A list of useful numbers for noise budget calculation.
entire setup (simplified version):
beat signal generation in more detail:
window is back on and pumping down over the weekend. Thermal insulation for vacuum chamber is back in place, so we should be ready to go for a new measurement on Monday afternoon after installation of the beat breadboard
had to replace one of the valves/regulators of the table. It started releasing air after a few minutes without any reason. Adjusting it a couple of times didn't fix the problem, after a few minutes at started again. After replacing it with a spare one everything works now fine. Tara measured the seismic noise with the Guralp of the floated and unfloated table and the effect on the beat signal which will be posted soon.
I clean the vented screws and peek pieces for cavity mount with ultra sonic bath, I'll check if I need to bake them or not.
TFs between 1)vertical seismic and beat, 2) v seismic and ACAV feedback, and 3) v_seismic and TTFSS feedback are measured. The contribution from vertical seismic to beat signal is mostly from ACAV.
I used frequency response measurement (FFT1/FFT2) to measure frequency response [dB], phase [dB], and coherence between.
The calibration for beat signal[D] is 7kHz/V, for ACAV actuator point [C] is 7kHz/V, for RCAV fast actuator [B] is 3.07 MHz/V, for accelerometer [A] is 1023mV/g (psl:716)
1)calibrated signal, in the unit of Frequency noise in beat/ acceleration [Hz/ (m/s^2) ]
fig1: calibrated frequency response, with 250 vector avg.
The plots show that the seismic contribution in the beat is mostly coupled through ACAV. RCAV is not sensitive to seismic at all, since the coherence is almost zero. We have to open the chamber and fix the ACAV's support.
From 40m page, COMSOL FEA gives us the coupling (from vertical seismic to frequency noise ) to be 53 [kHz / (m/s2)].
Fig1: TF measurement( from PSL:735). This time the estimation from FEA is plotted as well.
fig 2: Signal and Noise in TF measurement between RCAV noise and seismic.
The NPRO free running noise is from psl:617. Seismic noise is measured by an accelerometer (PSL:716)and converted to frequency noise using coupling from FEA result (53kHz / (m/s^2))
We tried to damp mechanical peaks from each optics. For now, by putting a rubber piece on a mirror mount can suppress mechanical peaks effectively. We are still thinking about more robust way to damp the peaks.
Beat signal has a lot of acoustic peaks from 100Hz up to 1kHz, and they may mask any improvement we work on flat noise. Damping them is necessary before we can work on the flat noise hidden underneath.
By tapping each optic, we can see peaks raising up in beat signal or feedback signal to ACAV AOM. We used the feedback to ACAV AOM to identify peaks in ACAV path first. The curve mirror behind AOM has a strong peak which can be damped by a rubber cone placed on top of the mount, see fig1 below.
fig1: Mirror mount1, with a damping rubber on top.
We also tried using different mounts to see if the peak would be reduced. The original mount was an anodized aluminium mount. We switched to different two stainless steel mounts, mount1 and mount2. The spectrum of the feedback signal to AOM (not calibrated) between two mounts with and without damping rubber are shown below. From the spectrum, there are not much different between the current anodized Al mount (not shown) and the steel mount in fig1.
Note: We also tried to damp the mirror mount with small rubber pieces placed between the frame and the body of the mount, but it did not help at all. The springs of the mount are stronger than the rubber, so this method is not effective.
To sum up,
We are damping most of the optics with rubber cones. There are a few peaks that we still could not find their origins. We are thinking to build an acoustic insulation box to cover the setup.
[details will be added soon]
I measured beat signal, after damping most of the optics, realigning the beams to the cavities, measured the slope of error signals and applied it to the measured detection noise. Acoustics peaks around 200Hz to 1kHz still present.
Fig1: beat measurement, I added shot noise and electronic noise from both cavities to a single trace called detection noise (from measurement).
I turned off the HEPA fans on the table and on the clean bench before measured the beat signal (after I finished, I turned on the fans as usual).
The peak at 58 Hz shows up this time. I think this is the peak from beam line motion of the stacks, see PSL:716. (I think that was before we switched to the softer springs, I'll double check). Note that the air springs were not activated during the measurement, we can try using it and see if there is any improvement.
There is a good improvement on minimizing the acoustic peaks, although still not enough. Also, increasing the modulation depth seems to help with the flat noise part at high frequency, we may really sit on detection noise.
