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ID Date Author Typedown Category Subject
  57   Sun Jan 23 23:24:01 2011 FrankUpdateCavityfirst setup for cavity test

below a picture of the first setup using one fiber coupled laser diode (right) mode matched to the FS cavity (left). First modes can be seen in transmission of the cavity. Further optimization required.


  60   Mon Jan 24 16:40:35 2011 FrankUpdateHVACparticle count - updated graph for the last week


  61   Mon Jan 24 23:17:30 2011 FrankUpdateCavitycavity locked (for a short time)

can lock it  for a second or so before loosing lock, but didn't optimize loop parameters.Still having problems getting sidebands so this is currently No 1 on my priority list.
I actually don't know what i'm locking to, but can lock to individual modes. It looks like there is kind of a zero crossing, but not really.

Using Zach's resonant EOM at 33MHz at the moment. Had to switch PD from Thorlabs PDA10CS to the 2GHz diode.
With a 13dBm mixer and 23dBm into the resonant EOM the "signal" is only about 7mV large and does not like a n error signal at all.
More like some funny oscillation. Probably due to the high frequency noise. Also tried other frequencies, mixers, photodiodes. Needs more investigation.

Modematching into the cavity is only about 25%. Could be either a non impedance matched cavity or our calculation for the mode matching is wrong. Will check this tomorrow.
Nevertheless this can't explain the non-existing error signals.

  62   Tue Jan 25 11:56:20 2011 FrankUpdateDrawingsinitial cavity test setup


  78   Wed Feb 16 16:24:19 2011 DmassUpdateGeneralRoad Map for Cryo Lab

I want to generate a more coherent (recorded) roadmap for the cryolab so that we can better prioritize our course of action. Before I put together some visual diagram representing this information (which I think will be useful for us), I am going to write down a list of the stuff we know we want to do, as well as the more far fetched things we might one day want to do. Here is the list by category, PLEASE ADD THINGS IF YOU WANT - if you reply to this post with suggestions, I will try to incorporate them into edits of this post. In no particular order, we have:


  • Heat load analysis (DC) - compare to LN2 volume
    • G10, radiation, aluminum  
  • Thermal pole estimation from the above materials / joints
  • Thermal equivalent circuit analysis (and possible LISO model - uber LOW priority)
  • Windows - choose the substrates we want -
    • We can get 100$ lambda/10 sapphire 1" substrates from CVI
    • MDC brazes covar to the sapphire substrates, (after this is our first opportunity to coat them), then ships them to Dick who will weld the brazed sapphire to his flange. We have a few choices:
      • We can get MDC to have their coating company (American Photonics) do a v-coating run on them (I will call them to see if they seem good or not - quantitatively) before shipping them to Dick
      • We can get MDC to ship them to CVI then ship them to Dick
      • We can let Dick weld them into complete flanges (~2-3 inches in diameter), then have ATF coat them
      • We can use them uncoated to start (this might even be OK because we have such a large angle of incidence and can dump the ghost beams), then we can coat them later if we want by sending the flange-window assemblies to ATF (or someone else) - though we would be without an operational cryostat while we did this.
  • We need to decide on what vacuum pump(s) we want - for the inner chamber we will probably copy the cart setup in the ATF that Alastair is using (with a Turbo). For the outer vacuum chamber we dont need a very hard vacuum, which opens up different pump technologies
  • Check out what the state of the indium recycling loop is for Caltech so that we don't pay 100-200$ per seal / pumpdown (maybe some paperwork to fill out?)
  • Verify that we can keep a LN2 dewar down in the lab (or at least in the hallway), possibly paperwork affiliated with this as well.


  • Finish mocking up one of the temperature control ideas by putting in material properties and seeing what poles we can make easily
  • Make a noisebudget for the temperature noise of the cavity + temperature control loop
  • Think about / make a seismic noisebudget once we have a preliminary suspension scheme
  • Get a spacer! (Frank is in negotiations with companies - status = ?)
  • Mirror choice for the cavity
    • Choose a g-factor (see this elog for HOM spacing)
    • Choose a Finesse
    • Think a bit about how how Finesse(T) goes, and make sure that a 10^5 Finesse at room temperature can't turn into a 10^6 Finesse at 123K or 18K
      • Just model it as a basic stack of whatever materials we are using, then see about the signs of thermorefractive and thermoelastic derivaties
  • Optically contacting vs glue - Is this debate closed? Do we know the downsides of each?
    • Frank was looking into yield strains of glue vs contacting, and since Si isn't amorphous, we may have to worry about differential contraction even with Si mirrors and a Si spacer if we can't identify the relative directions of the crystal axes



  • Diode vs Fiber laser
  • We can't lock the diode to the cavity as built with ULE mirrors and Fused Silica spacer
    • We think this means we need a filter cavity (a PMC with a PZT)
    • We need to think a tad about choosing the Finesse in a quantitative way for this cavity...
    • This means we need to understand WHY we can't lock the laser to the cavity right now in a quantitative way
    • To this end we need to:
  • Get a real frequency noise measurement of the laser diodes
    • Lock it to a cavity and get a bound on the error signal between the two (didn't work!)
    • Sweep a cavity and check that we are actually single mode (Frank played around with sweeping, results?)
    • Use a PLL and calibrate the error signal to the VCO to determine frequency noise of the beat (bad idea - overly complicated and a VCO with the right range might not exist)
    • Use a PFD (Phase Frequency Discriminator) like they did at the 40m to measure the frequency noise directly - probably easy with such high noise
      • THIS is the measurement of choice of the above options.


