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ID Date Authorup Type Category Subject
  7571   Thu Oct 18 02:42:38 2012 DenUpdateSUS PITCH damping needed



I think we can put ø2mm × 10mm long magnetic material inside 4 holes with actuation magnets. Then magnetic field on the other side of the mirror will be close to one produced by actuation magnet. Magnetic cylinder center of inertia will be in the vertical plane where mirror's center of inertia is. So this should not change alignment significantly. Eddy current dumping will be applied to the end of the magnetic cylinder opposite to the magnet using aluminium disks, we have them in the clean room.

 I've tested this approach. As we do not have required cylinders with high magnetic permittivity, I replaced them with magnets simular to actuator magnets ø2mm × 3mm long. Using them and aluminium disks from other TT I've made a "pitch dumping" construction.


Pitch Q reduced but not that much as I could expect. I did a ringdown test. 


yaw ringdown using original construction     |  yaw ringdown with added pitch damping


pitch ringdown using original construction   |  pitch ringdown with added pitch damping

    yaw_nodamp_20.JPG   yaw_damped_13.JPG

pitch_nodamp_30.JPG     pitch_damped_10.JPG


 From this data I've estimated Q factor for yaw (135 vs 88) and pitch (192 vs 77) (original vs added pitch damping). Thess results diverges with the ones obtained by designes. They measured Q~40-50 for original construction. Pitch and yaw have 2 close resonances so this time domain method can not be very precise. I've measured the same with SR785.


In these comparison plots excitation was not the same as coils are not plugged in yet, but resonance Q factors can be compared.


  7575   Thu Oct 18 12:02:32 2012 DenUpdateIOOMCL, WFS triggers



 I've redone the WFS triggers.  I left the MCL trigger alone (for now....I'll come back to it). 

The trigger was setup such that (a) it was totally unclear what was going on, by looking at the WFS screen.  Koji and I spent some time confused before I remembered that Den did this work recently.  Also, for some reason, the triggers were just plain thresholding, not a schmidt trigger, so any time the cavity flashed, the WFS came on.  Since the cavity can flash before the mcdown script has a chance to turn off the WFS servos, the outputs of the WFS filters are trying to output thousands of counts, and the signal goes through any time the cavity flashes.  Not so good.

 Your schmitt trigger has 2 threshold values - min and max. Set thresholding value in my trigger to the max of your schmitt trigger and you get the same behavior for MC,  triggers are not supposed to turn anything on in this realization as they do for locking with flashing.

  7580   Fri Oct 19 12:45:12 2012 DenUpdateCDSc1lsc is up after reboot
  7583   Fri Oct 19 18:30:07 2012 DenUpdateSUS PITCH damping needed



 From this data I've estimated Q factor for yaw (135 vs 88) and pitch (192 vs 77) (original vs added pitch damping).

 I've made a more precise measurement of pitch damping using spectrum analyzer.

damp.png   pitch.png

Measurements confirm that damping using small actuation magnets reduces pitch Q by a factor of 4 and is not enough.

  7585   Sat Oct 20 01:23:56 2012 DenUpdateSUS PITCH damping needed


Measurements confirm that damping using small actuation magnets reduces pitch Q by a factor of 4 and is not enough.

 I've tested the idea to use coils as eddy current dampers. I terminated them with a wire and measured Q factor during the ringdown test. Sadly, I did not see any significant damping and Q was ~150. We need stronger magnets if we want eddy current dumping down to Q~1.

P1010059.jpg      P1010060.jpg    P1010058.jpg

  7586   Sat Oct 20 20:37:55 2012 DenUpdateSUS PITCH damping needed



 We need stronger magnets if we want eddy current dumping down to Q~1.

 I've inserted 10mm * 10mm magnets to the 4 corner holes on the front side of the mirror frame according to actuation magnets polarity. I realigned TT and measured Q factor for pitch and yaw, it was 5-10.

DSC_4778.JPG     pitch.JPG   yaw.JPG


I was able to do it for 1 TT only, because others have smaller (~0.1 mm) hole diameter and magnets can't go inside. I tried to warm holes up to 850 F but still was not able to insert a magnet.


  7593   Tue Oct 23 01:46:53 2012 DenUpdateSUS PITCH damping needed



Too bad - I thought it would at least give a little damping. Since we want the viscous-like energy loss to be ~49x larger, we need to have the field modulation in the damper (not dumper) increase by ~7.

 I've made SolidWorks models of damping bracket and eddy current disk. They will me manufactured and used instead of old ones. New bracket will be mounted in exactly the same place where the old one was. Drawings might not be complete but all dimensions are in the models so we can fix drawing tomorrow before going to machine shop.

I think we can use ring magnets for passive damping. Then we won't have the vent problem. I've found some at K&J Magnetics, we can get them any time. Magnets are Ni-Cu-Ni (fine for vacuum?) Diameter is 3/8'' with advertised tolerence 0.004'', so they should fit the holes.

Attachment 1: Mirror_Holder_ECD_NEW_DRAWING.PDF
  7598   Tue Oct 23 17:12:30 2012 DenUpdateSUS PITCH damping needed

 Koji and Steve pointed out that previous design  of a damping bracket was a bit complicated to manufacture. So I made it simpler and also added a tap hole for original yaw damping. We'll give drawing to Mike in the machine shop tomorrow morning.