I forgot to change the code to disable the air springs, now the seismic coupling makes more sense.
I planned to measure the beat at night with the air springs activated, but the power went out around 11:45 pm. I think the temperature servo got a kick and it is drifting very fast. So I cannot keep the cavities locked long enough for the low frequency measurement. I'm just turning the systems back on for now.
The laser, 3 Marconis for 14.75MHz EOM, for ACAV AOM, for beat are set back to the original setup, PMC medm screen are back on, the air springs are up and working.
The linux machine is on but I forgot the password, will ask Frank tomorrow.
I'm looking for the new table legs. The height will be 13.5". The plate that connects to the table will have 3 holes, 4" inches away from the center. I need to check what is the weight of the table and if the new legs can be mounted with the table or not.
For New port legs, (set of 4), the price are around $2500 (can be cheaper for less weight requirement). I'll check what is the weight of our table.
They also offer Pneumatic Vibration Isolators with Automatic Re-leveling legs (I don't know what are the differences), but the height are wrong for our setup, the shortest one starts at 16" height. I looked into this category because our current legs also say Pneumatic
We have "Pneumatic Vibration Isolators with Automatic Re-leveling". Height is 16in from top to bottom, so that would raise the table height by 2.5in which i think is not gonna be a problem as i'm pretty sure we can adjust the height of the horizontal beams of the frame and don't have other constraints except the clearance of the ion pump to the HEPA which should be fine. Do you have a price for the 16" ones? (S-2000A-416). The problem with the new legs could be how to mount the table to them. The mounting looks different (diameter, holes etc.)
We should probably consider using the newer version we have currently under the cryo table and the table in the richter lab. Using those would eliminate the need of working on our frame and those tables don't really care what legs they are using at the moment.
The price for the custom made legs are $ 9295, and for the standard 16" are $ 3710
The table is not floated. Either the legs are broken, or there is a leak in the tube system. I think it is likely that one (or more) of the legs is broken. Since it happened before with the older legs. Their rubber part in the leg gradually failed over time. We might need to reconsider buying brand new legs again. The pump connected to the table could not keep up with the leaking rate, so I turned it off.
We have 4 Newport XL-A legs 13.5" high in the 40m. You can try them. You may have to replace some of the floating actuators but otherwise they should work just fine.
Those are the ones we are using right now and break after some while because they are too old (the rolling rubber diaphragm is too brittle now and you get small cracks). The tables were resting on the rubber for 15 years and they've been not used floating for the last decade or more. The leakage is small so that you don't feel or hear it (soap water does not work when installed. Pressure loss is 15psi of a 3gal compressor within 1 hour or so, not big but enough to be annoying. We wouldn't care if we would have a constant high pressure air supply.
We have 4 Newport XL-A legs 13.5" high in the 40m. You can try them. You may have to replace some of the floating actuators but otherwise they should work just fine.
view factor for two cylinders to calculate heat transfer to and from cavity via radiation
from Michael F. Modest "Radiative Heat Transfer", Second Edition
voltage variable attenuator
This will be used for ISS in ACAV loop. It will be connected between the oscillator and the amplifier (see the schematic below).
The feedback signal will be sent to the attenuator to change the amplitude, thus changing the power of the diffracted beam in order to stabilize the power.
Saturday: 4 AM - 12 PM
Since the VCO has been borrowed, I decide to work on RefCav path again. To optimize the RefCav alignment, PMC will be locked to the laser while the laser frequency is modulated by a function generator. This is where a problem comes in. The PMC servo cannot catch up with the laser. Even though I lower the modulating frequency and amplitude to 4 Hz, 1 Vpp ,which roughly corresponds to ~1MHz shift in laser frequency, the PMC servo cannot stay stable for longer than a minute. so I measure the transfer function of the PMC servo, and it does not look right, see figure1. The real magnitude which goes to the PZT has higher value, since the signal comes out of the out mon channel passes through a voltage divider.
I also measured TFs of FSS servo, both Fast and PC paths look ok. I measure TF by using swept sine measurement , the source is split by a T connector, one goes to chA of SRS785, another one goes to TF1 test (where demodulated signal goes.) The output is taken from out mon (for PMC servo), fast mon (for FSS' fast path), PC mon (for FSS's PC path), and connected to chB of SRS785.
