched up well in both the ITM and ETM spectra (the drive was in the same number of counts).

So it doesn't look like there is any strange actuation imbalance between the ITM and ETM as a result of the recent electronics work, which makes sense as the other control loops acting on the suspensions (local damping, Oplevs etc seem to work fine).
2. The way the dither servo is set up for the Y-arm, the tip-tilts are used to set the input axis to the cavity axis, while actuation to the ITM and ETM takes care of the spot centering. The problem lies with one of these subsystems.
• We tried disabling the ASS servo inputs to all the spot-centering loops - but even with just actuation on the TTs, the arm transmission isn't maximized.
• We tried the other combination - disable actuation path to TTs, leave those to ITM and ETM on - same result, but the divergence is much faster (lock lost within a couple of seconds, large offsets appear in the ETM_PIT_L / ETM_YAW_L error signals.
• Tried turning on loops one at a time - but still the arm transmission isn't maximized.
3. Something is funny with the IR transmon QPD / ETMY Oplev.
• I quickly measured Oplev PIT and YAW OLTFs, they seem normal with upper UGFs around 5Hz and phase margins of ~30 degrees.
• We had no success using either of the two available Transmon QPDs
• Looking at the QPD quadrants, the alignment isn't stellar but we get roughly the same number of counts on all quadrants, and the spot isn't drastically misaligned in either PIT or YAW.

For whatever reasons, it appears that dithering the cavity mirrors at frequencies with amplitudes that worked ~3 weeks ago is no longer giving us the correct error signals for dither alignment. We are out of ideas for tonight, TBC tomorrow...

13808   Thu May 3 00:42:38 2018 KevinUpdatePonderSqueezeCoil driver contribution to squeezing noise budget

In light of the discussion at today's meeting, Guantanamo and I looked at how the series resistance for the test mass coil drivers limits the amount of squeezing we could detect.

The parameters used for the following calculations are:

• 4.5 kΩ series resistance for the ETM's (this was 10 kΩ in the previous calculations, so these numbers are a bit worse); 15 kΩ for the ITM's
• 100 ppm transmissivity on the folding mirrors giving a PRC gain of 40
• PD quantum efficiency of 0.88

Since we need to operate very close to signal recycling, instead of the current signal extraction setup, we will need to change the macroscopic length of the SRC. This will change the mode matching requirements such that the current SRM does not have the correct radius of curvature. One solution is to use the spare PRM which has the correct radius of curvature but a transmissivity of 0.05 instead of 0.1. So using this spare PRM for the SRM and changing the length of the SRC to be the same as the PRC we can get

• 0.63 dBvac of squeezing at 205 Hz for 1 W incident on the back of PRM
• 1.12 dBvac of squeezing at 255 Hz for 5 W incident on the back of PRM

This lower transmissivity for the SRM also reduces the achievable squeezing from the current transmissivity of 0.1. For an SRM with a transmissivity of 0.15 (which is roughly the optimal) we can get

• 1 dBvac of squeezing at 205 Hz for 1 W incident on the back of PRM
• 1.7 dBvac of squeezing at 255 Hz for 5 W incident on the back of PRM

The minimum achievable squeezing moves up from around 205 Hz at 1 W to 255 Hz at 5 W because the extra power increases the radiation pressure at lower frequencies.

14024   Wed Jun 27 18:12:04 2018 gautamUpdateElectronicsCoil driver dewhitening

Summary:

I've been thinking about what we need to do to the de-whitening boards for the ITMs and ETMs, in order to have low noise actuators. Noting down what I have so far, so that people can comment / point out things I've overlooked.

Attachment #1: Block diagram schematic of the de-whitened signal path on D000183 as it currently exists. I've omitted the unity gain buffer stage at the output, though this is important for noise considerations.

Some considerations, in rough order of priority:

1. Why do we need de-whitening?
• Because we want the Johnson noise of the series resistor (4.5 kohm) in the coil driver path to dominate the current noise to the coils at ~200 Hz where we want to measure the squeezing.
2. What should the shape of this de-whitening filter be?
• The DAC noise was measured to be ~1 uV/rtHz at 200 Hz.
• The Johnson noise spectral density of 4.5 kohm at 300 K is ~9 nV/rtHz
• So we need ~60dB of attenuation at 200 Hz relative to DC. Currently, they have ~80dB of attenuation at 200 Hz.
• However, we also need to consider the control signal multiplied by the inverse of this shape in the digital domain (required for overall flat shape). This should not saturate the DAC range.
• Furthermore, we'd like for the shape to be such that we don't have a large transient when transitioning between high range and low noise modes. We should use the DARM control signal estimate to inform this choice.
3. What about the electronics noise of the de-whitening filter itself?
• This shows up at the input of the coil driver stage, and gets transmitted to the coil with unity gain.
• So we should aim for < 3nV/rtHz at 200 Hz, such that we are dominated by the Johnson noise of the 4.5 kohm series resistance [the excess will be 5%].
• This can be realized by using the passive network which is the final stage in the de-whitening (there is a unity gain output buffer stage implemented with LT1128, which we also have to account for).