I've purchased K&J magnets for eddy current damping, they should be here in 2 days. 

Attachment 1: simple_drawing.PDF
  7614   Wed Oct 24 22:20:24 2012 DenUpdateAdaptive Filteringmicrophone noise


  We have to change the sample rate and AA filter for the mic channels before going too far with the circuit design.

 PEM model is running at 64K now. It turned out to be tricky to increase the rate:

  • BLRMS are computationally expensive and original pem model did not start at any frequency higher then 16k ( at 16k cpu meter readings were 59/60 ). Also when we go higher then 16k, front-end gives the model less resources. I guess it is assumed that this model is iop and won't need too much time. So in the end I had to delete BLRMS blocks for all channels except for GUR2Z and MIC1.
  • Foton files are modified during model compilation: lines with sampling rate and declaration of filters in the beginning of the file are changed only. Sos-representation and commands are the same. I hoped that filter commands will let me change sos-representation quickly. I've opened Foton and saved the file. However, Foton modified commands in such a way that the ratio of poles and zeros to sampling rate is preserved. I guess all filters have to be replaced or this process should be done in another way.
  • BLRMS block uses low-pass filters below 0.01 Hz, increasing the sampling rate by a factor of 32 might make calculations incorrect. I'll check it.

We should also increase cut off frequency of the low-pass filter in the microphone pre-amplifier from 2 kHz up to ~20-30 kHz.

Attachment 1: mic_64k.pdf
mic_64k.pdf mic_64k.pdf
  7623   Thu Oct 25 14:39:14 2012 DenUpdateAdaptive Filteringmicrophone noise


  That's no good - we need BLRMS channels for many PEM channels, not just two. And the channel names should have the same name as they had in the past so that we can look at long term BLRMS trends.

I suggest:

  1. Have a separate model for Mics and Magnetometers. This model should run at 32 kHz and not have low frequency poles and zeros. Still would have acoustic frequency BLRMS.
  2. Have a low frequency (f_sample = 2 kHz) model for seis an acc. Seismometers run out of poop by 100 Hz, but we want to have the ACC signal up to 800 Hz since we do have optical mount resonances up to there.
  3. Never remove or rename the BLRMS channels - this makes it too hard to keep long term trends.
  4. Do a simple noise analysis to make sure we are matching the noise of the preamps to the noise / range of the ADCs.
  5. Immediately stop using bench supplies for the power. Use ONLY fused, power lines from the 1U rack supplies.

Ayaka, Den

 C1PEM model is back to 2K.

We created a new C1MIC model for microphones that will run at 32K. C1SUS machine is full, we have to think about rearrangement.

For now, we created DQ channels for microphones inside iop model, so we can subtract noise offline.

We provided 0-25 kHz bandwidth noise to AA board and saw the same signal in the output of ADC in the corresponding channel. So cut-off frequency is higher then 25 kHz. There is a label on the AA board that all filters are removed. What does this mean?

We've turned off AA bench power supply, prepare to use fused from 1U.

  7626   Thu Oct 25 21:02:34 2012 DenUpdatePEM1x7 dc power

 We now stop using bench DC power supplies for microphone preamp and PEM AA board. DC power is wired from 1x5 rack suppliers. I've installed a beam to mount fuse houses in the 1x7 as we did not have one.


  7634   Fri Oct 26 19:06:14 2012 DenUpdateAdaptive FilteringMicrophone noise again


The circuit noise improves so much, but many line noises appeared.
Where do these lines (40, 80, 200 Hz...) come from?
These does not change if we changed the microphones...

Anyway, I have to change the circuit (because of the low-pass filter). I can check if the circuit I will remake will give some effects on these lines.

I do not think that 1U rack power supply influenced on the preamp noise level as there is a 12 V regulator inside. Lines that you see might be just acoustic noise produced by cpu fans. Usually, they rotate at ~2500-3000 rpm => frequency is ~40-50 Hz + harmonics. Microphones should be in an isolation box to minimize noise coming from the rack. This test was already done before and described here

I think we need to build a new box for many channels (32, for example, to match adc). The question is how many microphones do we need to locate around one stack to subtract acoustic noise. Once we know this number, we group microphones, use 1 cable with many twisted pairs for a group and suspend them in an organized way.

  7640   Mon Oct 29 18:14:55 2012 DenUpdateSUS PITCH damping needed


 We've received all parts that we need for eddy current damping. I've made an estimate of Q with dirty tip-tilt. It looks fine (Q~1)

We need to check ring magnets for vacuum compatibility. Bob start baking on Friday.

DSC_4787.JPG     DSC_4791.JPG

  7643   Wed Oct 31 01:06:31 2012 DenUpdateAlignmentYarm


 Jenne, Den

We looked at beam spots on ITMY and ETMY. We switched to smaller apertures on the other side of the rulers. For ITMY beam spot was 1mm below and 1mm south (right if you look in the direction ITMY -> ETMY) from the aperture center, for ETMY - 4 mm up and 3mm north from the aperture center. We made a correction for this using PZT 1 and 2. Now beam spots are in the middle of the apertures on ITMY and ETMY.

