[Anchal, Yuta]

We think we have narrowed down the source of 60 Hz noise to one fo the following possibilities:

• Ground loop present along the MC1 suspension damping loop
• 60 Hz DAC noise on inputs of MC1 coil driver
• 60 Hz noise injected at dewhitening board before the dewhitening filter

The second and third cases are unlikely because we see 60 Hz noise present only in MC1 coils, not MC3 coils while they both share the same connection from DAC to SOS dewhitening filter boards as they share the SOS dewhitening board D000316-A. So it is unlikely that only the MC1 channels have this noise while the MC3 channels do not.

This inference was made from following observations:

Note: Turning ON analog dewhitenign on MC1 coil is done by turning off FM9 switch which is the simulated digital dewhitening filter. Also note that theanalog dewhitening filter has an attenuation of 30 dB at 60 Hz.

MC1 has an unconvetional setup where the satellite amplifier is from the new generation while the coil driver and dewhitening boards are from the old generation. The new generation satellite amplifiers sen PD signal through differential ended signals but the old generation PD whitening interface expects single ended inputs, so we ahve been using PD monitor outputs from the satellite amplifier which connects the ground of the two boards to each other. Maybe this is the reason for the ground loop.

[JC, Yuta]

We have found that MC1 coils are causing 60 Hz noise.
Tripping watchdogs for MC1 coils reduced 60 Hz noise seen in YARM by a factor of 100.

Method:
 - Locked YARM with POY11 and measured YARM sensitivity to use it for 60 Hz frequency noise monitor0.187493**0.5
 - Tripped MC1, MC2, MC3 coil output watchdogs to see if they are causing this 60 Hz frequency noise. IMC WFS were turned off.

Result:
 - Attachment #1 is YARM sensitivity and MC_F in Hz with MC1,2,3 untripped (dotted) and MC1 tripped (solid).

YARM (PSL locked vs Yarm), MC1,2,3 untripped: 6.0e2 Hz/rtHz (2.6e2 Hz RMS)
MC_F (sum of noises in IMC loop), MC1,2,3 untripped: 4.8e4 Hz/rtHz (2.1e4 Hz RMS)
YARM (PSL locked vs Yarm), MC1 tripped: 6.6e0 Hz/rtHz (2.9e0 Hz RMS) -- reduced by a factor of 100
MC_F (sum of noises in IMC loop), MC1 tripped: 4.7e4 Hz/rtHz (2.0e4 Hz RMS)

 - We have also tried tripping MC2 and MC3 coils, but they didn't make much difference.
 - Untripping only one of MC1 face coils created 60 Hz frequency noise, so all the face coils seem to have the same level of 60 Hz noise.

Next:
 - Inspect around MC1 coil driver

[Anchal, Yuta]

Measurements yesterday (40m/17458) suggested that 60 Hz noise is injected after MC_F is picked-off.
So, we terminated PSL PZT input at several points to see where 60 Hz noise is injected.
It seems like the 60 Hz frequncy noise we see in MC_F is from TTFSS box, but the 60 Hz noise we see in YARM is not limited by this.

The 60 Hz noise we see in YARM is probably limited by IMC length noise.

Method:
 - We terminated PZT input to the PSL laser at various points one by one and monitored 60 Hz frequency noise using BEATX. PSL shutter was closed and IMC was not locked.

Result:
 - Below is the result at 60 Hz (RMS is calculated using a bandwidth of 0.187493 Hz)

Reference from 40m/17458, YARM (PSL locked vs Yarm): 6.5e2 Hz/rtHz (2.8e2 Hz RMS)
Reference from 40m/17458, MC_F (sum of noises in IMC loop): 4.9e4 Hz/rtHz (2.2e4 Hz RMS)
MC_F when PSL shutter is closed but MC servo board configuration at IMC locked state: 2.7e2 Hz/rtHz (1.2e2 Hz RMS) -- this gives IMC loop gain enhanced sensing noise

BEATX free (PSL free vs Xend free): 3.5e3 Hz/rtHz (1.5e3 Hz RMS) -- consistent with previous measurements
With PZT input to NPRO terminated (Attachment #1): 8.1e2 Hz/rtHz (3.5e2 Hz RMS)
Connected a terminated small box (we see in Attachment #1) before NPRO PZT: 6.3e2 Hz/rtHz (2.7e2 Hz RMS)
Connected input terminated Thorlabs PZT driver (MDT694): 5.9e2 Hz/rtHz (2.6e2 Hz RMS)
Connected input terminated summing amp (Attachment#2): 4.4e2 Hz/rtHz (1.9e2 Hz RMS)
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=-10dB, C1:PSL-FSS_FASTGAIN=-10dB): 3.9e3 Hz/rtHz (1.7e3 Hz RMS) -- consistent with "BEATX free (PSL free vs Xend free)" measurement
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=-10dB, C1:PSL-FSS_FASTGAIN=+10dB): 7.6e3 Hz/rtHz (3.3e3 Hz RMS)
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=+4dB, C1:PSL-FSS_FASTGAIN=+19dB): 2.9e4 Hz/rtHz (1.3e4 Hz RMS) -- Nominal gains when IMC is locked; consistent with "MC_F" measurement 40m/17458
Connected input terminated TTFSS (C1:PSL-FSS_MGAIN=+19dB, C1:PSL-FSS_FASTGAIN=+4dB): 1.1e4 Hz/rtHz (4.8e3 Hz RMS)

Discussion:
 - Connecting TTFSS increased 60 Hz frequency noise, which suggests that TTFSS is creating this 60 Hz frequency noise.
 - Setting TTFSS gains to nominal gains to IMC locked, 60 Hz frequency noise matched with frequency noise measurement using MC_F. This quantitatively supports that TTFSS is creating this 60 Hz frequency noise.
 - Increasing C1:PSL-FSS_MGAIN and reducing C1:PSL-FSS_FASTGAIN reduced 60 Hz frequency nosie. This means that some portion of 60 Hz noise is from between these two gains.
 - Note that having 60 Hz noise in TTFSS does not necessarily mean that our YARM noise is limited by this, because IMC loop suppresses the TTFSS noise. Assuming all 1.3e4 Hz RMS is all from TTFSS noise, it is suppressed to less than 1.3e4 Hz RMS/2e5 = 6.5e-2 Hz RMS (where 2e5 is IMC loop gain without super boosts, but it is actually higher with them) as frequency noise we see in YARM. YARM noise is measured to be 6.5e2 Hz/rtHz (2.8e2 Hz RMS), so it is not limited by TTFSS noise.
 - Also dark noise measured at MC_F (1.2e2 Hz RMS) tells you that the dark noise is not limiting the frequency noise we see in YARM.

Touching various parts around TTFSS:
 - We moved on to touch various parts around TTFSS to see if 60 Hz noise reduces in MC_F. We removed unused cables around TTFSS interface, touched power cables into TTFSS (both at TTFSS interface in the rack and TTFSS box on PSL table), BNC cables into TTFSS, disconnected slow controls, tried to avoid grounding of cables going into EOM (there is a small box that sums FSS feedback signal and 33.5 MHz; Attachment #3), but 60 Hz noise we see in MC_F didn't change significantly.

Next:
 - Check grounding situation around TTFSS box.
 - Check IMC length noise and error point noise by monitoring BEATX.
 - Check coil drivers for MC1, MC2, MC3 by disconnecting drivers while IMC is locked.
 - Try feeding back IMC servo also to MC2 with 60 Hz resonant gain to cancel 60 Hz noise


Note added at 23:50 to clarify:
nIMC : IMC length noise in frequency
nPSL: PSL free run noise in frequency
ne: sensing noise in frequency
nf: feedback noise in frequency
G: IMC loop gain (estimated to be 2e5 at 60 Hz without boosts)

MC_F = G/(1+G) * (nIMC + nPSL + ne + nf) + [noises in MC_F DAQ]
 = 2.2e4 Hz RMS
 MC_F when dark, MC servo nominal gain = G * ne
 = 1.2e2 Hz RMS
PSL frequency noise after IMC lock = G/(1+G) * (nIMC + ne) + 1/(1+G) * (nPSL + nf)
YARM = [PSL frequency noise after IMC lock] + [noises from YARM loop]
 = 2.8e2 Hz RMS
BEATX when PSL is free run, TTFSS low gain connected = nPSL + [noises from Xend AUX and BEATX sensing]
 = 1.7e3 Hz RMS
BEATX when PSL is free run, TTFSS nominal gain connected = nPSL + nf + [noises from Xend AUX and BEATX sensing]
 = 2.9e4 Hz RMS
BEATX when IMC is locked = [PSL frequency noise after IMC lock] + [noises from Xend AUX and BEATX sensing]
 = 3.8e2 Hz RMS
 
So, our estimate is
ne ~ 1.2e2/G Hz RMS (small)
nPSL ~ 1.7e3 Hz RMS
nf ~ 2e4 Hz RMS (this dominates MC_F, but already suppressed enough in [PSL frequency noise after IMC lock])
[PSL frequency after IMC lock] ~ 3e2 Hz RMS (this dominates YARM and BEATX when IMC is locked)
nIMC ~ 3e2 Hz RMS (this dominates [PSL frequency noise after IMC lock])

Today I updated the ETMY suspension model to include 4 new filters at the output of the position, pitch, yaw and side summers and before the "To Coil Matrix". The library that was changed and updated is "sus_single_control_new". These callibration filters are labeled in the orange box as POSCAL, PITCAL, YAWCAL, and SIDECAL. The four filters are important as the will allow us to callibrate the position and side from counts to micro meters, and pitch and yaw from counts to micro radians.