I will experiment with a few different shapes and investigate noise and de-whitened digital signal levels based on these considerations. At the very least, I guess we should remove the x3 gain on the ETM boards, they have already been bypassed for the ITMs.

Attachment 1: DeWhiteningSketch.pdf
13728   Thu Apr 5 04:36:56 2018 KevinUpdateIOOCoil driver noise

[Gautam, Kevin]

We measured the MC coil driver noise at the output monitors of the coil driver board with an SR785 in order to further diagnose the excess IMC frequency noise.

Attachments 1 and 2 show the noise for the UL coils of MC3 and MC2 with various combinations of output filters engaged. When the 28 Hz elliptic filter is on, the analog dewhitening filter is off, and vice versa. The effect of the analog low pass filter is visible in MC3, but the effect of the digital low pass filter is swamped by the DAC noise.

We locked the arms and measured the ALS beatnote in each of these filter combinations, but which filters were on did not effect the excess IMC frequency noise. This suggests that the coil drivers are not responsible for the excess noise.

Attachment 2 shows the noise for all five coils on MC1, MC2, and MC3 as well as for ITMY, which is on a different DAC card from the MCs. All filters were on for these measurements.

Attachment 1: MC3.pdf
Attachment 2: MC2.pdf
Attachment 3: CoilDriver.pdf
13730   Thu Apr 5 12:13:18 2018 KojiUpdateIOOCoil driver noise

Why is MC2 LR so different from the others???

13738   Fri Apr 6 22:23:53 2018 KevinUpdateIOOCoil driver noise

 Quote: Why is MC2 LR so different from the others???

The previous measurements were made from the coil driver output monitors. To investigate why the MC2 LR coil has less noise than the other coils, I also measured the noise at the output to the coils.

The circuit diagram for the coil driver board is given in D010001 and a picture of the rack is on the 40m wiki here. The coil driver boards are in the upper left quadrant of the rack. The input to the board is the column of LEMOs which are the "Coil Test In" inputs on the schematic. The output monitors are the row of LEMOs to the right of the input LEMOs and are the "FP Coil Volt Mon" outputs on the schematic. The output to the coils "Coil Out" in the schematic are carried through a DB15 connector.

The attachment shows the voltage noise for the MC2 LR coil as well as the UL coil which is similar to all of the other coils measured in the previous measurement. While the LR coil is less noisy than the UL coil as measured at the output monitor, they have the same noise spectrum as measured at the output to the coils themselves. So there must be something wrong with the buffer circuit for the MC2 LR voltage monitor, but the output to the coils themselves is the same as for the other coils.

Attachment 1: MC2_coil_driver.pdf
16162   Wed May 26 02:00:44 2021 gautamUpdateElectronicsCoil driver noise

I was preparing a short write-up / test procedure for the custom HV coil driver, when I thought of something I can't resolve. I'm probably missing some really basic physics here - but why do we not account for the shot noise from DC current flowing through the series resistor? For a 4kohm resistor, the Johnson current noise is ~2pA/rtHz. This is the target we were trying to beat with our custom designed HV bias circuit. But if there is a 1 mA DC current flowing through this resistor, the shot noise of this current is $\sqrt{2eI_{\mathrm{DC}}} \approx$18pA/rtHz, which is ~9 times larger than the Johnson noise of the same resistor. One could question the applicability of this formula to calculate the shot noise of a DC current through a wire-wound resistor - e.g. maybe the electron transport is not really "ballistic", and so the assumption that the electrons transported through it are independent and non-interacting isn't valid. There are some modified formulae for the shot noise through a metal resistor, which evaluates to $\sqrt{2eI_{\mathrm{DC}}/3} \approx$10pA/rtHz for the same 4kohm resistor, which is still ~5x the Johnson noise.