We tried to look at reflected beam from ETMY but it was hard to see the dependence between ETMY DC offset and reflected beam. We'll continue tomorrow.

  7650   Wed Oct 31 22:56:41 2012 DenUpdatePEMacoustic noise

Microphone preamp box had a low-pass filter at 2kHz, Ayaka changed it to 20 kHz by replacing 100pF capacitor with a 10pF.

We've measured frequency response of the box. Signal from the microphone was split into two. One path went to the box, while another was amplified by the gain 20 (and bandpass filter 1Hz - 300kHz) and sent to spectrum analyzer. Coherence and frequency response were measured using box output and amplified input. Low-pass filter in the box does not limit our sensitivity.

Acoustic noise significantly decreases at frequencies higher then 2kHz. So we need to modify the circuit by adding whitening filter.

pre_after_mic.png  freq_resp.png

I've plugged in PMC length channel into PEM board CH15 through and amplifier (gain=200) that is AC coupled to avoid ~2.5 DC V coming from PMC servo.  I measured coherence with microphone that was located ~30 cm higher. Measurements show contribution of acoustic noise to PMC length in the frequency range 20-50 Hz. In this range PMC length / MC length coherence is ~0.5.

Acoustic noise couples to PMC length in a non-stationary way. 5 minutes after the first measurement I already see much higher contribution. This was already discussed here. I've made C1:X02-MADC3_TP_CH15 a DQ channel at 64kHz. This a fast PMC length channel.

Next step will be to use several microphones located around PMC for acoustic noise cancellation.

DSC_4792.JPG    DSC_4793.JPG

Attachment 3: pmc.pdf
pmc.pdf pmc.pdf
Attachment 4: pmc_high.pdf
  7676   Tue Nov 6 18:39:16 2012 DenUpdatedigital noiseifo checking system

Matlab version of ifo digital noise estimation code is almost ready. It estimates digital noise introduced by each filter bank in each model. I'm waiting for NDS group to complete function to download online data to Matlab. Now code downloads data from the past that is not great because not all _IN1 channels are recorded and some of them are recorded at lower frequencies.

There might be some useful functions in this code for other applications as I've heard during the meetings. This is what it does

  • reads model names from the input list
  • for each model
    • finds corresponding Foton file and extracts modules with sos filters and sampling rate of the model
    • finds corresponding MDL file and makes a search for subsystems with "top_names" tag and "biquad=1" tag
    • creates _IN1 channel names using module names and subsystems with "top_names" tag
    • for each channel inside the model
      • reads filter bank parameters (which filters are ON, switches, limit, offset...)
      • downloads data
      • calculates output and estimates digital noise
      • checks that output is less them limit if it is on
      • reports if something is wrong

NDS group plans to release the function to download online data this week. Hopefully, it will be possible to download ~30 channels at a time. Code will need a few minutes of data for each channel. So it will be possible to check the whole ifo during the night.

At this point I've checked 40m using DQ channels. We have ~40 IN1_DQ channels with non-empty filter banks. These are osems channels. Digital noise is low for them.

  7708   Tue Nov 13 21:05:35 2012 DenUpdateAdaptive Filteringonline and simulation

For a last few days I've been working on oaf and simulink model to simulate it. First I did online subtraction from MC when MC_L path was enabled. Inside my code I've added a sum of squares of filter coefficients so we can monitor convergence of the filter.

coeff.png     online.png

To to this I've measured path from OAF output to input without AA and AI filters. Then made a vectfit using 2 poles and zeros. Foton command

zpk( [-2.491928e+03;5.650511e-02], [-4.979872e+01;-3.278776e+00], 6.011323e+00)

mag.png    phase.png

My simulink model consists of 3 parts:

  • cavity with seismic noise at low frequencies, 1/f^2 noise at medium frequencies and white noise at high frequencies
  • this cavity is locked using feedback compensation filters that we use to lock arms
  • locked cavity with adaptive filter

Adaptive filter in the model uses online c-code. It is connected to simulink block through an S-function. Sampling frequency of the model is 10 kHz. It works fairly fast - 1 sec of simulation time is computed in 1 sec.

overview.png       af.pngsim.png  sim_coeff.png

I've tested FxLMS algorithm and MFxLMS algorithm that is faster. I plan to test 2 iir adaptive algorithms that are already coded.

  7713   Wed Nov 14 21:59:09 2012 DenUpdateCDSdaq errors

I tried to add a test point to C1MCS model and spent next two hours rebooting front-ends, restarting models and realigning MC.

dmesg told me that DAQ channels can not be allocated as they already exist. Last time we met this problem Jamie emailed Alex about it. Jamie, what is the output? Restarting iop model does not help this time.

  7714   Thu Nov 15 02:18:24 2012 DenUpdateModern ControlBS oplev

I've applied LQR feedback technique to BS oplev in pitch. I think the most inconvenient thing in using LQR controller is the amount of additional states created during cost function shaping. It requires 1 filter bank for each state. To avoid this I wrote state estimation code so all states are calculated inside one function.