  • Get PMA to install a longer corkboard by the CryoLab / Greg's lab so that we can post more results on the fly
  • Use compressed air to blow the remaining dust off the fixtures / continue to mop frequently until we truly decimate the particle count...we have gotten it down another order of magnitude to 2K/ft3 (from 30K/ft3) from our cleaning efforts if we are not present in the lab, so the main source is stirring up all the dust from the surfaces



  79   Thu Feb 17 12:35:25 2011 Dmass, FrankUpdateLasermore laser characterization work going on

PK borrowed two nice Scopes for evaluation (Agilent MSO7104B and Tek MSO4101, both 1GHz and 4 or 5MSP/s). They look more like small TV's with a lot of knobs (nice large screens).

So we have two ~$20K scopes to have a closer and probably more detailed look into what's going on when beating the laser diodes and measuring the linewidth / frequency jitter.
We started last night and got a little more familiar with the Agilent scope and how to sample the beat signal, do an FFT and some statistics. It's really nice !

We will continue today and the next days and post the results as soon as we know we think to measure



  115   Mon Mar 28 12:38:15 2011 FrankUpdateCavityupdated refcav drawings

made some slight changes to the spacer drawing. updated files below:




  129   Fri Apr 15 14:00:26 2011 FrankUpdateGeneralspacer/mirror quotes on wiki updated

see https://nodus.ligo.caltech.edu:30889/CryoWiki/doku.php?id=equipment:spacer_quotes

  130   Fri Apr 15 15:49:31 2011 DmassUpdateGeneralspacer/mirror quotes on wiki updated


see https://nodus.ligo.caltech.edu:30889/CryoWiki/doku.php?id=equipment:spacer_quotes

 Checked the update - w.r.t. a certain company- they were nonresponsive (to use the nomenclature) when I asked them to quote on the spacer. As far as we are concerned, they are just another Si supplier. Your concern about that supplier sounds to me like we are asking them to give us certain surface quality / precise geometry, neither of which I think we need from the raw materials, but from what I understand, we have very limited requirements for the spacer BEFORE machining.

Or did you mean you were concerned that there weren't things like purity, doping, not being broken specifically in the quote. This all seems sort of moot, since it seems like a not-so-hot idea to use something with the fabrication/shipping process and lead times given in the elog.

  132   Thu Apr 21 08:59:41 2011 FrankUpdateGeneralspacer/mirror quotes on wiki updated

i thought the company we are talking about is doing everything (drilling, polishing) except the polishing of the part which requires flatness for contacting. The second company is then doing the re-polishing of the end surfaces, right?



see https://nodus.ligo.caltech.edu:30889/CryoWiki/doku.php?id=equipment:spacer_quotes

 Checked the update - w.r.t. a certain company- they were nonresponsive (to use the nomenclature) when I asked them to quote on the spacer. As far as we are concerned, they are just another Si supplier. Your concern about that supplier sounds to me like we are asking them to give us certain surface quality / precise geometry, neither of which I think we need from the raw materials, but from what I understand, we have very limited requirements for the spacer BEFORE machining.

Or did you mean you were concerned that there weren't things like purity, doping, not being broken specifically in the quote. This all seems sort of moot, since it seems like a not-so-hot idea to use something with the fabrication/shipping process and lead times given in the elog.


  138   Tue Apr 26 16:25:23 2011 FrankUpdatePurchasesPMC mirrors ordered

submitted the order, my credit card has been charged already so they might actually ship them this time

  140   Wed Apr 27 13:43:21 2011 FrankUpdatePurchasesNIR CCD camera

bought one of the NIR intensified CCDs which have the phosphor coating on the chip as we need at least one good one for mode identification. My home-made ones need still too much power, so you can't identify higher order modes
Edmund has one with 15% discount at the moment, so it's "only"  $1700. Also bought two turning mirrors to see how they are. Specs are not bad, but so far i couldn't find any turning mirror not being frosted on the back.
A full beam analyzer for 1550nm is about $6k, which me might wanna buy in the future if we do more 1550nm stuff. For now i think we don't need one.