In the case of the HV coil driver circuit, the passive filtering stage I added at the output to filter out the excess PA95 noise unwittingly helps us - the pole at ~0.7 Hz filters the shot noise (but not the Johnson noise) such that at ~10 Hz, the Johnson noise does indeed dominate the total contribution. So, for this circuit, I think we don't have to worry about some un-budgeted noise. However, I am concerned about the fast actuation path - we were all along assuming that this path would be dominated by the Johnson noise of the 4kohm series resistor. But if we need even 1mA of current to null some DC DARM drift, then we'd have the shot noise contribution become comparable, or even dominant?

I looked through the iLIGO literature, where single-stage suspensions were being used, e.g. Rana's manifesto, but I cannot find any mention of shot noise due to DC current, so probably there is a simple explanation why - but it eludes me, at least for the moment. The iLIGO coil drivers did not have a passive filter at the output of the coil driver circuit (at least, not till this work), and there isn't any feedback gain for the DARM loop at >100 Hz (where we hope to measure squeezing) to significantly squash this noise.

Attachment #1 shows schematic topologies of the iLIGO and proposed 40m configs. It may be that I have completely misunderstood the iLIGO config and what I've drawn there is wrong. Since we are mainly interested in the noise from the resistor, I've assumed everything upstream of the final op-amp is noiseless (equivalently, we assume we can sufficiently pre-filter these noises).
Attachment #2 shows the relative magnitudes of shot noise due to a DC current, and thermal noise of the series resistor, as a function of frequency, for a few representative currents, for the slow bias path assuming a 0.7Hz corner from the 4kohm/3uF RC filter at the output of the PA95.

Some lit review suggests that it's actually pretty hard to measure shot noise in a resistor - so I'm guessing that's what it is, the mean free path of electrons is short compared to the length of the resistor such that the assumption that electrons arrive independently and randomly isn't valid. So Ohm's law dictates $I=V/R$ and that's what sets the current noise. See, for example, pg 432 of Horowitz and Hill.

Attachment 1: coilDriverTopologies.pdf
Attachment 2: shotVthermal.pdf
13870   Sun May 20 23:43:50 2018 gautamUpdateIOOCoil driver noise re-measurement

Summary:

In the IMC actuation chain, it looks like the MC1/MC3 de-whitening boards, and also all three MC optics' coil driver boards, are showing higher noise than expected from LISO modeling. One possible candidate is thick film resistors on the coil driver boards. The plan is to debug these further by pulling the board out of the Eurocrate and investigating on the electronics bench.

Why bother? Mainly because I want to see how good the IR ALS noise is, and currently, the PSL frequency noise is causing the measurement to be worse than references taken from previous known good times.

Details:

Sometime ago, rana suggested to me that I should do this measurement more systematically.

• Attachments #1, #2 and #3 show noise measurements in various conditions for MC1, MC2 and MC3 respectively.
• In the above three attachments, I stitched together multiple spans from the SR785, and so the bin-width is different. The data is downloaded from the analyzer normalized by the bin-width (PSD units).
• The roll-off at ~800Hz in the orange trace for MC1 and MC3 is consistent with an 800 Hz LPF that was used for anti-image filtering from the old 2 kHz era.
• While it may look like the analog de-whitening isn't being switched on in some of these plots, I confirmed by transfer function measurement that it is indeed switching.
• Data used to make these plots are in Attachment #4. Unfortunately, the code requires some of my personal plotting libraries and so I'm not uploading it.
• Sketch of measurement setup is shown in Attachment #5. It is not indicated in the schematic, but the SR560 was operated in battery mode for this measurement.
• For MC1, I did the additional measurement of terminating the LEMO input to the coil driver and measuring (what should have been) just the coil driver electronics noise. But this measurement doesn't look very clean, and hence, the decision to pull the board out to continue debugging.
• While at 1X6, Rana tightened the LEMO connectors going to MC1. We should opportunistically do MC2 and MC3 as well.
• Some changes to be made:
• Thick film ---> thin film.
• Reroute HPF-ed back-plane Vmon output to the front panel LEMO.

I've now restored all the wiring at 1X6 to their state before this work.

Attachment 1: MC1_coilDriver.pdf
Attachment 2: MC2_coilDriver.pdf
Attachment 3: MC3_coilDriver.pdf
Attachment 4: MC_coilDriverNoises.tgz
Attachment 5: ActuationChainNoiseMeas.pdf
14019   Tue Jun 26 16:28:00 2018 gautamUpdateSUSCoil driver protoboard characterization

I wanted to investigate my coil driver noise measurement technique under more controlled circumstances, so I spent yesterday setting up various configurations on a breadboard in the control room. The overall topology was as sketched in Attachment #1 of the previous elog, except for #4 below. Summary of configurations tried (series resistance was 4.5k ohm in all cases):

1. Op 27 with 1kohm input and feedback resistors.
2. LT1128 with 1kohm input and feedback resistors.
3. LT1128 with 400 ohm input and feedback resistors.
4. LT1128 with 400 ohm input and feedback resistors, and also the current buffer IC LM6321 implemented.