On the plots below cost function and oplev feedback controller performance are shown.

lqr_cost.png    olpit_hg.png

  7721   Sat Nov 17 18:02:14 2012 DenUpdateAlignmentred in arms


POY11 does not go out of the vacuum

 It does but slighty low and does not get on mirrors. We need to change optic mounts to adjust the height. Red is flashing in yarm at 00 and 10 modes. TRY is ~0.4-0.5.

I've adjusted BS angle, camera and TRX PD at ETMX table so I can see red flashing at 03 mode while green is locked to 00 and its transmission is maximized. I thought that by adjusting BS angle, I will be able to align red to 00 not disturbing green, but this was not the case. Maximum TRX I could get was 0.1. I've adjusted POX to get into PD and I can see PDH signal though I can't lock as cavity is still misaligned for red.

  7763   Thu Nov 29 09:58:06 2012 DenUpdatePEMDecreased RMS in Seismometers


[Den, Ayaka]

We found that seismometer was working and the calibration in the filter banks should have been wrong.
We turned off the all FM2 filter in RMS filter banks.

We also installed STS seismometer. It is under the BS. Now we have spectrum of three seismometers;

RA: the above plot is kind of unreadable and useless. Please replace with something legible and put in some words about why there is a wrong filter, what exactly it is, etc., etc. etc. And why would you leave in a filter which is not supposed to be on? We might as well leave a few secretly broken chairs in the control room...

 First of all, STS-2 is in the end of X arm, GUR2 is under BS, GUR1 is in the end of Y arm.

BLRMS were small because we applied calibration from counts to um/s two times. In the past we had calibration in the RMS BP filter bank (vel2vel = FM2). Now we have calibration in the seismometer input filter bank so we can save calibrated _OUT channels.

  7764   Fri Nov 30 02:40:44 2012 DenUpdateAdaptive FilteringYARM

I've applied FIR adaptive filter to YARM control. Feedback signal of the closed loop was used as adaptive filter error signal and OAF OUT -> IN transfer function I assumed to be flat because of the loop high gain at low frequencies. At 100 Hz deviation was 5 dB so I've ignored it.

I've added a filter bank YARM_OAF to C1LSC model to account for downsampling from 16 kHz to 2 kHz and put low-pass filter inside.

I've used GUR 1&2 XYZ channels as witnesses. Bandpass filters 0.4-10 Hz we applied to each of them. Error signal was filters using the same bandpass filter and 16 Hz 40 dB Q=10 notch filter. As an AI filter I used 32 Hz butterworth 4 order low-pass filter. Consequently, AI, bandpass and notch filters were added to adaptive path of witness signals.

I've used an FIR filter with 4000 taps, downsampling = 16, delay = 1, tau = 0, mu = 0.01 - 0.1. Convergence time was ~3 mins.


  7769   Fri Nov 30 22:11:50 2012 DenUpdateAdaptive FilteringARMS


This is interesting. I suppose you are acting on the ETMY.
Can you construct the compensation filter with actuation on the MC length?
Also can you see how the X arm is stabilized?

This may stabilize or even unstabilize the MC length, but we don't care as the MC locking is easy.

If we can help to reduce the arm motion with the MCL feedforward trained with an arm sometime before,
this means the lock acquisition will become easier. And this may still be compatible with the ALS.

Why did you notched out the 16Hz peak? It is the dominant component for the RMS and we want to eliminate it.

 I actuate on ETMY for YARM and ETMX for XARM. For now I did adaptive filtering for both arms at the same time. I used the same parameters for xarm as for yarm.

I've notched 16 Hz resonance because it has high Q and I need to think more how to subtract it using FIR filter or apply IIR.

I'll try MC stabilazation method.

Attachment 1: arms_oaf.pdf
  7771   Sat Dec 1 00:13:16 2012 DenUpdateAdaptive FilteringARMS and MC



 I actuate on ETMY for YARM and ETMX for XARM. For now I did adaptive filtering for both arms at the same time. I used the same parameters for xarm as for yarm.

I've notched 16 Hz resonance because it has high Q and I need to think more how to subtract it using FIR filter or apply IIR.

I'll try MC stabilazation method.

 Adaptive filtering was applied to MC and X,Y arms at the same time. I used a very aggressive (8 order) butterworth filter at 6 Hz as an AI filter for MC not to inject noise to ARMS as was done before

Mu for MC was 0.2, downsample = 16, delay = 1. I was able to subtract 1 Hz. Stack subraction is not that good as for arms but this is because I used only one seismometer for MC that is under the BS. I might install accelerometers under MC2.

EDIT, JCD, 18Feb2013:  Den remembers using mu for the arms in the range of 0.01 to 0.1, although using 0.1 will give extra noise.  He said he usually starts with something small, then ramps it up to 0.04, and after it has converged brings it back down to 0.01.

Attachment 1: arms_mcl_oaf.pdf
  7775   Sun Dec 2 00:37:49 2012 DenUpdateSUSTT cable problem

 This week I've got all TT stuff baked and today was testing eddy current damping and electronics.

In the beginning everything was good: ring magnets fit mirror holder holes and their interaction with actuation magnets is strong enough to keep damping magnets in the wholes. I've put the frame horizontally and kicked it, magnets were still in the whole. Brackets also fit to the TT frame.  