  143   Wed May 4 13:06:04 2011 FrankUpdatePurchasesPMC mirrors

Unfortunately the concave mirror i've ordered and which was in stock according to their online shop turned out to be out of stock 

So i've changed the order to a similar one. The only difference is that the new one doesn't have a wedge which shouldn't matter for our prototype as the transmission is only 50ppm (and it's still AR-coated on the back)

  144   Thu May 5 11:33:15 2011 ranaUpdatePurchasesPMC mirrors

 I agree - wedge probably doesn't matter with a T=50 ppm

  145   Thu May 5 12:24:11 2011 FrankUpdatePurchasesPMC mirrors shipped
Monday, 05/09/2011, by 10:30 A.M.

UPS tracking number: 1ZER25556663912015

  146   Fri May 6 03:23:14 2011 DmassUpdateSchematicsTriangular PMC Schematics

Here are the drawings I submitted to the local machine shops for our 1550 nm triangular metal PMC.


The round trip path length is 2 x 6.3 inches. We want to use either 1m or 0.5m curved mirrors in the back, which give a waist size of:

1m => 425 um waist

0.5m => 340 um waist

 Cavity FSR is***:

936 MHz

 The PZT we have ordered and plan to use, the PI P-016.10H, has a 15 um range with a 1000V max voltage. Assuming linearity gives us 15 nm / V.

The voltage required to move 1.5 FSR is:

1.5 * (dL = L x FSR / f) * V / 15 nm = (6.3" x 0.0254 m/") x 936 MHz / (1.93x10^14 Hz) * V / (10^-8 m) = 77 V

Frank wanted to get some (specific) 60V power supplies, if we use these we only get a 1.17 FSR full range. Is this "good enough?" It means that we might not be able to sweep out two TEM00 modes in the full range unless we tune its length with a heater.





*** I am guessing a tiny bit. Since the FSR of a Fabry Perot of length L is c/2L, and the triangular cavity is like a flat/curved Fabry Perot with 2L = roundtrip length of triangular cavity, I think the FSR of a triangular cavity is c/(roundtrip length)

Attachment 1: pmc_drawings.pdf
pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf
Attachment 2: pmc_endcap.PDF
  147   Mon May 9 15:00:37 2011 DmassUpdateSchematicsTriangular PMC

I have updated the Wiki (here) with the information about quotes from the two machine shops.

  148   Mon May 9 22:28:16 2011 FrankUpdatePMCPMC mirrors arrived

they arrived today

I scanned all the measured spec sheets and put it on the wiki

  176   Thu Jun 2 00:45:24 2011 FrankUpdateSensorstemp sensor selection

i had a closer look into cryo temp sensors and what we might wanna use for the first tests.
The comparison posted some time ago (link) showed that platinum RTDs seem to be a good choice in terms of stability / repeatability of the cryo controllers.

I found the following publications which go into more details, but they agree with the above statement that platinum RTDs are a good choice for 120K:

Resolution and Accuracy of Cryogenic Temperature Measurements

A review of cryogenic thermometry and common temperature sensors

I extracted some plots from the above publications. The red line indicates ~120K, our first setpoint. The curves are for different types of sensors. Detailed description below the graphs.
They show that PT RTDs are a good choice in terms of sensitivity and temp resolution for ~120K. Other sensors are much better at lower temperatures.
The platinum RTD plot is for a 100Ohm sensor. So by using a 1k or 10k PT RTD we can get even better. The cryo controller we bought can handle higher RTD values.
Later we might wanna try some high resistive NTCs/PTCs which have much higher gain and so much less noise. The drawback is that the range is very limited and there are issues with the repeatability.



  179   Thu Jun 2 19:31:29 2011 FrankUpdatePurchasesitems to finalize

Below a list of items i was working on in the past which i think we can finalize but want to double check a last time.

