Increased the transimpedance gain of the MC-Trans-Mon QPD ckt

The gain of this QPD was insufficient to see the light transmitted through the MC2.  The resulting voltage output was about  10 steps of the 16-bit ADC card.  As the input power, which is currently held at about 40mW may be increased to the vicinity of 2W (total output of the NPRO) we would have 500 ADC steps.  But the dynamic range of the ADC is 64k and  increasing the gain of this QPD ckt by a factor of 50 would enable us to utilise this dynamic range effectively.  However as we do not need a response faster than 10Hz from this ckt its response time has been limited by increasing the feedback capacitance value.

The ckt diagram for the QPD ckt is D980325-Rev-C1  .  The particular unit we are dealing with has the Serial No. 110.  The resistors R1, R2, R3, R4 are now 499 kOhm.  As per the guidelines in the ckt diagram, we increased the capacitance values C3,C4,C5,C6 to 2.2 nF.  The current cut off frequency for the MC-Trans-Mon is 145 Hz (computed).

Initially, while reassembling the QPD unit, the IDC 16 connector to the ckt board was reversed by mistake and resulted in the OP497 chip over-heating.  Consequently one of the opamps on the chip was damaged and showed monotonously increasing ouput voltage.  Todd Etzel gave us a spare OP497 and I replaced the damaged chip with this new one. The chips are also available from  Newark Stock No. 19M8991 . The connector has been marked to indicate the correct orientation. The ckt was checked by temporarily connecting it in the place of the PRM Optical lever QPD.  It worked fine and has been put back in its place at the MC2 Transmission.  The QPD was wiped with a lens tissue+Methanol  to remove dust and finger prints from its surface.

It may need to be repositioned since the beam would have shifted under the MC realignment procedure.

(Suresh, Yuta)

Background:
  Last week, we reduced the common mode displacement of the beam through MC1 to MC3. 
  Next work is to tilt the beam and center it.

What we did:
  1. Changed the offset going into 1201 Low Noise Amplifier(1201 is for adding +5V offset so that the feedback signal will be in the range of 0-10V)
  2. Using the last steering mirror(SM@PSL) and IM1, tilted the beam
  3. As the beam height changed alot(~0.5cm higher at IM1), MC1 reflection could not reach MCREFL PD. So, we tilted the mirror just after MC1, too.

Result:


Plan:
  - continue to tilt IM1 in small increments in order to reduce PIT/YAW to length coupling
      If large increments, it takes so much time re-aligning MC to get flashing!

By the way:
    The signal we kept saying "MCL" was not the error signal itself. It was a feed back signal(output of the mode cleaner servo board). The cable labeled "MC REFL" is the error signal. Compare MEDM screen C1IOO_MC_SERVO.adl and the mode cleaner servo board at 1X2. You will be enlightened.

(Suresh, Yuta)

Summary:
  We need MC to be locked and aligned well to align other in-vac optics.
  We continued to align the incident beam so that the beam passes the actuation nodes of MC1 and MC3.
  From the previous measurement, we found that beam height at IM1 has to be increased by ~3cm.
  Today, we increased it by ~1cm and achieved about 1/3 of the required correction.
  But we cannot proceed doing this because the beam is hitting IM1 at the edge already.

What is the goal of this alignment?:
  If the beam doesn't hit MC optics in the center, we see angle to length coupling, which is not good for the whole interferometer.
 
  Also, if the beam is tilted so much, transmitted beam though MC3 cannot go into FI at right after MC3.
  Say, FI has an aparture of 3mm and MC3-FT distance is 300mm. The beam tilt should be smaller than 3/300 rad. MC1-MC3 distance is 200mm, so the displacement at each mirror should be smaller than ~1mm.
  1mm is about 7% (see Koji's elog #2863) TO_COIL gain imbalance in A2L measurement.
 
  We are currently assuming that each coils are identical. If they have 5% variance, it is meaningless to try to reduce the beam displacement less than ~5%.

  So, we set the goal to 7%.

What we did:
  1. Leveled the MC table.

  2. Measured the table height using DISTO D3 laser gauge.
    PSL table 0.83m (+-0.01m)
    OMC table 0.82m
    MC table  0.81m

  3. Using the last steering mirror(SM@PSL) and IM1, tilted the beam vertically

Result:


  At t=0 (this morning), the beam tilt was ~40%/(MC1-MC3 distance). Now, it is ~30%/(MC1-MC3 distance).
  30%/(MC1-MC3 distance) is ~5/200 rad.

Plan:
 We have to somehow come up with the next story. Too much vertical tilt. What is wrong? Table leveling seems OK.
 - measure in-vac beam height
 - maybe OSEMs are badly aligned. we have to check that.

It didn't make sense in several points.

1. Is the Faraday aperture really 3mm? The beam has the gaussian radius of ~1.5mm. How can it be possible to go through the 3mm aperture?

2. Why the MC3-FT distance is the matter? We have the steering mirror after MC3. So we can hit the center of the Faraday.
But if we have VERTICAL TILT of the beam, we can not hit the center of the Faraday entrance and exit at the same time.
That would yield the requirement.

3. If each coil has 5% variance in the response, variance of the nodal point (measured in % of the coil imbalance) by those four coils will be somewhat better than 5%, isn't it?