Attachments:

Attachment #1: Picture of the breadboard setup.

Attachment #2: Noise measurements (input shorted to ground) with 1 Hz linewidth from DC to 4 kHz.

Attachment #3: Noise measurements for full SR785 span.

Attachment #4: Apparent coupling due to PSRR.

Attachment #5: Comparison of low frequency noise with and without the LM6321 part of the fast DAC path implemented.

All SR785 measurements were made with input range fixed at -42dBVpk, input AC coupled and "Floating", with a Hanning window.

Conclusions:

• I get much better agreement between LISO and measurement at a few hundred Hz and below with this proto setup. So it would seem like the excess noise I measure at ~200 Hz in the Eurocrate card version of the coil driver could be real and not simply a measurement artefact.
• I am puzzled about the 10 Hz comb in all these measurements:
• I have seen this a few times before - e.g. elog13655.
• It is not due to the infamous GPIB issue - the lines persist even though I disconnect both power adaptor and GPIB prologix box from the SR785.
• It does not seem to be correlated with the position of the analyzer w.r.t. the DC power supply (Tektronix PS280) used to power the circuit (I moved the SR785 around 1m away from the supply).
• It persists with either of the two LN preamp boxes available.
• It persists with either "Float" or "Ground" input setting on the SR785.
• All this pointed to some other form of coupling - perhaps conductive EMI.
• The only clue I have is the apparent difference between the level of the coupling for Op27 and LT1128 - it is significantly lower for the latter compared to the former.
• I ruled out position on the breadboard: simply interchanging the Op27 and LT1128 positions on the breadboard, I saw higher 10 Hz harmonics for the Op27 compared to the LT1128. In fact, the coupling was higher for the DIP Op27 compared to an SOIC one I attached to the breadboard via an SOIC to DIP adapter (both were Op27-Gs, with spec'ed PSRR of 120 dB typ).
• To test the hypothesis, I compared the noise for the Op27 config, on the one hand with regulated (via D1000217) DC supply, and on the other, directly powered by the Tektronix supply. The latter configuration shows much higher coupling.
• I did have 0.1uF decoupling capacitors (I guess I should've used ceramic and not tantala) near the OpAmp power pins, and in fact, removing them had no effect on the level of this coupling
• As a quick check, I measured the spectrum of the DC power used to run the breadboard - it is supplied via D1000217. I used an RC network to block out the DC, but the measurement doesn't suggest a level of noise in the supply that could explain these peaks.
• The regulators are LM2941 and LM2991. They specify something like 0.03% of the output voltage as AC RMS, though I am not sure over what range of frequencies this is integrated over.
• But perhaps the effect is more subtle, some kind of downconversion of higher frequency noise, but isn't the decoupling cap supposed to protect against this?
• The 19.5 kHz harmonics seem to originate from the CRT display of the SR785 (SVGA).
• The manual doesn't specify the refresh rate, but from a bit of googling, it seems like this is a plausible number.
• The coupling seems to be radiative. The box housing the Busby preamp provides ~60dB attentuation of this signal, and the amplitude of the peaks is directly correlated to where I position the Busby box relative to the CRT screen.
• This problem can be avoided by placing the DUT and preamp sufficiently far from the SR785.

Punchlines:

1. The actual coildriver used, D010001, doesn't have a regulated power supply, it just draws the +/- 15V directly from Sorensens. I don't think this is good for low noise.
2. The LM6321 part of the circuit doesn't add any excess noise to the circuit, consistent with it being inside the unity gain feedback loop. In any case, with 4.5 kohm series resistance with the coil driver, we would be driving <2.5 mA of current, so perhaps we don't even need this?
Attachment 1: IMG_7060.JPG
Attachment 2: ETMXstitchced.pdf
Attachment 3: ETMXfullSpan.pdf
Attachment 4: PSRR.pdf
16512   Thu Dec 16 12:21:16 2021 AnchalUpdateBHDCoil driver test failed for S2100619-v1

Today I found one of the coil driver boards, S2100619 failed the test on CH2. There appears to be an extra phase lag after 10 kHz and some resonant-like feature at 7 kHz. This of course is very high-frequency stuff and maybe we don't care about these deviations. But it could mean something is off with the channel and could potentially lead to failure in the relevant frequency band in the future. I'll need help to debug this. Please see the attachment for details of test failure.

