New all organic machine.
On Friday, I grabbed the Zurich Instruments HF2LI lock-in amplifier and brought it home. As time permits, I will work towards developing a similar readout script as we have for the SR785.
I returned the Zurich Instruments analyzer I borrowed some time ago to test out at home. It is sitting on first table across from Steve's old desk.
3f modulation cancellation theory http://nodus.ligo.caltech.edu:8080/40m/11005
3f modulation cancellation adjustment setup http://nodus.ligo.caltech.edu:8080/40m/11029
Receipe for the 3f modulation cancellation http://nodus.ligo.caltech.edu:8080/40m/11032
Modulation depth analysis http://nodus.ligo.caltech.edu:8080/40m/11036
I wonder if DRMI can be locked on 3f using this lower 55 MHz modulation depth. It seems that PRMI should be unaffected, but that the 3*f2 signals for SRCL will be too puny. Is it really possible to scale up the overall modulation depths by 3x to compensate for this?
This KTP crystal has the maximum allowed RF power of 10W (=32Vpk) and V_pi = 230V. This corresponds to the maximum allowed
modulation depth of 32*Pi/230 = 0.44. So we probably can achieve gamma_1 of ~0.4 and gamma_2 of ~0.13. That's not x3 but x2,
so sounds not too bad.
Then Kiwamu's triple resonant circuit LIGO-G1000297-v1 actually shows the modulation up to ~0.7. Therefore it is purely an issue
how to deliver sufficient modulation power. (In fact his measurement shows some nonlinearity above the modulation depth of ~0.4
so we should keep the maximum power consumption of 10W at the crystal)
This means that we need to review our RF system (again!)
- Review infamous crazy attn/amp combinations in the frequency generation box.
- Use Teledyne Cougar ampilfier (A2CP2596) right before the triple resonant box. This should be installed closely to the triple resonant box in order to
minimize the effects of the reflection due to imperferct impedance matching.
- Review and refine the triple resonant circuit - it's not built on a PCB but on a universal board. I think that we don't need triple
resonance, but double is OK as the 29.5MHz signal is small.
We want +28V supply at 1X1 for the Teledyne amp and the AOM driver. Do we have any unused Sorensen?
Rana showed me that if c1sus machine runs c1mcs stuff(and c1x02 stuff) only, we can use dataviewer without crashing fb.
Also, if we set correct NDS server and port(fb/8088), we can use diaggui on every machine.
During my investigation on what he did, I accidentally deleted daqd......
I am very very sorry.
I don't know if it helps or not, but all I have is the following information:
[What I deleted]
-rwxr-xr-x 1 controls controls 6583071 Oct 1 11:57 daqd
[help message for daqd existed]
CDS Data Acquisition Server, Frame Builder, version 2.0
California Institute of Technology, LIGO Project
Client communication protocol version 11.4
daqd [-f <input frame file name>]
[-c <configuration file (default -- $HOME/.daqdrc)>]
[-s <frame writer pause usec (default -- 1 sec)>]
This executable compiled on:
Fri Oct 1 10:33:18 PDT 2010
Linux fb 220.127.116.11 #7 SMP Fri Sep 24 14:09:53 PDT 2010 x86_64 Dual-Core AMD Opteron(tm) Processor 8220 AuthenticAMD GNU/Linux
Please help me, Joe.
Missing daqd file, i.e. the framebuilder executable.
1) Go to /opt/rtcds/caltech/c1/core/advLigoRTS/
2) Look in the Makefile for a likely build suspect. In this case it was build dc, which stands for data concentrator.
3) So we ran "make dc"
4) Go to the sub-directory build/dc/ and then copy the daqd file there to the /opt/rtcds/caltech/c1/target/fb directory
5) Test it to ensure we're getting channels (Yay!)
Place the new target directory under SVN control.
c1x01 timing issue was solved. Now all of the models on c1iscex are nicely running.
- c1x01 was synchronized to 1PPS in stead of TDS
- C1:DAQ-DC0_C1X01_STATUS (Upper right indicator) was red. The bits were 0x4000 or 0x2bad.