I made sure that I switch to the right path in the medm control screen when I measure the TFs
I widen the beam holes on the outer foam box. Now all the holes are ~ 0.75" in diameter.
We are concerned about the scattering on the insulation, so we decided to increase the holes' size.
I used a heat gun to heat up a steel rod to melt the foam panel.
As the insulation box was opened, I checked for scattering light inside the box. I did not see any scattering ligth except
on the ACAV inner insulation opening.
Also, there is a little scattering light at RCAV's insulation cap, so I measured the beat noise when I opened RCAV's inner cap.
There is no significant change, see fig 1. The trace with higher noise was taken when I opened the cap, probably because of too few average.
The scattering on RCAV cap might be negligible for now.
as Mott can't finish the installation of the wifi bridges for the gpib-to-ethernet adapters a configured 4 devices today.
Username and password are clearly labeled on each device, they are the usual ones for administrator rights.
The 4 new devices have the following IP adresses:
i will finish configuring the gpib-to-ethernet adapters on Friday, one for each instrument in the labs.
i will update the network diagram as soon i decided which ip addresses the will get
I'm checking the properties/prices/availability of window for the vacuum chamber.
Plan1: 10" diameter window (6" window opening)
Plan2: 10" diameter blank with 2 smaller windows (1.5"/2" diameter)
Most of the manufacturers do not have good window for laser with 10" flanges. Finding two smaller windows with good optics properties is probably easier.
If we go with plan2,
1)window and flange
2) Two Half-Nipple will be welded to the blank on the 10" flange. They will be 3" apart, as the input beams are. We might need something smaller than 2.75" diameter for accessing all the screws.
3) blank 10" flange: I think Frank said that we have one in the lab. For another one, we can order it from N-C, blank. It is ~$ 300.
I'm not sure how to mount the window and the flange together. If we buy the window set from Thorlab, I think it can be directly assemble them similarly to the current 10" flange, see figure below. Or we might need to mount the windows like Zach does for Gyro, see ATF:1601.
I'm searching DCC for window/viewport examples. The following drawings give me some ideas how to make a window for our setup.
TCS viewports details
septum window flange
For small window option, I can either have it made from scratch ( based on LIGO's drawing) or buy the commercial windows from Thorlabs. Here I listed down all pros and cons for each choice as I discussed it with Frank. I 'll ask Steve tomorrow for his opinions.
== Using Thorlabs 2.75" OD windows:==
==Making custom parts (like LIGO, see quote window)==
I asked Steve about the choices, he thought the Thorlabs window should be ok for us.
What Steve suggested are:
About the blank with two openings for beam access, he said a vacuum company could do it for us. I'll make a drawing and get a quote from Nor-Cal and MDC. I have to specify that the blank will be for ultra high vacuum system (UHV).
I don't know how you gonna make the knife edge on the 10" flange of centered and wedged! If you put the small CF flanges on the big one you have parasitic cavities between the window and the cavity even if the window is wedged (only the outside is tilted relative to the flange, the inside is parallel by design. I also suggest going for a metal seal, but not copper as getting those knife edges will be complicated and expensive i guess. So why not using indium or the other single-use metal seal replacement techniques for o-rings available and you only need a flat surface on the big flange and a few tapped blind holes?
Request 2 degrees off set the the 2.75"cf knife edge and tapped holes on the 10" flange. The location is custom anyhow. You can gain some space this way. Or can you tip your chamber?
Check how parallel you cavity is with your chamber
cavity mirrors are parallel to the end surface of the chamber (not completely, but pretty close; changes every time we touch the stack as we can't fully control the position after sliding the stack into the long chamber. However we should rethink our procedure how we align the stack once in the chamber)
I got the reply from Thorlab the flange can't accept the thicker optical windows. So I think we have to make our own custom small flanges. I'll check TCS small windows design and make a drawing and consult with Steve again.
Thank you very much for your response. It looks like our flanges can only fit
windows 0.1 mm thicker, with a tolerance of +0.0/-0.2 mm, so these flanges would not
be cross-compatible with existing windows. I apologize for any inconvenience this
may cause. Please let me know if you have additional inquiries, as I am very happy
Nice reference for O-ring + groove design. I'll put it on CTN wiki as well.