Attachment 1: D1100687_S2100619-v1_TF_CH2_Not_Matching.pdf
16516   Thu Dec 16 17:41:12 2021 KojiUpdateBHDCoil driver test failed for S2100619-v1

Good catch. It turned out that the both + and - side of the output stages for CH2 were oscillating at ~600kHz. If I use a capacitance sticks to touch arbitrarily around the components, it stops their oscillation and they stay calm.
It means that the phase margin becomes small while the circuit starts up.

I decided to increase the capacitances C6 and C20 (WIMA 150pF) to 330pF (WIMA FPK2 100V) and the oscillation was tamed. 220pF didn't stop them. After visually checked the signal behavior with an oscilloscope, the unit was passed to Anchal for the TF test.

The modification was also recorded in the DCC S2100619

Attachment 1: PXL_20211217_001735762.jpg
Attachment 2: PXL_20211217_001719345.jpg
Attachment 3: PXL_20211217_005344828.jpg
Attachment 4: PXL_20211217_010131027.PORTRAIT.jpg
Attachment 5: PXL_20211217_011423823.jpg
Attachment 6: HAMA_Driver_V4.pdf
15480   Tue Jul 14 16:52:47 2020 gautamUpdateElectronicsCoil drivers for the test masses

Summary:

Koji and I had a discussion last Friday about the suspension electronics. I think there are still a few open questions - see Attachment #1. We should probably make a decision on these soon.

1. High-voltage coil driver circuit - D1900163
• This board is ready to be fabricated and tested on the bench.
• The way the connectors J2 and J3 are designed currently is meant to interface with the existing coil driver electronics.
• Depending on the eventual coil driver we choose for the fast path, it may be benificial to change the signals on the connectors J2 and J3, to avoid the need for a custom interface board.
2. HAM-A coil driver noise analysis.
• The linked attachment evaluates the noise for the design value of the fast path series resistor, which is 1.2 kohms.
• Iff we still have ambitions of measuring ponderomotive squeezing, we will need the resistance to be much higher, ~10 kohms (in the linked noise budget, only the Johnson noise of the series resistor is considered, but in reality, the OpAmp voltage and current noises also matter).
• This corresponds to a maximum current of 10V/10kohms = 100uA
• Looking at signals to the ETMs from the current lock acquisition sequence, the RMS current to a single coil is approximately _____ (to be filled in later).
• So we may need a version of the fast coil driver that supports a low noise mode (with large series resistance) and a high-range mode (with lower series resistance for lock acquisition).
3. You can follow the links to DCC entries for other parts from Attachment #1.
Attachment 1: coilDriverSchem.pdf
15494   Mon Jul 20 17:23:46 2020 gautamUpdateElectronicsCoil drivers for the test masses

Summary:

Looking at the signals to the test mass coils, it seems borderline to me that we will be able to acquire lock and run in a low noise configuration with the same series resistor in the coil driver circuit. The way I see it, options are:

1. Use a moderately high series resistance (e.g. 5 kohms) for the time being, and go ahead with the HAM-A coil driver.
• This will mean a current noise of ~3pA/rtHz, which translates to ~3e-18 m/rtHz @ 100 Hz in DARM displacement noise (assuming the ITMs have much higher series resistance than the ETMs).
• If the lock acquisiton looks smooth, double the resistance to 10 kohms.
• With 5 kohm series resistance, there is negligible possibility of measuring ponderomotive squeezing for any of the input powers we consider feasible, but this is under the assumption that we will expose coil driver noise, which is very optimistic imho.
2. Re-design a new coil driver that allows switchable impedance, so we can have a higher noise acquisition mode for acquiring and holding the ALS lock, then transition to a lower noise, lower range config once the RF / BHD lock has been acquired.
• On paper, this solves all the problems, but the design of such a circuit is probably pretty non-trivial and time consuming.

Details:

I only looked at the ETMs for this study. The assumption is that we will have no length actuation on the ITMs, only local damping and Oplev loops (and maybe some ASC actuation?), which can be sufficiently low-pass filtered such that even with coil de-whitening, we won't have any range issues.

