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ID Date Author Type Categoryup Subject
  2178   Thu Nov 5 05:07:22 2009 ranaUpdateLSCX Arm Cavity transfer Function

I would have guessed that you have to calibrate the detectors relative to each other before trying this. Its also going to be tricky if you use 2 different kinds of ADC for this (c.f. today's delay discussion in the group meeting).

I think Osamu used to look at fast transmission signals by making sure the PD at the end had a 50 Ohm output impedance and just drive the 40m long cable and terminate the receiving end with 50 Ohms. Then both PDs go into the SR785.

 

  2184   Thu Nov 5 19:25:11 2009 AlbertoUpdateLSCX Arm Cavity transfer Function

Quote:

I would have guessed that you have to calibrate the detectors relative to each other before trying this. Its also going to be tricky if you use 2 different kinds of ADC for this (c.f. today's delay discussion in the group meeting).

I think Osamu used to look at fast transmission signals by making sure the PD at the end had a 50 Ohm output impedance and just drive the 40m long cable and terminate the receiving end with 50 Ohms. Then both PDs go into the SR785.

 

On Rana's suggestion I measured the trasfer function between the two photodiodes PDA255 that I'm using.

I took the one that I had on the end table and put it on the PSL table. I split the MC transmitted beam with a 50% beam splitter and sent the beams on the two diodes. (Rana's idea of picking off the beam and interposing the PDs before the ISS PDs was not doable: ISS PDs would be too close and there would be no room to install the PDA255 before them). See picture with the final setup.

DSC_0958.JPG


The transfer function also includes the 40m long cable that I was using for the Arm Cavity measurement.

Here's what I got. It looks rather flat. Yesterday the calibration was probably not the problem in that measurement.

PDA255CalibrationTF03.png
 I'm now going to install the PD back on the end table and measure the TFs between the excitation and several points of the loop.

(Trivia. At first, the PDs were saturating so Koji attached attenuation filters on to them. Suddenly the measurement got much nicer)

  2185   Thu Nov 5 22:30:09 2009 AlbertoUpdateLSCX Arm Cavity Transfer Function

It seems that just repeating the measurement was enough to get a good transfer function of the x arm cavity. Here's what I got.

XarmTF01.png

I'm going to fit the data on matlab, but at first sight, the pole seems to be at about 1.7KHz (that is where the phase is 45deg): as expected.

Probably it was useful to realign the beam on the Transmission PD. (btw, I'm using the PDA255 that was still on the X end table since the AbsL experiemtn that measured the arm length)

  2186   Thu Nov 5 23:09:34 2009 AlbertoUpdateLSCY Arm Cavity Transfer Function

As for the X Arm, this the transfer function I measured for the Y arm cavity.

YarmTF01.png

This time I'm using a different photodiode than the PDA255 on the Y end table.

The diode I'm using is the PDA520 from where TRY comes from.

I'm going to repeat the measurement with PDA255.

  2188   Fri Nov 6 00:24:06 2009 AlbertoUpdateLSCY Arm Cavity Transfer Function

Quote:

As for the X Arm, this the transfer function I measured for the Y arm cavity.

YarmTF01.png

This time I'm using a different photodiode than the PDA255 on the Y end table.

The diode I'm using is the PDA520 from where TRY comes from.

I'm going to repeat the measurement with PDA255.

 Measurement repeated with the PDA255 PD at the end but not big changes

YarmTF02.png

  2189   Fri Nov 6 00:40:29 2009 AlbertoUpdateLSCEverything put back as it was

I disconnected the setup for the arm cavity TF measurement. I opened the scitation switch on the ISS medm screen. I reconnected the OMC ISS EXC cable to the breakout box on the floor.

The photodiode on the Y end is stilll connected.

Also the RFAm (whish is not disbaled anymore) still has a 50% beam splitter before it.

I'm also running the Align Full IFO script.

  2208   Mon Nov 9 11:11:19 2009 AlbertoConfigurationLSCMC2 Watchdogs tripped

The MC2 watchdogs tripped. I just restored them.

I also had to relock the MZ and then the Mode Cleaner.

  2217   Mon Nov 9 15:11:02 2009 AlbertoUpdateLSCEverything put back as it was

Quote:

I disconnected the setup for the arm cavity TF measurement. I opened the scitation switch on the ISS medm screen. I reconnected the OMC ISS EXC cable to the breakout box on the floor.

The photodiode on the Y end is stilll connected.

Also the RFAm (whish is not disbaled anymore) still has a 50% beam splitter before it.

I'm also running the Align Full IFO script.

 

I removed the beam splitter and the PDA 255.

the beam path to the RFAM photodiode is clear again.

