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ID Date Authorup Type Category Subject
  1250   Fri Jan 23 14:00:02 2009 YoichiUpdatePSLPMC transmission is down

Quote:
The PMC transmission is going down.
I have not relocked the PMC yet.


I tweaked the alignment to the PMC.
The transmission got back to 2.65. But it is still not as good as it was 3 days ago (more than 3).

It is interesting that the PMC transmission is inversely proportional to the NPRO output.
My theory is that the increased NPRO power changed the heat distribution inside the power amplifier.
Thus the output mode shape changed and the coupling into the PMC got worse.
MOPA output shows a peak around Jan-21, whereas the NPRO power was still climbing up.
This could also be caused by the thermal lensing decreasing the amplification efficiency.
Attachment 1: LaserPower.png
LaserPower.png
  1254   Wed Jan 28 12:42:51 2009 YoichiUpdatePSLMOPA dying
Yoichi, Jenne, Peter

As most of you know, the MOPA output power has been declining rapidly since Jan 21. (See the attachment 1)
There was also an increase in the NPRO power observed in LMON, which is an internal power monitor of the NPRO.
Similar trend can be seen in 126MON, which picks up some scattered light from the NPRO but there may be some contributions from the PA output.

The drop in the AMPMON, LMON and CURMON (NPRO current) from the middle of Jan 26 to the end of Jan27 was caused by me.
I tried to decrease the NPRO current to put the NPRO power back to the level when the MOPA output was higher. But it did not bring back the MOPA power.
So I put back the current after an hour. This caused the sharp power drop on Jan26.
By mistake, I did not fully recover the current at that time and left it like that for a day. This accounts for the long power drop period continued until Jan27.

Shortly after I tweaked the current, the MOPA output power started to fluctuate a lot. This drives the ISS crazy.
To see if this was caused by the NPRO or power amplifier,
we decided to fix the 126MON to monitor the real NPRO power.
We opened the MOPA box and installed a mirror to direct a picked off NPRO beam to the outside of the box through an unused hole.
We set up a lens and a PD outside of the MOPA box to receive this beam. The output from the PD is connected to the 126MON cable.
So 126MON is now serving as the real monitor of the NPRO power. It has not yet been calibrated.

The second attachment shows a short time series of the MOPA power and NPRO power. When the beam is blocked, the 126MON goes to -22.
So the RIN of the NPRO is less than 1%, whereas the MOPA power fluctuates about 5%. There is also no clear correlation between the power fluctuation of the MOPA and the NPRO. So probably the MOPA power fluctuation is not caused by NPRO.

At this moment, all the feedback signals (current shunt, slow and fast actuators) are physically disconnected from MOPA box so that we can see the behavior of MOPA itself.
Attachment 1: Recent10Days.png
Recent10Days.png
Attachment 2: 126_MOPA.png
126_MOPA.png
  1255   Wed Jan 28 12:51:32 2009 YoichiUpdateComputersMegatron is dying
For the past three days, Megatron has been making a huge noise. Sounds like a fan is failing.
There is an LED with "!" sign on the front panel. It is now orange. Looks like some kind of warning.
We can login to the machine. "top" shows the CPU load is almost zero.
Shall we try rebooting it ?
  1256   Wed Jan 28 19:08:50 2009 YoichiUpdatePSLLaser is back (sort of)
Yoichi, Peter, Jenne

Summary:
We found that the chiller water is not going to the NPRO base. It was hot whereas it was cold when I touched it a few months ago.
I twisted the needle valve on the water line to the NPRO base. Then we heard gargling noise in the pipe and the water started to flow.
The laser power is now climbing up slowly. The noisiness of the MOPA output is reduced.

I will post more detailed entry explaining my theory of what actually happened later.
Attachment 1: Improving.png
Improving.png
  1257   Thu Jan 29 13:52:34 2009 YoichiUpdatePSLLaser is back (sort of)
Here is what I think has happened to the laser.

After the chiller line to the NPRO base clogged, the FSS slow slider went down to keep the laser frequency constant.
It is evident in the attachment 1 that the behavior of the slow slider and the DTEC (diode temp. stabilization feedback signal) are almost the same except for the direction. This means the slow servo was fighting against the increased heat caused by the lack of the cooling from the bottom.
DTEC was doing the same thing to keep the diode temperature constant.

Even though the slow actuator (a Peltier on the crystal) worked hard to keep the laser frequency constant, one can imagine that there was a large temperature gradient in the crystal and the mode shape may have changed.

Probably this made the coupling of the NPRO beam to the PA worse. It may also have put the NPRO in a mode hopping region, which could be the cause of the noisiness.

Right now, the MOPA power is 2.7W.
The FSS, PMC, MZ are locked. At first, the PMC locked on a sideband. I had to twiddle the phase flip button of the PMC servo to lock the PMC. Probably this is another sticky channel, which needs to be tweaked after a reboot of c1psl. I added a code to do this in /cvs/cds/caltech/scripts/Admin/slider_twiddle.

Currently the ISS is unstable. Kakeru and I are now taking OPLTF of the servo.
Looks like the phase margin at the lower UGF is too small.
Attachment 1: SlowDC.pdf
SlowDC.pdf
  1260   Thu Jan 29 18:10:13 2009 YoichiUpdatePSLISS Bad
Kakeru, Yoichi

As we noted before, the ISS is unstable. You can see the laser power oscillation around 3Hz.
We took the open-loop transfer function of the ISS around the lower UGF.
The phase margin is almost non-existent.
It was measured with the ISS gain slider at 2dB (usually it was set to 7dB).
So if we increase it by 3dB, it is guaranteed to be unstable.