RA: Go, go, go

  • Photodetection
    • photodiodes will be standard InGaAs photodiodes (2mm PerkinElmer, C30642GH). QE is excellent at 1550nm and we also know that we can build reasonable detectors with them. So no need to go for something different.
    • Copy new electronics design from Gyro, make a couple of small changes, mainly footprints of some parts. We need a minimum of 6 boards, 2 times PMC + RefCav and one for the beat + 1 spare.
      The PSL will need some as well (2x RefCav, beat, spare) so we can order the boards together. 6 boards are $645. Going from 6 to 15 boards is $50 more.
  • Servo Box
    • Zach will finalize the board this week. We should build one or two of the old ones with some modifications for a start and then replace them later by the new design once we know the new one is working
    • Parts for current (old) design exist.
  • Vacuum pump
    • would go for a "Pfeiffer Vacuum HiCube 80 Eco, DN 63 CF-F, MVP 015 with DCU 002", a slightly modified version of the one Alastair bought about a year ago. Will be about $5k.
    • http://www.pfeiffer-vacuum.com
  • Power supplies
    • would go for Sorensen XEL-P series. They are linear regulated and super low noise and come in a 1/4 rack style with rack adapter. So we can mount a dual 30V/3A supply and two additional 250V supplies in the rack if we want. Have front and rear terminals, can be locked so that we can bump the knobs and nothing happens :-) Do also have remote sensing, control etc.
    • waiting for a last quote. Items are in stock except for the rack mount kit.
  • Temp sensors / Cryo controller
    • will go for PT sensors in the beginning (see yesterdays entry). The cryo controller (SRS CTC 100) has 4 independent inputs, 6 analog outputs, 2 of them with power drivers to directly drive heaters. Any input can servo to any output, different TFs can be saved for different temp ranges, inputs can be switched depending on temperature, etc. So we can use one input to cool down to 124K and once reached a specified temp window we can switch to a different sensor and/or output. So heating/cooling to 124K seems to be easy as everything can be programmed within the controller. It can also run scripts for temp cycling to measure thermal expansion coefficient etc. It also has digital outputs, so we can e.g. start automated pumping the exchange gas once reached 120K or something like that. Datalogging function is nice and also has standard interfaces to network, computer etc.
  • 1550nm CCD
    • ordered one of the 1460-1625nm Near-Infrared Cameras 3 weeks ago, but they say they don't have one even if the system says one in stock. Have to poke them.
    • should think about getting a beam analyzer like the Wincam we already have. Might be nice to have for the future.
  • Optomechanics/Optics
    • more optomechanics / optics has been ordered


  203   Mon Jun 20 19:29:44 2011 FrankUpdateVacuumall parts ordered

Warren checked the vacuum system this morning, so i placed all orders for the remaining parts.
The vacuum pump is the longest lead item with 3-5 weeks (still before the cryostat arrives). Everything else is in stock and should be here end of the week.

  204   Wed Jun 22 07:49:56 2011 FrankUpdateSensorsCryo temp sensors - slight delay

the shipping of the cryo PT sensors from Heraeus will be delayed a little bit.
They still didn't ship the sensors as the still didn't receive a correct PO.
Our Techmart database is out of date and contains a wrong company name.
So i'm waiting for the change request paperwork being  done before we can resend the order.
They also don't collect sales tax and need proof/conformation that we do not resale the parts or pay sales tax somehow.
I hope we can figure that out by end of the week. Parts are still in stock.

  205   Wed Jun 22 08:07:30 2011 FrankUpdateCoatingscoatings from REO

Unfortunately, REO is not making low value or small quantity coating runs anymore. After their internal meeting this morning the sales guy contacted me to let us know that they won't do small coating runs anymore.
This is what i got from them:

We do have the capability but our business model has shifted to focus on recurring optical opportunities or large high value programs, as we focus our limited engineering resources.

  206   Wed Jun 22 10:22:54 2011 FrankUpdateVacuumvaccum pump station shipping date changed

i got confirmation that the pump including all options and adapter will be shipped August 5. They don't have any in stock at the moment.
I hope it won't delay anything as the cryostat will be delivered first week of August as well.

Will update the project file on the svn.

  215   Tue Jun 28 20:07:52 2011 FrankUpdateCavityMirrors

We might have a problem with the current vendor for our Silicon mirror substrates.
According to the Caltech export control guys this company is currently blacklisted, so we are not able to buy from them.
However, i've called that company today and they say that they are not blacklisted and can do unlimited business with anyone and our people might have an old list and are not up-to-date.
The have been on that list a few years back when the were accused of illegally exporting defense technology. However this case is settled and they paid a small fine (link).

I've forwarded some contact information to Rod who will forward it to our people on campus so that they can get in touch with their attorney to clarify this. That's what they offered me today.
He was sure that they will figure that out on a very short timescale. I will wait another day or two as we don't have a real alternative at the moment (with short lead time) and would have to start the whole bidding process again.
In parallel i will make a list of companies i didn't ask already and then we start with those. We will also talk to all the others to see if we can get something with less quality earlier.

  221   Thu Jun 30 13:18:40 2011 Dmass, FrankUpdateCavityupdated mirror quotes

we talked to a couple of vendors today and relaxed the specs a little bit. Four of them will quote us within the next 24h.

Specs are now:
Silicon mirror, 1m cc, 30min wedge
L/10 @ 1.5um
SD20-10 both sides
<3nm rms
(annulus only if possible on short time scale)

  236   Wed Jul 13 15:01:51 2011 FrankUpdatePurchasesall orders checked

checked all open orders. Everything is on time or only delayed by a few days except for the dual power supply which is still missing (we got the high voltage one and the rack mount kit).

The dual 30V-3A supply is currently backordered with a delivery date of Aug 24th. They quoted it to be in stock but sold all of them before our order was placed.
I don't know if it makes sense to look for an alternative place which has it in stock as we don't need this super urgent and we can always borrow something from the PSL for a few weeks.