  2226   Tue Nov 10 13:02:36 2009 AlbertoUpdateLSCX and Y Arm Cavity Poles Measurement

From fitting the arm cavity transfer functions I got the following values for the cavity pole frequencies.

X ARM: fp_x = (1720 +/- 70) Hz

Y ARM: fp_y = (1650 +/- 70) Hz

Attached are the plots from the fitting.

Attachment 1: SummaryOfFits.pdf
SummaryOfFits.pdf SummaryOfFits.pdf
Attachment 2: CodeAndData.tar
  2247   Thu Nov 12 02:02:18 2009 ranaSummaryLSCArm Locking with no feedback to the ETM or ITM

Steps:

1) Turn off feedback to ETMY (the ETMY button on the LSC screen).

2) Put a 1 into the YARM->MC2 output matrix element on the LSC screen.

3) Turn off FM6 (comb), FM7 (0.1:10) on the MC2_MCL filter bank. This is to make the IOO-MCL loop more stable and to reduce the IOO-MCL low frequency gain.

4) Set the MC2-LSC gain to 0.5, turn the output ON, turn ON FM4 & FM5 & FM6 of the MC2-LSC filter bank.

5) Turn on the input of MC2-LSC and the arm should now lock.

6) After locking, set the MC2-MCL gain to zero. Hopefully with a few second ramp time.

Voila!

(A comment by KA - c.f. this entry )

Attachment 1: nohands-2.pdf
nohands-2.pdf
  2277   Mon Nov 16 17:35:59 2009 kiwamuUpdateLSCOMC-LSC timing get synchronized !

An interesting thing was happened in the OMC-LSC timing clock.

Right now the clock of the OMC and the LSC are completely synchronized.

 The trend data is shown below. At the first two measurements (Oct.27 and Nov.1),  LSC had constant retarded time of 3Ts (~92usec.).

The last measurement, on Nov.15, number of shifts goes to zero, this means there are no retarded time.

Also the variance between the two signal gets zero, so I conclude the OMC and the LSC are now completely synchronized.

The measurement on Nov.8 is somehow meaningless, I guess the measurement did not run correctly by an influence from megatron(?)

 

OMC-LSC.png

 

  2317   Mon Nov 23 21:30:29 2009 JenneUpdateLSCMeasured MC length

With Koji's help, I measured the length of the Mode Cleaner.

The new modulation frequencies (as quoted on the Marconi front panels) are: 

165.980580 MHz

 33.196116 MHz

132.784464 MHz

199.176696 MHz

The Frequency Counter readback is 165980584.101 Hz (a 4Hz difference).  All of the Marconi's front-panel frequencies read ###.##### MHz Ext, and the Frequency standard has it's "locked" light illuminated, and the 1pps input light blinking, so I think everything is still nicely locked to the frequency standard, and the frequency standard is locked to the GPS.

While changing the marconi's, I accidentally touched the MC's 29.5 MHz marconi.  It is set back to the nominal value (according to Kiwamu's rack photos) of 29.485MHz.  But the phase might be sketchy, although hopefully this doesn't matter since we don't do a double demodulation with it.

I also ran the scripts in the wiki page: How To/Diagonalize DRMI Length Control to set the DD Phases.

 

 

  2319   Tue Nov 24 08:00:16 2009 ranaUpdateLSCMeasured MC length

I propose that from now on, we indicate in the elog what frequencies we're referring to. In this case, I guess its the front panel readback and not the frequency counter -- what is the frequency counter readback? And is everything still locked to the 10 MHz from the GPS locked Rubidium clock?

Plus, what FSS Box? The TTFSS servo box? Or the VCO driver? As far as I know, the RC trans PD doesn't go through the FSS boxes, and so its a real change. I guess that a bad contact in the FSS could have made a huge locking offset.

 

  2320   Tue Nov 24 10:36:21 2009 KojiUpdateLSCMeasured MC length

What I meant was the VCO driver, not the FSS box.

As for the frequency, all written numbers were the Marconi displays.
The number on the frequency counter was also recorded, and so will be added to the previous entry shortly... 

Quote:

I propose that from now on, we indicate in the elog what frequencies we're referring to. In this case, I guess its the front panel readback and not the frequency counter -- what is the frequency counter readback? And is everything still locked to the 10 MHz from the GPS locked Rubidium clock?

Plus, what FSS Box? The TTFSS servo box? Or the VCO driver? As far as I know, the RC trans PD doesn't go through the FSS boxes, and so its a real change. I guess that a bad contact in the FSS could have made a huge locking offset.

 

  2350   Thu Dec 3 15:55:24 2009 AlbertoAoGLSCRF AM Stabilizer Output Power

Today I measured the max output power at the EOM output of one of the RF AM Stabilizers that we use to control the modulation depth. I needed to know that number for the designing of the new RF system.