1. We didn't measure the aperture size last night. We have to check that.

2. We have to measure the length of FI. Or find a document on this FI.

3. Yes, 5%/sqrt(4). But I didn't think the factor of 2 is important for this kind of estimation.

1. Look at the Faraday.

2. Look at the wiki. There is the optical layout in PNG and PDF.

3. 5% (0.8mm) and 2.5%(0.4mm) sounds a big difference for the difficulty, but if you say so, it is not so different.

Actualy, if you can get to the 5% level, it is easy to get to the 1-2% level as I did last time.
The problem is we are at the 15-20% level and can not improve it.

For Yuta's business, I intentionally misaligned the wideband EOM slightly to Yaw direction.  Good luck.

It should show a big AM component at photo detectors.

I touched only the top right knob on the EOM mount and tweaked it by exactly  2 turns in counterclockwise direction.

[Suresh, Jenne]

We have put together the new-old ETM towers.  These are the ones which were hanging out on the flow bench down the arm for years and years, and have recently been re-baked.  Interestingly, these are predominantly steel, whereas the newer ones are mostly aluminum.  This caused momentary drama while we scrounged for the correct screws (we needed more silver-plated screws than anticipated, since we were screwing into steel and not aluminum), however the miscellaneous clean hardware collection came to the rescue.  We did however use up all of the 1/4-20 3/4" silver plated screws, so hopefully no one else needs more later...

We only found 5 (enough for one of the two towers) spring plungers which are used to hold the OSEMs in place.  Suresh is sending an email to Steve to ask him to buy some more, so we can get them cleaned in time for use.  This is important, but not super urgent, since we have ~ 2 weeks before the ETMs will be ready for installation. 

Koji has not yet had a chance to inspect the ETM data sheets and choose for us which pair of ETMs to use (ATF sent the 4 ETMs in matched pairs).  So we will not begin the "arts and crafts" until tomorrow-ish.

[Koji and Kevin]

I was trying to characterize the REFL11 photodiode by shining a flashlight on the photodiode and measuring the DC voltage with an oscilloscope and the RF voltage with a spectrum analyzer. At first, I had the photodiode voltage supplied incorrectly with 15V between the +15 and -15 terminals. After correcting this error, and checking that the power was supplied correctly to the board, no voltage could be seen when light was incident on the photodiode.

We looked at the REFL55 photodiode and could see ~200 mV of DC voltage when shining a light on it but could not see any signal at 55 MHz. If the value of 50 ohm DC transimpedance is correct, this should be enough to see an RF signal. Tomorrow, we will look into fixing the REFL11 photodiode.

(Koji, Jenne, Yuta)

We found one of DAC cables had a poor contact.
That probably caused our too much "tilt" of the beam into MC.

Story:
  From the previous A2L measurement and MC aligning, we found that the beam is somehow vertically "tilted" so much.
  We started to check the table leveling and the beam height and they looked reasonable.
  So, we proceeded to check coil balancings using optical levers.
  During the setup of optical levers, I noticed that VMon for MC1_ULCOIL was always showing -0.004 even if I put excitation to coils.
  It was because one of the DAC cables(labeled CAB_1Y4_88) had a poor contact.
  If I push it really hard, it is ok. But maybe we'd better replace the cable.

What caused a poor connection?:
  I don't know.
  A month ago, we checked that they are connected, but things change.

How to prevent it:
  I made a python script that automatically checks if 4 coils are connected or not using C1:IOO_LOCKIN oscillator.
  It is /cvs/cds/caltech/users/yuta/scripts/coilchecker.py.
  It turns off all 3 coils except for the one looking at, and see the difference between oscillation is on and off.
  The difference can be seen by demodulating SUSPOS signal by oscillating frequency.
  If I intentionally unplug CAB_1Y4_88, the result output for MC1 will be;

==RESULTS== (GPS:973512733)
MC1_ULCOIL      0.923853382664 [!]
MC1_URCOIL      38.9361304794
MC1_LRCOIL      55.4927575177
MC1_LLCOIL      45.3428533919

Plan:
 - Make sure the cable connection and do A2L and MC alignment again
 - Even if the cables are ok, it is better to do coil balancings. See the next elog.

(Suresh, Yuta)

Background:
  Previous A2L measurement is based on the assumption that actuator efficiencies are identical for all 4 coils.
  We thought that the unbelievable "tilt" may be caused by imbalance of the coils.

Method:
  1. Setup an optical lever.
  2. Dither the optic by one coil and demodulate oplev outputs(OL_PIT or OL_YAW) in that frequency.
  3. Compare the demodulated amplitude. Ideally, the amplitude is proportional to the coil actuation efficiency.