DSC_4945.JPG     DSC_4946.JPG

I've tested eddy current dumping during ring down measurements, it was strong enough.

DSC_4947.JPG    DSC_4948.JPG

Then I started to test electronics. I've provided signal to TT1 channels and could see it in the clean room. But then things went terrible. I just could not connect TT cables to OSEMS, there is not enough space in the OSEM for the connector to plug in.

DSC_4949.JPG     DSC_4952.JPG

Connector should be machines to be more narrow. There is actually no reason for a connector to have this shape. I think it was designed to fit perfectly the OSEM frame but turned out to be ~0.5 mm wider then it should be.

  7783   Tue Dec 4 18:06:35 2012 DenUpdateSUSTTs are ready

 Using instructions from Bram and Suresh, I was able to plug in connectors to BOSEMs. Today I've tested electronics, everything works good. Jamie made an medm screen and channels for TTs. Sliders for pitch and yaw go from -100 to 100 counts. Calibration to angle is 1e-5 rad / count.

TTs are in the clean room waiting for installation.

IMG_0105.JPG    IMG_0108.JPG

  7787   Tue Dec 4 21:57:04 2012 DenUpdateSUSTTs are ready


Please leave here what was the instruction by Bran and Suresh so that the other people can redo it sometime later!

 The connectors can be plugged into the BOSEMs if we loosen the two screws which hold down the mini-D connector and the flex circuit.  Tighten the screws after the connector is pluged in.

  7788   Tue Dec 4 23:08:46 2012 DenOmnistructureComputersnew (beta) version of nds2 installed on control room machines


I've installed the new nds2 packages on the control room machines.

 I've tried new nds2 Java interface in Matlab. Using findChannels method of the connection class I see only slow, DQ and trend channels. I could even download data online using iterate method. When it will be possible to do the same with fast non-DQ channels?

>> conn = nds2.connection('fb', 8088);
>> conn.iterate({'C1:LSC-XARM_OUT'})
??? Java exception occurred:
java.lang.RuntimeException: No such channel.
    at nds2.nds2JNI.connection_iterate__SWIG_0(Native Method)
    at nds2.connection.iterate(connection.java:91)

  7790   Wed Dec 5 03:25:32 2012 DenUpdateASCdithering

I wanted to center beams on the XARM cavity mirrors using c1ass model. I've run XARM setup script and then turned dithering on. Cavity went out of lock because calculated offsets were incorrect.

I was using TRX only and calculated rotation phases for ITM and ETM pitch and yaw. For this I've added a low pass filter into Q-quadrature bank and made DC value at the output to be zero by adjusting the phase. I've put gains (+1 or -1)  in the I quadrature such that output was positive.

Then I've set the sensing matrix to identity as I decided to deal with separate loops. Of coarse, they are mixed by the cavity, but at least in the control system they are distinguished. Old matrix summed error signals in one degree of freedom from both mirrors. This makes more sense but still not precise because coils are not ideally diagonalized.

Then I've adjusted gains for control loop for every degree of freedom. I've ended up with (0.1; 0.1; 0.1; -0.1). I did not use large gains as I wanted slow convergence because of the demodulation low-pass filter time response constant of 20 sec. Coupling (I quadrature) was reduced from (0.9, 0.3, 2.4, 1.2) to zeros (0-0.1) in ~5 minutes, TRX increased from 0.73 to 0.90.

There is one thing that I do not understand yet. I think controllers should minimize angle -> length coupling that is proportional to I-quadrature if phase is correct. But phase depends on alignment and when the feedback loops are on, phase drifts. I could see it during my measurement. But I did not find any script that smoothly tunes phase such that coupling is all in I-quadrature. I guess this is not hard to set a gradient descent algorithm that minimizes DC value of Q-quadrature. Or how this is usually done?

  7795   Thu Dec 6 02:55:46 2012 DenUpdateAlignmentc1ass

Today I've set c1ass model to improve alignment of X and Y arms. I've added all measured parameters to ASS scripts. I've also added a script to c1ass.adl that downloads calculated OFFSETs to corresponding ASC filter banks and blocks outputs. It should be called after alignment convergence.

XARM phase rotation and sensing matrix

Demodulator Phase rotation, degrees
ETM_P_T -5
ETM_Y_T -10
ITM_P_T -62
ITM_Y_T 163




-0.6116 -0.560 0.5660
ETM_Y_T -0.1600 1.0000 0.2310 -0.3979
ITM_P_T -0.0794 0.4960 1.0000 -0.8791
ITM_Y_T 0.0624 -0.3903 -0.4787 1.0000


Output gains were (-0.5, 0.5, -0.25, -0.25). XARM Gain was set to 0.5.


YARM phase rotation and sensing matrix

Demodulator Phase rotation, degrees
ETM_P_T 10
ITM_P_T 107
ITM_Y_T -35




0.3899 -0.515  -0.0309
ETM_Y_T 0.1017 1.0000 -0.3143 -0.5269
ITM_P_T -0.3505 0.0565 1.0000 -0.0945
ITM_Y_T -0.2085 -0.3607 0.6042 1.0000

Output gains were (-0.25, 0.25, 0.7, -0.7). YARM Gain was set to 0.8.