Attachment #1 shows the time-domain traces of the coil driver signals as we transition from POX/POY lock to the ALS lock. There are some transients, but I think we will be able to hold the lock even with a 5 kohm resistor (~twice what is on ETMX right now). From just these numbers, it would seem we can even go up to 10 kohms right away and still be able to acquire lock, especially if we re-design the digital feedback loop to have better low-pass filtering of the high-frequency ALS noise, see the next attachment.

Attachment #2 shows the f-domain picture, once the arm lengths are fully under ALS control (~25 seconds onwards in Attachment #1). The RMS is dominated by high frequency ALS length loop noise, which we can possibly improve with better design of the digital control loop.

Finally, Attachment #3 shows the situation once DARM control has been transitioned over to AS55_Q. Note that the vertex DoFs are still under 3f control, so there is the possibility that we can make this even lower noise. However, one thing that is not factored in here is that we will have to de-whiten these signals to low-pass filter the DAC noise (unless there is some demonstrated clever technique with noise-mons or something to subtract the DAC noise digitally). Nevertheless, it seems like we can run safely with 5 kohms on each ETM coil and still only use ~2000 cts RMS, which is ~1/10th the DAC range (to allow for dealing with spurious transients etc).

 Quote: Looking at signals to the ETMs from the current lock acquisition sequence, the RMS current to a single coil is approximately _____ (to be filled in later).
Attachment 1: ALSlock_timeDomain.pdf
Attachment 2: ALSlock.pdf
Attachment 3: RFlock.pdf
13082   Tue Jun 27 16:11:28 2017 gautamUpdateElectronicsCoil whitening

### I got back to trying to engage the coil driver whitening today, the idea being to try and lock the DRMI in a lower noise configuration - from the last time we had the DRMI locked, it was determined that A2L coupling from the OL loops and coil driver noise were dominant from ~10-200Hz. All of this work was done on the Y-arm, while the X-arm CDS situation is being resolved.

To re-cap, every time I tried to do this in the last month or so, the optic would get kicked around. I suspected that the main cause was the insufficient low-pass filtering on the Oplev loops, which was causing the DAC rms to rail when the whitening was turned on.

I had tried some loop-tweaking by hand of the OL loops without much success last week - today I had a little more success. The existing OL loops are comprised of the following:

• Differentiator at low frequencies (zero at DC, 2 poles at 300Hz)
• Resonant gain peaked around 0.6 Hz with a Q of ______ (to be filled in)
• BR notches
• A 2nd order elliptic low pass with 2dB passband ripple and 20dB stopband attenutation

THe elliptic low pass was too shallow. For a first pass at loop shaping today, I checked if the resonant gain filter had any effect on the transmitted power RMS profile - turns out it had negligible effect. So I disabled this filter, replaced the elliptic low pass with a 5th order ELP with 2dB passband ripple and 80dB stopband attenuation. I also adjusted the overall loop gain to have an upper UGF for the OL loops around 2Hz. Looking at the spectrum of one coil output in this configuration (ITMY UL), I determined that the DAC rms was no longer in danger of railing.

However, I was still unable to smoothly engage the de-whitening. The optic again kept getting kicked around each time I tried. So I tried engaging the de-whitening on the ITM with just the local damping loop on, but with the arm locked. This transition was successful, but not smooth. Looking at the transmon spot on the camera, every time I engage the whitening, the spot gets a sizeable kick (I will post a video shortly).  In my ~10 trials this afternoon, the arm is able to stay locked when turning the whitening on, but always loses lock when turning the whitening off.

The issue here is certainly not the DAC rms railing. I had a brief discussion with Gabriele just now about this, and he suggested checking for some electronic voltage offset between the two paths (de-whitening engaged and bypassed). I also wonder if this has something to do with some latency between the actual analog switching of paths (done by a slow machine) and the fast computation by the real time model? To be investigated.

GV 170628 11pm: I guess this isn't a viable explanation as the de-whitening switching is handled by the one of the BIO cards which is also handled by the fast FEs, so there isn't any question of latency.

With the Oplev loops disengaged, the initial kick given to the optic when engaging the whitening settles down in about a second. Once the ITM was stable again, I was able to turn on both Oplev loops without any problems. I did not investigate the new Oplev loop shape in detail, but compared to the original loop shape, there wasn't a significant difference in the TRY spectrum in this configuration (plot to follow). This remains to be done in a systematic manner.

Plots to support all of this to follow later in the evening.

Attachment #1: Video of ETMY transmission CCD while engaging whitening. I confirmed that this "glitch" happens while engaging the whitening on the UL channel. This is reminiscent of the Satellite Box glitches seen recently. In that case, the problem was resolved by replacing the high-current buffer in the offending channel. Perhaps something similar is the problem here?