What we did:
[MC2]
  MC2 is the least important, but the easiest.
  1. Placed a red laser pointer at MC2 trans table. During the installation, I moved the mirror just before QPD.
  2. Made a python script that measures coil actuation efficiency using the above method. I set the driving frequency to 20Hz.
  It is /cvs/cds/caltech/users/yuta/scripts/actuatorefficiency.py.
  The measurement result is as follows. Errors are estimated from the repeated measurement. (Attachment #1)

MC2_ULCOIL 1
MC2_URCOIL 0.953 ± 0.005
MC2_LRCOIL 1.011 ± 0.001
MC2_LLCOIL 0.939 ± 0.006

[MC1]
  For MC1, we can use the main laser and WFS1 QPD as an oplev.
  But we only have slow channels for QPD DC outputs(C1:IOO_WFS1_SEG#_DC).
  So, we intentionally induce RF AM by EOM(see Kiwamu's elog #3888) and use demodulated RF outputs of the WFS1 QPD(C1:IOO_WFS1_I/Q#) to see the displacement.
  1. Replaced HR mirror in the MCREFL path at AP table to BS so that we can use WFS1.(see Koji's elog #3878)
    The one we had before was labeled 10% pick-off, but it was actually an 1% pick-off.
  2. Checked LO going into WFS1 demodulator board(D980233 at 1X2).
    power: 6.4dBm, freq: 29.485MHz
  3. Turned on the hi-voltage(+100V) power supply going into the demodulator boards.
  4. Noticed that no signal is coming into c1ioo fast channels.
    It was because they were not connected to fast ADC board. We have to make a cable and put it in.

[MC3]
  Is there any place to place an oplev?

Plan:
 - prepare c1ioo channels and connections
 - I think we'd better start A2L again than do oplev and coil balancing.

I just wanted to remind you that the most up to date resource about the RF system upgrade, including photodiodes, is the SVN.

https://nodus.ligo.caltech.edu:30889/svn/trunk/alberto/40mUpgrade/RFsystem/

https://nodus.ligo.caltech.edu:30889/svn/trunk/alberto/40mUpgrade/RFsystem/RFPDs/REFL11/REFL11Schematics/40mUpgradeREFL11schematic.pdf

Because I was doing new things all the time, the wiki is not up to date. But the SVN has all I've got.

Please remember to cover the optical tables !

The cause is apparent! The connectors on the cables are wrong!
Currently only 50% of the pin length goes into the connector!

The hold-in range of the PLL must be greater than +/- 4MHz in order to bring the arm cavity to its resonance. 

(Hold-in range is the range of frequencies over which the PLL can track the input signal.)

However as I mentioned in the past elog (see this entry), the PLL showed a small hold-in range of about +/- 1MHz which is insufficient.

In this entry I explain what is the limitation factor for the hold-in range and how to enlarge the range.

(Requirement for hold-in range )

 We have to track the frequency of the green beat signal and finally bring it to a certain frequency by controlling the cavity length of the arm.

For this purpose we must be able to track the beat signal at least over the frequency range of 2*FSR ~ +/- 4MHz.

Then we will be able to have more than two resonances, in which both the end green and the PSL green are able to resonate  to the arm at the same time. 

And if we have just two resonances in the range, either one of two resonances gives a resonance for both IR and green. At this phase we just bring it to that frequency while tracking it.

  Theoretically this requirement can be cleared by using our VCO because the VCO can drive the frequency up to approximately +/- 5MHz (see this entry)

 The figure below is an example of resonant condition of green and IR. The VCO range should contain at least one resonance for IR.

(In the plot L=38.4m is assumed)

(an issue) 

However the measured hold-in range was about +/- 1MHz or less. This is obviously not large enough.

According to a textbook[1], this fact is easily understandable.

The hold-in range is actually limited by gains of all the components such as a phase detector's, a control filter's and a VCO's gain.

Finally it is going to be expressed by,

                         [hold-in range] = G_pd * G_filter * G_vco

 At the PD (Phase Detector which is a mixer in our case) the signal does not exceed G_pd [V] because it appears as G_pd * sin(phi).

When the input signal is at the edge of the hold-in range, the PD gives its maximum voltage of G_pd to maintain the lock.

Consequently the voltage G_pd [V] goes through to G_filter [V/V] and G_vco [Hz/V].

This chain results the maximum pushable frequency, that is, hold-in range given above equation.

In our case, the estimated hold-in range was 

                      [hold-in range] ~ 0.4 [V] * 3 [V/V] * 1 [MHz/V]

                          = 1.2 [MHz]

This number reasonably explains what I saw.

In order to enlarge the hold-in range, increase the gain by more than factor of 5. That's it.

* reference [1]  "Phase-Locked Loops 6th edition" Rolan E. Best

 We installed the ISS AOM in the PSL. The AOM was placed right after the EOM. The beam diameter is ~600 um at the AOM. The AOM aperture is 3 mm.

We monitored the beam size by scanning the leakage beam through the turning mirror after the AOM. The beam diameter changed from 525 um to 515 um at a fixed point. We decided that the AOM thermal lensing is not large enough to require a  new scan of the mode going into the PMC and we can proceed with PMC mode matching using the scan that was taken without the AOM (to be posted).

In order to enlarge the hold-in range I modified the control filter and increased the gain by factor of 25 in the PLL.

It successfully enlarged the range, however the lock was easily broken by a small frequency change.

So I put a low frequency boost (LFB) and it successfully engaged the PLL stiffer.

Now it can maintain the lock even when the frequency disturbance of about 1MHz/s is applied.

(enlargement of the hold-in range)

I modified the control filter by replacing some resistors in the circuit to increase the gain by factor of 25.

        - R18 390 [Ohm]  => 200 [Ohm]

    - R20 1000 [Ohm] => 5000 [Ohm]

    - R41 39 [Ohm] => 10 [Ohm]

 This replacement also changes the location of the pole and the zero

    - pole 1.5 [Hz] => 0.3 [Hz]

    - zero 40 [Hz] => 159 [Hz]

 Note that this replacement doesn't so much change the UGF which was about 20 kHz before.