There are also some special nuts missing to mount them to the rack kit. I talked to the company and they figured out that they are missing in all brand new kits they ship . So will have to wait for them as well.

  240   Thu Jul 14 02:52:56 2011 FrankUpdateDrawingsCAD drawings updated

CAD drawings are now up to date on the svn including all mates and fasteners (outer shield to cavity, no cold plate support yet)

the following details are still missing:

  • long holes for frame length adjustment and mounting
  • holes for accessing set screws for fixing cavity from outside
  • cold plate support structure
  • location/holes for temp sensors/heater cables
  • location/holes for temp sensors

other not important features:

  • material properties for fasteners
  • set screws for frame
  • set screws for fixing cavity


  243   Thu Jul 14 18:57:23 2011 JennyUpdatePlotsMore MATLAB curve fitting

I tried fitting the same curve (radiation and conduction in a simplified cavity setup) in MATLAB to a product of exponentials. 

Two equations I tried:



where u(x) is the Heaviside step function. The second one simply allows for a time delay of t_0 in the second exponential.

I used fminsearch again with these new functions and got out very similar fits.



 Essentially no difference. Also, there's very little difference between these fits and the single pole fit I did before. I tried to do weighted fitting like DMass suggested (multiplying my error vector by 1/time) but I couldn't get it to produce a good fit.


  252   Wed Jul 20 09:19:52 2011 JennyUpdateSimulationModel parameter sweeps: temp step and emissivities

I did some simulations of my simplified cavity and surrounding enclosure while changing parameters. The parameters I changed were

  • cavity emissivity
  • surrounding stainless steel enclosure emissivity
  • temperature step

I recorded the time constant (assuming a single pole and looking at where the curve reaches 1-1/e of the temperature step).


Temperature Step Sweep


I used 10 second time steps in the simulation and got the following table (with cavity emissivity e_cav = 0.7 and surrounding enclosure emissivity e_s = 0.1)


temp step [K]

time const [s]













As the temperature step gets smaller, variation between any step responses diminishes. If I normalize the responses so that the all start at 0 and end at 1, as the

following graph shows, the curves that correspond to smaller temperature steps lie on top of each other, whereas those corresponding to larger temperature steps differ more.

Top Graph: Temperature response to a boundary step function for different temperature step sizes, as a fraction of the temperature step.

Bottom Graph: Difference between fractional temperature response for different step sizes relative to temp response for Tstep=0.01K (absolute value)



So for smaller temp steps it appears that I am limited by the number of decimal places recorded in the solver. Currently the solver is outputting 10 decimal places,

which may be fewer than the number it's actually using in its calculations, so I may be able to go to even smaller temp steps if necessary. The

responses are essentially identical for 0.1 K temp steps and below. For larger temperature steps, it is likely that the linear approximation no longer holds,

and the time constant begins to depend on the temperature step.

I also tried a range of temperature steps for different input emissivities and saw the same trend.


Emissivity Sweeps:

I chose a temp step of 0.01K. Here are my data and fits:

For e_s=0.01: tau(e_cav)=(3100±30)*e_cav^(0.994±0.004)+(27870±50) 

For e_s=0.05: tau(e_cav)=(3080± 20)*e_cav^(-0.996 ± 0.003)+(5980± 40)

For e_s=0.2: tau(e_cav)=(3070± 30)*e_cav^(-0.997 ± 0.003)+(1800± 40)



For a constant surroundings emissivity, the time constant goes as 1/e_cav. For a constant cavity emissivity, the time constant goes as 1/e_s.

This is consistent with David's calculation which gave heattransferpoletau.jpg , assuming small e1 and e2 such that the e1e2 term can be neglected.

Here's a 3-D Plot: surfaceplot.jpg

And here''s the actual data in a table: 

temp step=.01K    
e_ cav e_s tau (s) notes
0.1 0.01 58400 100 s timesteps
0.2 0.01 43200  
0.3 0.01 38100  
0.4 0.01 35600  
0.5 0.01 34000  
0.7 0.01 32300  
0.9 0.01 31300  
0.1 0.05 36500  
0.2 0.05 21300  
0.3 0.05 16200  
0.4 0.05 13650 50 s timesteps
0.5 0.05 12100 100 s timesteps
0.7 0.05 10400  
0.9 0.05 9400  
0.1 0.2 32300 50 s time steps
0.2 0.2 17100  
0.3 0.2 12000  
0.4 0.2 9450  
0.5 0.2 7900 20 s timesteps
0.7 0.2 6200  
0.9 0.2 5220  

  257   Thu Jul 21 22:32:53 2011 FrankUpdatePurchasesalmost all parts arrived

short update:

  • Today and yesterday most of the vacuum parts arrived. We now have all flanges, adapters, hoses, blanks, the vacuum gauges, valves etc.
  • The feedthrough connectors already arrived beginning of the week.
  • We also have all temp sensors, cryo glue, cryo wire, Kapton tape and small cold connectors for sensors and heaters.
  • The cryo temp controller has been shipped today and is scheduled to arrive on Monday (tracking number 1Z9096080347555840)
  • Parts for vaccum feedthroughs, both shields and end caps are being fabricated.