The next steps for utilizing this update will be

    - create a few experiments to find the callibration constants for the 4 degrees of freedom

    - edit and update the ETMY Suspension screen to include selectable filter boxes to implement the callibration constants

For future reference, preform the update and restore the models to their previous states you may use the following:

to install the models we ssh into the computers running the ETMY suspension models (for example)

     ssh c1sus

then for each model using the suspension library (we used c1sus c1mcs c1scx c1scy c1su2 c1su3) do

     rtcds build-install c1sus

the watchdogs will need to be shut down for c1sus and the model will need to be restarted next

     rtcds restart c1sus

Now we restore the filter values to the last saved point (about an hour before the update) in cds folder

     python burtRestoreRTSepics.py -m c1sus c1mcs c1scx c1scy c1su2 c1su3 -o 10

Last we reset the watchdogs again using the following script in SUS>medm

     python resetFromWatchdogTrip.py MC1 MC2 MC3 BS PRM SRM ITMX ITMY ETMX ETMY
 

[Anchal, Yuta]

Yesterday, we have measured the frequency noise of PSL with IMC locked/unlocked using ALS BEATX/Y to narrow down where the 60 Hz is coming from.
All the measurements so far is consistent with a hypothesis that 60 Hz noise injected after MC_F is picked-off (it could be from MC_F DAQ readout or something in the IMC loop).

Method:
 - Measured YARM noise spectra when YARM is locked with POY11 to measure the frequency noise with respect to YARM, and compared with MC_F
 - Measured ALS BEATX and BEATY spectra when PSL is free running and when IMC is locked. Here, when "PSL is free running" is done with PSL shutter closed, but all the cables remained the same and FSS loop was in "down" state. Shutters at both ends were closed, and PZT inputs to AUX lasers were terminated to avoid noise injection from PDH locking with dark noise (this was necessary to reduce noise in BEATY).

Result:
 - Attachment #1 is YARM noise calibrated into Hz, and Attachment #2 is BEATX and BEATY spectra with PSL free running (solid lines) and IMC locked (dotted lines). Below are summary of noise level at 60 Hz (RMS is calculated using a bandwidth of 0.187493 Hz)

YARM (PSL locked vs Yarm): 6.5e2 Hz/rtHz (2.8e2 Hz RMS)
MC_F (sum of noises in IMC loop): 4.9e4 Hz/rtHz (2.2e4 Hz RMS)
BEATX free (PSL free vs Xend free): 3.3e3 Hz/rtHz (1.4e3 Hz RMS)
BEATX locked (PSL locked vs Xend free): 8.8e2 Hz/rtHz (3.8e2 Hz RMS)
BEATY free (PSL free vs Yend free): 1.6e4 Hz/rtHz (6.9e3 Hz RMS)
BEATY locked (PSL locked vs Yend free): 1.5e4 Hz/rtHz (6.5e3 Hz RMS)

Discussion:
 - "BEATX locked" measurement suggests that PSL locked to IMC (and Xend free) has noise less than 3.8e2 Hz RMS. This is roughly consistent with YARM measurement of frequency noise, and suggests that Yarm is stable enough to measure the PSL locked frequency noise.
 - "BEATX free" measurement suggests that PSL free run (with cables connected) has noise of 1.4e3 Hz RMS (note that Xend free is less than 3.8e2 Hz RMS).
 - MC_F measurement is the sum of noises in IMC loop, including IMC length noise + noise injected at error point (3.8e2 Hz RMS), PSL free run noise (1.4e3 Hz RMS), noise injected at feedback. Therefore, this suggests that 2.2e4 Hz RMS we see in MC_F is from noise injected after MC_F pickoff point (or in the MC_F DAQ readout).
 - BEATY having large 60 Hz noise probably comes from noise in the beat measurement.

Next:
 - Use BEATX to monitor 60 Hz noise.
 - Try terminating PZT input to see if 60 Hz noise reduces. Try different gains at different point of MC servo board and TTFSS when IMC is unlocked to see where exactly 60 Hz noise is coming from.

I just noticed that c1sus2 crashed again. Following 40m/17335, I fixed it by running

controls@c1sus2:~$ rtcds restart --all

"global diag reset" made all FE STATUS green.
Burt restored at 2023/Feb/8/19:19 for c1sus2 models.
Watchdogs reset for BHD optics and now all look fine.

I did a quick step response test today with YARM WFS loops running. Steps were put in as offsets in channels C1:SUS-I/ETMY_ASCPIT/YAW_OFFSET to not let transmission go below 0.6-0.7 out of 1. I waited 30 seconds between each step by simply running sleep 30 on my terminal. Once finished, dtt still was taking a long time to get recently measured data even for 16 Hz channels. I used cdsutils getdata to get the measurement and calculate time constants for each loop. Time constant is defined by the time it took for C1;SUS-I/ETMY_ASCPIT/YAW_OUT16 channel to come to 1/e of the offsetted value. Inverse of this time constant is also printed as text on the plot. Note that I redid step on ETMY PIT as the first pass seemed not strong enough to me. See attachment 2 for settings.

The Pit loops seem to be bit faster with about 5s time constant while YAW loops have about 10s.

[Anchal, Yuta]

We have measured OLTF of IMC loop, and revisited IMC error point calibration again.
Also, we have tried to break the ground loop between MC servo board and TTFSS, but didn't help.

IMC OLTF measurement:
 - IMC OLTF was measured using SR785 at TP1A and TP1B. MC servo board settings are the following.
   - +4 dB in IN1
   - 40 Hz pole, 4000 Hz zero filter was on
   - 0 boost
 - Eye-ball fit of OLTF gives zeros at [30e3,30e3] Hz, poles at [40,3e3,3e3] Hz (Attachment #1). 40 Hz pole is from 40:4000 Hz fiter in MC servo board and 4kHz zero is compensated by IMC cavity pole (~ 3.79 kHz). We are not sure where two 3k:30k are from.
 - Anyway, eye-ball fit gives OLTF gain of 1.7e5 at 60 Hz, which is accidentally roughly the same as previous estimate (40m/17446).

Revisiting IMC error point calibrations:
 - We realized that error signal calibration of 13kHz/V a while ago in 2018 (from 40m/14691, which is from 40m/13696) is a calibration for IN1.
 - So, 70 uV/rtHz at 60 Hz at TP1A corresponds to 70 uV/rtHz / 4dB / (4e3/60) * 13kHz/V = 0.009 Hz/rtHz, which corresponds to 1.2e-15 m/rtHz.
 - The estimated frequency noise at the output of IMC in terms of arm length is 1.2e-15 m/Hz * (1+G) = 2.0e-10 m/rtHz (or 1.4e-10 m RMS considering 0.5 Hz bandwith).
 - Noise measured with the same condition but PSL shutter closed was 7 uV/rtHz at 60 Hz (40m/17431). This correspond to 1.2e-16 m/rtHz (or 8.5e-17 m RMS), which is an estimated dark noise.

Summary of frequency noise measurements at 60 Hz:
 - 1.4e-10 m RMS (or 1.0e3 Hz RMS) as measured at TP1A (estimate of unsuppressed noise difference between IMC and PSL)
  - This being smaller than MC_F measurement is strange, as this should be an estimate of total unsuppressed noise (if 60 Hz noise is coherently cancelling each other, this can be explained).
 - 3.1e-9 m RMS (or 2.2e4 Hz RMS) as measured at MC_F
 - 4.3e-11 m RMS (or 3.1e2 Hz RMS)  as measured using XARM and YARM
 - 1.8e-10 m RMS as measured using FPMI DARM

Buffering MC servo board output to TTFSS:
 - We have inserted a battery-powered SR560 in between MC servo board output to TTFSS, trying to break the possible ground loop between 1X2 rack and PSL.
 - To do this, we had to lower IN1 gain to -6dB, to avoid saturation of SR560.
 - This didn't make any difference in MC_F or POY during YARM lock.