It becomes able to track the input frequency range of +/- 5MHz if I slowly changes the frequency of the input signal. 

However the PLL is not so strong enough to track ~ 1 kHz / 0.1s frequency step.  

(make the PLL stiffer : a low frequency boost)

One of the solution to make the PLL stiffer is to put a boost filter in the loop.

I used another channel to more drive the VCO at low frequency. See the figure below.

The 80MHz VCO box originally has two input channels, one of these inputs was usually disabled by MAX333A.

This time I activated both two input channels and put the input signal to each of them.

Before signals go to the box, one of the signal path is filtered by SR560. The filter has G=20000, pole=0.3Hz. So it gives a big low frequency boost.

Once the PLL was achieved without the boost, I increased the filter gain of SR560 to 20000 because locking with the boost is difficult as usual.

 The PMC mode matching was initially done at low power ~150 mW. It was expected and found that at full power ~2 W (injection current 2.1 A) the mode matching got much worse:

the visibility degraded from 80% to 50% (1 - refl locked/refl unlocked) . The thermal lensing could be in the laser, EOM, or FI.

The first attached plot shows the scan of the beam after the EOM at low and full laser power. At full power the waist position is 10 mm after the turning mirror after the EOM and the waist size is 310 um.

The second plot shows the ABCD calculation for the mode matching solution.

I removed the MM lens PLCX-25.4-77.3-C and placed the PLCX-25.4-180.3-UV about 20 mm after the first PMC periscope mirror (the second mirror after the EOM).

The PMC visibility improved to 94% and the power through the PMC, as measured by the PMC transmission PD, went up by a factor of 2.

I connected the c1iscex computer to the dedicated DAQ network switch (located in 1X7).

This does not seem to have helped c1iscex stop spewing out "OMX: Failed to find peer index of board 00:00:00:00:00:00 (Peer Not Found in the Table)" at the rate of ~1 Gigabyte per minute.

c1iscex is currently off until a solution can be found.

[Koji / Yuta]

There were the guys who used the PENTEK 40pin connectors into the IDC 40pin connectors.
Those connectors are not compatible at all.

==> We replaced the connectors on the cables from DAC to IDC adapters to the dewhitening board for the vertex SUSs.

In addition, I found one of the Binary OUT IDC50pin connector has no clamp.

==> We put the IDC50pin clamp on it.

PENTEK connectors were inserted. The latches are not working!

the vertical pitch is different between PENTEK and IDC!

Wow! Where is the clamp???

[Jenne, Suresh]

Selection of ETMs

Of the four ETMs (5,6,7 and 8) that are with us Koji gave us two (nos. 5 and 7) for use in the current assembly.  This decision is based on the Radius of Curvature (RoC) measurements from the manufacturer (Advanced Thin Films).   As per their measurements the four ETMs are divided into two pairs such that each pair has nearly equal RoC. In the current case, RoCs are listed below:

The discrepancy between the measurements from these two companies leaves us in some doubt as to the actual radius of curvature.  However we based our current decision on the measurement of Advanced Thin Films. 

Assembly of ETMs

We drag wiped both the ETMs (5 and 7) and placed them in the Small Optic Gluing Fixture.  The optics are positioned with the High Reflectace side facing downwards and with the arrow-mark on the Wire Standoff side (big clamp).  We then used the microscope to position the Guide Rod and the Wire Standoff in the tangential direction on the ETMs (step 4 of the procedure specified in E010171-00-D)

We will continue with the rest of the assembly tomorrow.

We decided to ignore the computer script outputs for the beam positions and use instead the eyeball method to get the beam into the MC:

1. Adjust PSL launch beam to get the beam centered on IM1.
2. Eyeball the beam to hit the center of MC1. We can get this pretty good by using the brackets to get the vertical and using the centering of the input/refl beams to center it horizontally.
3. Use MC3 suspension to hit the center of MC2. We did this by hitting each of the 3 EQ stop screw heads and triangulating the MC3 bias settings.
4. Use MC2 bias to hit the center of MC1.
5. Use MC1 to get good flashes.
6. Use all 3 MC sus biases to maximize the transmitted light and minimize the REFL DC.

With this rough alignment in place, we leave it to Yuta to finish the coil balancing and the A2L. We will have an aligned MC in the morning and will start the BS chamber alignment.

[Jenne and Kevin]

I started testing the REFL55 photodiode. With a light bulb, I saw ~270 mV of DC voltage from the photodiode but still could not see any RF signal. I connected the RF out from the spectrum analyzer to the test input and verified that the circuit was working.

I then set up the AM laser and looked at the laser light with REFL11 and an 1811 photodiode. I was able to see an RF signal and verified that the resonant frequency is 55 MHz.

The current setup is not very reliable because the laser is not mounted rigidly. Next, I will work on making this mounting more reliable and will continue to work on finding an RF signal with a flashlight.

Background:
  Last night, we found that one of DAC channels are poorly connected, so we fixed the connectors.
  Rana and Koji used their incredible eyeballs to roughly align MC.
  Next thing to do is to balance the coils, but it takes some time for the setup.
  So, we decided to do A2L anyway.

What I did:
  Using the last steering mirror at PSL table and IM1, changed the incident beam direction to align MC.

Result:

 
  I was amazed by their eyeballs.
  I turned the nobs of SM@PSL and IM1 in small increments, so I never lost TEM00.