The higher UGF has also a small phase margin (about 12deg.).
With the ISS gain slider at 2dB, the upper UGF is too low, i.e. the UGF is located at the beginning of the 1/f region.
So we if we make the lower UGF stable by lowering the gain, the upper UGF becomes unstable.

We took out the ISS box from the PSL table.
Kakeru and Peter are now trying to modify the filter circuit to give more phase margin at the lower UGF.
Attachment 1: OPLTF1.png
OPLTF1.png
  1267   Mon Feb 2 19:23:53 2009 YoichiUpdateGeneralNew optical layout plan
The attached is a plan of the optical layout in the central part for the upgrade.
I included, the folded recycling cavities, oplevs for the core optics, POX, POY, POB and video views.
I have not worked out how to handle the beams outside the chambers. It should not be that difficult.
I also did not include beam dumps for unwanted beams.

I used pink for main beams, brown for picked off beams, red for oplevs.

Comments, suggestions are welcome.
Attachment 1: 40mUpgradeOpticalLayoutPlan01.pdf.zip
  1269   Tue Feb 3 19:24:14 2009 YoichiUpdateGeneralNew optics layout wiki page
I uploaded a slightly updated version of the new optics layout on the 40m wiki.
http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_08/Optical_Layout

I also uploaded the Mathematica notebook I used to calculate various parameters of the new recycling cavities, including the lengths, asymmetry, ROCs, PRM reflectivity and TT-mirror loss margin etc.
It would be nice if someone could check if the calculation is reasonable.
There is a PDF version of the document for non-Mathematica users.
  1271   Wed Feb 4 17:45:39 2009 YoichiUpdateGeneralMode matching of the upgraded IFO
I did mode matching calculations for the new optical layout.
For the input mode matching, we have to change the focal length of the second mirror from 687mm to 315mm and the distance between the two MMT mirrors from 137mm to 149.2mm.
For the mode matching to the OMC, we only have to change the distance between the OMMT mirrors from 384mm to 391mm. No need to change the mirrors.

Details of the calculations can be found in
http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_08/Optical_Layout?action=AttachFile&do=get&target=NewRecyclingCavities.zip
(Mathematica notebook)
or if you prefer PDF, here
http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_08/Optical_Layout?action=AttachFile&do=get&target=NewRecCav.pdf
  1272   Wed Feb 4 19:22:57 2009 YoichiUpdateGeneralDo we need off-axis parabolic mirrors ?
I also estimated the mode matching degradation caused by the astigmatism.
Since the incident angles to the mode matching mirrors are not 0, the effective focal lengths in the incident plane and the perpendicular plane are different.
This effect leads to astigmatism of the beam.
When there is astigmatism, the maximum achievable mode matching rate becomes less than 100%.
According to my calculation, the mode matching cannot be better than 94% for the input beam.
For the output mode matching, we can theoretically achieve more than 99% even with the astigmatism.
The difference comes from the fact that the OMMT is longer, thus the incident angle is smaller.

If we don't like this 94%, we have to use off-axis parabolic mirrors, or modify the IMMT to a longer one.
I prefer to make it longer. Just 5" elongation will increase the mode matching rate to 99.4%.
We have a room for this 5" elongation.

Again, the details of the calculation are added to the Mathematica notebook below.


Quote:
I did mode matching calculations for the new optical layout.
For the input mode matching, we have to change the focal length of the second mirror from 687mm to 315mm and the distance between the two MMT mirrors from 137mm to 149.2mm.
For the mode matching to the OMC, we only have to change the distance between the OMMT mirrors from 384mm to 391mm. No need to change the mirrors.

Details of the calculations can be found in
http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_08/Optical_Layout?action=AttachFile&do=get&target=NewRecyclingCavities.zip
(Mathematica notebook)
or if you prefer PDF, here
http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_08/Optical_Layout?action=AttachFile&do=get&target=NewRecCav.pdf
  1274   Thu Feb 5 10:42:33 2009 YoichiUpdateGeneralDo we need off-axis parabolic mirrors ? No way !
I made a mistake in estimating the astigmatism problem.
If we use the current MMT1 as it is, this one is already an off-axis parabolic (OAP) mirror.
In this case, the astigmatism of this mirror is very small (if we use it with the correct angle). I did not include this effect in the previous calculation.
It turned out that the maximum achievable mode matching becomes far smaller (only 77%) if we use the OAP for MMT1 and a spherical mirror for MMT2.
This is not acceptable.
The reason behind this is that when we use spherical mirrors for both MMT mirrors, the astigmatism caused by the MMT1 is somewhat canceled by the astigmatism of MMT2. We don't get this cancellation if we mix OAP and spherical mirrors.

We should either (1) change MMT1 to a spherical mirror and keep the length of the input MMT as it is, or (2) change MMT1 to a spherical mirror and elongate the length of the input MMT.
In the case of (1) the maximum achievable mode matching is 94%. The focal length of MMT2 should be 315.6mm.
If we do (2), the mode matching rate can be as high as 99.8%. The focal lengths are MMT1 = -301.3mm, MMT2=558mm. The distance between the mirrors is 262mm.
We have enough space to do this elongation. But we have to mechanically modify the MMT mount.
I prefer (2).

As usual, the document on the Wiki was updated to include the above calculations.
  1276   Thu Feb 5 21:42:28 2009 YoichiUpdatePSLMy thoughts on ISS

Today, I worked with Kakeru on ISS.