It would be great if you could calibrate these ASC channels into physical units (e.g. urad or nrad). I am curious to see how the noise spectra compares to the IMC WFS.

Since the data is still on disk, you can probably use the oplev channels to calibrate the WFS. Also, you can calibrate either WFS or oplev by moving the SUS alignment sliders until the arm power goes down by sqrt(2) or 2.

To get data faster with DTT, I ask only for data sampled at 16 Hz. You can either just read the EPICS channels (OUT16) or ask DTT for a BW=16 Hz for the fast channels. No need for high sample rate for step response plots.

I uploaded this measured output matrix to the YARM WFS model:

        WFS1 PIT         WFS2 PIT         WFS1 YAW         WFS2 YAW
   0.628+/-0.022   -0.031+/-0.007   -0.027+/-0.020    0.039+/-0.004  to ITMY PIT
  -0.431+/-0.020    0.146+/-0.007   -0.002+/-0.018 -0.0099+/-0.0030  to ETMY PIT
  -0.086+/-0.031    0.078+/-0.010    0.728+/-0.029   -0.029+/-0.008  to ITMY YAW
   0.097+/-0.009 -0.0377+/-0.0030    0.126+/-0.008 -0.0555+/-0.0020  to ETMY YAW

Then I played witht the signs of the gains and their values in the C1:AWS-YARM_WFS1/2_PIT/YAW filter banks until I saw a correct response for steps on ETMY and correction within 10-20 s.

I measured the OLTF of the loops with noise injection in each loop simultaneously. This test takes ~10 min. Except for the WFS2 YAW loop, all other loops behaved as expected with UGFs in WFS1 PIT 0.02 Hz, WFS1 YAW 0.04 Hz, and WFS2 PIT 0.035 Hz.

I left this state On for 1 hour and the YARM retained transmission. Attachment 2 shows the history.

Then I conducted another toggle test to see how the step response is. Attachment 3 shows the same results as last post for the new output matrix. Note high sensitivity of WFS2 YAW signal to PIT actuations. The worst row was for WFS2 YAW degree as expected (see page 3 attachment 3).

The new calculated output matrix (after product with the existing matrix) is:

                                                         YARM WFS Estimated Output Matrix

        WFS1 PIT         WFS2 PIT         WFS1 YAW         WFS2 YAW
     0.70+/-0.05    0.011+/-0.014   -0.203+/-0.032   -0.093+/-0.010  to ITMY PIT
    -0.42+/-0.04   -0.111+/-0.010    0.025+/-0.025    0.019+/-0.007  to ETMY PIT
    -0.00+/-0.05   -0.091+/-0.016      0.76+/-0.04    0.041+/-0.013  to ITMY YAW
   0.201+/-0.022    0.062+/-0.007    0.244+/-0.015    0.067+/-0.005  to ETMY YAW

With this matrix in, I had to change all gain signs to negative and teh loop was stable to my kick test on ITMY and ETMY on both PIT and YAW DOFs. OLTFs can be tuned further. Maybe later, I'll do another toggle testin hope of getting an identity matrix.

[Anchal, JC]

During shimmer test yesterday, the man laser tripped again. This morning, JC and I went to inspect the situation closer. We figured that if we can take a look inside the controller, we can get the replacement fan part number. Attached are some photos of inside. To open the controller, all you need to do is take out the two standoffs that are at the edges in the back side, then the top or botttom cover can slide out. Inside, all heatsinks of heat generating ICs are clamped to a larged metal heat sink which is covered on all side but one at the rear end. Through two holes in the top of this cavity, two fan push air through the heat sink to the back. This prompted us to understand that if the externam cooling fan direction is wrong, it would be pshing in air rather than pulling it out. So we decided to try the configuration where the fan is pulling out air. We think the direction of the fan was wrong till now which might be causing the laser controller to shut down. Now we need to wait and watch. For now, the laser is up and running.

Bt the way, we could not get any part number from the fans inside. We are still looking around in the lab if we have the replacement fans in hand as steve said they procured some.

I came in today and it seems like the main laser tripped again yesterday around 3:00 pm.

There was a series of earthquakes in Turkey today, but all our suspension seem to be okay.

For the loop calculation, don't you have to consider the IMC cavity pole? What about the analog filter on the output of the HV driver for the laser PZT?

Our main laser has tripped suspiciously twice since the power shutdown. The last time it happened on Thursday Feb 2 night (the day of power outage happened). Next morning Paco turned the laser back on, I'm not sure if he did anything else other than turning the diode current driver ON. Paco, please add anything else you did.

Chris reported that the laser tripped again last night on Feb 4th around 6 pm. I came today to see the same situation, laser diode turned OFF. After a discussion with a friend in the weekend, it turned out that sometimes when brief power outages happen, the TEC circuit for mainitaing laser tremperature turns OFF while the current driver keeps running. I'm not sure if that is the case for us but that can cause such tripping due to over heating. So today instead of simply turning on the current driver again, I power cycled the laser controller. Laser is back on and mode cleaner is locked with fewer counts though since PMC transmission dropped. I don't have time to realign PMC today and I think it might be the case that the transmission would increase once laser has reached a steady state. On Monday, we need to consult with people with more experience and understand why our laser is tripping. I hope it is not sick.

Filter and scripts setup

I copied IOO_WFS1_I filter bank to AWS_WFS1/2_I/Q filter banks to copy the dewhitening and 60comb filters. Then I turned them on.

Similarly, I copied IOO_WFS1_PIT filter bank to AWS_YARM/XARM_WFS1/2_PIT/YAW filter banks. I created a generalised script to handle all WFS on/off.hold/onfromhold operations here. I also generalized toggleWFSoffsets script to be used for measuring DC sensing matrix.

DC sensing matrix measurement

This measurement folllowed the method used by Koji in 40m/17354. The measurement is pushed here. Ntoe that when using this method, while the test finishd in ~1000 seconds, it takes dtt >20 min to retrieve the timeseries data from DQ channels. Thisis weird because cdsutils.getdata does not have this lag. If anyone knows why this is the case, it would be helpful in making this method faster.

• Locked YARM and misaligned ITMX and ETMX
• Centered the AS beam on WFS using DC value.
• Ran ASS on YARM to get to best aligned cavity state.
• Unlocked YARM and ran C1AWS_YARM_WFS_MASTER>!Actions>Correct WFS RF offsets to zero teh offsets.
• Locked YARM again and waited for >120 seconds.
• Ran python /opt/rtcds/caltech/c1/Git/40m/scripts/AWStoggleWFSoffsets.py AWS BOTH -a YARM -t 120
  • Measurement start time: 04/02/2023 22:37:00 UTC
• The offset values required for step response test above were determined by trying out values and making sure that transmission does not go down by more than 15%.
• I had to leave by 3:30 pm, so I couldn't complete the analysis of measured data.I'll post data here soon.

Additions Sun Feb 5 18:06:54 2023:

Data analysis

I got the step response data using cdsutils.getdata and measured the sensing matrix and took and inverse with error propagation. Attachment 1 page 1 shows the raw data measured. Then the data was segmented based on step response time data and a linear fit is used to get linear trend of each channel in null configuration. This is used to remove bias later while measuring the step heights in each sensor. Page 2 shows this data. Page 3 shows final detrended and normalized step response data that was used to measure the sensing matrix. It came out to be:

                                                             YARM WFS DC Sensing Matrix

        ITMY PIT         ETMY PIT         ITMY YAW         ETMY YAW
   1.94 +/- 0.02    0.83 +/- 0.07   -0.15 +/- 0.04      1.3 +/- 0.1  to WFS1 PIT
   5.62 +/- 0.05      8.8 +/- 0.2     -0.2 +/- 0.1      2.5 +/- 0.2  to WFS2 PIT
  -0.43 +/- 0.03   -1.13 +/- 0.07    1.51 +/- 0.04     -0.9 +/- 0.2  to WFS1 YAW
  -1.42 +/- 0.05     -7.1 +/- 0.2      3.3 +/- 0.1    -19.5 +/- 0.4  to WFS2 YAW

Taking it's inverse with uncertainties supported matrix inverse function gave following output matrix to be used:

        WFS1 PIT         WFS2 PIT         WFS1 YAW         WFS2 YAW
   0.628+/-0.022   -0.031+/-0.007   -0.027+/-0.020    0.039+/-0.004  to ITMY PIT
  -0.431+/-0.020    0.146+/-0.007   -0.002+/-0.018 -0.0099+/-0.0030  to ETMY PIT
  -0.086+/-0.031    0.078+/-0.010    0.728+/-0.029   -0.029+/-0.008  to ITMY YAW
   0.097+/-0.009 -0.0377+/-0.0030    0.126+/-0.008 -0.0555+/-0.0020  to ETMY YAW

[Paco, Yuta]

We devised a plan to systematically hunt for the line noise source assuming it has something to do with BH44 and/or our recent changes in the LSC rack. Our noise estimate is the IMC_error point (TP1A) at the MC servo board. Our traces from Attachment #1 represent, in the following order:

PSL shutter open, IMC locked, C1:IOO-MC_SW1 = 1

PSL shutter closed, IMC unlocked, C1:IOO-MC_SW1 = 1

PSL shutter closed, IMC unlocked, C1:IOO-MC_SW1 = 0

PSL shutter open, IMC locked, C1:IOO-MC_SW1 = 1,  rewired the delay box on LSC rack.