Is it enough?:
  The length of the whole faraday is about 20cm and aperture diameter is about 12mm. (I couldn't measure the aperture size of the core)
  The beam is about 9mm diameter at 6w.
  So, if the beam is vertically tilted at more than ~3/200rad, it(6w) cannot go through.
  3/200 rad is about 20% difference in position at MC1 and MC3.
  So, the result meets the requirement.

  Also, assuming that coils have 5% imbalance, the beam position I measured have ~3% error.
  So, to do more precise beam centering, we need to balance the coils.

Test:

Look at the effects of the ADC voltage range on the ADC noise floor.

ADC input was terminated with 50 ohms.  We then looked at the channel with DTT. This was at +/- 10 V range.  We used C1:SUS-PRM_SDSEN_IN1 as the test channel.

The map.c file (in /opt/rtcds/caltech/c1/core/advLigoRTS/src/fe/ ) then had two lines added at line 766.

//JCB temporary 2.5V test, remove me
  adcPtr[devNum]->BCR &= 0x84240;

This hard coded the 2.5 V range (we default to the 10 V range at the moment).

We then rebuilt the c1x02 model and reran the test.

Finally, we reverted the code change to map.c and rebuilt c1x02.

Results:
I've attached the DTT output of the two tests.

It appears the ADC is limited by 1.6 uV/rtHz.  Hence the increase in noise in counts by a factor of 4 when we drop to +/- 2.5 V from +/- 10 V.

 I've been trying to get a PID loop running for the green locking and I've discovered that some of the directories in the path for the Perl Modules are now obselete. Specifically, since the scripts directory has been moved from /cvs/cds/caltech/scripts to /cvs/cds/rtcds/caltech/c1/scripts the following locations in the Perl @INC path list need to be changed:

• /cvs/cds/caltech/scripts/general
• /cvs/cds/caltech/scripts/general/perlmodules

I've added the above directories to the PERL5LIB path in /cvs/cds/caltech/cshrc.40m.

setenv PERL5LIB /cvs/cds/caltech/scripts/general:

/cvs/cds/caltech/scripts/general/perlmodules:

/cvs/cds/caltech/libs/solaris9/usr_local_lib/perl5/5.8.0/:

/cvs/cds/rtcds/caltech/c1/scripts/general:

/cvs/cds/rtcds/caltech/c1/scripts/general/perlmodules

 I've set up a PID script that senses the EX-PSL Green Beat note (from the frequency counter) and actuates on the temperature of the end laser to drive the beat note to a given setpoint.

• I've added the necessary EPICS channels to c1iscaux and rebooted it so that the channels are live. They are listed in a new database file slow_grnx_pid.db
• This database was added to the list of those loaded by startup.cmd.  
• The PID script, GRNXSlowServo, is just a modified version of FSSSlowServo.
• The version I've been running is currently in /cvs/cds/caltech/users/abrooks/.
• There's also an MEDM screen in this directoy, C1LSC_EX_GRN_SLOW.adl, there that shows the PID settings.

Right now the script only passes the initial sanities checks, that is:

1. It runs.
2. You can enable/disable it without any errors and it starts actuating.

The settings all need to be tuned up - e.g. maximum_increment, hard_stops, time_step, PID constants.

Additionally, the units in the whole thing are pretty useless - some of the channels are in VOLTS, others in WATTS. I'd like to change all these to be in Hz. 

EPICS channels added:

• grecord(ao,"C1:LSC-EX_GRN_SLOWKD")
• grecord(ao,"C1:LSC-EX_GRN_SLOWKP")
• grecord(ao,"C1:LSC-EX_GRN_SLOWKI")
• grecord(ao,"C1:LSC-EX_GRN_PID_SETPT")
• grecord(ao,"C1:LSC-EX_GRN_TIMEOUT")
• grecord(stringin,"C1:LSC-EX_GRN_SLOWVERSION")
• grecord(bi,"C1:LSC-EX_GRN_SLOWLOOP")
• grecord(bi,"C1:LSC-EX_GRN_DEBUG")
• grecord(bi,"C1:LSC-EX_GRN_SLOWBEAT")

I maximized the laser power by rotating the HWP after the NPRO.

If someone works on the MC locking, one should decrease it again.

[Koji Yuta]

We found one of the ADC cables were left unconnected. This left the MC suspensions uncontrollable through the whole afternoon.
Please keep the status updated and don't forget to revert the configuration...

We changed the range of the two SUS AA boards in the corner from +/-2 V to +/-10 V by changing the supply voltage from +/-5 V to +/-15 V. The change was made by switching the AA power feed wires on  the cross connect. The max supply according to the spec of DRV134/INA134 is +/-18 V.

We checked the new range by applying the voltage to the input of AA and measuring the output going to the ADCs. The local damping MC1,2,3 appears to work.

Motivation:
  MC is aligned from the A2L measurement, but to do the beam centering more precisely, we need coils to be balanced.
  There are several ways to balance the coils, like using oplev or WFS QPD RF channels.
  But oplev takes time to setup, especially for MC3. Also, c1ioo WFS channels were newly setup and haven't been checked yet.
  So, I decided to use OSEM sensors.
  An OSEM sensor itself is sensitive to every DOF of an optic motion, but we can diagonalize them using 4 OSEM sensors and proper input matrix.