When the EPICS slider of the 166 MHz modulation depth is at 0 the modulation depth is max (the slider's values are reversed : 0 is max, 5 is min; it is also 0 for any value above 5, sepite it range from 0 to 10).

I measured 9.5V from the EOM output, that is 32 dBm on a 50 Ohm impedance.

  2384   Thu Dec 10 13:10:25 2009 AlbertoConfigurationLSC166 LO Disconnected

I temporarily disconnected the Heliax cable that brings the 166MHz LO to the LSC rack.

I'm doing a couple of measurement and I'll put it back in as soon as I'm done.

  2389   Thu Dec 10 17:05:21 2009 AlbertoConfigurationLSC166 MHz LO SMA-to-Heliax connection repaired

I replaced the SMA end connector for the 166 MHZ Local Oscillator signal that goes to the back of the flange in the 1Y2 rack. The connector had got damaged after it twisted when I was tigheting the N connector of the Heliax cable on the front panel.

  2393   Thu Dec 10 18:31:44 2009 AlbertoConfigurationLSC166 LO Disconnected

Quote:

I temporarily disconnected the Heliax cable that brings the 166MHz LO to the LSC rack.

I'm doing a couple of measurement and I'll put it back in as soon as I'm done.

 These are the losses I measured on a RG-174 cable for the two frequencies that we're planning to use in the Upgrade:

@11MHz Loss=0.22dBm/meter

@55MHz Loss=0.41dBm/meter

(The cable was 2.07m long. The input signal was +10dBm and the output voltages at the oscilloscope where: Vpk-pk(11MHz)=1.90V, Vpk-pk(11MHz)=1.82V )

  2395   Fri Dec 11 09:30:09 2009 KojiConfigurationLSC166 LO Disconnected

They must not be dBm, must be dB

Quote:

Quote:

I temporarily disconnected the Heliax cable that brings the 166MHz LO to the LSC rack.

I'm doing a couple of measurement and I'll put it back in as soon as I'm done.

 These are the losses I measured on a RG-174 cable for the two frequencies that we're planning to use in the Upgrade:

@11MHz Loss=0.22dBm/meter

@55MHz Loss=0.41dBm/meter

(The cable was 2.07m long. The input signal was +10dBm and the output voltages at the oscilloscope where: Vpk-pk(11MHz)=1.90V, Vpk-pk(11MHz)=1.82V )

 

  2396   Fri Dec 11 11:42:26 2009 AlbertoConfigurationLSC166 LO Disconnected

Quote:

They must not be dBm, must be dB

Quote:

Quote:

I temporarily disconnected the Heliax cable that brings the 166MHz LO to the LSC rack.

I'm doing a couple of measurement and I'll put it back in as soon as I'm done.

 These are the losses I measured on a RG-174 cable for the two frequencies that we're planning to use in the Upgrade:

@11MHz Loss=0.22dBm/meter

@55MHz Loss=0.41dBm/meter

(The cable was 2.07m long. The input signal was +10dBm and the output voltages at the oscilloscope where: Vpk-pk(11MHz)=1.90V, Vpk-pk(11MHz)=1.82V )

 

I apologize for the lack of correctness on the units in yesterday's elog entry, but I wasn't very sharp last night.

I repeated the measurement today, this time also making sure that I had a 50ohm input impedance set in the scope. These the results for the losses.

RG-174 Cable 0.053 dB/m @ 11MHz  0.155 dB/m @ 55 MHz

 I also measured the losses in the Heliax cable going from the 166 MHz LO to the LSC rack:

166MHz LO Heliax 0.378 dB @ 11MHz  1.084 dB @ 55 MHz

 

  2398   Fri Dec 11 14:12:32 2009 ranaConfigurationLSC166 LO Disconnected

 

 Seems like very strange cable loss numbers. The Heliax is lossier than the RG-174? I wonder how these compare with the specs in the cable catalog?

  2402   Fri Dec 11 19:51:13 2009 AlbertoConfigurationLSC166 LO Disconnected

Quote:

 

 Seems like very strange cable loss numbers. The Heliax is lossier than the RG-174? I wonder how these compare with the specs in the cable catalog?

In my last entry there was a typo for the measurement of the Heliax at 55 MHz. I corrected it. It was 1.084 dB instead of 1.084 dB/m.
For the Heliax I don't have the measurement of the loss per meter since I don't know the cable actual length.
 
Except for that, I checked the values I found on the Internet.
My measurements for the RG-174 seem comparable to the loss specified in the catalog (here): 6.6dB in 100ft @ 55 MHz, that is 0.22 dB/m, that compare with 0.155 dB/m that I measured.

I did the measurement on a 4.33 meter long cable with SMA connectors at the ends.