The problem is sort of elusive. Some time, the laser power looks fine, but after a while you may see many sharp drops in the power. Some times, the power drops happen so often that they look almost like an oscillation.

We made several measurements today and Kakeru is now putting the data together. Meanwhile, I will put my speculations on the ISS problem here.

The other day, Kakeru took the transfer function of the ISS feedback filter (he is supposed to post it soon). The filter shape itself has a large phase margin ( more than 50deg ?) at the lower UGF (~3Hz) if we assume the response of the current shunt to be flat. However, when we took the whole open loop transfer function of the ISS loop, the phase margin was only 20deg. This leads to the amplification of the intensity noise around the UGF. The attached plot is the spectrum of the ISS monitor PD. You can see a broad peak around 2.7Hz. In time series, this amplified intensity noise looks like semi-oscillation around this frequency.

Since it is very unlikely that the PD has a large phase advance at low frequencies, the additional phase advance has to be in the current shunt. We measured the response of the current shunt (see Kakeru's coming post). It had a slight high-pass shape below 100Hz (a few dB/dec). This high-pass response produces additional phase advance in the loop.

There seems to be no element to produce such a high-pass response in the current shunt circuit ( http://www.ligo.caltech.edu/docs/D/D040542-A1.pdf )

This Jamie's document shows a similar high-pass response of the current ( http://www.ligo.caltech.edu/docs/G/G030476-00.pdf  page 7 )

Now the question is what causes this high-pass response. Here is my very fishy hypothesis :-)

The PA output depends not only on the pump diode current but also on the mode matching with the NPRO beam, which can be changed by the thermal lensing. If the thermal lensing is in such a condition that an increase in the temperature would reduce the mode matching, then the temperature increase associated with a pump current increase could cancel the power increase. This thermal effect would be bigger at lower frequencies. Therefore, the intensity modulation efficiency decreases at lower frequencies (high-pass behavior). If this model is true, this could explain the elusiveness of the problem, as the cancellation amount depends on the operation point of the PA. 

To test this hypothesis, we can change the pump current level to see if the current shunt response changes. However, the PA current slider on the MEDM screen does not work (Rob told me it's been like this for a while). Also the front panel of the MOPA power supply does not work (Steve told me it's been like this for a while). We tried to connect to the MOPA power supply from a PC through RS-232C port, which did not work neither. We will try to fix the MEDM slider tomorrow.

Attachment 1: INMONPD_Spectrum_1-10Hz.pdf
INMONPD_Spectrum_1-10Hz.pdf
  1281   Fri Feb 6 16:20:52 2009 YoichiUpdatePSLMOPA current slider fixed

I fixed the broken slider to change the current of the PA.

The problem was that the EPICS database assigned a wrong channel of the DAC to the slider.

I found that the PA current adjustment signal lines are connected to the CH3 &CH4 of VMIC4116 #1. However in the database file (/cvs/cds/caltech/target/c1psl/psl.db), the slider channel (C1:PSL-126MOPA_DCAMP) was assigned to CH2. I fixed the database file and rebooted c1psl. Then the PA current started to follow the slider value.

I moved the slider back and forth by +/-0.3V while the ISS loop was on. I observed that the amount of the low frequency fluctuation of the MOPA power changed with the slider position. At some current levels, the ISS instability problem went away.

Kakeru is now taking open-loop TFs and current shunt responses at different slider settings.

  1284   Mon Feb 9 16:02:42 2009 YoichiUpdatePSLPSL relative intensity noise
I attached the relative intensity noise of the PSL.
There is no bump around the lower UGF (~1Hz), but at the higher UGF (~30kHz) there is a clear bump.
When the ISS gain slider was moved up to 21dB, the peak got milder, because there is larger phase margin at higher frequencies with the current filter design.
We may want to optimize the filter later.
Attachment 1: RIN-13dB.png
RIN-13dB.png
Attachment 2: RIN-21dB.png
RIN-21dB.png
  1285   Mon Feb 9 16:05:01 2009 YoichiUpdateLSCDRMI OK

After the ISS work, I aligned the IFO and confirmed that DRMI locks with good SPOB and AS166 values.

  1286   Mon Feb 9 17:09:51 2009 YoichiUpdateComputersA bunch of updates for the network GPIB stuff.
During the work on ISS, we noticed that netgpibdata.py is very unreliable for SR785.
The problem was caused by flakiness of the "DUMP" command of SR785, which dumps the data from the analyzer to the client.
So I decided to use other GPIB commands to download data from SR785. The new method is a bit slower but much more reliable.

I also rewrote netgpibdata.py and related modules using a new class "netGPIB".
This class is provided by netgpib.py module in the netgpibdata directory. If you use this class for your python program, all technical details and dirty tricks are hidden in the class methods. So you can concentrate on your job.
Since python can also be used interactively, you can use this class for a quick communication with an GPIB instrument.

Here is an example.
>ipython #start interactive python
>>import netgpib #Import the module
>>g=netgpib.netGPIB('teofila',10) #Create a netGPIB object. 'teofila' is the hostname of
#the GPIB-Ethernet converter. 10 is the GPIB address.
>>g.command('ACTD0') #Send a GPIB command "ACTD0". This is an SR785 command meaning "Change active display to 0".
>>ans=g.query('DFMT?') #If you expect a response from the instrument, use query command.
#For SR785, "DFMT?" will return the current display format (0 for single, 1 for dual).
>>g.close() #Close the connection when you are done.

Sometimes, SR785 gets stuck to a weird state and netgpibdata.py may not work properly. I wrote resetSR785.py command to reset it remotely.
Wait for 30sec after you issue this command before doing anything.