Method:
  1. Measure transfer functions between
     ULSEN and URSEN (H_UR(f))
     ULSEN and LRSEN (H_LR(f))
     ULSEN and LLSEN (H_LL(f))

  2. Make a matrix A.

    A =  [[ 1           1           1          ]
          [ H_UR(f_pos) H_UR(f_pit) H_UR(f_yaw)]
          [ H_LR(f_pos) H_LR(f_pit) H_LR(f_yaw)]
          [ H_LL(f_pos) H_LL(f_pit) H_LL(f_yaw)]]

    where f_dof are resonant frequencies.

  3. A is

    s = Ad

   where vectors s^T=[ULSEN URSEN LRSEN LLSEN] and d^T=[POS PIT YAW].
   So,

    d = Bs = (A^TA)^(-1)A^Ts

   where A^T is transpose of A.

   B is the input matrix that diagonalizes 3 DOFs.

What I did:
  1. Measured the TFs using diaggui and exported as ASCII.

  2. Made a script that reads that TF file, calculates and sets a new input matrix B.
    /cvs/cds/caltech/users/yuta/scripts/inputmatrixoptimizer.py
   You need to set resonant frequencies to use the script.

   New input matrices for MCs are;

C1:SUS-MC1_INMATRIX
[[ 1.17649712  0.94315611  0.85065054  1.02969624]
 [ 0.55939288  1.28066594 -0.85235358 -1.3075876 ]
 [ 1.23467139 -0.74521928 -1.29394051  0.72616882]]

C1:SUS-MC2_INMATRIX
[[ 1.12630748  1.01451545  0.9013457   0.95783137]
 [ 1.03043025  0.67826036 -1.37270598 -0.91860341]
 [ 0.83546271 -1.26311029 -0.6456881   1.2557389 ]]

C1:SUS-MC3_INMATRIX
[[ 1.18212117  1.26419447  0.77744155  0.77624281]
 [ 0.79344415  0.84959646 -1.10946339 -1.247496  ]
 [ 1.00225331 -0.84807863 -1.21772132  0.93194674]]

  I ignored SIDE this time.

Result:
  Spectra of each SUSDOF_IN1_DAQ before diagonalization (INMATRIX elements all 1 or -1) were


  After diagonalization, spectra are


  As you can see, each SUSDOF has only single peak (and SIDE peak) after the diagonalization.
  SUSSIDE still has 4 peaks because SIDE is not included this time.

  For MC2, POS to SUSPIT and POS to SUSYAW got worse. I have to look into them.

Effect of resonant frequency drift:
  As you can compare and see from the spectra above, resonant frequencies of MC1 are somehow drifted(~0.5%) from Nov 9 to Nov 13.
  If resonant frequency you expected was wrong, calculated input matrix will be also wrong.
  The effect of 0.5% drift and wrong input matrix can be seen from this spectra. DOFs are not clearly separated.
 

Plan:
 - learn how to use diaggui from command line and fully automate this process
 - balance the coils using these diagonalized SUSPOS, SUSPIT, SUSYAW

Now that we have increased the range of the AA to +/- 10 V I have increased the PRM side OSEM transimpedance from 29 kV/A to 161 kV/A by changing the R64 in the satellite box. The first attached plot shows the ADC input spectrum before and after the change with analog whitening turned off. The PD voltage readback went up from 0.75 to 4.2 V. The second attached plot shows the sensor, ADC, and projected shot noise with analog whitening turned on and compensated digitally. The ADC calibration is 20 V/ 32768 cts. The PRM damping loops are currently disabled.

I checked for oscillation by looking at the monitor point at the whitening board. There was no obvious oscillation on a scope - the signal was 20 mV p-p on 1 us scale which was very similar to the LL channel.

Since Nodus is a Solaris machine it can barely handle doing the ImageMagick commands (such as convert and import). I removed the auto MEDM snapshot routine from it

awhile ago and I think the rate of ELOGD crashes has decreased, although its not definitive.

The snapshots have now been re-actived to run on MAFALDA, after I fixed the absolute pathnames in the scripts and installed (via yum) the packages that mafalda

needed to run this (Xvfb, openmotif, compat, etc.). The snapshots web page is now refreshing by itself and the statScreen/cronjob.sh is running on mafalda 5x per hour.

https://nodus.ligo.caltech.edu:30889/medm/screenshot.html

We missed a factor of 2 in the ADC calibration: the differential 16 bit ADC with +/-10 V input has 20 V per 32768 counts (1 bit is for the sign). I confirmed this calibration by directly measuring ADC counts per V.

So the ADC input voltage noise with +/-10V range around 100 Hz is 6.5e-3 cts/rtHz x 20V/32768cts =  4.0 uV/rtHz. Bummer. 

The ADC quantization noise limit is 1/sqrt(12 fs/2)=1.6e-3 cts/rtHz. Where the ADC internal sampling frequency is fs=64 kHz. If this would be the limiting digitization noise source then the equivalent ADC input voltage noise would be 1 uV/rtHz with +/-10 V range.