  2485   Fri Jan 8 10:03:04 2010 AlbertoOmnistructureLSCSPOB shutter was closed

This morning I found that there was no light on the SPOB PD. I went looking at the photodetector and I found that the shutter in front of it was closed.

I switched the shutter driver from n.c. to n.o. which had the effect of opening it.

I guess we inadvertently closed the shutter with Rana when last week we were tinkering with the ITMY  camera.

  2491   Sat Jan 9 09:47:03 2010 AlbertoUpdateLSCProblems trying to lock the arms

This morning I've been having problems in trying to lock the X arm.

The X arm's filter FM6 in the LSC screen starts blinking as it was halfloaded. Then the transmitted power drops from 1 to ~0.5 and eventually the arm loses lock.
To me it looked like a computer related issue. So I decide to reboot C1ISCEX by powercycling it.

That doesn't seem to have solved the problem. The X arm can get locked but TRX slowly moves between 0.2 and 1.

  2492   Sat Jan 9 11:07:30 2010 AlbertoUpdateLSCProblems trying to lock the arms

Quote:

This morning I've been having problems in trying to lock the X arm.

The X arm's filter FM6 in the LSC screen starts blinking as it was halfloaded. Then the transmitted power drops from 1 to ~0.5 and eventually the arm loses lock.
To me it looked like a computer related issue. So I decide to reboot C1ISCEX by powercycling it.

That doesn't seem to have solved the problem. The X arm can get locked but TRX slowly moves between 0.2 and 1.

The X arm is now locked with TRX stable at ~1.

I think earlier on today I was having problems with running the alignment scripts from op540. Now I'm controlling the IFO from Rosalba and I can easily and stably lock all degrees of freedom.

I needed the X arm to be locked to align the auxiliary beam of the AbsL experiment to the IFO. To further stabilize TRX I increased the loop gain from 1 to 1.5.

Now the auxiliary beam is well aligned to the IFO and the beat is going through the PRC. I'm finally ready to scan the recycling cavity.

I also changed the gain of the PRC loop from -0.1 to -0.5.

  2552   Thu Jan 28 09:17:32 2010 AlbertoUpdateLSC166 Modulation turned off

I temporarily turned off the 166 modulation.

  2605   Tue Feb 16 10:01:16 2010 AlbertoConfigurationLSCArms and PRC not locking

Since last Friday either the arms or the PRC can't lock.

The montors show the beam flashing on the end mirrors, but the cavity can't get locked. The error signal looks fine. I suspect a computer problem.

Also PRC can't lock. SPOB is suspiciously stuck at about -95. Although that's not a fixed number, but covering the by hand the SPOB PD on the ITMY table doesn't change the number. I check the DC output of the photodetector and it is actually seen the beam.

Suspecting computer problems started after last Thursday's IP switch, I rebooted the frame builder, c1dcuepics, c1daqctrl and all the front ends. I then burtrestored to February 1st at 1:00 am.

Before I burtrestored c1iscepics, SPOB had gone back to more typical numbers around 0, as it usually read when PRC wasn't locked.

But burtrestoring c1iscepics, return it to the -95 of earlier.

Burterestoring to other times or dates didn't solve the problems.

  2607   Tue Feb 16 14:10:06 2010 josephb, rob, kojiConfigurationLSCArms and PRC not locking

Quote:

Since last Friday either the arms or the PRC can't lock.

The montors show the beam flashing on the end mirrors, but the cavity can't get locked. The error signal looks fine. I suspect a computer problem.

Also PRC can't lock. SPOB is suspiciously stuck at about -95. Although that's not a fixed number, but covering the by hand the SPOB PD on the ITMY table doesn't change the number. I check the DC output of the photodetector and it is actually seen the beam.

Suspecting computer problems started after last Thursday's IP switch, I rebooted the frame builder, c1dcuepics, c1daqctrl and all the front ends. I then burtrestored to February 1st at 1:00 am.

Before I burtrestored c1iscepics, SPOB had gone back to more typical numbers around 0, as it usually read when PRC wasn't locked.

But burtrestoring c1iscepics, return it to the -95 of earlier.

Burterestoring to other times or dates didn't solve the problems.

 Koji and I started poking around, trying to understand what was going on.  At first, we thought it might be related to a computer error, as it seemed.

Fortunately, Rob stopped by and explained that the boost stage of the filter comes under c1lsc control, and will be turned on or off depending on the power in the arms.  Although if you turn it off, it will remain off, it just if its manually selected on, it may go on or off.

Similarly, the output from the Xarm filter bank to the ETMX  filter input will be turned on or off depending on the power in the arm.

Anyways, the locking trouble turns out to be due to no RF sidebands at 33 MHz.  The output of the Marconi was unplugged.  I don't know who, or why did it, but I've plugged it in for now, so we can lock the arms.  Let us know if you need in unplugged.  Thanks.