Same as above, plus we connected a loose "ground" wire to the delay box supply.

Same as above, plus we removed the PD interface unit connection.

Same as above plus we disconnected the 44 MHz local oscillators and terminated their outputs at the RF distribution box.

Same as above plus we disconnected the RFPD (BH44) from the IQ demod board at the LSC rack.

Where all the measurements used +4 dB input gain, 40:4000 filter enabled, and Boost = 0 settings on the MC servo board. In between measurements 3 and 4 we had to replace the SR560 (buffer) because the starting one ran out of battery... We found a good one in the YEND, used to buffer the OLTF excitation for the YAUX loop TF measurements.

[Paco, Yuta]

We estimated the frequency noise of IMC output beam at 60 Hz using different methods to see if they are consistent.
They are not inconsistent, but seems hard to explain by an easy single dominating noise source (multiple noise sources at similar noise level?).

IMC suspension damping:
 - We checked that 60 Hz comb filters are all on for all OSEM sensors of MC1, MC2, MC3 (Attachment #1), and they all have comb(60,30,-40,3), which is 60 Hz comb filter of Q=30, -40 dB, 3 harmonics.

Revisiting IMC error point calibrations:

 - We revisited this calibration in 40m/17431. First, 0.9 Hz/rtHz corresponds to 1.3e-13 m/rtHz, as L/nu = 40 m / 282 THz = 1.4e-13 m/Hz.
 - Also, we need to add a loop correction. MC servo board settings when we took this data was as follows:
   - +4 dB in IN1
   - 40 Hz pole, 4000 Hz zero filter was on
   - 0 boost
  assuming 1/f around UGF of 200 kHz (40m/17009), and 1/f^2 between 40-4000 Hz, openloop gain at 60 Hz will be (4e3/60)**2*(200e3/4e3)=2e5. So, the estimated frequency noise at the output of IMC in terms of arm length is 1.3e-13 m/rtHz * (1+G) = 2.6e-8 m/rtHz (or 1.8e-8 m RMS considering 0.5 Hz bandwith).
  - Noise measured with the same condition but PSL shutter closed was 7 uV/rtHz at 60 Hz (40m/17431). This correspond to 1.3e-14 m/rtHz (or 9.2e-15 m RMS), which is an estimated dark noise.

Measuring frequency noise using arms:
 - We then proceeded to measure frequency noise using arms locked with POX11 and POY11. Attachment #2 and #3 is calibrated XARM and YARM noise using the error signals and feedback signals. For both, it is 1e-10 m/rtHz at 60 Hz (or 4.3e-11 m RMS considering 0.187493 Hz bandwidth). And this is more than x10 higher than what we have measured in August 2022 (dotted lines).
 - MC_F calibrated using 1.4e-13 m/Hz reads 7.1e-9 m/rtHz at 60 Hz (or 3.1e-9 m RMS considering 0.187493 Hz bandwidth).
 - Noise measured at DARM in FPMI locked with RF (but CARM with POX11+POY11, as 60 Hz was too much to switch to REFL55_I) was 3e-10 m/rtHz at 60 Hz (or 1.8e-10 m RMS considering 0.374994 Hz bandwidth) (Attachment #5), which is roughly the same as past measurements (40m/17414).
 - To check if MC_F is calibrated correctly, we injected a line at 57 Hz with 3000 counts in amplitude into MC2. Using MC2 actuation efficiency -14.17e-9 /f^2 m/counts in arm length (40m/16978), this should give

14.17e-9/(60**2)*3000 = 1.2e-8 m -> 0.93e-8 m RMS

 in XARM length noise. RMS value of YARM calibrated spectra reads 1.1e-8 m (Attachment #4), which is consistent within ~20%, so MC_F calibration is OK. Note that MC_F at 60 Hz are at the same level in August 2022 (green curves).

Summary of frequency noise measurements at 60 Hz:
 - 1.8e-8 m RMS as measured at IMC error point TP1A
    This gives you total of IMC length noise, error point noise, PSL free run noise, feedback noise.
    Estimated dark noise at error point TP1A is 9.2e-15 m RMS, and is small.
    Calibration might be wrong, as this rely on IMC loop gain estimate and error signal calibration of 13kHz/V a while ago in 2018 (from 40m/14691, which is from 40m/13696), which might not be true for TP1A at 60 Hz (note that there is a 40 Hz/4000 Hz filter).
 - 3.1e-9 m RMS as measured at MC_F
    This gives you total of IMC length noise, error point noise, PSL free run noise, but the noise injected at feedback point before MC_F is suppressed by ~2e5.
    As estimated dark noise is much less, it is IMC length noise, PSL free run noise or noise injected after MC_F.
    Note that typical NPRO free run noise at 60 Hz is 1e4/60 Hz/rtHz * 1.4e-13 m/Hz = 2.3e-11 m/rtHz, and is small, but we might be having large NPRO noise.
 - 4.3e-11 m RMS as measured using XARM and YARM
     This gives you total of IMC length noise, error point noise, but PSL free run noise and feedback noise are suppresed by ~2e5.
     But this also includes noise injected in XARM and YARM loops.
     If this is mainly from PSL free run noise or feedback noise, we expect 3.1e-9 m RMS/2e5 = 1.6e-14 m RMS, so it doesn't explain 4.3e-11 m RMS.
     If this is mainly from IMC length noise, this should be equal to frequency noise measured at MC_F, but MC_F is higher by nearly two orders of magnitude.
     Noise in POX11 or POY11 are smaller by a factor of more than 100 when dark (see 40m/17431), so contribution from dark noise of POX11 and POY11 at 60 Hz to XARM/YARM noise is negligible.
     These mean that the noise might be from combination of IMC and PSL. (For example, if noise injected at error point is 9.2e-15 m RMS, IMC length noise is 4.3e-11 m RMS, PSL free run noise is 3.1e-9 m RMS, and noise injected at feedback point is 1.8e-8 m RMS, it explains all the measurements so far.)
 - 1.8e-10 m RMS as measured using FPMI DARM
     Frequency noise in DARM should be suppressed by common mode rejection, but it is actually x3 higher than what we see in XARM and YARM.
     There might be extra noise from FPMI loops (note that CARM is controlled by POX11+POY11 in this measurement).

Next:
  - Check IMC error point calibration (is 13 kHz/V correct?) by driving MC2 at around 60 Hz (but not at 60 Hz) by known amount
  - Measure frequency noise at IN1 of MC servo board to avoid 40 Hz/4000 Hz filter
  - Check what exactly are we measuring at MC_F. Are there possibility of additional noise for MC_F, which is not fed back to laser frequency?
  - Drive MC2 at around 60 Hz (but not at 60 Hz) to see if MC_F and X/YARM spectra matches
  - Estimate IMC length noise from MC OSEMs
  - Touch electronics around 1X2 to see if 60 Hz at IMC error point changes (monitor the live spectrum!)

[Steve, Koji, JC]

Steve Vass came by today and was loaded with information. Here are a couple things we went over:
- Removal of the large optical table.
- Disconnecting the roughing pumps to prevent oil contamination. 
- Plexiglass End Enclosures
- TP1 maintenance Information

Removal of the large optical table. 

    Steve mention to us that there will be 2 machines that have to raise and rotate the optical. The optical table is 2 ft wide when rotated and this seems to easily give us clearance to get this guy out if we set it on piano dollies. The only issue we encountered is that we may have to disconnect the small power supply rack by 1X2 to make room for one of the machines that will rotate the table. If we manage to lift the table, slide it over to a more open area, lift again, and remove the dollies, then this may give us enough space for this machine and we won’t have to disconnect the power supply rack by 1x2. Overall, turning the table over on its side and maneuvering it into the aisle to go down the aisle along Xarm is the trickiest part. From there, we just have to find out where we are going to take this monster of an optical table.