We realized that the SRM sensors are connected to the readout but just sitting on the BS in vacuum table with no magnets and therefore no shadows in them. We swapped the inputs to the SRM and PRM satellite boxes to use the higher transimpedance gain of the PRM side sensor. The attached plot shows the current spectrum in this configuration. The PD readback voltage was 9.5 V. Since this is close to the rail we put a slightly higher voltage into the AA of this channel to test that we can read out more ADC counts to make sure we are not saturating. The margin was 15800 vs 15400 counts with p-p of 5 counts on the dataviewer 1 second trend. We returned all cables to nominal configuration.

The calibration from A to m is 59 uA/1 mm.

[Valera, Jenne]

We pondered the idea of clamping the PRM optic to measure the OSEM noise.  So we opened up the BS tank to give this a try.  We rediscovered that Jenne is too short to reach the other side of the PRM tower, so we couldn't fully clamp the optic (when is Jaime coming again? He's kind of tall...)  If we only did the back 2 EQ stops, the optic would still be able to rock, and thus defeat the purpose of clamping anyway.  So we didn't go for it. 

While we were in there we saw that the SRM OSEMs were just hanging out on the table, and decided to go with them.  See Valera's elog for details on our measurement.  We closed up the tank without making any changes to anything.

In other news, we still need to figure out how to change up the connectors to get those OSEMs over to the ITM table.  This needs to happen pretty soonish. 

IF I believe this calibration and IF I believe that the noise is the same with no magnet in there, then its almost 1 nm/rHz @ 1 Hz.

I am guessing that Jenne's calculation will show that this is an unacceptably high level of OSEM sensor noise, OAF-wise.

Problem:

c1iscex floods the network with about 1 gigabyte of error messages in a few seconds, writing to a log file in /opt/rtcds/caltech/c1/target/fb/logs/

Temporary change:

I commented out the following line in the rc.local file on the fb machine in the /diskless/root/etc/ directory:

#nice --20 ./mx_stream -s "$SYSTEMS" -d fb:0 >& logs/$HOSTNAME.log&

This disables the automatic start up of the mx_streams code on all the front ends.  This will prevent the network being brought to its knees by c1iscex while we debug the problem.

It also means on a reboot of the front ends, the mx_stream process needs to be started by hand until this change is reverted.

To do this, log into the front end and then change directory to /opt/rtcds/caltech/c1/target/fb

For c1sus, run:

./mx_stream -s c1x02 c1sus c1mcs c1rms c1rfm  -d fb:0

For c1ioo, run:

./mx_stream -s c1x03 c1ioo -d fb:0

Stabilizing the beat note frequency using Yuta's temperature servo (see this entry)

I was able to acquire the PLL of 80MHz VCO to the real green signal.

Some more details will be posted later.

Has C1PSL rebooted? Has burtrestore been forgotten? Even without elog?

We found some settings are wrong and the PMC has pretty low gain.

Yeah. Joe and I rebooted c1psl a couple of times this morning. I didn't realize the burtrestore wasn't automatic.

Since we are going to lock the MC today, I aligned it back to the default place.

[Valera Yuta Kiwamu Koji]

Kiwamu burtrestored c1psl. We measured the power levels around the PMC.

With 2.1A current at the NPRO:

Pincident = 1.56W
Ptrans_main = 1.27W
Ptrans_green_path = .104W

==> Efficiency =88%

----

We limited  the MC incident power to ~50mW. This corresponds to the PMC trans of 0.65V.
(The PMC trans is 1.88V at the full power with the actual power of 132mW)

[Steve, Jenne, Suresh, Koji]

The remaining test mass chambers have been opened, and have light doors in place.  Now we can do all of the rest of the IFO alignment, and then (hopefully) button up before the New Year.

Problem:

c1iscex was spamming the network with error messages.

Solution:

Updated the front end codes to current standards (they were on the order of months out of date).  After fixing them up and rebuilding the codes on c1iscex, it no longer had problems connecting to the frame builder.\

Status:

I can look at test points for ETMX.  It is not currently damping however.

To Do:

Move filters for ETMX into the correct files. 

Need to add a Binary output blue and gold box to the end rack, and plug it into the binary output card.  Confirm the binary output logic is correct for the OSEM whitening, coil dewhitening, and QPD whitening boards. 

Get ETMX damped.

Figure out what we're going to do with the aux crate which is currently running y-end code at the new x-end.  Koji suggested simply swapping auxilliary crates - this may be the easiest.  Other option would be to change the IP address, so that when it PXE boots it grabs the x-end code instead of the y-end code.

Current CDS status:

 I checked the slow servo and the PLL of 80MHz VCO using the real green beat note signal.

 The end laser is not locked to the cavity, so basically the beat signal represents just the frequency fluctuation of the two freely running lasers.

 The PLL was happily locked to the green beat note although I haven't fedback the VCO signal to ETMX (or the temperature of the end laser).

 It looks like we still need some more efforts for the frequency counter's slow servo because it increases the frequency fluctuation around 20-30mHz.

 (slow servo using frequency counter)

   As Yuta did before (see his entry), I plugged the output of the frequency counter to an ADC and fedback the signal to the end laser temperature via ezcaservo.

The peak height of the beat note is bigger than before due to the improvement of the PMC mode matching.

The peak height shown on the spectrum analyzer 8591E is now about -39dBm which is 9dB improvement. 

     The figure below is a spectra of the frequency counter's readout taken by the spectrum analyzer SR785.

When the slow temperature servo is locked, the noise around 20-30 mHz increased.

I think this is true, because I was able to see the peak slowly wobbling for a timescale of ~ 1min. when it's locked.