  7797   Fri Dec 7 02:02:23 2012 DenUpdateAlignmentc1ass

I suppose that there is also a similar system possible to align the arms in a continuous way; i.e. low level drives and very low bandwidth. Also something fast / slow for the the DRMI.

 c1ass was really useful today when we slowly aligned PZT and servo kept arms aligned to the input beam. I think it is possible to automate phase and matrix measurements. DRMI servo will be very useful.

Today I tried to investigate the mode in PRCL and MICH. I locked them but power build-up was only 27. The beam on the POP camera looked like interference of 00 mode and a long strip of fringes. (I wanted to make videocaptures but script is not working - the problem is that it is looking for /usr/lib/*.so.4 libraries but they were updated to *.so.5, I made a few links .so.4 -> .so.5 but this kept going for many libraries, so this should be fixed in a better way). 

We looked at PRM and BS faces and they had the same shape - interference of a circle with a strip. There were also a lot of bright spots all over the frames. Loops were closed and circle was not moving. Strip was oscillating at ~1Hz and also its position significantly changed with alignment. Looking at PRM face camera we made a conclusion that the length of the strip is ~5 cm and width ~1cm. Interesting that strip has plenty of power - approximately 10 times of transmitted beam when cavity is not locked. As a result POYDC was oscillating at the same frequency as a strip.

  7800   Sat Dec 8 04:12:38 2012 DenUpdateLSCprcl

 Today I wanted to check that AS and REFL beams are real and contain proper information about interferometer. For this I locked YARM using AS55_I and REFL11_I. Then I compared spectrum with POY11_I locking. Everything is the same. I've also adjusted phase rotations of AS55 (0.2 ->24) and REFL11 (-34.150 -> -43).

Then I've locked MICH and aligned EMTs such that ASDC was close to zero. Then I locked PRCL and aligned PRM. Power buildup was 50. 


  7801   Sun Dec 9 01:21:51 2012 DenUpdateLSCbeam inside DRMI is clipping on PR3 Tip-Tilt


 Today I wanted to check that AS and REFL beams are real and contain proper information about interferometer. For this I locked YARM using AS55_I and REFL11_I. Then I compared spectrum with POY11_I locking. Everything is the same. I've also adjusted phase rotations of AS55 (0.2 ->24) and REFL11 (-34.150 -> -43).

 I studied more carefully beam path inside DRMI using PRM face camera and found that beam is clipping on PR3 edge.

Step 1: PRCL LOCK, MICH LOCK, power build up 30.

Note: left is right and vice versa on the PRM camera


 Step 2: PRLC - UNLOCK, MICH - LOCK, PRM is still aligned. Right photo is AS port. I've slightly misaligned ITMs such that disturbance of AS beam is clearly seen.

PRM_UNLOCK.bmp       AS_UNLOCK.bmp


Step 3: PRCL - UNLOCK, MICH - LOCK, PRM misalined in yaw such such that the beam LASER -> PRM -> PR2 -> PR3 -> BS -> ITMX -> BS -> PR3 -> PR2 -> PRM -> PR2 -> PR3 is completely clipped on the TT edge. AS beam is now not clipped.


So the conclusion is that when PRC is not locked and beam is thin, it can avoid clipping. When PRC locked, beam size grows and it starts to clip. I think we need to move the mount next to PR3 because of it we to not have enough space to align the TT.

Step 4: PSL shutter is closed.


  7803   Mon Dec 10 03:02:03 2012 DenUpdateLSCbeam inside DRMI is clipping on PR3 Tip-Tilt



 Some explanation of how you define power buildup please. Also some plots showing the evidence.

 I think about power buildup as a ratio of the power in the cavity when it is locked and unlocked = (POYDC_LOCKED - POYDC_OFFSET) / (POYDC_UNLOCKED - POYDC_OFFSET). I do not multiply this number by PRM transmission.



For example, on the plot below power buildup is 15.


  7804   Mon Dec 10 10:13:41 2012 DenUpdateLSCbeam inside DRMI is clipping on PR3 Tip-Tilt


That's OK, but its best to use standard notation. The power recycling gain is defined as the power incident on the BS divided by the power incident on the PRM from the laser side. You should also compare it with the PRC gain that you expect from mirror transmissions.

  7806   Mon Dec 10 22:34:34 2012 DenUpdateLSCbeam inside DRMI is clipping on PR3 Tip-Tilt



That's OK, but its best to use standard notation. The power recycling gain is defined as the power incident on the BS divided by the power incident on the PRM from the laser side. You should also compare it with the PRC gain that you expect from mirror transmissions.

 I've made snapshots of PR2, PRM, ITMY and ITMX mirrors. Power buildup recycling gain (POWER BS / POWER PRM) was equal to 3-4.

PR2.bmp    PRM_LOCK.bmp    ITMY.png    ITMX.png

  7820   Thu Dec 13 03:20:48 2012 DenUpdateLSCbeam inside DRMI is clipping on PR3 Tip-Tilt



 I've made snapshots of PR2, PRM, ITMY and ITMX mirrors. Power buildup recycling gain (POWER BS / POWER PRM) was equal to 3-4.


 We've looked at PR2 face camera when PRM, BS and one of the ITMs were aligned. We saw an extra beam at PR2 when ITMX was aligned (right plot). This spot stays on the PR2 when prcl is locked.