I wrote two utility commands to perform measurements with SR785 automatically.
TFSR785.py commands SR785 to perform a transfer function measurement.
SPSR785.py will execute spectrum measurements.
You can control various parameters (bandwidth, resolution, window, etc) with command-line options.
Run those commands with '-h' for help.
It is recommended to use those commands even when you are in front of the analyzer, because they save various measurement parameters (input coupling, units, average number, etc) into a parameter file along with the measured data. Those parameters are useful but recording them for each measurement by hand is a pain.
  1287   Mon Feb 9 19:50:48 2009 YoichiConfigurationPSLISS disconnected
We are doing measurements on ISS.
The ISS feedback connector is disconnected and the beam to the MC is blocked.
  1291   Wed Feb 11 07:28:25 2009 YoichiUpdatePSLPA current and laser output
I think we should also plot the laser power at the MOPA output. The horizontal axis should be the absolute current value read from the PA current monitor channel, not the slider value.

This result is consistent with my hypothesis that the thermal effect is canceling the power change at low frequencies (see elog:1276).
But if it is really caused by thermal effect or not is still unknown.

I'd like to see a larger scan into the lower current region.


Quote:
I changed the PA current and measured laser output power (monitor PD signal).
The gain of ISS is 13dB
Attached figure is the relation of PA current and the average and standard diviation of laser output.
The average of output power decreas as current increase. It looks something is wrong with PA.
When current is -0.125, 0, 0.5, ISS become ocsilating. This looks to be changed from previous measurement.

I wrote matlab code for this measurement. The code is
/cvs/cds/caltech/users/kakeru/scripts/CS_evaluate.m
This function uses
/cvs/cds/caltech/users/kakeru/scripts/moveCS.m
  1292   Wed Feb 11 10:52:22 2009 YoichiConfigurationDAQC1:PEM-OSA_APTEMP and C1:PEM-OSA_SPTEMP disconnected

During the cleanup of the lab. Steve found a box with two BNCs going to the ICS DAQ interface and an unconnected D-SUB on the floor under the AP table.  It seemed like a temperature sensor.

The BNCs were connected to C1:PEM-OSA_APTEMP and C1:PEM-OSA_SPTEMP.

Steve removed the box from the floor. These channels can be now used as spare DAQ channels. I labeled those cables.

  1296   Thu Feb 12 11:21:54 2009 YoichiUpdateLSCLocking effort resumed
Last night, I restarted the locking work.
Quite some time was wasted by the disconnected REFL199 by Alberto for the cavity length measurement.
From now on, please put the interferometer back to the original state every day.
If possible, please refrain from changing the IFO settings (cabling, optics, etc).
It is also very important to always restore the full IFO alignment after you are done with your work.

While I was working on the optimization of the DD hand-off, the DRMI alignment got into a strange state.
Even when I did the whole dither alignment procedure from the beginning (from x-arm), the AS166Q did not go above 1000.
PRMI looks ok (SPOB goes above 1100). I could lock the DRMI but the lock position hops to other modes easily.
Manual tweaks of SRM did not help.
After running the whole alignment procedure several times in vain, I was too tired and went home.
I noticed that the single arm lock shows power drops again. There are some offsets in the arm lock loops.
This may have prevented the Michelson alignment from being optimal. I will check this today.
  1298   Thu Feb 12 17:43:33 2009 YoichiUpdateLSCSRC strangeness solved
I found the problem with the DRMI lock I had last night was caused by the zero gain in the PD11_I filter.
I don't know how it happened but putting it back to 1.000 made the DRMI lock far more stable and AS166Q got more than 3000.

I also re-centered POY PD to remove the offset in the y-arm loop. The large power drops while y-arm is locked by itself were eliminated.
  1301   Fri Feb 13 13:35:38 2009 YoichiUpdateLSCLocking status
Yoichi, Jenne, Alberto, Rob

Last night, the locking proceeded until the CARM -> MC_L hand-off.
However, the MC_F gets saturated (as expected) and the IFO loses lock soon after the hand-off.
So we need to offload MC_F.
We ran the offloadMCF script, but it did not work, i.e. just waiting for CARM mode.
Looks like an EPICS flag is not set right.
  1305   Sun Feb 15 09:35:00 2009 YoichiUpdateLSCLocking status

Quote:

I found a '$<' in the offloadMCF script. I don't know precisely what that construct means, but I think it caused the script to wait for input when it shouldn't.


'$<' acts like 'read' in csh. I might have put it in the offloadMCF script to debug the behavior of the script.
Sorry I probably forgot to remove it from the script when I left.
  1309   Mon Feb 16 14:12:21 2009 YoichiUpdateLSCFE system rebooted

Quote:

I can't restart the MC autolocker on c1susvme2 because it doesn't let me ssh in. I tried to reboot it a few times but it didn't work. Once you restart it, it becomes inaccessible and doesn't even respond to pinging. Although the controls for the MC mirrors are on.

The mode cleaner stays unlocked.


MC autolocker runs on op340m, not on c1susvme2.
I restarted it and now MC locks fine.
Before that, I had to reboot c1iool0 and restore the alignment of the MC mirrors (for some reason, burt did not restore the alignment properly, so I used conlog).
  1310   Mon Feb 16 15:54:07 2009 YoichiUpdateComputersmedm directory wiped on nodus

Quote:
I accidentally did an 'rm -rf' on the medm directory in nodus, instead of on my laptop as was intended.