  2608   Tue Feb 16 15:25:00 2010 AlbertoConfigurationLSCArms and PRC not locking

 

 shock.jpg

  2836   Fri Apr 23 21:02:14 2010 rana, joeUpdateLSCStarted dev of LSC FE

Joe and I started working on the new LSC FE control today. We made a diagram of the system in Simulink, but were unable to compile it.

Joe checked out the latest CDS software out of their new SVN and put it somewhere (perhaps his home directory).

We then copied the directory with the .mdl files and the CDS parts library into our real Simulink Model Directory:

/cvs/cds/caltech/cds/advLigo/src/epics/simLink

Use this and not someplace in Alex or Rob's home directory !

Joe will put in more details on Monday once he figures out how to build the new stuff. Basically, we decided not to support multiple versions of the CDS real time code here. We'll just stay synced to the latest stable ~versions.

I exported the current version of the LSC FE into our public_html/FE/ area on nodus where we will put all of the self-documenting FE diagrams:

https://nodus.ligo.caltech.edu:30889/FE/lsc_slwebview_files/index.html

To make a web setup like this, you just use the "Export to Web" feature from the top-level Simulink diagram (e.g. lsc.mdl). Choose the following options:

Untitled.png

Note: in order to get the web page to work, I had to change the apache httpd.conf file to allow AddType file overriding. Here's the term cap of the diff:

nodus:etc>diff httpd.conf httpd.conf~
155c155
< ServerAdmin jenne@caltech.edu
---
> ServerAdmin aso@caltech.edu
225d224
<     AllowOverride FileInfo

  2839   Sun Apr 25 02:56:07 2010 ranaUpdateLSCStarted dev of LSC FE

LSC Plant Model. That is all.

  2840   Sun Apr 25 10:40:21 2010 KojiUpdateLSCStarted dev of LSC FE

Once you made a CDS model, please update the following wiki page. This will eventually help you.

http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/Existing_RCG_DCUID_and_gds_ids

Quote:

LSC Plant Model. That is all.

 

  2841   Mon Apr 26 10:21:45 2010 josephbUpdateLSCStarted dev of LSC FE

Quote:

Joe and I started working on the new LSC FE control today. We made a diagram of the system in Simulink, but were unable to compile it.

Joe checked out the latest CDS software out of their new SVN and put it somewhere (perhaps his home directory).

The SVN checkout was done on megatron.  It is located under /home/controls/cds/advLigoRTS

So, to compile (or at least try to) you need to copy the .mdl file from /cvs/cds/caltech/cds/advLigo/src/epics/simLink to /home/controls/cds/advLigoRTS/src/epics/simLink on megatron, then run make SYS in the advLigoRTS directory on megatron.

The old checkout from CVS exists on megatron under /home/controls/cds/advLigo.

  2968   Fri May 21 16:24:11 2010 KojiUpdateLSC40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue.

1. Give us the designed arm length. What is the criteria?

2. The arm lengths got shorter as the ITMs had to shift to the end. To make them longer is difficult. Try possible shorter length.

  2973   Mon May 24 10:03:14 2010 ranaUpdateLSC40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue.

 

 If you have a working 40m Optickle model, put it in a common place in the SVN, not in your own folder.

I can't figure out why changing the arm length would effect the RF sidebands levels. If you are getting RF sidebands resonating in the arms, then some parameter is not set correctly.

As the RF sideband frequency gets closer to resonating in the arm, the CARM/DARM cross-coupling to the short DOFs probably gets bigger.

  2974   Mon May 24 11:32:05 2010 ranaUpdateLSC40mUpgrade Field Power and RF Power Spectrum at the ports. 38m/38.55m arm length issue.

Quote:

 

 If you have a working 40m Optickle model, put it in a common place in the SVN, not in your own folder.

I can't figure out why changing the arm length would effect the RF sidebands levels. If you are getting RF sidebands resonating in the arms, then some parameter is not set correctly.

As the RF sideband frequency gets closer to resonating in the arm, the CARM/DARM cross-coupling to the short DOFs probably gets bigger.

I uploaded the latest iscmodeling package to the SVN under /trunk. It includes my addition of the 40m Upgrade model: /trunk/iscmodeling/looptickle/config40m/opt40mUpgrade2010.m.

I don't know the causes of this supposed resonances yet. I'm working  to try to understand that. It would be interesting also to evaluate the results of absolute length measurements.

Here is what I also found:

reflRFpowerVsArmLength.png

It seems that 44, 66 and 110 are resonating.

If that is real, than 37.5m could be a better place. Although I don't have a definition of "better" yet.  All I can say is these resonances are smaller there.