But this servo is still useful because it drifts by ~5MHz in ~10-20min without the servo.

Next time we will work on this slow servo using Aidan's PID control (see this entry) in order to optimize the performance.

In addition to that, I will take the same spectra by using the phase locked VCO, which provides cleaner signal.

(acquisition of the PLL)

 In order to extract a frequency information more precisely than the frequency counter, we are going to employ 80MHz VCO box.

 While the beat note was locked at ~ 79MHz by the slow servo, I successfully acquired the PLL to the beat signal.

 However at the beginning, the PLL was easily broken by a sudden frequency step of about 5MHz/s (!!).

I turned off the low noise amplifier which currently drives the NPRO via a high-voltage amplifier, then the sudden frequency steps disappeared.

After this modification the PLL was able to keep tracking the beat signal for more than 5min.

(I was not patient enough, so I couldn't stand watching the signal more than 5min... I will hook this to an ADC)

I have selected a set of 16 magnets which have a B field between 900 to 950 Gauss (5% variation) when measured in the following fashion.

I took a Petri-dish, of the type which we usually use for mixing the glue, and I placed a magnet on its end.  I then brought the tip of the Hall-probe into contact with the Petri-dish from the opposite side and adjusted the location (and orientation) of the probe to maximise the reading on the Gauss meter.

The distribution of magnets observed is listed below

The set of sixteen has been have been placed inside two test tubes and left on the optical bench (right-side)  in the clean room.

(Koji, Yuta)

We aligned the Faraday after MC and we are now ready to install PRM.

Background:
  MC was roughly aligned (beam spot ~0.7mm from the actuation center).
  So, we started aligning in-vac optics.
  First thing to align was the Faraday after MC3.

What we did:
  1. Ran A2L.py for confirmation.(Second from the last measurement point on the A2L result plot)

  2. Aligned the Faraday so that MC3 trans can go through it. We moved the Faraday itself, while we didn't touch IM2.
     We turned the pitch nob of the last steering mirror at PSL table in CCW slightly in order to lower the beam at the Faraday by ~1mm.

  3. During the alignment, we found that the polarization of the incident beam was wrong. It should have been S but it was P.
     As there is the HWP right before the EOM, Rana rotated it so as to have the correct polarization of S on the EOM and the MC.
     Note that the PMC and the main interferometer are configured to have P-pol while the MC is to have S-pol.

  4. Setup the video camera to monitor the entrance aperture of the Faraday. It required 4 steering mirrors to convey the image to the CCD.

  5. Moved all of the OSEMs for MC1 and MC3 so that the sensor output can have roughly half of their maxima.

  6. Ran A2L.py. (The last measurement point on the A2L result plot)

  7. Aligned the IO optics so that the beam goes Faraday -> MMT1 -> MMT2 -> SM3.

Result:
  1. OSEM sensor outputs for MC1 and MC3 are;

  2. A2L result is;



     The beam position slightly got lower(~0.2mm), because we touched SM at PSL table.
     Alignment slider values changed because we moved MC1 and MC3 OSEMs.

  3. Now, MC_RFPD_DCMON is ~0.39 when MC unlocked and ~0.083 when locked.
     So, the visibility of MC is ~79% (for S-pol).

  4. Now the incident beam to the MC has S polarization, the cavity has higher finesse. This results the increased MC trans power.
     It was ~8e2 when the polarization was P, now it is ~4.2e3 when the MC is locked.

  5. The beam reached SM3 at BS table. The alignment of the SM2, MMT1, MMT2 were confirmed and adjusted.

  6. All pieces of the leftover pizza reached my stomach.

Plan:
  - Install PRM to the BS chamber.
  - Align PRM and get IFO reflection beam out to the AP table
 

 [Aidan, Kiwamu]

Kiwamu and I roughly calibrated the analogue output from the SR620 frequency counter yesterday. The input channel, intuitively named C1:PSL-126MOPA_126MON, now reads the measured frequency in MHz with an error of about 0.1MHz - this is, I think, due to the bit noise on the D/A conversion that Kiwamu discovered earlier. That is, the output range of the SR620 corresponds to around 100MHz and is digitized at 10-bit resolution, and ...

100MHz/(10^2) ~= 0.098MHz. [Sad Face]

Calibration:

We set the EPICS range to [-100, 100] (corresponding to [-5V, 5V]), connected a Marconi to the Freq Counter, input a variety of different frequencies and measured the counts on the EPICS channel.

The linear fit to the calibration data was F = 2.006*EPICScount - 0.2942. From this we worked out the maximum and the minimum for the range settings that give the channel in MHz: EGUF = -200.8942 and EGUL = 200.3058. The previous range was [-410, 410]

I restored C1:PSL-126MOPA_126MON to its original settings (EGUF = -410, EGUL = 410) and added a new calc channel called C1:LSC-EX_GRNBEAT_FREQ that is derived from C1:PSL-126MOPA_126MON. The calibration in the new channel converts the input to MHz.

grecord(calc, "C1:LSC-EX_GRNBEAT_FREQ")
{
        field(DESC,"EX-PSL Green Beat Note Frequency")
        field(SCAN, ".1 second")
        field(INPA,"C1:PSL-126MOPA_126MON")
        field(PREC,"4")
        field(CALC,"0.4878*A")
        }

I rebooted c1psl and burtrestored.