I then did an svn checkout. So everything should be current as of the last update, but I am sure that
we have not done a checkin on all of the latest screen enhancements. So...we may have to revert to the
Sunday morning tar to get the latest changes back.


Indeed, some changes to the medm directory I made were lost.
It was my fault not to check-in those changes.
I asked Alan to restore the directory from the daily rsync backup.
However, the backup job executed this morning have already overwritten the previous (good) backup with the current (bad) medm directory, which Rana restored from the svn. Alan will ask Stuart and Phil if there is still older backup remaining somewhere.

Anyway, I realized that we should stop the backup cron job whenever you think you made a mistake on /cvs/cds/ directory to prevent unwanted overwriting.
The procedure is:
(1) Login to fb40m
(2) Type 'crontab -e'. Emacs will open up in the terminal.
(3) Comment out the backup job (insert # at the beginning of the line containing /cvs/cds/caltech/scripts/backup/rsync.backup ).
(4) Save the file (Ctrl-x Ctrl-s) and exit (Ctrl-x Ctrl-c).

I will post this information on the wiki.
  1316   Tue Feb 17 05:20:11 2009 YoichiUpdateLSCLocking
Since we excluded *.snap and *.req files from the svn control in the medm directory and these were not restored by the svn co, the burt part of the align/mis-align scripts were not working correctly this evening. So I recreated .req files and cooked up some mis-aligned .snap files.
After some cut-and-try work, I was able to run the dither alignment scripts fine.

Due to the above mentioned delay, the locking work started around midnight.

Tonight, the DD hand-off was not robust. I spent sometime to optimize this.
After the optimization, the locking proceeded to the DC CARM/DARM control state stably.
The CARM->MCL hand-off failed because the LSC-MC offset button was off.
I added a line to turn on the button in the ontoMCL script.
Today, the offloadMCF script worked fine.

Next, the cm_step script stumbled on the "ENGAGERIZING" of the AO path.
I got a hunch that the AO path might not be connected to the MC board.
Indeed, OMC_OSC_FM was connected to the IN2 of the MC board. Looks like it was used for the optimization of the modulation frequencies.
Probably I had the hunch because I did it Smile

I was able to increase the arm power up to 3.9.
The script failed when it tried to switch the CARM signal from TR_DC to SPOB_DC.
I haven't tackled on this issue yet.
  1317   Wed Feb 18 03:17:40 2009 YoichiUpdateLSCLocking
Yoichi, Kakeru,

Last night, the cm_step script failed at the hand-off of CARM error signal from TR_DC to PO_DC.
This was fixed by reducing the PO_DC gain by a factor of 2.
Currently the script fails when changing C1:LSC-DEMOD_GAIN to zero.
To be honest, I don't fully understand the purpose of this step.
  1318   Wed Feb 18 03:25:25 2009 YoichiUpdateComputersmedm directory back
I restored the medm directory from the backup on the tape.
The directory had an svn property svn:ignore set and the value of the property included *.snap and *.req.
This resulted in the exclusion of those files from the repository.
I fixed this problem by changing the property of all the directories under /cvs/cds/caltech/medm.
After fixing several other svn problems, the current medm directory contents were checked in to the repository.
  1323   Thu Feb 19 04:16:17 2009 YoichiUpdateLSCLocking status
Rob, Yoichi

We checked the CM-MC cross over just before turning off the moving zero.
There was a slight bump in the gain of the MC_L loop at (I believe) the optical spring freq. (~400Hz) just below 0 dB. The phase margin there was very thin.
Removing the moving zero will increase the bump more and make the loop unstable.
Rob suggested to increase the AO gain a bit more.

To see if the AO path is really working, I connected the OUT2 of the MC board to a spare DAQ channel (C1:PEM-OSA_APTEMP).
I confirmed that the PO_DC signal is actually coming to the AO path input of the MC board.
I also hooked up the SR785 to the A excitation channel of the common mode board, so that we can measure the loop gain of the AO path.
After these preparation, the lock acquisition process became somewhat unstable. The ifo loses lock randomly at various places in the lock acquisition steps.
So, as of 4:00 am, I have not gotten a chance to try Rob's suggestion nor the TF measurement with SR785 yet.
I will continue the work tomorrow (i.e. tonight ??).

  1325   Thu Feb 19 16:29:43 2009 YoichiUpdateComputersMartian wireless router bad
The Martian wireless router is dead.
I rebooted it several times, but it hangs up in a minute.
I will ask steve to buy a new one.
  1329   Fri Feb 20 03:52:23 2009 YoichiUpdateLockingLocking Tonight
Yoichi, Peter

Tonight, we had a problem with the DD hand off.
It failed when the RG filters of MICH for the bounce-roll modes are engaged.
The reason for the failure was that the MICH UGF was too low (~10Hz).
As in the Peter's elog entry, we found that the AS PDs are mis-centered.
Even after we fixed the centering, the MICH UGF was still too low. So we increased the MICH feedback gain by a factor of 10.
The reason for the gain decrease is unknown. It seems almost like the BS coils get weaker.
I checked the UGF of the BS OL loops. These are around 4Hz, so fine. We should check the HWP on the AP table tomorrow.

After the DD hand-off goes ok, the switching of DARM signal from DC to RF failed.
I found that the gain and the polarity of the RF signal were wrong.
AS166 is one of the PDs we found mis-centered (and re-centered). But how can you flip the sign of the signal ?