C1:DAQ-DC0_C1X01_CRC_SUM kept increasing
- c1scx, c1spx, c1asx could not get started.
- login to c1iscex "ssh c1iscex"
- Run "sudo shutdown -h now"
sudo shutdown -h now
- Walk down to the x end rack
- Make sure the supply voltages for the electronics are correct (See Steve's entry)
- Make sure the machine is already shutdown.
- Unplug two AC power supply of the machine.
- Turn off the front panel switch of the IO chassis
- Wait for 10sec
- Turn on the IO chassis
- Plug the AC power supply cables to the machine
- Push the power switch of the realtime machine
When I finished my measurements, the modulation setup was reverted to the conventional one.
If someone wants to use the 3f cancellation setting, it can be done along with this HOW-TO.
The 3f cancellation can be realized by adding a carefully adjusted delay line and attenuation for the 55MHz modulation
on the frequency generation box at the 1X2 rack. Here is the procedure:
1) Turn off the frequency generation box
There is a toggle switch at the rear of the unit. It's better to turn it off before any cable action.
The outputs of the frequency generation box are high in general. We don't want to operate
the amplifiers without proper impedance matching in any occasion.
2) Remove the small SMA cable between 55MHz out and 55MHz in (Left arrow in the attachment 1).
According to the photo by Alberto (svn: /docs/upgrade08/RFsystem/frequencyGenerationBox/photos/DSC_2410.JPG),
this 55MHz out is the output of the frequency multiplier. The 55MHz in is the input for the amplifier stages.
Therefore, the cable length between these two connectors changes the relative phase between the modulations at 11MHz and 55MHz.
3) Add a delay line box with cables (Attachment 2).
Connect the cables from the delay line box to the 55MHz in/out connectors. I used 1.5m BNC cables.
The delay line box was set to have 28ns delay.
4) Set the attenuation of the 55MHz EOM drive (Right arrow in the attachment 1) to be 10dB.
Rotate the attenuation for 55MHz EOM from 0dB nominal to 10dB.
5) Turn on the frequency modulation box
For reference, the 3rd attachment shows the characteristics of the delay line cable/box combo when the 3f modualtion reduction
was realized. It had 1.37dB attenuation and +124deg phase shift. This phase change corresponds to the time delay of 48ns.
Note that the response of a short cable used for the measurement has been calibrated out using the CAL function of the network analyzer.
Huge random numbers are flowing into ETMX/ETMY ASC PIT/YAW. Because of this, I could not damp the ETMX/ETMY suspension at the beginning during the recovery from rebooting. (Attachment 1)
By turning off the output of the ASC filters, the mirrors were successfully damped.
Looking at the FE model view of the end RTSs, there were two possibilities: (Attachment 2)
- They are coming from RFM connection
- They are coming from ASXASY
ASX/ASY are not active and I could not see anything producing these numbers. Burtrestore didn't help.
The possibility was something at the other side of the RFM, or corruption of the RFM signal.
- Looking at the RFM model (Attachment 3), the ASC signals are coming from ASS and IOO. The ASS path has the filter module (C1:RFM-ETMX_PIT and etc). This FM is quiet and not guilty.
- Why do we have the RFM from IOO? I went to IOO and found the new ASC (WFS) model is there. I didn't realize the presence of this model. In fact ASC screen showed that these random numbers are flowing into the end SUSs.
So I did burtrestore of c1iooepics. Alas! they are gone.
Now I can go home.
Yeah, this is a known issue actually. We go to ASC screen and manually swich off all the outputs after every reboot. We haven't been able to find a way to set default so that when the model comes online, these outputs remain switched off. We should find a way for this.
you can hand edit the autoBurt file which the FE uses to set the values after boot up. Just make a python script that amends all of the OFF or ZERO that are needed to make things safe. This would be the autoBurt snap used on boot up only, and not the hourly snaps.