Disconnecting the roughing pumps to prevent oil contamination
    

Disconnecting the roughing pumps to prevent oil contamination. 

    Steve let us know that he would disconnect to oil vacuum pumps after getting to your nominal vacuum pressure. This prevents these pump from possibly feeding oil into the system. Each of these pumps have an intentional leak vale that keeps the pressure above 300 mtorr. If the pressure get any lower, the pumps will begin to back pressure oil into the system.

Plexiglass Enclosures

  

   I asked Steve about some information on the end enclosures and PSL Enclosure. For the end enclosures, these were custom made. The film on the enclosure was added by people who do car window tinting. This film is not as strong as the plexiglass for the PSL Table. I have to look through Steve’s physical documents to find a receipt, or information of where he purchase the custom enclosure. As for the PSL enclosure, the film is actually imbedded/ combined with the plexiglass. This can withstand much more power than the end enclosures.

TP1 Maintenance
    
    Steve has sent TP1 and the controller for maintenance before. It seems like we need to do this roughly ever 4-6 years and the last time TP1 was shipped out for maintenance was in 2018. During this, Steve said he thinks he was shipped a temporary pump to use in the mean time while TP1 was being repaired. When there is an error with the pump, it will pop up on the controller as show in [elog 14189](https://nodus.ligo.caltech.edu:8081/40m/14189)Anyways, it seems like TP1 will have some issues coming up.

Model and medm changes

After incrementally doing the model changes, I found out that the model was failing to build because of creation of a subsystem. If I just kept all divertor blocks out in the main model instead of in a single subsystem, the compilation works. Maybe the reason is because RCG can only take subsystems at base level which have top_names attribute. But I did nto test this, I just went with what works.

In summary, I added a new subsystem in c1ioo model called AWS (stands for Antisymmetric Wavefront Sensors). This subsystem and IOO subsystem receive teh WFS RF demodulated signals based on a single binary switch named C1:IOO-SEL_WFS_IMC_OR_AS. Value 0 connects the subsystem IOO to the inputs and value 1 connects AWS to the inputs. There is a switch on the left edge in the WFS screens now to select between the two.

Inside the AWS, the WFS I/Q phase rotation is done and then it goes into one of the two subsystems called AWS-XARM or AWS-YARM for using the AS for either XARM or YARM. THis is based on a single binary switch called C1:AWS-SEL_ARM_X_OR_Y. Value 0 selects output to XARM and value 1 selects output to YARM. There is a switch near top left of  C1AWS_XARM_WFS_MASTER.adl and C1AWS_YARM_WFS_MASTER.adl screens. I copied these screens from C1IOO_WFS_MASTER.adl, so they have same structure. See attachment 1. Any edits should be made to /opt/rtcds/caltech/c1/medm/c1ioo/master/C1AWS_XARM_WFS_MASTER.adl and simply run python opt/rtcds/caltech/c1/medm/c1ioo/master/createYARMWFSscreensFromX.py to create teh YARM screen from it.

Along with this, models c1scy and c1scx were edited also to take in IPC directly from c1ioo instead of going through RFM. We should phase out use of RFM eventually and directly connect all IPC connections with the ends.

First tests

[Anchal, Yuta]

After the model is up and running, we flipped the WFS path to use AS beam. I switched the 8 RF outputs of the WFS from IMC WFS boads to AS WFS boards and switched the IDC connectors to WFS. Attachment 2 shows teh photo in this flipped state. Then we misaligned both ITMX and ETMX. First simple test was to check if we see the YARM PDH error signal when YARM was flashing. And indeed we saw that on all 16 channels. So next we locked YARM and injected 311 Hz line with 300 counts amplitude at ETMY. We looked for this peak in the Q channels of WFS outputs and adjusted all phases to 0.1 degrees to minimize Q signal to the noise floor. For WFS2 case, teh SNR is bit higher due to more power than WFS1 and their phase angle might be adjusted to even better degree but we did not got for it.

Then I used C1AWS_XARM_WFS_MASTER.adl>!Actions>Correct WFS RF offsets button to remove offsets in all the RF demodulated signals. I have set this button to use /opt/rtcds/caltech/c1/Git/40m/scripts/RFPD/resetOffsets.py script.

At this point, we are ready to see if we have WFS sensitivity but I need to work on other projects today and Yuta and Paco took over interferometer for 60 Hz noise hunting.

[Anchal, JC, Radhika, Paco]

JC reported that power outage happened twice in 40m today at around 4:17 pm.

We followed instructions from this page mostly to recover today. Following are some highlights:

Main laser controller fan broke

Paco reported that the adhoc fan in the back of main laser controller slid down and broke. Their might be contamination on the table from broken fan parts. Paco replaced this fan with another fan which is larger. I think it is time to fix this fan on the controller for good.

Main volume valve V1 shutdown

The main volume valve shut down because c1vac turned off. We restored the vacuum state by simply opening this valve again. Everything else was same as until the final step in vacuum resetting steps.

Mode cleaner locking issues

The burt restore for mode cleaner board settings do not bring back the state of channels C1:IOO-MC_FASTSW and C1:IOO-MC_POL. This has been an issue which has puzzled us in the past too as we try to get the mode cleaner to lock after power outage recovery. I have now added these channels and their required state in autolocker settings so that autolocker scan in the correct state always. It seems like I added with Yuta's name in the commit author.

Today while aligning optics at the xend, my knee engaged the AUX laser interlock. I spent some time trying to disable the interlock, and I'm putting the solution here for mainly my reference: pull on the red interlock button. This shorts the two pins on the back of the Mephisto controller.

During my time shadowing Anchal, we discussed the need for digital control systems on the suspension systems for the 40 meter optics. The controls and diagnostics system (CDS) allows us to develop our own feedback controls and filters for the suspension systems by taking in analog signals from the shadow sensors. The feedback control system developed in the CDS then utilizes the OSEM actuators to dampen harmonic motion and noise on the suspension lines. While improving these feedback loops is an ongoing challenge, it is a problem that is likely non-linear, meaning the system must be understood on a much higher level to make further improvements. This brings us to the new addition of a wavefront sensor in the 40m lab, which will allow for constant monitoring of the active wavefront in the interferometer. The wavefront will soon be used for gathering training data for a neural net that will help further analyze the non-linear effects within the suspension and damping system. What Anchal was working on today was an update within a CDS model for clioo to allow for the integration of the wavefront sensor such that he may use a switch to change between connections in the mode cleaner and the arm cavity. The CDS models may be edited and updated using Matlab/Simulink to arrange blocks and code in a robust and visual manner. The final system designed in Simulink can then be saved and compiled using the real-time code generator (RCG), which cross-compiles the Simulink file into C code that can be read by the CDS system to assign inputs, outputs, and various logic or algorithms for filtering.

Chub mentioned to Paco and I that the Nitrogen seemed to be losing pressure quicker than usual. After looking over the previous 4 months on Dataviewer, the pressure has a pretty consistent slope. I have ran into the issue of the neck of the N2 tank slighty leaking, so this may have been the issue. For now, there does not seem to be any significant or obvious problem.

I reconnected the green REFL monitor channel and acquired its spectra when the laser was (mostly) locked. During the collection window, TEM00 would catch lock for a few seconds, drop, and catch again. As of today this is the longest the lock will hold. I'm uploading a screenshot for now but will replace with a proper .pdf spectra image.

There is a peak ~558 Hz and at its second harmonic. Additionally there is a less sharp peak at 760 Hz.

I wondered if Moku could have lied about its noise measurement since the RF source was the same Moku device. To avoid this bias, today I repeated this measurement with sendinf RF from Marconi. Marconi settings were:

• Carrier Frequency: 45 MHz
• RF Level: -2 dBm
• Mod AM ext DC: 90 %

The Marconi was fed noise from DAC output to match the measured BEATY RF amplitude like the previous posts: Attachment 1 shows AWGGUI settings required and attachment 2 shows the measured RF amplitude noise with the simulated source.