  3084   Thu Jun 17 17:09:44 2010 AlbertoUpdateLSCShort Cavity Length Adjustments

I calculated the phase shifts that the sidebands would pick up in the arms in the case we changed the arm length to 38.4m as proposed. I obtained the following values (in degrees):

phi(-f2) = 0.66; phi(-f1) = -0.71; phi(f1) = 0.71; phi(+f2) = -0.66

These are the plots with the results as I obtained from an Optickle simulation (the second zooms in around 38.4m).

sidebandPhaseRotation_73430639654.png sidebandPhaseRotation_73430656054.png

These values agree with what Koji had already estimated (see elog entry 3023).

Since we can't make the arm longer than that, to increase the distance from the resonance, we would like to adjust the length of the short cavities to compensate for that.  For f2 (=55MHz), 0.7 degrees correspond to about 5cm. That is about the length change that we expect to make to the design.

I simulated with Optickle the effect of changing the length of either the SRC or the PRC. The best way I found to do that, was to measure the cavity circulating power when the macroscopic lengths change.

The following plots show the effect of changing either the PRC or SRC length (left or right figure), on the circulating power of both cavities at the same time (top and bottom plots).

shortCavityCirculatingPower_73430666992.png prcCirculatingPower_73430665955.png

 You can compare these with the case of perfect antiresonance as in the following plots:

shortCavityCirculatingPower_73430668892.png shortCavityCirculatingPower_73430669604.png

It seems that the design length for the short cavities are not too bad. f1 is not optimized in the PRC, but changing the length of the cavity wold just make f2 worse in SRC.

These simulations seem to support the choice of not changing the design cavity lengths for PRC and SRC.

Of course these are only an "open loop" simulations. At the moment we don't know what would be the effect of closing the control loops. That is something I'm going to do later. It'll be part of my studies on the effects of cavity absolute length on the whole IFO.

  3086   Fri Jun 18 13:47:20 2010 KojiUpdateLSCShort Cavity Length Adjustments

You should have been in my lecture yesterday!
Power in the cavity is not a good index (=error signal) to judge the optimal length.
You should look at the phases of the length signals. (i.e. demodulation phase which gives you the maximum amplitude for CARM, PRC, SRC, etc)

You must move the SRC and PRC lengths at the same time.
The resonance of f1 (mostly) depends on the PRC length, but that of f2 depends on both the PRC and SRC lengths.

  3087   Fri Jun 18 15:07:26 2010 AlbertoUpdateLSCShort Cavity Length Adjustments

Quote:

You should have been in my lecture yesterday!
Power in the cavity is not a good index (=error signal) to judge the optimal length.
You should look at the phases of the length signals. (i.e. demodulation phase which gives you the maximum amplitude for CARM, PRC, SRC, etc)

You must move the SRC and PRC lengths at the same time.
The resonance of f1 (mostly) depends on the PRC length, but that of f2 depends on both the PRC and SRC lengths. 

Right. Ultimately the phase gain inside the cavity is what we look at. Calculating that for the SBs inside PRC and SRC is actually the first thing I did.

But I kept getting very small angles. Too small, I thought. Maybe there was some problem in the way I calculated it.

Then I made a power analysis to check if the SBs were getting affected at all by that 0.7degree phase shift they're picking up in the arms.

I wanted to show the point where I am, before leaving. But, I keep working on it.

  3227   Thu Jul 15 12:21:08 2010 AlbertoConfigurationLSCPRC and SRC length adjustements

Lately I've been trying to calculate the corrections to the recycling cavity lengths that would compensate for the phase that the sidebands will pick up from the arms in the upgraded interferometer.

To do that calculation , I tried two quite different ways, although equivalent in principle. They both use the optickle model of the 40m, but the calculation is made differently.

In the first way, I looked directly at the phases of the field: phase of [input field] / [reflected field], phase of [input field at PRM] / [transmitted field at SRM].

In the second way I looked at the demodulation phases of the LSC signals.

The first way is much simpler, especially from a computational point of view. It is the first I tried several weeks ago, but then I had abandoned because back then I thought it wasn't the correct way.

Anyway, both ways gave me the same results for the PRC length.
For the SRC length, the first way has given me a clear outcome. On the other hand, the second way has produced a less clear result.

According to these results, these would be the proposed adjustements to the cavity lengths:
dl(PRC) = -0.0266 m; dl(SRC) = 0.0612 m

I) 1st Way
a) case of arms ideal length (33.86 m)

sidebandPhaseRotation_73433447384.png sidebandPhaseRotation_73433447590.png


b) case arm length = 38.40 m

PRC

 sidebandPhaseRotation_73433447960.png zoom -> sidebandPhaseRotation_73433448864.png

SRC

sidebandPhaseRotation_73433445372.png zoom -> sidebandPhaseRotation_73433449354.png


II) 2nd Way
a) case of arms ideal length (33.86 m)

 demodPhaseVsRecCavLengths_73432637363.png


b) case arm length = 38.40 m

demodPhaseVsRecCavLengths_73433237349.png

  3228   Thu Jul 15 15:57:10 2010 KojiConfigurationLSCPRC and SRC length adjustements

Tell me whether it is correct or not. Otherwise I won't be able to sleep tonight.