The autoBurt file for FE already has the C1:ASC-ETMX_PIT_SW2 (and other channels for ETMY, ITMX, ITMY, BS and for YAW) present, and I checked the last snapshot file from Feb 7th, 2022, which has 0 for these channels. So I'm not sure why when FE boots up, it does not follow the switch configuration. Fr safety, I changed all the gains of these filter modules, named like C1:ASC-XXXX_YYY_GAIN (where XXXX is ETMX, ETMY, ITMX, ITMY, or BS , and YYY is PIT or YAW) to 0.0. Now, even if the FE loads with switches in ON configuration, nothing should happen. In future, if we use this model for anything, we can change the gain values which won't be hard to track as the reason why no signal moves forward. Note, the BS connections from this model to BS suspension model do not work.
This did the trick - I simply ran
sudo systemctl restart daqd_*
on FB1, and now all the CDS overview lights are green again.
I thought I had done this already, but I realize that I was supposed to restart the daqd processes on FB1 (which is where they are running) and not on c1ioo .
Thanks Jamie for the speedy resolution!
From page 21 of T1100625, DAQ status "0x2000" means that the channel list is out of sync between the front end and the daqd. This usually happens when you add channels to the model and don't restart the daqd processes, which sounds like it might be applicable here.
It looks like open-mx is loaded fine (via "rtcds lsmod"), even though the systemd unit is complaining. I think this is because the open-mx service is old style and is not intended for module loading/unloading with the new style systemd stuff.
We added a channel on c1psl in order to monitor the temperature of the PPKTP sitting on the PSL table.
To take continuous data of the temperature we added the channel by editing the file: target/c1psl/c1psl.db
We named the channel "C1:PSL-PPKTP_TEMP".
To reflect this change we physically rebooted c1psl by keying the crate.
Is this a setpoint temperature that we can change by writing to the channel or is it a readout of the actual temperature of the oven?
This is a readout channel just to monitor the actual temperature.
Rana and I found that the QPD for the optical lever at X end are showing small signals.
At this moment each of the segments exhibits approximately 200 counts when the oplev beam is centered.
These small numbers may be due to the coating of ETMX, but we are not sure.
Probably we have to increase the gain of the QPD depending on situations.
So a set of the tomorrow's daytime task is:
1. check the trend data of the QPD outputs to see how much signals were there in the past.
2. check the whitening filters to make sure if it's on or off.
3. If it's necessary, increase the gain of the QPD to have reasonable readouts.
I am going to ask somebody to do this task.
Something happened about 8 years ago.
Old iLog entry by AJW (2003/Sep/8)
Old iLog entry by AJW (2003/Sep/9)
Last night I noticed that PZT1 didn't work properly
In the last week Matt and I modified the MFD configuration because the mixer had been illegally used.
Since the output from the comparator is normally about 10 dBm, a 4-way power splitter reduced the power down to 4 dBm in each output port.
In order to reserve a 7 dBm signal to a level-7 mixer, we decided to use an asymmetric power splitter, which is just a combination of 2-way and 3-way splitter shown in the diagram above.
With this configuration we can reserve a 7 dBm signal for a mixer in the fine path.
However on the other hand we sacrificed the coarse path because the power going to the mixer is now 2.2 dBm in each port.
According to the data sheet for the mixer, 1 dB compression point for the RF input is 1dBm. Therefore we put a 1 dB attenuator for the RF port in the coarse system.
In the delay line of the fine path we found that the delay cable was quite lossy and it reduced the power from 2.2 dBm to about 0 dBm.
Using 2 dBm for a Level 7 mixer is so bogus, that I will dismantle this as soon as I come over.
PLEASE DO NOT DISMANTLE THE SETUP !
Actually we tried looking for a level-3 or a smaller mixer, but we didn't find them at that moment. That's why we kept the level-7 mixer for the coarse path.
As you pointed out we can try an RF amplifier for it.
Here is a picture of the latest ABSL setup at the east part of the AP table.
(Some notes )
- The ABSL laser is injected from the AP port.
- A 90 % reflection BS was installed just after the NPRO, this is for sampling a 10% of the laser to the PSL table.
However, I've just realized that this is not a nice way because the 10 % beam doesn't go through the Faraday. Whoops.