This source was then fed one by one to DFD + Phase tracker system (attachment 3) and then Moku Phasemeter setup (attachment 4). The phasemeter settigns were same as the previous post. Attachment 5 shows the two transfer functions of AM to frequency coupling on the same plot for comparison. Attachment 6 shows the comparison of frequency noise floor between the two methods on the same plot. In this measurement, I rechecked by DAC actuation calibration by measuring it directly. For Marconi AM modulation slope, I took into account the fact that the slope is in %/Vrms. I got it crosschecked with Paco this time. I think the calibration is correct. Moku phasemeter is indeed better by atleast 20 times in the frequency region of interest. The nosie floor is a factor of 3 less. I think this measurement clears Moku phasemter as the choice of frequency discriminator for calibration project. Any comments/opinions are welcome.

Last week I captured the closed-loop error signal of the xend green PDH loop. Green transmission was around 2.5, and the laser was locking for about 3 seconds every couple minutes or so. The servo gain knob was set to 5.0. Repeating this with higher transmission/locking time is worthwhile.

Attachments 1 and 2 are two separate lock durations, with x-axes spanning 1 second each. The trace of interest (error signal out of mixer) is Channel 1. Channel 2 contains the control signal outputted by the PDH servo box.

The error signal is contained in a slow-moving envelope at ~4.5 Hz, zoomed in with time cursors in Attachments 3 and 4.

Zooming in further, the error signal has a fast component at ~150 Hz (Attachments 5, 6).

Before taking these traces, I captured the green REFL signal and open-loop PDH error signal shapes (Attachment 7). This error signal linear range spans ~500 mVpp. From looking at this signal it seems like the closed loop contains excess noise.

From considering the above traces and loop calculations I can start to infer the closed loop shape and/or UGF, and what direction we need to move in to recover good locking.

Model changes and addition of Moku Phasemeter

Today I setup Moku:Pro MP1 with phasemeter app to replace DFD + Phase tracker.

Phasemeter settings:

• Both channels:
  • Frequency: Auto (Auto track frequency)
  • Bandwidth: 1 MHz
• Advanced:
  • Freewheeling: ON
  • Single input: ON (Used for now, later the two channels will use different inputs)
• Output for both outputs:
  • Signal: Freq offset
  • Scaling: 1.000 mV/Hz
  • Invert: off
  • Offset: 0.0000 V

Moku Input output settings:

• In 1 and In 2:
  • AC: 50 Ohm
  • -20 dB attenuation: 4 Vpp range
• Out1 and Out2:
  • +14 dB gain: 10 Vpp range

The phasemeter is set to autotrack the frequency with PLL bandwidth fo 1 MHz. The output of the phasemeter (frequency offset) is sent out through the output channels at 1mV/Hz rate. These are digitized at c1lsc ADC and are available as an alternative to phase tracker output channel. One can switch between the two ways of measurement by using C1:ALS-SEL_PHASE_SOURCE channel. See attachment 1 and 2 for the two mode options. For this, I modified c1lsc model today

Moku Phasemeter calibration

I used marconi to send 45 MHz RF output as -2 dBm level with internal FM modulation of peak 200 Hz at 211 Hz. This was used to calibrate the Moku Phasemeter outputs to set channels

C1:ALS-BEATX_MOKU_PHASE_OUTPUT_HZ and C1:ALS-BEATY_MOKU_PHASE_OUTPUT_HZ in units of Hz. This method is not very reliable as I do not know if marconi actually sent 200 Hz peak. The calculations from ADC conversion and moku slope of 1mV/Hz give similar numbers though. However, if we want to be accurate in our calibration project, more detailed calibration of these channels is required with a better technique. For now, I assumed that this value is good atleast to a 1% level.

AM coupling test and noise measurement

I followed the exact same setup as in 40m/17409 to create a RF signal using MP1 waveform generator which is AM modulated by awggui noise excitation to create similar AM noise as measured for BEATY RF output. The measurement can then take AM coupling transfer function measurements. Attachment 3 are the results of this measurement. In comparison to DFD + Phase tracker system, the transfer function is 2 orders of magnitude less. Even if my calibration of AM modulation is wrong, same calibration is sued for both transfer functions, so the difference measured is real. We are mostly measuring noise in this measurement as the coherence is also very low for all of the frequency range. See the 4th plot to see the inferred measurement noise of Moku phasemeter setup. Attachment 4 shows this data in comparison to data taken in 40m/17409 with DFD + Phase Tracker setup. Moku Phasemter setup provides roughly factor of 4 less noise in our calibration line frequency band.

The 0x2000 error happens when the rtcds model can not acquire the requested number of channels at their data rates. Basically, there is a maximum total data acquisition that one model can do (which is unknown to me). To fix this, I removed 2048 Hz acquiring of C1:CAL-SENSMAT_<DOF>_<RFPD>_<I/Q>_DEMOD_SIG_IN1. This would not allow us to do software demodulation of calibration lines ourselves. but C1:CAL-SENSMAT_<DOF>_<RFPD>_<I/Q>_DEMOD_<I/Q>_IN1 are still acquired at 2048 Hz to do our own low pass filtering in software and C1:CAL-SENSMAT_<DOF>_<RFPD>_<I/Q>_DEMOD_<I/Q>_OUT are acquired at 256 Hz.

This removal worked, and restarting DAQD worked and now c1cal does not have any DC errors. Current total data acquisition C1:DAQ-FEC_50_TOTAL is 2521 which is less than our other heavy models like c1lsc, c1sus etc. So c1cal can probably acquire more in future, but care is required while adding new channels. This issue happened because we added BH44 to the calibration model.

[JC, Paco]

I tried restarting all models this afternoon to see if the DC error 0x2000 on c1cal model cleared (currently no frame data is being written from c1cal). By running ./restartAllModels.sh on the scripts/cds/ folder, and then BURT restoring, but unfortunately this didn't work. I also tried restarting DAQD without success. Finally, I guess since the error has been related to channel inconsistencies in the model's .INI file (what where when?) I tried rtcds build c1cal and rtcds install c1cal and then another full restart. No success.

PMC hit a drop around mid-day on Saturday and has been going down since. As of now,

C1:PSL-PMC_PMCTRANSPD - 0.664

I will go in and adjust now.

One of these V beam dumps was installed for BH44 RF PD.
The rest is now stored in the box in the shelf along Yarm, together with RF PD mounts.

So far different measurements are consistent with the hypothesis that the 60 Hz noise is from PSL frequency noise (40m/17423).
We have done several measurements in REFL55 and POX/POY to show this hypothesis, and all are consistent with the frequency noise hypothesis.
However, 60 Hz noise in the IMC error point seems too small to explain the 60 Hz noise in DARM.
 

[Koji, Paco, Yuta]

REFL55 attenuation experiment:
 - To check if the 60 Hz is in the light or not, we have compared the spectrum of REFL55_I_IN1 with different ND fiters in front of REFL55 RF PD.
 - Attachment #1 shows the result. Spectrum was taken when both arms are locked indivitually using POX and POY, feeding back to ETMs, MICH freely swinging. Red curve is nominal, blue is with OD0.5, and green is with OD1.
 - Attenuation in 60 Hz noise and side lobes are consistent with OD filter attenuation, which suggets that the noise is from the light.
 - Note that having side lobes is natural, as MICH is fringing (sorry for confusing plot). However, if the side lobes come from the RF saturation, we expect side lobes to decrease more than OD filter attenuation, but this was not the case.

Phase measurements between POX and POY:
 - When both arms are locked indivitually using POX and POY, feeding back to ETMs, transfer function from POX to POY had gain of ~1 and the phase of -10 deg (Attachment #2).
 - With PSL shutter is closed, transfer function from POX to POY had gain of ~0.1 and the phase of -100 deg, with lower coherence (Attachment #3).
 - These also support that 60 Hz noise in POX and POY when the arms are locked are from common origin, such as frequency noise.

[Michael, Paco, Yuta]

IMC error point measurement:
 - Attachment #4 shows the IMC Servo Board configuration we used for the all three measurements below.

For this measurement we took TP1A (from MC Servo board) and buffered it with a battery powered SR560 (DC coupled, low noise, gain x1) before connecting it to the single ended A1 channel on a SR785. The noise level was set to -42 dBVpk, and three different noise spectra were acquired:

• In Blue, the IMC is locked
• In Orange, IMC is unlocked by closing PSL Shutter (dark)
• In green, IMC is unlocked by closing PSL Shutter and the Servo board IN1 is disabled.

The estimated (in loop) line noise (60 Hz) levels are 70 uV/rtHz, which using the calibration 13 kHz/Vrms (from 40m/14691) amounts to 0.9 Hz/rtHz of (supressed) frequency noise at IMC Error point.

This number (0.9 Hz/rtHz) in terms of displacement corresponds to 1.28e-15 m/rtHz. The measured DARM noise (2e-10 m/rtHz @ 60 Hz from 40m/17414) is not accounted for by this amount.