PR2_ITMX.png   PR2_ITMY.png

Then we looked at PR3 transmission mirror and saw that the main beam is not on the edge of the mirror. Secondary beam is clipping on the mirror mount of PR3 that we see on BS_PRM camera.


Measured beam spot positions:

Optics Pitch, mm Yaw, mm
ITMX 5.6 1.5
ETMX -1.5 1.5
ITMY 4.8 -1.5
ETMY -1.4 5.6
PRM 2.7 4.1

"+" for pitch means that the beam is too high, "-" too low

"+" for yaw means that the beam is left if you look from the back, "-" is right

Beam spots were measured using x, y arm and prcl locking to the carrier.

  7821   Thu Dec 13 04:29:34 2012 DenUpdateSUSTT angle of incidence

I think the angle of incidence on TT inside BSC will be too large because of eddy current damping brackets. I've measured max possible angle of incidence

  Max angle of incidence, degrees
No bracket 72
Original bracket 45
New bracket (with no screws for tiny yaw magnets) 52

This means that we do not have too much range and there is a probability that 45 degree incident beam will start clipping. I think we should just cut off the central part of the bracket. We do not need it anyway, our eddy current damping due to corner magnets is good enough.

I've left the brackets near the laptop in the clean room.

  7822   Thu Dec 13 04:42:32 2012 DenUpdateSUSITMX local damping

Tonight we've noticed that ITMX local damping was kicking the optics. This happened because LR shadow sensor was not working. In ~30 minutes it started to work again. Evan and I were working on installation, moving and focusing cameras and locking prcl and mich. We've installed a camera on BSC and plugged it in to PSL_SPARE input.

I'm not sure that this can be correlated to ITMX LR shadow sensor behaviour.



  7825   Thu Dec 13 21:21:34 2012 DenUpdatePEMseismometers



 Looking at the PEM BLRMS, I noticed that the GUR1Z channel had a much reduced microseism compared to the GUR1X. Looking at the BLRMS screens everything seems ON, although its a mess (too many filters in the banks, etc. - clean this up, PEM people).

 Looking at the Z channel in DTT, I see that the Z spectra looks double high pass filtered below ~1 Hz.     Needs some attention in the daytime.

From Den and Ayaka's elog entry from Nov 29, its clear that this problem is there at that time. It seems that the seismometer was not even hooked up before then. Perhaps Tara returned the seismometer around Thanksgiving and then someone here hooked it up but neglected to log this work? If so, please make an elog now describing the installation of this sensor at the 40m and log any future work which takes place at the 40m lab even if you think it is inconsequential.

 Yesterday I wanted to recenter Guralps. I turned them off, understood that would be able to center them because we do not have power cable to Guralp box from Tara yet and turned them back on.

I've switched Guralp cables and spectrums are fine now.

Attachment 1: gur.pdf
Attachment 2: gur_fix.pdf
  7826   Fri Dec 14 01:42:53 2012 DenUpdateSUSTT angle of incidence

I've estimated max possible angle of incidence on TT if we allow 20mm tolerance for the beam size and 5 mm tolerance for spot location on the mirror. It turns out to be

alpha = 43 degrees

So we need to cut the central part of the bracket. Then the max possible angle of incidence will be

alpha = 63 degrees



We can start the vent on Monday and use TT with an old bracket for yaw damping and later during the week we can install the brackets after they will be baked.

  7945   Mon Jan 28 17:01:19 2013 DenUpdateLockingVideo of PRM-flat test cavity

What mode will you get if lock the cavity PRM - ITMY/ITMX/TEST MIRROR without PR2, PR3 and BS?

Is it possible to skip MC1, MC3 and lock the laser to this test cavity to make sure that this is not actuator/electronics noise?

  8048   Fri Feb 8 23:22:48 2013 DenSummaryModern Controlprogress report

 I wrote a small document on the application of LQG method to a Fabry-Perot cavity control.

Attachment 1: LQG.pdf
LQG.pdf LQG.pdf LQG.pdf LQG.pdf LQG.pdf LQG.pdf LQG.pdf
  8434   Wed Apr 10 03:59:41 2013 DenConfigurationIOOTurn on MCL


 My belief is that the frequency noise from the unstabilized MC is making the PRC locking harder. This will be investigated by tuning the shape of the MCL/MCF crossover so that we can turn it on without ruining the arm cavity spectra. Since the PRC length is ~2x smaller than the MC, we would expect it to be less sensitive to the MC frequency noise. But, since there is some common mode rejection in there, this may not be true. We'll only know by measuring PRC control signal with MCL on/off.

 I think if we make MCL UGF higher then 20 Hz, arm cavity spectra will feel it. It might be possible to use a combination of feedback and feedforward control from ground seismometers. I made MCL UGF at 3 Hz to reduce 1 Hz motion of the pendulum; feedforward OAF subtracted the stack at 3.3 Hz. Once OAF converged, I blocked adaptation and the filter became static FIR. MC length RMS was reduced by a factor of 10 and arm cavity spectra was not affected at frequencies >20 and became better at low frequencies. We'll see if this enough.