- A polarzser cell at the input side of the Faraday doesn't let any beam go through it for some reasons (broken ?).
Therefore instead of having such a bad cell, a cube PBS was installed.
- A room was left on the table for the AS165 RFPD (green-dashed rectangular in the picture).
- Also a picture of the setup will be uploaded in the morning.
Last night I was making a script which will measure the sensing matrix using the realtime LOCKIN module.
The script is a kind of expansion of Jamie's one, which measure the asymmetry, to more generic purpose.
It will shake a suspended optic of interest and measure the response of each sensor by observing the demodulated I and Q signals from the LOCKIN module.
I will continue working on this.
- made a function that drives the LOCKIN oscillator and get the data from the I and Q outputs.
- checked the function with the MICH configuration.
ITMX, ITMY and BS were shaken at 100 Hz and at different time.
Then the response of AS55_Q showed agreement with what I got before for the actuator calibration (see this entry).
It means the function is working fine.
Here is the conclusive result for the circuit configuration for aLIGO BBPD and 40m Green PD.
- Use Mini-circuits MAR-6SM for the RF preamplifier. The 50Ohm input impedance is used for the RF transimpedance.
The maximum output is ~4dBm.
- Use Mini-circuits GALI-6 for the RF middle power amp. The gain is 12dB and the amplifier is linear up to +17dBm. i.e. This is still linear at the maximum output level of MAR-6SM.
- The total RF transimpedance is ~2k. The DC transimpedance is also 2k.
- The bandwidth is 80MHz with FFD100 and internal 25V bias. When S3399 is used, the bandwdith goes up to 180MHz
although the responsivity of FFD100 at 1064nm is better than S3399 by a factor of 1.5. At the 40m we will use S3399 for the green BB PD.
- By adding an LC network next to the PD, one of the unnecessary signal can be notched out.
As an example, 9MHz notch was placed for the FFD100 case.
- Noise level: ~10pA/rtHz as a floor noise level at around 30MHz. This corresponds to the equivalent dark current of 0.4mA.
Matt has finished the PCB layout. We will order small first batches, and stuff it for the test. Some of these will be the 40m green PD.
Minicircuits ERA-5SM was used for the RF amp of the BBPD. This amp is promising as a replacement of Teledyne Cougar AP389
as ERA-5SM gave us the best performance so far among the BBPDs I have ever tested for the aLIGO BBPD/Green.
The -3dB bandwidth of ~200MHz and the noise floor at the shotnoise level of 0.7mA DC current were obtained.
The aLIGO BBPD candidate (LIGO Document D1002969-v7) employs Teledyne Cougar AP389 as an RF amplifier.
This PD design utilizes the 50Ohm termination of the RF amp as a transimpedance resistance at RF freq.
However, it turned out that the bandwidth of the transimpedance gets rather low when we use AP389, as seen in the attachment2.
The amplifier itself is broadband upto 250MHz (the transfer function was confirmed with 50Ohm source).
The reason is not understood but AP389 seems dislike current source. Rich suggested use of S-parameter measurement
to construct better model of the curcuit.
On the other hand, the RF amplifiers from Minicircuits (coaxial type like ZFL-1000LN+), in general, exhibit better compatibility with PDs.
If you open the amplifier case, you find ERA or MAR type monolithic amplifiers are used.
So the question is if we can replace AP389 by any of ERA or MAR.
- The large gain of the RF amp is preffered as far as the output does not get saturated.
- The amplifier should be low noise so that we can detect shot noise (~1mA).
- The freq range of the useful signal is from 9MHz to 160MHz.
The advanced LIGO BBPD is supposed to be able to receive 50mW of IR or 15mW of 532nm. This approximately corresponds to
5mA of DC photocurrent if we assume FFD-100 for the photodiode. At the best (or worst) case, this 5mA has 100% intensity modulation.
If this current is converted to the votage through the 50Ohm input termination of the RF amp, we receive -2dBm of RF signal at maximum.
This gives us a dilemma. if the amp is low noise but the maximum output power is small, we can not put large amount of light
on the PD. If the amp has a high max output power (and a high gain), but the amp is not low noise, the PD has narrow power range
where we can observe the shotnoise above the electronics noise.