Attachment #2: Summary of the ITMY UL coil output spectra under various conditions.

Attachment 1: ETMYT_1182669422.mp4
Attachment 2: ITMY_whitening_studies.pdf
4900   Tue Jun 28 15:23:21 2011 steveUpdateElectronicsCoilcraft RF-design kits are restocked

Our design kits are full again. They are waiting for a new brilliant PD design.

Attachment 1: P1070917.JPG
Attachment 2: P1070915.JPG
13862   Fri May 18 09:13:41 2018 PoojaUpdateSUSColored GigE image

To obtain a colored version with good contrast of the grayscale image of scattering of light by dust particles on the surface of test mass, got using GigE camera. The original and colored images are attached here.

Attachment 1: Image__2017-11-14__08-25-13_100k100g1V_colored.png
Attachment 2: Image__2017-11-14__08-25-13_100k100g1V.tiff
5676   Mon Oct 17 10:43:14 2011 MirkoUpdateCDSCommited changes to c1rfm

I want to make changes to c1rfm. Found uncommited changes to it from Sept 27. Since we recompiled it since then it should be safe to commit them, so I did. See svn log for details.

12145   Wed Jun 1 16:28:28 2016 ericqUpdateElectronicsCommon board Op amp input offsets

I used a Eurocard extension board to peek at the inputs and outputs of each of the gain-ladder AD829s on input B of the CM board in the +31dB configuration with the input terminated. (i.e with the following stages active in this order: +16dB, +8dB, +4dB, +2dB, +1dB).

The voltages I observed imply that the +8dB stage has an input voltage offset of -2mV, whereas all the other positive gain stages show around +-0.5mV. This could explain the shift observed at the +15->+16 transition. (However, since both input channels show a jump here, maybe its something more systemic about the board...)

In any case, it should be simple enough to swap out a new AD829 in place of U9B and see if it improves things, before getting too deep into the muck. (In principle, the AD829 has offset nulling pins, but I'm not sure how to do it in a non-hacky way since the board doesn't have any pads for it.)

12147   Fri Jun 3 12:53:44 2016 ericqUpdateElectronicsCommon board Op amp input offsets

I replaced some of the AD829s with other AD829s, but the offset situation didn't improve.

However, I figured that we don't really need the ~100MHZ bandwidth of the AD829, since the IMC loop limits us to a ~10kHz CARM bandwidth. Also, since we don't routinely use IN2 for anything, I felt free to try something else.

Specifically, I replaced all of the positive gain AD829s in the input 2 gain ladder with OP27s (U8B->U12B on D1500308), which should have input offset voltages ~30x lower than the AD829s.

Here is a comparison of the outputs these configurations perform, normalized to the output at the +0dB gain setting - where all of the op amps in the gain ladder are bypassed.

So, most of the transitions now result in an output offset change of less than 0.5mV, which is nice.

The exception seems to be where the +8dB stage is switched in or out. I may try replacing this one, as these transitions cause a lock loss now when trying to lock the arm with high bandwidth using POY.

8922   Thu Jul 25 12:53:45 2013 CharlesUpdateISSComparator + Triggering Prototype

I realized I totally forgot to post this last week, but I prototyped the comparator and boost triggering portion of the ISS, at least in part. Below is a schematic that shows the prototype circuit I made. Note that it includes ports for the oscilloscope channels that appear in the second image included. Essentially, I was able to verify that the output from the LT1016, as it's currently constructed in the ISS schematic, would be sufficient logic to switch the MAX333a.

Below, we can first see that the comparator is switching its output as desired. When the DC level of the input drops below a certain threshold (~1.6 V) the output of the comparator switches on to ~4 V. When the DC level of the input goes back up above the upper threshold (~3.2 V), the comparator switches off to ~0.3 V. The exact values of the threshold voltages can be determined/tuned at a later date, but this is the basic behavior that the comparator circuit will have.

To detect whether or not the MAX333a was switching properly, I connected the common terminal of one of the switches to a +5 V supply, and looked at the voltage coming off both the 'open' and 'closed' terminals of said SPDT switch. We can see that with Logic 0 (comparator output ~0.3 V) Channel 4 exhibits a ~5 V signal, just as we would expect from the above schematic. With Logic 1 (comparator output ~4 V), Channel 3 exhibits the characteristic 5 V signal.