After this, the cm_step script goes until the activation of the moving zero, but fails when the arm power is increased to 0.7.
Also the ontoMCL script succeeds only 50% of the time.
  1330   Fri Feb 20 19:31:16 2009 YoichiUpdateLSCMICH low gain problem
Last night, we found that MICH UGF was too low. Even after re-aligning the PDs, it was still too low.
Today, I compared the UGFs of MICH and PRC when in the DRMI configuration locked with the single demod. signals.
In this configuration, MICH signal comes from REFL33Q and the PRC signal comes from REFL33I (the same PD).
The PRC UGF was about 100Hz whereas MICH was only ~10Hz.
Since they uses the same PD, the low gain is not caused by the PD.
I checked conlog history and confirmed there is no change in the MICH->BS path in the last few days.
I also checked the svn history of chans directory for changes in filters. Nothing problematic found.

Then I noticed that the susvme computers were overloaded.
This time, I rebooted all the FE computers just in case.

Then the MICH gain was somewhat recovered (by a factor of 3 or so). Don't know why.

I adjusted the DD_handoff script to set the MICH gain to 0.7 before the bounce-roll filter is engaged.
  1334   Tue Feb 24 02:23:40 2009 YoichiUpdateLockingLocking - MC board bad
Rob, Yoichi, Alberto, Kiwamu, Kakeru

We found that the OMC alignment feedback was on for the POS X loop even though the OMC was not locked.
This caused the PZT mirror to be tilted in yaw a lot. This was probably the reason for the mysterious shift in the AS beam last week, because the AS RF beam is picked up after this PZT mirror.
Rob aligned the OMC and we re-centered the AS PDs and the CCD.
This changed the DARM RF gain, so we changed it from 3 to 1. This gain used to be -1. It is still not understood why the polarity was changed.
The MC length was changed ? We should check the sideband transmission.

After this, we reached to the arm power 4. But the IFO loses lock immediately after the moving zero is turned off.
At this stage, the CARM loop bandwidth is supposed to be high enough that the moving zero is no longer necessary.
However, when we measured the MCL loop gain with several different AO path gains, the loop shape did not change at all.
This led us to suspect the AO path may not be connected. The cabling from the common mode board to the MC board seemed ok.
We tested the signal flow in the MC board using a signal generator and an oscilloscope.
Then we found that a signal injected to the IN2 (AO path) does not reach to the TP1A (right after the boost stages), though the signal is visible in the OUT2 (monitor BNC right after the initial amplifier (B-amp) for the AO path). The signal from IN1 (MC REFL) can be observed at TP1A. This means something is broken between the B-amp and the sum-amp in the AO path.
We will check the MC board tomorrow.
  1336   Wed Feb 25 03:10:24 2009 YoichiUpdateLockingLocking status
Rob, Yoichi, Kakeru, Kiwamu

Tonight, CARM -> MCL hand off was not stable. The MCF signal monotonically went up to +2V after CARM and MCL gain was turned down to zero.
This was repeatable and it only goes up (not down).
After a while, we found that putting sleep (~5sec) between the zeroing of CARM gain and MCL gain prevents this problem.

Handing off of CARM error signal from TR to PODC was also not robust.
It seems that the suitable gain changes every time.

tdsavg started to exit with errors. We rebooted fb40m.
When tdsavg returns an error, the cm_step script tries to write NaN into SPOB DC offset.
To prevent this, I put the tdsavg in a while loop which runs until tdsavg returns something other than NaN.

I was able to hand off to PODC several times, but could not proceed further because the IFO lost lock soon.
  1338   Thu Feb 26 00:36:53 2009 YoichiSummaryComputersC1:LSC-TRX_OUT broken (and fixed later).
Today, Kakeru tried to convert C1:LSC-TRX_OUT and C1:LSC-TRY_OUT to DAQ channels.
He edited C1LSC.ini in the chans/daq directory to add the channel but it did not work.
Then he reverted the file back to the original one.
But after we still could not access these channels from dataviewer nor tds tools.
We restarted daqd and tpman on fb40m, but the problem persisted. Even rebooting the whole fb40m did not help.
After inspecting the log file of daqd, it was clear that tpman was failing to create test points for those channels.
I rebooted c1daqawg and then restarted tpman and daqd on fb40m again.
This time, the problem went away.
  1339   Thu Feb 26 01:24:44 2009 YoichiUpdateComputersMartian wireless is back
Today, a new wireless router arrived.
I configured and installed it. Now the martian wireless network is back.
I updated the wiki page about the wireless network.
http://lhocds.ligo-wa.caltech.edu:8000/40m/Network
  1340   Thu Feb 26 19:20:08 2009 YoichiConfigurationGeneralETMX camera centered. POX, POY PDs centered
Alberto, Yoichi

We centered the ETMX camera.
Alberto centered the POX and POY PDs.
We also updated the offset values of PD3 and PD4.
  1341   Thu Feb 26 19:59:23 2009 YoichiUpdateLockingDaytime locking
Osamu, Yoichi

We tried locking today from about 2PM.
It took about 1000sec on average to acquire the initial lock.
After the initial lock is achieved, the hand-off/ramp-up steps were reasonably robust, although the AS beam sometimes fluctuates a lot (not good for mental health).

Like last night, the IFO loses lock at around arm-power=8.
We measured the CARM AO path loop gain at arm-power=4. We used the SR785 connected to the A-excitation channel of the common mode board through my TFSR785.py script.