Next:
  - Check the IMC error signal calibration
  - Measure the calibrated out-of-loop frequency noise using various signals (POX, POY, REFL55, AS55 with single arm, ALSBEAT, PMC_CTRL)

Timeline (as far as written in the elog):
 - Dec 20: FPMI BHD locked using BH55 (40m/17367).
 - Dec 21: FPMI RF locked, but not BHD, DARM noise 1e-11 m/rtHz @ 60 Hz (40m/17369).
 - Jan 10-11: AS WFS boards testing at 1X2 (40m/17391, 40m/17393).
 - Jan 11: FPMI BHD locked using BH55, DARM noise 2e-11 m/rtHz @ 60 Hz (40m/17392).
 - Jan 13 2pm: FPMI BHD locked using BH55, DARM noise 2e-11 m/rtHz @ 60 Hz (40m/17399).
  - After measuring the sensing matrix etc., LO_PHASE locking became unstable and FPMI BHD could not be recovered (I thought something similar to Dec 21 is happening).
 - Jan 13 6pm: FPMI BHD locked using BH55 recovered. DARM noise 2e-11 m/rtHz @ 60 Hz. Discovered that the 60 Hz noise is higher when LO_PHASE locking is unstable (40m/17400).
 - Jan 17: BH44 hardware/software installed. Found IQ demod board needs tuning (40m/17401).
 - Jan 18: Tuned IQ demod board for BH44 installed (40m/17402).
 - Jan 19: BH44 RF PD placed and connected to IQ demod board. FPMI RF locked, LO_PHASE locked with BH44, but found 60 Hz noise everywhere (40m/17405).
 - Jan 24: FPMI RF locked (with CARM locked with POX11+POY11 instead of REFL55_I). DARM noise 2e-10 m/rtHz @ 60 Hz (40m/17414).
 - Jan 24: AS WFS boards mounted in 1X2 (40m/17416).
 - Jan 25: Isolating BH44 setup didn't help (40m/17423).
 - Jan 26: Fixed tripping of -5V supply in 1X1 (40m/17425).
 - Jan 27: IMC error point measurements at 1X2 (this elog).

this is very exciting! Its the beginning of the task of reducing vast amounts of PEM data into human-useful (bite sized) info. Imagine if we had 60 Hz BLRMS on various channels - we would know exactly when ground loops were happening or disappearing.

@OMC Lab
EP30-2 Epoxy bonding of V beam dumps for LSC PDs.

- Supplied 1"x0.5" glass pieces from the stock in the OMC lab.
- The black glass pieces were cleaned by IPA / Aceton / Aceton+Cotton Qtip scrub / First Contact
- 3 beam dumps are built. They require ~24 hrs to get cured.

=> Handed to Yuta on Jan 27, 2023

I implemented the BLRMS on WFS1/2_I_PIT/YAW outputs and using there value, a HEPA state can be defined. I've currently set it up to use average of 10-30 Hz noise on WFS signals low passed at 0.3 Hz. For ON threshold of 100 and OFF threshold of 50, it is working for my limited testing time. To read HEPA state, one can do caget C1:IOO_HEPA_STATE. I've turned OFF HEPA for tonight's shimmer test. This is bare bones quick attempt, people can make the screen more beautiful and add more complexity if required in future.

PMC aligned (Attachment #1).
Over the past month, PMC transmission is actually slowly growing from 0.68 to 0.70 (Attachment #2), since it suddenly dropped from 0.72 on Dec 27 (40m/17390).

[Yuta, Anchal]

The mounting of two additional WFS demodulation boards drew too much current on -5V rail which tripped the sorenson on 1X1. This was undetected until today. Because of this, the existing WFS boards were not working either. After investicgation to beam paths and PD to board signal chain, we found out this issue. We raised the current limit on -5V supply and it came back to 5V. This brought back functioning of the exisitng WFS boards as well. We increased the current limit slightly on +5V supply too as these boards take a lot of current on +/5 V rails. But we should do this more properly by knowing what current limit the supply is set to. We'll do this part in near future after reading the manuals/wiki.
IMC WFS loops are now working.

Connect any video signal supported by the adapter. Use Windows / Mac or any other OS. If it keeps complaining, contact Magwell support.

[Paco, Anchal, Yuta]

Isolating BH44 setup from the rest didn't help reducing the 60 Hz noise.
Frequency noise from IMC also seems unchanged before and after BH44 installation.

Isolating BH44:
  - To see if BH44 setup installed is causing the 60 Hz issue, we compared the spectra of FPMI sensors with BH44 setup and with BH44 setup disconnected.
  - In the latter configuration, BH44 setup was isolated from the rest by disconnecting the SMA cables and the RFPD power cable, as shown in Attachment #1.
  - There was no significant difference in the spectra with BH44 and with BH44 isolated.
We have even put the old AS156 IQ demodulator board we have pulled out to insert BH44 IQ demodulator board back, but didn't change.
  - We have also disconnected the 22 MHz generation setup around 40m Frequency Generation Unit at 1X2 for switchable IMC/AS WFS, but it also didn't help.
  - Attachment #2 is the orignal spectra with both arms locked with POX and POY, feeding back to respective ETMs (MICH is not locked), and Attachment #3 is those with BH44 setup isolated, AS156 IQ demod back, and 1X2 22MHz generation isolated. Both look basically the same.
  - BH44 setup was reverted after the comparison.

IMC frequency noise:
  - As adding a resonant gain at 60 Hz helped reducing the 60 Hz noise (40m/17419), the noise might be from frequency noise. It also explains why it is not present in MICH when ETMs are mis-aligned, and only present when one of the arms is involved (40m/17413).
  - To see if the frequeny noise at 60 Hz increased after BH44 installation, I compared the spectrum of C1:IOO-MC_F_DQ on January 11 (same Wednesday) with that measured today at almost the same time.
  - Attachment #4 is the result. 60 Hz noise and its harmonics seems almost the same in MC_F. It is rather noisy today in other frequencies, but not at 60 Hz.

Next:
  - Read the book.

Thus far, the software needed for the Magewell video encoder has been successfully installed on Donatella. OBS studio has also been installed and works correctly. OBS will be the video recording software that can be interfaced via command line once the SDI video encoder starts working. (https://github.com/muesli/obs-cli)

So far, the camera can not be connected to the Magewell encoder. The encoder continues to have a pulsing error light that indicates "no signal" or "signal not locked". I have begun testing on a secondary camera, directly connected to the Magewell encoder with similar errors. This may be able to be resolved once more information about the camera and its specifications/resolution is uncovered. At this time I have not found any details on the LCL-902K by Watec that was given to me by Koji. I will begin looking into the model used in the 40 meter next.

Kapton tape is a good insulator, so its a good block for 60 Hz. But it is mostly useless for RF since the capacitance between the mount and the table is

C = epsilon * A / d

For Kapton the dielectric constant is 3.5, the PD mount area is 10 cm x 10 cm, and the film thickness is ~50 um. So C ~ 5 nF.

Z ~ 1 / (2 * pi * 44 MHz) / C

  ~ 0.5 Ohms

I returned the half-wave plates on the XEND table back to their original angles, and restored the loop configuration with the PDH servo box. I returned the PD gain to 40 dB (original setting), and set the servo gain knob to 6. This was the region of highest loop stability, with the lock holding for a few seconds (as before). The control signal on the scope did not look intuitive - the peaks of the control signal corresponded with zero crossings of the error signal. 

Paco encouraged me to retake transfer function measurements of the PDH servo box. The main takeaway is the PDH servo (boost on) has the expected frequency response at a gain setting of 3 or under, up to 100 mVpp of input. Attachment 1 shows the frequency response at a servo gain of 2, for varying input amplitudes. 

The rest of the bode plots correspond to servo gain of 4, 6, 8, and 10 (boost on). The saturation LED would turn on above a gain value of ~3.25, so these results can't be analyzed or interpreted. But it does seem like a steep, low-frequency jump is a signature of the saturated servo. This jump doesn't appear with 10 mVpp input, at least at or above 1 Hz. 

Following was done to investigate 60 Hz noise issue, but no significant change in the FPMI noise observed.


REFL55 inspection:
  - Even before BH44 installation, we have been experiencing flaky REFL55 RF output. When some work was done at AP table or something, sometimes the amplitude of REFL55_I and REFL55_Q goes very low, and/or offset changes. This was usually fixed by touching the RF output of REFL55.
  - So, we took out REFL55 and opened the back lid to inspect. RF output seemed rigid and the SMA connector was properly grounded to the box; didn't find any issue (Attachment #1).
  - REFL55 was put back to its original position, and the cables were also put back.