What we need is powerful, high gain, and low noise RF amplifier!
Teledyne Cougar AP389 was almost an ideal candidate before it shows unideal behavior with the PD.
Among Minicircuits ERA and MAR series, ERA-5 (or ERA-5SM) is the most compatible amplifier.
Considering the difference of the gain, they are quite similar for our purpose. Both can handle upto -2dBm,
which is just the right amount for the possible maximum power we get from the 5mA of photocurrent.
A test circuit has been built (p.1 attachment #1) on a single sided prototype board.
First, the transfer function was measured with FFD-100. With the bias 100V (max) the -3dB bandwidth of ~200MHz was observed.
This decreases down to 75MHz if the bias is 25V, which is the voltage supplied by the aLIGO BBPD circuit. The transimpedance
at the plateau was ~400Ohm.
Next, S3399 was tested with the circuit. With the bias 25V and 30V (max) the -3dB bandwidth of ~200MHz was obtained although
the responsivity of S3399 (i.e. A/W) at 1064nm is about factor of 2 smaller than that of FFD-100.
The noise levels were measured. There are many sprious peaks (possibly by unideal hand made board and insufficient power supply bypassing?).
Othewise, the floor level shows 0.7mA shotnoise level.
The RF amplifier of the prototype BBPD has been replaced from ERA-5SM to MAR-6SM.
The bandwidth is kept (~200MHz for S3399 with 30V_bias), and the noise level got better while the maximum handling power was reduced.
MAR-6SM is a monolithic amplifier from Minicircuits. It is similar to ERA-5SM but has lower noise
and the lower output power.
The noise floor corresponds to the shotnoise of the 0.4mA DC current.
Now the mess below 50MHz and between 90-110MHz should be cleaned up.
They are consistently present no matter how I change the PD/RF amp (ERA<->MAR)/bias voltage.
I should test the circuit with a different board and enhanced power/bias supply bypassing.
- Assume 5mA is the maximum RF (~50mW for 1064nm, ~15mW for 532nm). This is already plenty in terms of the amount of the light.
- 100% intenisty modulation for 5mA across 50Ohm induces -2dBm RF power input for the amplifier.
- Assume if we use MAR-6 for the preamplifier. The max input power is about -18dBm.
This corresponds to 16% intensity modulation. It may be OK, if we have too strong intensity modulation, we can limit the power
down to 0.8mA in the worst case. The shot noise will still be above the noise level.
- In the most of the applications, the RF power is rather small. (i.e. 40m green beat note would expected to be -31dBm on the RF amp input at the higherst, -50dBm in practice)
So probably we need more gain. If we can add 10-12dB more gain, that would be useful.
- What is the requirement for the power amplifier?
Search result for Freq Range 10-200MHz / Max Gain 14dB / Max NF 15dB / Min Power Out 13dBm
GVA-81 is available at the 40m. ERA-4SM, ERA-6SM, HELA-10D are available at Downs.
Conversion between nV/rtHz and NF (in the 50Ohm system)
SN1: Connect signal source (50Ohm output) to a 50Ohm load.
Power ratio between the noise and the signal
SN1 = (4 k T (R/2)) / (S/2)^2
SN2: Connect signal source (50Ohm output) to an RF amp.
Only the voltage noise was considered.
SN2 = (4 k T (R/2) + Vn^2) / (S/2)^2
10 Log10(SN2/SN1) = 10. Log10(1 + 2.42 (Vn / 1nVrtHz)^2)
Vn: 0 nVrtHz ==> 0dB
Vn: 0.5 nVrtHz ==> 2dB
Vn: 1 nVrtHz ==> 5dB
Vn: 2 nVrtHz ==> 10dB
Vn: 3 nVrtHz ==> 13.5dB
- The BBPD circuit has been constructed on the aLIGO BBPD board
- It still keeps 200MHz BW with FDD-100 Si PD for the 100V bias.
- The noise spectrum has been cleaned up a lot more. It shows the noise level of the 0.4mA shotnoise between 9-85MHz.