  • Missing parts are the pump and the adapter from pump to the first hose which are scheduled to arrive next week.
  • The supporting frame from the coldplate and the frame for the cavity itself have to be submitted.
  • Have to check status of 26-pin cable to rack.
  • Have to order Kapton heater. They are stocked and i didn't order them as i didn't know how much heating power we actually need as we didn't have the final design for the first support frame and so no number for the heat loss due to conduction (i have to specify the resistance for best SNR (digital resolution of the output is limiting)).

Do we want a cavity dummy which is equivalent in thermal mass and size for testing the thermal stuff?
I think it's a good idea to not play with the silicon rod at the beginning but still being able to measure the thermal characteristics right from the beginning.

(and test the mechanical stuff as well)

  258   Thu Jul 21 23:13:58 2011 DmassUpdatePurchasesalmost all parts arrived

Cavity dummy:

Is 1k too steep to pay for the dummy? If not we can just get a 4inch length of 2inch Si crystal from Virginia Semi

  259   Fri Jul 22 00:38:45 2011 FrankUpdatePurchasescavity dummy

i thought more about a $20 aluminum tube with same length and diameter and matched thermal mass.

  261   Fri Jul 22 13:16:46 2011 Warren JohnsonUpdatePurchasesshould play with your new toys


You should play with your new toys.   You can start with the simplest cryogenic system, a dewar filled with LN2 (liquid nitrogen), attach the temperature sensors to a wood stick

(careful they can't slip off), wire them up to the electronics, and lower them into the the dewar, pausing for a minute or two when they are in the cold vapor, but have not touched

the liquid yet.  Then start to test stuff, like how much temp fluctuation do you see in boiling liquid (probably not small, and how much temp gradient inside the dewar, etc. 

Then borrow a simple test cryostat from somebody, mount two thermometers on the same piece of cold plate, cool down the cold plate with a modest stream of liquid, so

it take 30-60 minutes to reach 77K, and then monitor the temp difference between the two thermometers.   etc.   etc.    Have fun.

  270   Sat Jul 30 01:14:23 2011 FrankUpdateCryoupdate
  • the machine shop fixed the problem with the feedthrough connectors. Picked them up and also got DI water from the 40m to clean the parts downstairs.
    Bob is pretty busy with ALigo stuff and the parts are very tiny but totaly covered with oil. So i will use our ultrasonic bath in the PSL lab  to clean them.
  • Will then assemble and test the feedthroughs. Have to either get our pump back from Vladimir or could also wait for our new pump which should be delivered beginning next week.
    Have to make some cables for the vacuum gauges anyway so once i have everything ready i will see which way to go.
  • Will get a first cryo sensor ready on the weekend. Have to borrow a small dewar for the 40m as we still didn't get our own. However we have all our other safety equipment by now
  • Tested the cryo temp controller the last couple of days to get familiar with the interface. Seems to be OK so far, don't need a manual to set everything up (which is good). Will try to hook it up to the network and access it from remote to see how to communicate with it. Even it is recording everything to a local USB stick we would like to read/ write values using Epics( or our RT control system later).
  • We also might get our radiation shields next week. I've seen parts of it already so they might be able to finish them next week. Have to finalize the order for the heater. Have to come up with a good estimate for the heating power we need to pick a good value for the resistance to not choose a totally stupid one. We have the choice of 6 to 12 values from 10Ohms to 500Ohms depending on the size we choose.
  271   Mon Aug 1 05:44:06 2011 DmassUpdateProject ScheduleGannt Update

Frank and I had been unintentionally fighting over the gannt chart because I failed to RTFM for the SVN. I will conspicuously omit most details for now, but all my updates since the gannt chart's inception have not gone into the svn because they were made to the wrong version.

I found a charger for my computer (am overseas) and thus was able to make my delinquent gannt chart update (not full syntax on the calls)):

  1. svn update
    • Revised my local checkout of the Cryolab dir on the svn
  2. svn lock
    • locked Cryo.gan file
  3. svn commit
    • committed lock
  4. Made changes to gannt chart
    • (I think I got all tasks with my name on them, and I added a few)
  5. svn unlock
    • unlocked Cryo.gan file
  6. svn commit
    1. Committed the unlock and my changes

One conspicuous absence on the chart was the Silicon spacer, though I thought this was already on it, not sure if I was mistaken or it if got deleted some time ago

  273   Wed Aug 3 19:53:48 2011 FrankUpdateVacuumall vacuum parts arrived

today the remaining parts including the pump arrived. Assembled everything, programmed the turbo controller and tested the vacuum gauges.