The first attachment is the transfer function measured right after the arm power was ramped up to 4.
The overall bandwidth of the CM servo is only 400Hz. Note that since this is the loop gain of only the AO path, the low frequency gain is eaten by the MCL path.
The second attachment is the same transfer function measured after the AO path gain was increased by 6dB.
It is evident that the AO path is working.
We increased both the AO path and MCL gain by 18dB. The third attachment is the AO path TF in this state.
We then increased the arm power but lost lock at arm-power=6. We should have checked the DARM loop too.
BTW, these plots are automatically generated when you use TFSR785.py for transfer function measurements.


I added -notickle option to c1_watch_dr_bang, since tickling seems to be not necessary during the daytime (actually the initial lock was easier with no tickling).

As the construction work in the next building is now calmed down, I think it is ok to do locking during the day time, though I still plan to come at night.
The improvement of my brain efficiency during the day time may compensate for the longer wait time for initial lock.
Attachment 1: CM1.png
CM1.png
Attachment 2: CM2.png
CM2.png
Attachment 3: CM3.png
CM3.png
  1342   Thu Feb 26 20:09:32 2009 YoichiHowToComputersSR785 python scripts now produce plots
I updated the python scripts to remotely perform measurements with an SR785.
Now these scripts can plot the results immediately using python's matplotlib capability. The sample plots can be seen in my previous elog entry.
In addition to the transfer function (TFSR785.py) and spectrum measurement (SPSR785.py) scripts, I also wrote a script for time series measurements (TSSR785.py).
This is useful when you want to check the signal level flowing in the channels before determining the excitation amplitude.
TSSR785.py will measure and show the time series and histogram of the signal measured by the SR785.
More detailed usage is explained in this wiki page:
http://lhocds.ligo-wa.caltech.edu:8000/40m/netgpib_package
  1344   Mon Mar 2 03:57:44 2009 YoichiUpdateLockingSunday night locking
Tonight's locking started with a boot fest of the FE computers which were all red when I came in.
It also took me sometime to realize that C1:IOO-MC_F was returning always zero to tdsavg, causing the offloadMCF script to do nothing.
I fixed this by rebooting c1iovme and c1iool0.

Like Rob on the thursday night, I was only able to reach arm power around 10.
This time, I turned down the MC WFS gain to 0.02 (from 0.3).
I also checked gains of most of the loops (MICH, PRC, SRC, DARM, CARM-MCL, CARM-AO).
All the loops looked fine until the lock was lost suddenly. Also the spectrum of MC_F did not change as the arm power was ramped up.
Actually, I was able to reach arm power=10 only once because I spent a long time checking the loop gains and spectrum at fine steps of the arm power.
So it is quite possible that this loss of lock was just caused by a seismic kick.
  1346   Mon Mar 2 21:16:32 2009 YoichiUpdateLockingLow-gain High-gain PD switching may not be working well
Osamu, Yoichi

This afternoon, I run the locking script while doing calculations for the upgrade.
The IFO lost lock even at lower arm powers (around 6) if it was operated for a while (~ 5min).
It seemed as if there were some intermittent glitches (seismic? laser?) causing the lock losses.
We also saw once the TRX and TRY signals saturated at around arm power = 11 when there was a large fluctuation in the arm power.
Osamu suggested that it looked like the high-gain to low-gain PD switching was not working.

I won't come tonight as I may have caught a cold, but if someone comes tonight, it is worth checking the PD switching.
  1350   Tue Mar 3 19:26:44 2009 YoichiUpdateLockingLow-gain High-gain PD switching may not be working well
I checked the switching of the QPDX from high gain to low gain.
Switching happens as expected, but the low gain QPDX output was very low compared to QPDY.
Also the digital gain for the high gain TRX was not matched with the low gain one. So when the switching happens, there is a large jump in the TRX.

I also found that the offset values for the low gain QPDX were totally wrong. I adjusted it.
Then I removed a beam splitter in front of the QPDX to increase the power falling on it.
But still the low gain QPDX output is four times lower than the low gain QPDY.

I'm still working on it. So don't expect the switching to work correctly at this moment.
I'm planning to be back after the dinner.


Quote:
Osamu, Yoichi

This afternoon, I run the locking script while doing calculations for the upgrade.
The IFO lost lock even at lower arm powers (around 6) if it was operated for a while (~ 5min).
It seemed as if there were some intermittent glitches (seismic? laser?) causing the lock losses.
We also saw once the TRX and TRY signals saturated at around arm power = 11 when there was a large fluctuation in the arm power.
Osamu suggested that it looked like the high-gain to low-gain PD switching was not working.

I won't come tonight as I may have caught a cold, but if someone comes tonight, it is worth checking the PD switching.
  1351   Tue Mar 3 23:59:26 2009 YoichiUpdateLockingLow-gain High-gain PD switching may not be working well

Quote:
I checked the switching of the QPDX from high gain to low gain.
Switching happens as expected, but the low gain QPDX output was very low compared to QPDY.
Also the digital gain for the high gain TRX was not matched with the low gain one. So when the switching happens, there is a large jump in the TRX.

I also found that the offset values for the low gain QPDX were totally wrong. I adjusted it.
Then I removed a beam splitter in front of the QPDX to increase the power falling on it.
But still the low gain QPDX output is four times lower than the low gain QPDY.

I'm still working on it. So don't expect the switching to work correctly at this moment.
I'm planning to be back after the dinner.



This sounds like the QPD whitening gain sliders may be stuck. The slider twiddling script should be run, or the sliders should be twiddled by hand.
  1352   Wed Mar 4 03:37:51 2009 YoichiUpdateLockingLow-gain High-gain PD switching may not be working well

Quote:

This sounds like the QPD whitening gain sliders may be stuck. The slider twiddling script should be run, or the sliders should be twiddled by hand.