The noise at 160MHz is the noise level of the 1mA shotnoise.
Some of the noise peaks at around 97MHz came from the bias voltage.
What to do next
- Confirmation of the performance with the original aLIGO BB PD configuration.
- Notch filter for 9MHz (for aLIGO).
- Implementation of a power amplifier. (issues: power supply and heat removal)
aLIGO EOM crystal replacement
I have been working on the aux beat setup on the PSL table between 9PM-3AM.
This work involved:
- Turning off the main marconi
- Turning off the freq generation unit (incl IMC modulation)
- Closing the PSL shutter
After the work, these were reverted and the IMC and both arms have been locked.
Chris Wipf has been developing a new Noise Budget code that allows us to use our existing Simulink models to handle all of the noise transfer functions. This is mainly by being clever about avoiding the numerical pitfalls that we encounter when doing linearization of Simulink models (e.g. linmod or linmod2).
In this model, the optical plant is done with analytic TFs using the formulae from the Sigg Frequency Response doc. The big Orange block has just the DAC and some simple pendulum TFs. The upper section contains the simulated digital system: input matrix, digital filter TFs, and output matrix. The digital filters are just based on my memory of iLIGO. The CARM path is made to be fast to approximate the high gain of the Common Mode servo. Without this high gain the PRC optical plant is unstable due to the right half plane zeros. This simple model is used just so that we could see the NB work on a multi-loop system. For the next steps of getting it to work for the 40m, we will use the Optickle TFs instead of analytic functions and also load the digital filters directly from the FOTON files. For the LLO DRMI, we'll add some simplified version of the SUS Simulink models for triples and quads.
Yesterday, Nic and I took my old iLIGO IFOmodel.mdl Simulink model and added the new NB hooks that allowed us to use the new code. The screenshot below is from a run of this code:
1) Figure 1 shows the DARM Noise budget. So far we have included shot noise in DARM, CARM, MICH, & PRC. Radiation pressure noise on the ITMs and ETMs. Coating thermal noise on all mirrors.
2) Figure 2 shows the breakdown of how each of the shot noises at each port couple to the DARM readout. The RED trace is the AS port DC readout shot noise. The GREEN trace is the MICH shot noise feeding through the MICH loop and being mostly cancelled by the scalar MICHdamp feedforward path.
3) Figure 3 shows that we've set the coating thermal noise to be equal on all 4 TMs.
4) Figure 78754 is a set of Bode plots of the open loop gains of the 4 LSC loops (inferred from the closed loop TF). Also plotted is the residual MICH2DARM TF (with the MICHdamp cancellation path ON).
5) Figure 9911123 are the step responses of the LSC loops: step inserted at the error point and response measured just after the excitation point.
The editor window on the left shows how simple the NB code is to use once the Simulink model has had all the hooks added to it.
Before installation, I performed a bunch of tests on the aLIGO sat amp. All the measurements were made with the dummy suspension box substituting for an actual suspension. Here are the results.
Attachment #1: Transimpedance amplifier noises.
Attachment #2: LED drive current source noises. I mainly wanted to check a claim by Rich in a meeting some time ago that the LED intensity fluctuations are dominated by inherent LED RIN, and not by RIN on the drive current.
I will update with the MC1 suspension characterization (loop TFs, step responses etc) later.
Yeah, it's really inconsistent. You had 35mA LED drive and the current noise of the noisy channel was 5e-7 A/rtHz at 1Hz. The RIN is 1.4e-5 /rtHz. The approx. received photocurrent is 30uA as we discussed today and this should make the noise around 4e-10 A/rtHz at 1Hz. However, the readout noise level is better than this level. (well below 1e-10 A/rtHz)
BTW, the IMC seemed continuously locked for 5 hours. Good sign.
After this work, the IMC locked fine, the AS camera has the Michelson fringing, the fast CDS indicators are all green, and the seismometer BLRMS all look good - therefore, I claim no lasting damage was done as a direct result of today's work at 1X4. I will connect up the actual suspension at my leisure later today. Note that the MC1 glitches seem to have gone away, without me doing anything about it. Nevertheless, I think it's about time that we start testing the new hardware.