Everything is working.

did some leak test of individual components like valves, gauges and also the first 24-pin vac feedthrough.
Seems to be OK, however i will seal it using the GE varnish to reduce the remaining leakage.

The only problem so far is that i can't read the good vacuum gauge with the software the provide. It reads the model number but not more.
However the same cable, software and computer can read the other one. I can also talk to it using a terminal program, so i guess it's a software problem.

  277   Mon Aug 8 01:35:43 2011 FrankUpdateCryoradiation shield parts almost done

checked with Rick on Friday. I've seen the 4 polished shields already and the PEEK parts for the cavity support.
Could have taken those parts already but will wait for everything beeing done to see if everything fits together, especially the cavity support itself which has to slide into the inner shield.
Monday they will start with the PTFE insulator and the cavity SS304 frame.

  279   Mon Aug 8 12:57:44 2011 JennyUpdateSimulationSimplified cryo cavity simulation

I made a simplified cryogenic model.


This is a 2D axisymmetric model. The inner cavity is silicon and the outder shields are both aluminum.

The dimensions are the same as those in the drawings for the physical cryogenic cavities being built.


I wanted to see how long the inner radiation shield took to cool to the temperature of the outer shield, first first with no conductive links between the cavity and either of the shields.

I set the entire system to 120K initially except for the outer edge of the outer radiation shield, which is set to 125K at time t=0. The cavity and inner shield cool to 120K during the duration of the simulation. 

The inner radiation shield has changed by 1-1/e of the temperature step after 3.0 x 10^5 s or 83 hrs

The cavity interior hadschanged by 1-1/e of the temp step after 4.25 x 10^5 s or 118 hrs.  

This further supports Frank's finding that if time constants of the thermal coupling in this system are to be on the order of an hour, the dominating form of heat transfer will be conduction through the links between the shields and the cavity. 


It makes sense that this system I have modeled would have two radiative poles. Fitting this on matlab may allow for identifying them separately from one another.

My next step in modeling is to add a conductive link and run the same simulation. Since I'm working in 2D axisymmetric mode, the link will be a thin disk. To account for the added cross-sectional area through which heat can flow, I'll decrease the thermal conductivity of the material accordingly. 


  289   Sat Aug 20 11:39:04 2011 FrankUpdateCryobreakout box finished

finished the breakout box and testes (measured) all connections and for shorts between channels next to each other.
Missing parts for a final cryo test with the cryostat are:

  • cables from breakout box to cryo temp controller (have only one for testing) (LEMO 4-pin to D-SUB 9-pin and 2-pin to ?? for heaters)
  • second 25ft-long cable from vacuum feedthrough to breakout box (Fischer 24-pin to D-SUB 25)
  • all wiring inside the cryostat ( from 300K to 77K cold plate and from there to the individual connectors on the frame and to heaters and sensors)
  294   Fri Sep 9 01:20:25 2011 FrankUpdateCavitygot all remaining rad shield parts

picked them up from the machine shop and cleaned them today. The only parts missing are now the frame and small adapters for the cold plate connectors. Will start putting one shield assembly together next week to figure out where to drill additional holes for sensors and cables. Will drill those myself. We could also think about putting the assemblies in one of the refcav chambers with an RGA attached to see how dirty they are with all the sensors, heaters and cables.

  303   Mon Oct 3 14:55:52 2011 FrankUpdateCavityATF coating specs - V6-593/594

below the scanned documents for the measured specs for our cavity coatings. Coating run number was V6-593 for the HR coating and V6-594 for the AR coating.
Measured specs @1550nm are R=0.05% and T=165ppm which corresponds to a cavity finesse of ~18000.


DYM: Is it common for the AR coating (%T) to be so wiggly on a ~nm scale? Not saying I think this is good or bad, I'm just used to seeing smoother traces and was curious, though maybe I just haven't looked at many %T graphs

  318   Sun Oct 23 23:32:41 2011 neat freakUpdateCleanlinessworking on a dump...

don't know how other people can work in an environment like this. Currently it looks like the situation is out of control and the lab transforms into a dump as foreseen in post 218, some people work on that intensively. After one of the tables and desks didn't have a single square inch to work on anymore people started taking over the workbench and the other desk!  Looks like we have to start daily cleaning from now on...


Oh, if you miss equipment in the EE shop check the crackle area. Chances are excellent to find what you are looking for, but you might have to dig a little bit.





As we have to give a plan to the PMA people by EOB this Tuesday for the cabinet and desk installation, we will toss everything which will be left on the desks by Tuesday afternoon. If you want to save something then move it ...