Yes, it was indeed the whitening gain slider problem.
I moved them and the QPDX gain went up suddenly. I reinstalled the BS in front of the QPDX and adjusted the offsets, gains accordingly.
Now the high-gain to low-gain switching is fine.
  1353   Wed Mar 4 03:50:17 2009 YoichiUpdateLockingStill won't go above arm power 10
Yoichi, Kentaro

The IFO still loses lock at around arm power 10.
I attached time series of various error signals when losing lock.
In all of the three cases, both of the arm powers go up rapidly just before losing lock.
(The first attachment was taken before I fixed the QPDX switching, so you can see saturation in TRX.)
But PD1_DC (the DC power in the PRC) did not go up in the third case.

I should also check correlations with laser power, CARM length (OSEM signals), seismic noise etc.
Attachment 1: lockLoss1.png
lockLoss1.png
Attachment 2: lockLoss2.png
lockLoss2.png
Attachment 3: lockLoss3.png
lockLoss3.png
  1356   Wed Mar 4 17:59:14 2009 YoichiConfigurationComputersezca tools and tds tools work around
Some of ezca commands and tds commands sporadically fail with a segmentation fault on linux machines.
As far as I know, ezcawrite, ezcastep, ezcaswitch, and tdswrite have this problem.
These are commands to write values into epics channels. So usually people do not check the exit status of those commands in their scripts.
This could cause incomplete execution of, for example, down scripts.
Ideally, this problem should be fixed in the source codes of the problematic commands.
However, I don't have a patience to wait it to happen, and I needed to fix these problems immediately for the lock acquisition.
So I resorted to a hacky solution.
I renamed those commands to *.bin, e.g. ezcawrite -> ezcawrite.bin.
Then wrote wrapper scripts to repeatedly call those commands until it succeeds.
For example, ezcawrite now looks like,
#!/bin/csh -f
setenv POSIXLY_CORRECT
while (! { ezcawrite.bin $* })
      echo "Retry $0 $*"
end
So, when ezcawrite.bin fails, the command retries it and show a message "Retry ....".

If you need to call the original commands, you can always do so by adding ".bin" at the end of the command name.
Currently the following commands are wrapped.
ezcawrite, ezcaservo, ezcastep, ezcaswitch, tdswrite, tdssine.

Please let me know if you have any trouble with this.
  1361   Thu Mar 5 05:07:09 2009 YoichiUpdateLockingWednesday night locking
Tonight, I was having a problem with the PO_DC hand-off.
It fails most of the time.
I increased the averaging time for the PD1_DC offset measurement.
I also wrote a script to match the gain of the transmission DC and the PO_DC signals.
This script (/cvs/cds/caltech/scripts/CM/matchPODCGain ) measures the gains of the old (TRX+TRY) and new (PO_DC) signals at 150Hz and returns the optimal value to be put into the input matrix.
cm_step script calls matchPODCGain to determine the matrix element value for the PO_DC signal.

Even with this script, the hand-off was still unreliable.
I checked the AO path loop gain just before the hand off. It looked normal.
Then I realized that the oscilloscope I hooked up to the PO_DC signal using a T-BNC may be introducing some noise into the channel.
So I removed it. Then the PO_DC hand off went well at least once.
The IFO still loses lock at around arm power 10.

I attached time series of the latest lock loss. The second attachment is a zoom of the first one.
This time, there is a glitch in the ETM feedback signals, which is also present in the DARM and CARM and error signals.
I saw this kind of glitches several times today.
Attachment 1: lockLoss5.png
lockLoss5.png
Attachment 2: lockLoss5-zoom.png
lockLoss5-zoom.png
  1364   Fri Mar 6 05:44:14 2009 YoichiUpdateLockingLocking distracted by the QPD whitenning problem again
Tonight, I was able to ramp up the arm power to around 20. Then the DARM loop started to oscillate and the IFO lost lock in a few seconds.
I repeated this several times, then realized that the transmission QPDs were not working properly again due to the well known sticky slider problem.
I should have run slider_twiddle script. Since the DARM RF signal is normalized by the sqrt(TRX+TRY), it is reasonable that the DARM loop got unstable.

The fact that I was able to go up to arm power = 20 means there is nothing saturating below this power level.
  1365   Fri Mar 6 15:23:39 2009 YoichiUpdateLockingLocking distracted by the QPD whitenning problem again
By looking at the time series of DARM signal at the time of a lock loss, the oscillation frequency was about 3.5kHz (see the attm1 and its zoomed version attm2).
I will measure the DARM loop gain around this frequency next.


Quote:
Tonight, I was able to ramp up the arm power to around 20. Then the DARM loop started to oscillate and the IFO lost lock in a few seconds.
I repeated this several times, then realized that the transmission QPDs were not working properly again due to the well known sticky slider problem.
I should have run slider_twiddle script. Since the DARM RF signal is normalized by the sqrt(TRX+TRY), it is reasonable that the DARM loop got unstable.

The fact that I was able to go up to arm power = 20 means there is nothing saturating below this power level.
Attachment 1: lockLoss3.pdf
lockLoss3.pdf
Attachment 2: lockLoss3-zoom.pdf
lockLoss3-zoom.pdf
  1366   Fri Mar 6 18:14:58 2009 YoichiUpdateComputersawg not working
Starting from this afternoon, the awg is not working.
I rebooted FE computers, c0daqawg as well as tpman and daqd processes on fb40m several times.
But the problem is still there.
I sent an email to Alex.
ELOG V3.1.3-