Unrelated to this work: while I was testing some characteristics of the MC1 suspension (before we did any work in the VEA, you can see the timestamp in the ndscope), I noticed that the MC1 UL coil channel cannot actually be used to actuate on the optic. The coil driver Vmon channel demonstrates the appropriate response, which means that the problem is either with the Satellite box (it is just a feedthrough, so PCB trace damaged?) or with the OSEM itself (more likely IMO, will know more once I connect the new Satellite Amplifier up). I only show comparison for UL vs UR, but I checked that the other coils seem to be able to actuate the optic. This means we have been running for an indeterminate amount of time with only 3 face actuators on MC1, probably related to me having to do this work.
Also unrelated to this work - while poking around at 1X5 rear, I noticed that the power connections to the existing Satellite Boxes are (understatedly) flaky, see connections to T1-T4 in Attachment #2..
There is some non-trivial sign flipping in the sensors/coils in this new setup because it is a hybrid one with the old interfacing electronics (D000210, D010001) and the new Satellite Amplifier (D080276). So I haven't yet gotten the damping working. I am leaving the PSL shutter closed and will keep working on this today/tomorrow. I have made various changes to the c1mcs realtime model and the c1susaux database record where MC1 is concerned. I have backups of the old ones so we can always go back to that if we so desire.
In the meantime, the PSL shutter is closed and there is no light to the IFO.
Update 1700: I've implemented some basic damping and now the IMC is now locked. The WFS loop runs away when I enable it, probably some kind of weird interaction with the (as of now untuned) MC1 local damping loops. I will write up a more detailed report later.
Update 2300: Did the following:
Dropping this for tonight, I'll continue tomorrow. Meanwhile, the OSEM input matrix measurement is being repeated overnight. PSL shutter is closed.
The WFS servo was recommissioned. The matrix can be tuned a bit more, but for now, I've recovered the old performance and the alignment doesn't seem to be running away, so I defer further tuning for later. The old Satellite box was handed over to Yehonathan for his characterization of the "spare" OSEMs.
This finishes the recovery of the MC1 suspension, I am now satisfied that the local damping loops are performing satisfactorily, that the WFS servo is also stable, and that POX/POY locking is recovered. On MC1, we even have 4 actuatable face OSEMs and the PIT(YAW) bias adjust slider even moves the optic in PIT(YAW), what a luxury.
I've SDFed all the changes, and have backup of the old realtime model and C1SUSAUX_MC1 database files if we want to go back for whatever reason. The changes required to make this suspension work are different from what will eventually be required for the BHD suspensions (because of the hybrid iLIGO/aLIGO electronics situation), so I will not burden the readers with the tedious details.
I'm a little mystified. Peeking inside the aLIGO demod board, I saw that the reason that two of the channels weren't working was that their power connectors weren't plugged in, so no real mystery there.
I hooked up the board at the electronics bench, and found the noise to be completely well behaved, in contrast to the measurements I made when it was in the LSC rack. I've taken it back out to the LSC rack, and given it the X beatnote, and it seems to be performing pretty well.
I switched between the aLIGO demod board and beatbox during the same lock / beat. The LSC board performs margnially better from 3-100 Hz. The high frequency noise comes from the green PDH loop (coherence is near one above a few hundred Hz), so we don't expect any difference there.
To me, the beatbox noise looks like there is a broad feature that is roughly the same level as the real cavity motion in the 10-100 Hz range. So, I think we should use the aLIGO board afterall, presuming the noise doesn't shoot back up when I remount it in the rack...
The ALS noise is getting low enough where our normal approach of measuring ALS sensing noise by simply taking the PSD of the signal when the arm is PDH locked is not quite valid anymore, as it is sensing the real cavity fluctuations. Doing a frequency domain coherent subtration of the PSDs suggests a sensing noise RMS of ~150Hz for ALSX.