On the attached plot red color shows MC_F with MC_L OFF, blue - MC_L is ON, green - MC_L and OAF are ON.

Then I locked PRCL (using AS_Q and REFL55_I) to carrier and aligned the cavity. Power RIN was 50-70% and 00 beam on the POP camera was moving significantly. BS oplev was shaking the optics at 5 Hz. I fixed it, but there should be something else as RIN was still high.

Attachment 1: MCL.pdf
  8439   Thu Apr 11 02:49:18 2013 DenUpdateLockingPRCL on carrier

Jenne, Den

We suspect PRM shows significant length to angle coupling due to large oplev beam angle in yaw.  Tonight we locked PRCL with ITMs.

We could lock PRCL on carrier to power recycling gain of 15. Lock continued for a few hours but power rin RMS was 0.15.

We triggered and normalized on POP_DC. MICH gain was -1 (filters FM3-5), PRCL gain was -8 (filters FM2,4,5,6,9).

MC_L was OFF during locking.


Attachment 1: pop_rin.pdf
Attachment 2: power.png
  8440   Thu Apr 11 03:23:12 2013 DenUpdateGeneralMCL threshold

MC down script is too slow to block MC_L when the cavity goes out of lock. As a result the loop strongly kicks MC2. We decided to make a threshold inside MCS model on MC TRANS that will block MC_L during lock loss. This is a lower threshold. Upper threshold can be slow and is implemented inside MC up script.

Fast threshold can be set inside MC2 POS. I did not correct MC2 top level medm screen as it is the same for all core optics.

Note: Fast trigger will also block ALS signal if MC loose lock.

  8442   Thu Apr 11 03:38:40 2013 DenUpdateLockingangular motion

Spectra of BS, PRM, ITMX, ITMY are attached with oplevs ON and OFF (in units of urad). Loops reduce RMS from ~2urad to ~0.3urad but phase margin should be increased. REF traces show loop OFF. <-- really?

Note how PRM pitch and yaw spectra are different in the frequency range 0.5 - 7 Hz; yaw is factor of 50 larger then pitch at 2 Hz.

Attachment 1: oplevs.pdf
oplevs.pdf oplevs.pdf oplevs.pdf oplevs.pdf
  8446   Fri Apr 12 02:56:34 2013 DenUpdateLockingprcl angular motion

I compared PCRL and XARM angular motions by misaligning the cavities and measuring power RIN. Divergence angles for both cavities I calculated to be 100 urad.

XARM pointing noise sums from input steering TTs, PR2 and PR3 TTs, BS, ITMX, ETMY.

PRCL noise - from input TT, PRM, PR2 and PR3 TT, BS, ITMX, ITMY.

I would expect these noises to be the same as angular motion of different optics measured by oplves is simular. We do not have oplves on TT but they are present in both passes.

I measured RIN and converted to angle. Sharp 1 Hz resonance at XARM pointing spectrum is due to EMTX, it is not seen by PRCL. Other then that XARM is much quiter, especially at 3 - 30 Hz.

As PRM  is the main difference in two passes, I checked its spectrum. When PRCL was locked I excited PRM in pitch and yaw. I could see this excitation at RIN only when the peak was 100 times higher then background seismic noise measured by oplev.


Attachment 2: oplev_exc.pdf
  8449   Fri Apr 12 13:21:34 2013 DenUpdateLockingprcl angular motion


 How is the cavity g-factor accounted for in this calculation?

 I assume that pointing noise and dc misalignment couples 00 to 01 by a factor theta / theta_cavity

Inside the cavity 01 is suppressed by 2/pi*F*sin(arccos(sqrt(g_cav))).

For the XARM this number is 116 taking g-factor to be 0.32. So all pointing noise couples to power RIN.

Suppression factor inside PRC is 6.5 for g-factor 0.97. This means that 85% of jitter couples to RIN, I accounted for this factor while converting RIN to angle.

I did not consider translational motion of the beam. But still PRC RIN can not be explained by oples readings as we can see exciting optics in pitch and yaw. I suspect this RIN is due to PR3, as it can create stronger motion in yaw than in pitch due to incident angle and translational motion of the mirror. I do not have a number yet.

  8451   Sat Apr 13 23:11:04 2013 DenUpdateLockingprcl angular motion


For the PRM, it is also a mostly translation effect as calculated at the PRC waist position (ITM face).

I made another estimation assuming that PRCL RIN is caused by translation of the cavity axis:

  • calibrated RIN to translation, beam waist = 4mm
  • measured PRM yaw motion using oplev
  • estimated PR3 TT yaw motion: measured BS yaw spectrum with oplev OFF, divided it by pendulum TF with f0=0.9 Hz, Q=100 (BS TF), multiplied it by pendulum TF with f0 = 1.5 Hz, Q = 2 (TT TF with eddy current damping), accounted for BS local damping that reduces Q down to 10.

PRM and TT angular motion to cavity axis translation I estimated as 0.11 mm/urad and 0.22 mm/urad assuming that TTs are flat. We can make a more detailed analysis to account for curvature.

I think beam motion is caused by PR3 and PR2 TT angular motion. I guess yaw motion is larger because horizontal g-factor is closer to unity then vertical.

Attachment 1: pointing.pdf
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