Quote:

According to these results, these would be the proposed adjustements to the cavity lengths:
dl(PRC) = -0.0266 m; dl(SRC) = 0.612 m

  3229   Thu Jul 15 16:16:51 2010 AlbertoConfigurationLSCPRC and SRC length adjustements

Quote:

Tell me whether it is correct or not. Otherwise I won't be able to sleep tonight.

Quote:

According to these results, these would be the proposed adjustements to the cavity lengths:
dl(PRC) = -0.0266 m; dl(SRC) = 0.612 m

 Sorry. I was in a rush to go to the LIGO "all hands" meetings when I posted that elog entry, that I forgot a zero in the SRC length value. The correct values are:

dl(PRC) = -0.0266 m; dl(SRC) = 0.0612 m

The cavity absolute lengths are then:

L(PRC) = 0.5/2/f1*c - 0.0266 = 6.7466 m

L(SRC) = c/f2 + 0.0612 = 5.4798 m

where c is the speed of light; f1 = 11065399 Hz; f2 = 55326995 Hz

  4005   Thu Dec 2 00:34:32 2010 ranaHowToLSCHow Does Cavity Locking Work (answered by Nikon)

https://nodus.ligo.caltech.edu:30889/gw.swf

Dr. Koji Arai and Nikon
  4131   Tue Jan 11 01:05:29 2011 kiwamuUpdateLSCobtained Xarm PDH signal

[Jenne, Zach, Kiwamu]

 

 We made some efforts to lock the X arm cavity with the infrared beam.

We eventually obtained the PDH signal from a photo diode at AS port, we are still in the mid way of the lock.

The PDH signal now is going into c1lsc's ADC.

We have to make sure which digital channel corresponds to our PDH signal,

 

(what we did)

- split the LO signal, which comes from a Marconi, just before the EOM into two path.

     One is going to the EOM and the other is going to the AP table for the demodulation, The driving frequency we are using is 11MHz.

- put RF amplifiers to make the RF signal bigger. The raw signal was small, it was about ~-50 dBm in the spectrum analyzer.

   So we connected two ZLN amplifiers. Now the RF signal is at about 0 dBm

- connected the LO and RF signals to a mixer.  Additionally we put a 9.5-11.5 MHz bandpass filter at the LO path since there was some amounts of 29.5MHz due to the RF reflection at the EOM resonant box.

     After a low pass filter by SR560 the signal shows typical PDH behaviors.

- strung a BNC cable which connects the demodulated signal and c1lsc.

    In order to connect the signal to the current working ADC, we disconnected AS166_I from a whitening board and plug our cable on it.

- tried checking the digital signal but we somehow couldn't configure DAQ setting, So actually we couldn't make sure which channel corresponds to our signal.

 

  4141   Wed Jan 12 01:39:49 2011 kiwamuUpdateLSClocked X arm

[Suresh, Kiwamu]

 We eventually succeeded in locking X arm with the infrared beam.

The PDH signal is taken at MCL's ADC instead of c1lsc's, and fedback to MC2_POS through the MCL path.

Right now the lock is not so stable for some reasons, so we need to investigate it more.

 

(what we did)

 - strung a long BNC cable to connect the demodulated signal and the ADC of c1ioo.

          We didn't touch anything on the demodulation system, so the setup for the demodulation is exactly the same as that of yesterday (see here).

 - disconnected the actual MCL cable from the ADC breakout board at 1X2 rack. And put the demodulated signal onto it.

 - checked the analog dewhitening filter state for the MC2 coil driver, found the analog filter are always off.

  So we just made simDW and invDW always on.

- changed the gain of the MCL loop to have a stable lock for the X arm.

    right now a reasonable setup in the MCL filters are:

         FM1:ON, FM10:ON, G=0.1

 - In fact the lock of the MC is not so stable compared to before, frequently an attempt of locking the X arm leads to the unlock of the MC.

  4153   Fri Jan 14 01:55:26 2011 kiwamuUpdateLSCX arm locked with C1LSC digital control

 [Koji, Kiwamu]

 We succeeded in locking the X arm with the C1LSC digital control.

As we did on the day before yesterday, the feedback signal goes to MCL (#4141), but this time the signal is transfered from C1LSC through the RFM.

 


 (key points) 

- checking the state of the analog whitening filters at C1LSC rack.

   We took the transfer function of them and found that they were always on regardless of the clicking any buttons on medm.