Attachment 8: 8.jpg
  319   Mon Oct 24 11:56:37 2011 FrankUpdateCavitySi cavity dimensions

measured the Si cavity dimensions. All the mechanics was/is designed for a 2"x4" cavity, but the cavity is smaller and we might have to modify things...

hole at optical axis: 0.53"
venting hole: 0.25"

  365   Thu Nov 17 11:13:27 2011 FrankUpdateLab WorkCryostat

As we still don't have

  • the o-rings
  • indium wire
  • eye bolts
  • crane equipment to lift the thing
  • any other mechanism to lift and handle the cryostat

i will stop working on the cryostat (incoming inspection, leak checks, cleaning, etc) and transfer the responsibility of all those things to Dmass

  366   Sun Nov 20 15:54:03 2011 FrankUpdateVacuumboth vacuum gauge scripts running

after monitoring the first script for a few days  for crashes or other unexpected things i decided to adapt the code for the other gauge as well. Both scripts are running now and frames are written.

Additional things i would like to add (which are already in the code but not tested) and test/modify :

  • the "blinky light", adopted from the perl temp control scripts to see if the scripts are still running
  • stuff is currently running as root. Has to be transferred to controls. Have to check that all python modules are compiled with the right user
  • short overview diagram which device is connected to which port
  • short introduction how to compile the python scripts to executables
  • create native epics modules to allow write operations to the devices (e.g. using the StreamDevice module) . Currently only reading is supported.
  375   Tue Dec 6 21:38:33 2011 FrankUpdateCryoToo much precision

tried to close the exp chamber from the cryostat for baking. Gave up after 4h of trying different positions. The holes don't line up whatever i tried and i can't add more than ~15 screws at a time. There is probably only a single position where it works.

  376   Wed Dec 7 18:33:17 2011 DmassUpdateCryoA PROBLEM:

What's actually going on:

  • Frank tried to re-seal the experimental chamber yesterday (large indium seal) after I rigged it up to the crane from Alastair's expt.
  • He got the correct alignment of the "experimental chamber shield (the part with windows) cold plate holes" from the initial pictures (picasa)
  • In both of the positions which are consistent with the picture, not all the screws fit through the clearance holes
  • We flipped the DEWAR right-side up today, placed the shield on top in the correct position, and checked the screw holes,
  • Not all tapped helicoil inserts lined up with the through holes on the experimental chamber shield
  • I noticed that the through holes themselves had damage inside them from the initial seal
  • It looks like they used elbow grease to do the initial seal, forcing the screws in that didn't line up
  • I took pictures of the damage with the 40m Olympus (picasa link)
  • All 8-32 holes are supposed to be clearance / were clearance at one point, but some are so damaged they look tapped

 We need to figure out what to do about this...

  1. Send it back?
  2. Ream / Drill them out ourselves?
  3. Use it as is and just use more elbow grease?
    • Might dmg helicoils, one is already damaged
    • Would create Al dust at the indium seal
    • Seemsbad.

Let's decide this tomorrow at the meeting

  377   Wed Dec 7 22:46:31 2011 FrankUpdateCryoA PROBLEM:

Use it as is and just use more elbow grease? - Not an option. We already have one ripped Helicoil and we even didn't use the thing. The risk of breaking the Helicoils is too high if we open it frequently (which we will do). If you break the thread for the Helicoil then goodbye Crystat and we need a new coldplate/LN2 chamber. We would also get all the metal parts from cutting the thread into the clearance hole on the sealing surface.

They are actually not 1/4-20, they are all #10-32.


What's actually going on:

  • Frank tried to re-seal the experimental chamber yesterday (large indium seal) after I rigged it up to the crane from Alastair's expt.
  • He got the correct alignment of the "experimental chamber shield (the part with windows) cold plate holes" from the initial pictures (picasa)
  • In both of the positions which are consistent with the picture, not all the screws fit through the clearance holes
  • We flipped the DEWAR right-side up today, placed the shield on top in the correct position, and checked the screw holes,
  • Not all tapped helicoil inserts lined up with the through holes on the experimental chamber shield
  • I noticed that the through holes themselves had damage inside them from the initial seal
  • It looks like they used elbow grease to do the initial seal, forcing the screws in that didn't line up
  • I took pictures of the damage with the 40m Olympus (picasa link)
  • All 1/4-20 holes are supposed to be clearance / were clearance at one point, but some are so damaged they look tapped

 We need to figure out what to do about this...

  1. Send it back?
  2. Ream / Drill them out ourselves?
  3. Use it as is and just use more elbow grease?

Let's decide this tomorrow at the meeting


  378   Thu Dec 8 14:15:29 2011 DmassUpdateCryoA solution

Rana and Warren don't seem to think this is that big of a deal - suggested solution is to give it to Mike by the 40m to machine out the holes.

Rana suggests doing this through Steve, however Steve is sick. Shall I wait for him to get back, or try to hunt down Mike myself and get this in the Q. If we do this we don't draw on Steve's experience, and I don't know if there are any special instructions I would need to give him in doing the job. Holding off for now.

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