BH44 Kapton tape:
  - I realized that other RFPDs have Kapton tape in between the RFPD golden box and the black mount, but not for BH44 we recently installed.
  - I have checked that the golden box of BH44 and the optical table is not grounded when RF output and the DB15 cable was disconnected, but is gounded when they are connected, just like BH55.
  - Anyway I removed BH44 and put a Kapton tape (Attachment #2), just in case, and BH44 was put back to its original position, and the cables were also put back.

FPMI noise spectra after the work:
  - Attachment #3,4,5 are noise spectra of FPMI BHD sensors when FPMI is RF locked with AS55_Q, REFL55_I, and REFL55_Q, and LO_PHASE is locked with BH55 with the following configurations.
  - Attachment #3: whitening/unwhitening filters for AS55, REFL55, POX11, POY11, BH55, BH44 turned on (nominal configuration after lock acquisition)
  - Attachment #4: whitening/unwhitening filters for AS55, REFL55, POX11, POY11, BH55, BH44 turned off. No significant change except for expected whitening filter transfer function.
  - Attachment #5: whitening/unwhitening filters for AS55, REFL55, POX11, POY11, BH55, BH44 turned on, 30 dB resonant gain at 60 Hz, Q=10 in CARM loop. Significant 60 Hz reduction everywhere. This was not observed when resonant gain at 60 Hz was put in DARM loop (only 60 Hz at AS55_Q was reduced). 60 Hz noise mainly coming from something in CARM loop?

Don't forget to:
  - Put a beam dump for BH44

We came this morning and noticed the FSS_FAST channel was moving very rapidly. Short inspection showed that MC3 watchdog got tripped. After reenabling the watchdog the issue was fixed and the MC is stable again.

There is a spike in the seismometers 8 hours ago and it was probably due to the 4.2 magnitude earthquake that happened in Malibu beach around that time.

1) Turning the whitening filter before the ADC on/off didn't changed the relative height of 60 Hz peak compared with the noise floor. When the whitening filter was turned on, increase of the dark noise measured at C1:LSC-****_(I|Q)_IN1 was roughly consistent by eye with the whitening filter transfer function (gain of 1 at DC, ~15 Hz zero x2, ~150 Hz pole x2), which suggests the 60 Hz pickup is before the whitening filter.

2) Attached is the electronics diagram around BH44 and BH55.

I completed the mode matching calculation today and found good solution with 360.6 mm ROC PLCX lens at -1.2 m from z=0 point. I placed the lens there today and aligned all mirrors to get centered beam on both WFS PDs when the flipper mirrors are flipper up. This alignment would probably require tweaking everying we flip the mirrors as the flipper mirrors do not come back to same position usually.

I mounted the modified WFS boards 111B and 112B next to the whitening filter boards of existing WFS. Now to switch over, onewould need to transfer the 8 RF lemo cables and the 2 IDE ribbon cables.

I'm working on rtcds model to read AS WFS data and handle it separately. I'll keep a WPICS binaruy switch to switch between IMC WFS or AS WFS. I need to figure out some build issues on this work still.

1) do a comparison with the whtiening before the ADC on/off. This will tell us if it is pickup before the whtiening filter or not.

2) If there are ground loops made by 44 MHz setup, we want to draw a simple diagram which includes which sides are grounded and which have transformers. How about make a drawing to bring to the group meeting tomorrow? IN the lab we have these coaxial BALUNs for making a 1:1 transformer coupling.

3) Another source of 60 Hz is the unintentional demodulation of spikes made by the Sorensen switching supplies: they produce spikes all the way up to 100 MHz, so if they land near 44 MHz, you may get some 60 Hz on the demodulation. You should be able to see this with a dipole antenna or a hoop antenna.

Just to show how bad 60 Hz noise is, I compared FPMI displacement noise with pre-BH44 era (measured on Jan 13, 40m/17400).
Blue curve in Attachment #1 is the sensitivity with FPMI locked with RF in pre-BH44 era, and pink curves are that measured today (C1:CAL channels are currently unavailable due to 0x2000 appeared after running restatAllModels.sh).
60 Hz + harmonics pedestals are apparent today, but was not there on Jan 13. Today, DARM could be handed over to AS55_Q from POX11-POY11, but CARM could not be handed over to REFL55_I from POX11+POY11 (this was possible last night).
Attachment #2 shows FPMI error signals when electronic FPMI is locked. Too much 60 Hz, especially in REFL55_I_ERR and AS55_I_ERR (note that REFL55_Q is used for MICH lock, but AS55_Q is not in-loop yet when this screenshot was taken.)

Next:
  - Fix c1cal 0x2000 issue
  - Fix REFL55 loose RF output
  - Disconnect cables in BH44 to open possible ground loops made during BH44 installation (especially 44 MHz generation part??).

[Paco, Yehonathan, Yuta]

Since we have installed BH44, we are seeing side lobes of 60 Hz + harmonics in AS55, REFL55, BH55, BH44, preventing us from locking FPMI BHD (40m/17405).

BH55 RF amp removed:
  - We have noticed that the side lobes are there in BH55 (but not in BH44) when LO-ITMX single bounce is fringing (ETMs and ITMY mis-aligned).
  - Changing whitening gains and turning on/off whitening/unwhitening filters didn't help.
  - When LO-ITMX single bounce is locked with BH55, the side lobe in BH55 reduces.
  - Dithering LO1 at 11 Hz created 180 +/- 11 Hz signal, which confirms that this side lobes are from the up conversion of optic motion.
  - We thought it could be from RF saturation, so we have put a 55-67 MHz bandbass filter (SBP-60+) in between BH55 RFPD and RF amp (ZFL-1000LN+; 40m/17195). Didn't help.
  - We then removed the RF amp. This largely reduced the side lobes (but still some at 180 Hz). We could lock LO-ITMX single bounce without the RF amp, so we decided to remove it for now.

Side lobes only when one of the arms is locked:
  - When ETMs are mis-aligned, MICH fringing and BHD fringing, there are 60 Hz + harmonics, but the side lobes are not there.
  - But with Xarm is locked (ETMY, ITMY mis-aligned) or Yarm is locked (ETMX, ITMX mis-aligned), the side lobes appear in AS55, REFL55, BH55, BH44.
  - Changing whitening gains and turning on/off whitening/unwhitening filters didn't help.
  - As the error signals are normalized by TRX and TRY, we turned on/off the power normalization, but didn't help.
  - Switching 60 Hz comb in BS, ITMX, ITMY, ETMX, ETMY suspension damping didn't help.

POY11 Investigations:
  - When ETMs are mis-alined, POX11 had relatively large 60 Hz + harmonics, but almost none in POY11 (unlike other RFPDs; see Attchment #1).
  - However, when ETMY is aligned and Yarm is loked with POY11, the side lobe grows in POY11.
  - Changing the feedback point from ETMY to ITMY or MC2 didn't help.
  - We have unplugged the IQ demod board for BH44 from the eurorack (without removing the cables) and removed the fuse for the power supply of the RF amp for 44 MHz generation (40m/17401), but these also didn't help.
  - We have also tried locking Yarm with REFL55(= ~2 x POY11), BH55(= ~10 x POY11), ALSY(= ~2000 x POY11), but the side lobes were always there.
  
Next:
  - Disconnect cables in BH44 to open possible ground loops made during BH44 installation (especially 44 MHz generation part??).
  - Check if the noise was there before BH44 installation using past data.

I measured the expected beam profile by WFS photodiodes by measuring the beam when mode cleaner was unlocked from the point where beam is picked for WFS. See attachment 1 for beam details. z=0 is the point in the path where AS beam will merge.

For measuring the beam profile of AS beam, I had to focus it using a lens. I picked up a 360.6 mm ROC lens and placed it at z=-67 inch point. Then I profiled the beam at some comfortable section of the path and fitted it. with reverse z-axis. Using this method, I can place the lens back and obtain the original beam back. Attachment 2 shows this fitting process and identification of the original beam profiles. I plotted the AS beam profiles again in attachment 3 and saved them for seeding mode matching effort later. Note that we don't want to be super accurate here, so I did not do any error analysis, just wanted to finish this fast. Also pardon me for the bad quality plots, I did not want to learn Matlab plotting to make it beautiful.

Note: There is significant astigmatism in both IMC reflection beam and AS beam. This could be due to beam going through far off-center on lens. Something to keep in mind, again this measurement is not ideal in terms of precision but this large an astigmatism could not be due to measurement error.

Next:

• Identify correct len(s) and their positions
• Align the AS beam to WFS heads
• Test the full signal chain.