To cancel the filter shape of the whitening, we put an unWhitening filter so that these transfer functions becomes flat in total.

The whitening filter approximately has : pole:150Hz, pole:150Hz, zero:15Hz, zero:15Hz (although these numbers came from by our eye ball fitting)   

 

 - demodulation phase adjustment

   We performed the same measurement as that of Suresh and Koji did yesterday (#4143) to adjust the phase of the PDH demodulation.

By changing the cable length we roughly adjusted the I-phase to eventually ~10 deg, which is close enough to 0 deg.

(probably some more efforts should be made as a part of daytime tasks)

Note that we are currently using the REFL33 demodulation board for this purpose (#4144). The LO power we put is about 16dBm.

The angle between I and Q at 11MHz is actually almost 90 deg.

This fact has been confirmed by putting a sinusoidal signal with a slightly different frequency (~100Hz) from that of the LO onto the RF input.

 

 - attenuation of RF signal

  Since the PDH signal taken by C1LSC's ADC had been saturated somewhat, we introduced a ND filter of 10 on the photo diode to attenuate the RF signal.

As a result the amplitude of the PDH signal on dataviewer became more reasonable. No more saturations.

 

(some notes)

 unWhitening filter           pole:15Hz. pole:15Hz, zero:150Hz, zero:150Hz

 C1LSC_MC_FM1   pole:1kHz, zero:10Hz

 Gain in digital control       G ~ -1

measured UGF  ~  200-300 Hz

 measured RFM delay ~ 125 usec 

  4154   Fri Jan 14 11:29:00 2011 kiwamuUpdateLSCexpected open loop TF of X arm locking

Here shows a plot of the expected open loop transfer function (TF) for the X arm locking.

xarm_oltf.png

I assume that the delay time of the digital system associated with the ADC/DAC and the digital filtering process is ~100 usec independently from the RFM delay according to Yuta's measurement (#3961).

Also I assume the MC2 pendulum has a pole at 1Hz with Q of ~5, and the X arm has its cavity pole at ~3kHz.

When the lock acquisition takes place, we used the red curve shown above in order to avoid a big DC feedback onto MC2.

Once the X arm became resonant at TEM00, we manually switched FM3 on, which is a boost filter containing a pole at  1Hz and a zero at 50Hz in order to suppress the residual motion below 1Hz.

The expected curve for the boosted state is drawn by the blue curve in the plot. 

With this open loop TF, the UGF can be realized only around 100-300 Hz due to the phase margin condition.

This expectation of the UGF is consistent with our measurement because we obtained the UGF around 200-300Hz.

In fact above 300Hz we observed that the control became unstable and started oscillating.

 

Quote:

 (some notes)

 unWhitening filter           pole:15Hz. pole:15Hz, zero:150Hz, zero:150Hz

 C1LSC_MC_FM1   pole:1kHz, zero:10Hz

 Gain in digital control       G ~ -1

measured UGF  ~  200-300 Hz

 measured RFM delay ~ 125 usec 

 

  4156   Fri Jan 14 12:34:08 2011 KojiUpdateLSCX arm locked with C1LSC digital control

My feeling was that the saturation was caused by the LSC whitening filter which was always on.
Once the LSC whitening filter is controlled from C1LSC, we would be able to remove the attenuator.

Quote:

  - attenuation of RF signal

  Since the PDH signal taken by C1LSC's ADC had been saturated somewhat, we introduced a ND filter of 10 on the photo diode to attenuate the RF signal.

As a result the amplitude of the PDH signal on dataviewer became more reasonable. No more saturations.

 

  4180   Thu Jan 20 22:17:12 2011 ranaSummaryLSCFPMI Displacement Noise

I found this old plot in an old elog entry of Osamu's (original link).

It gives us the differential displacement noise of the arms. This was made several months after we discovered how the STACIS made the low frequency noise bad, so I believe it is useful to use this to estimate the displacement noise of the arm cavity today. There are no significant seismic changes. The change of the suspension and the damping electronics may produce some changes around 1 Hz, but these will be dwarfed by the non-stationarity of the seismic noise.

Attachment 1: osamu-1140657006.pdf
osamu-1140657006.pdf
  4186   Fri Jan 21 23:55:25 2011 ranaConfigurationLSCPhase Noise Measurement filter

We've set up a beat note measurement between the VCO driver and the Marconi (see Suresh's elog).

Here's the 'unWhiten' filter for compensating the SR560 TF.

It has poles = 1 mHz, 5 kHz, 5 kHz

and  zeros = 30 mHz, 1 kHz

The gain is set to be ~0.001 in the 1-100 Hz band to compensate the G=1000 of the SR560.

Attachment 1: a.gif
a.gif
ELOG V3.1.3-