1172   Wed Dec 3 20:10:09 2008 Jenne, RanaUpdatePEMComparing Wiener subtraction with different seismometers
Attached is a plot of MC_L, and then the residual MC_L after static Wiener filtering, using different combinations of our accelerometers and seismometers.

This is the same type of plot that Rana has included in the past few weeks, using Wiener filters calculated with c1wino.m

This data is from GPS 912312914, duration = 7200 sec, sometime during the night last night.

Unfortunately, it doesn't look like adding the Guralp seismometer to the Accelerometers and the Ranger did much, especially at low frequencies (all sensors = black curve). We'll have to investigate why this is true, and what we can do to get some low-frequency subtraction going on.

In the legend, "Residuals Accels, Guralp, Ranger" implies that the residual has been calculated using all of the sensors listed.
Attachment 1: Dec032008_c1wino_seisCombos.png
1173   Wed Dec 3 20:36:07 2008 Jenne, RanaUpdatePEMComparing Wiener subtraction with different seismometers
The Ranger has now been moved over to sit underneath the MC2 tank (it was previously close to the PSL rack). It
is still pointed in the +Y direction (towards ETMY, aka south).

New spectra attached - looks like the coherence is still there between the Guralp and the Ranger which are now
seperated by the MC length (~12 m). At LLO, I have witnessed a coherence of less than 0.3 above 1 Hz for these
distances. Curious.

L960019-00-F describes measurements done at SLAC on seismic coherence. The iLIGO LSC PDD
(http://www.ligo.caltech.edu/docs/T/T970122-00.pdf) discusses in sec 4.2 how this was incorporated into the LSC design.

When we get our next Guralp, it will be interesting to move them around and determine what the cross-spectrum
is between different points in the lab during typical times.

In the second attachment, I have plotted the square of the quantity used in the LSC PDD (S_xy) which I think is
what we now plot in DTT as 'Coherence'.

The third attachment shows the coherences among the TM SUSPOS_INs. I've turned off the oplev servos for this but
the OSEM damping is still on. Its not quite the same as the theory, but we could probably measure/tweak the
seismic velocity and then get better agreement.
Attachment 1: d.pdf
Attachment 2: sco.png
Attachment 3: fly.pdf
379   Fri Mar 14 14:59:51 2008 josephbConfigurationCamerasComparison between GC650 (CCD) and GC750 (CMOS) looking at ETMX
Attached are images taken of ETMX while locked.

The first two are 300,000 microsecond exposure time, with approximately the same focusing/zoom. (The 750 is slightly more zoomed in than the 650 in these images). The second are 30,000 microsecond exposures. The la

The CMOS appears to be more sensitive to the 1064 nm reflected light (resulting in bright images for the same exposure time). This may make a difference in applications where images are desired to be taken quickly and repeatedly.

Both seem to be resolving individual specks on the optic reasonably well.

Next test is to place both camera on a Gaussian beam (in a couple different modes say 00, 11, and so forth), probably using the PMC.
Attachment 1: ETMX_z2_exp_300000_650.tiff
Attachment 2: ETMX_z2_exp_300000_750.tiff
Attachment 3: ETMX_z2_exp_30000_650.tiff
Attachment 4: ETMX_z2_exp_30000_750.tiff
4632   Thu May 5 04:38:20 2011 KojiSummaryLSCComparison between S3399 and FFD-100

Comparison between Hamamatsu S3399 and Perkin Elmer FFD-100

These are the candidates for the BB PD for the green beat detection as well as aLIGO BB PD for 532nm/1064nm.

FFD-100 seems the good candidate.

Basic difference between S3399 and FFD-100

- S3399 Si PIN diode: 3mm dia., max bias = 30V, Cd=20pF

- FFD-100 Si PIN diode: 2.5mm dia., max bias = 100V, Cd=7pF

The circuit at the page 1 was used for the amplifier.

- FFD-100 showed 5dB (= x1.8) larger responsivity for 1064nm compared with S3399. (Plot not shown. Confirmed on the analyzer.)

- -3dB BW: S3399 180MHz, FFD-100 250MHz for 100V_bias. For 30V bias, they are similar.

Attachment 1: PD_response.pdf
1999   Thu Sep 24 20:17:05 2009 ranaSummaryLSCComparison of Material Properties for the new RFPD Mounts
 Steel Brass Aluminum Delrin Density (kg/m^3) 7850 8500 2700 1420 CTE (ppm/C) 12 19 23 100 Young's Modulus (GPa) 200 110 69 2 Hardness Color grey gold light silver any

ELOG V3.1.3-