When the X arm is locked on ALS, POX sees about 250Hz RMS out of loop noise, which isn't the greatest; however, I used to be happy with 500Hz. By eye, sweeping through IR resonance is smoother. The real test is to get the Y arm ALS running, and swing it through PRFPMI resonance...
Fair warning, the LSC rack area is not so tidy right now, the demod board is resting on a stool (but not in the way of walking down the arm). I'll clean this up tomorrow.
ALS is not currently limited by the demod board or whitening electronics.
The noise budget in the green locking paper shows the main noise sources to be these two, plus the residual fluctuations of the green PDH loop.
So, one next step is AUX PDH noise budget.
However, I wonder how much of the low frequency noise can be explained by instability of the beat alignement on the PSL table, and how this might be quantified.
Yesterday, I put together a few measurements to asses whether the new demod board has moved us in the right direction. Specifically I measured the output of the phase tracker in the following states, adjusting the phase tracker gain to maintain a ~2kHz UGH (but no boost on):
Results: The beat frequency spectrum is above the measured demod board and whitening chassis/ADC noise at all frequencies. It's a little close at 10Hz.
One nice feature is that the beat spectra are far more similar to each other than they used to be. RMS noise is in the 300-400Hz range, which isn't mindblowing, but not terrible. On the order of 50 pm for each arm. Most of this comes from below 10Hz.
Another thing to note is that, when we switch in the 50m cables, we should win a fair bit of Hz/V gain and push down these noises futher. (We're currently using 30m cables.)
By looking at some coherences, we can attribute some of the noise when IR locked to both colors of PDH loops.
Specifically, the coherence with the Green PDH error implicates the residual frequency noise of the AUX laser above a few hundred Hz, whereas the feature from 20-50Hz is probably real cavity motion, not ALS sensing noise. Some of the 1-3Hz noise is from real suspension/stack resonances too.
If it turns out that we do want to push the demod board noise down further, we could think about increasing the RF amplification. Driving the board harder translates directly to better noise performance. The 60Hz harmonics aren't so exciting, but not the end of the world.
Data files are attached, if you're in to that sort of thing.
We received 20pcs of stuffed demodulator boards from Screaming Circuits today. Some caveats:
I removed 1 from the group to stuff some components that weren't sent to Screaming Circuits and test the functionality on the benchtop, the remaining have been stored in a plastic box for now as shown in Attachment #1. The box has been delivered to Chub who will stuff the remaining 19 boards once I've tested the one piece.
The lack of AA filter for MCL signal is RFM model strongly disturbed entering to OAF signal
This morning we attempted to replace the c1sus front end machine with a spare that had been given a second CPU, and therefore 6 additional cores (for a total of 12). The idea was to give c1sus more cores so that we could split up c1rfm into two separate models that would not be running on the hairy edge of their cycle time allocation. Well, after struggling to get it working we eventually aborted and put the old machine back in.
The problem was that the c1sus model was running erratically, frequently jumping up to 100 usec of a 60 usec clock allocation. We eventually tracked the problem down to the fact that the CPUs in the new machine are of an inferior and slower model, than what's in the old c1sus machine. The CPU were running about 30% slower, which was enough to bump c1sus, which nominally runs at ~51 usec, over it's limit.
This is of course stupid, and I take the blame. I skimped on the CPUs when I bought the spare machines in an attempt to keep the cost down, and didn't forgot that I had done that when we started discussing using one of the spares as a c1sus replacement.
I think we can salvage things, though, by just purchasing a better CPU, one that matches what's currently in c1sus. I'll get Steve on it:
In any event, the old c1sus is back in place, and everything is back as it was.
To make things faster, I think we can just make a LOCKIN which has 3 inputs: it would have one oscillator, but 6 mixers. Should be simple to make.
I think the idea of having multiple inputs in a LOCKIN module is also good for the LSC sensing matrix measurement.
Because right now I am measuring the responses of multiple sensors one by one while exciting a particular DOF by one oscillator.
Moreover in the LSC case the number of sensors, which we have to measure, is enormous (e.g. REFL11I/Q, REFL33I/Q, REFL55I/Q, ... POY11I/Q,...) and indeed it has been a long-time measurement.