The o-ring I plan to use for 2" OD window is #223, 0.139" thickness, ID = 1.609", OD = 1.887". McMasterCarr.
I finished the drawing for new vacuum windows. The o-ring for the windows will be #223 (1/8" thickness). I'll consult with Steve one more time before I submit the drawings.
A few comments about this desing:
I edited the drawing for 10" flange. The wedge surfaces for 2" windows are tilted by 2 degrees sideway.
I tried to assemble the pieces with 2" OD window, 0.25" thickness (without Oring). I think the clearance for the window might be too tight. I'll fix it.
2" optics with 2 degrees of wedge will have 0.375" thickness as std - get optics specification now
I thought about the design after talking to you yesterday:
a, use standard 3 3/8" od flange for your windows
b, the 2 degrees of off- set into the 10" cf design will have to be assembled in horizontal position so the teflon gaskit would stay in place
c, the vertical assembly requires that you put the 2 degrees off-set into the 3.37" flange ( one side CF - the other o-ring groove) and delrin cover plate on top of it
The wooden cabinet is mounted to the wall as required by PMA.
ws1 is unable to read and write on some EPICS channels while I can see these channels in fb4 or acromag1. These channels are:
I'm not sure what is causing this. I have rebooted cromag1 several times but this problem persists. Interestingly, there are a lot of channels which are getting updated on medm screens so the origin of the problem is probably localized to a single .db file. But everything looks fine to me, at least after first few debugging trials.
Well, because of this, it is impossible almost impossible to even manually tune the beatnote frequency to the required point. I'll first fix this because it seems like an error which shouldn't be ignored. Suggestions are welcome as I am new to EPICS-Modbus-upstart-docker things and might be missing something silly.
I have installed apache2 on ws3 and made dailyNoisebudgetPlotter.py save Beatnote_CurrentASD.png to /var/www/html/, and created a website on our new server which updates itself every minute with the latest beatnote ASD.
We still need to add port forwarding from the gateway to ws3. Once we do, to see our beatnote webpage, go to http://ws3.ligo.caltech.edu/Beatnote_CurrentASD.html.
EDIT: Added port forwarding from gateway (public IP: 126.96.36.199, local IP: 10.0.1.1) to ws3 (local IP: 10.0.1.34) on port 8088 for both servers. Had to modify both /etc/apache2/ports.conf and /etc/apache2/sites-enabled/000-default.conf to listen to port 8088 instead of 80, then run sudo service apache2 restart.
To visit our website, go to http://188.8.131.52:8088/.
Made crontab on ws3 make calibrated beatnote spectra every 5 minutes. One example is below.
Plot is made in ~/Git/cit_ctnlab/ctn_noisebudget/dailyNoisebudgets/dailyNoisebudgetPlotter.py. Calibration is just the Marconi FM Deviation multiplied by the ASD. Full calibration requires the whole PLL open loop gain.
Made a bash script nbPlotterRunner.sh which runs dailyNoisebudgetPlotter.py. It runs the plotter, and can be called by crontab.
Overall Hz/rtHz levels seem okay.
For some reason medm and striptool were unable to access channels on ws3. At the time I built the computer last week I didn't test any of the LIGO tools.
After a bit of fiddling with the network settings we moved ws3 back from 10.0.1.23 to 10.0.1.33 and we were able to access channels again. It is not clear exactly why this worked. We should debug it, but we'll leave it for now.
Before we found the IP address fix I purged all the ligo cds tools, updated apt-get and installed again. This time around I was able to install the cds-workstation package.
Jamie et al have a standard install with a couple of lines for all the ligo cds tools: https://git.ligo.org/cds-packaging/docs/wikis/home. These were the instructions I followed, last week it was throwing a bunch of errors about not being able to retrieve things.
I activated superuser and purged all the ligo related packages out of the system with
apt-get purge lscsoft-archive-keyring cds-unstable-archive-keyring etc
apt-get purge lscsoft-archive-keyring
I then ran
apt-get -y --force-yes install lscsoft-archive-keyring cds-unstable-archive-keyring
The packages were then re downloaded and up to date. After that I ran
apt-get install cds-workstation
which actually worked this time (first). A blue screen popped up asking me about kerbose servers or something. I just left it blank and hit enter, hopefully this is ok.
All good for now although the mystery IP issue is unresolved.