#8 FAQ - Deuterium Gas handling systems for fusors

[Doug Coulter]

Tyler,
You may not need to go that far to get some. I don't have a fed ID number, as my company is a proprietorship and only hires "contractors", and that was enough. It has a checking account in the company name (C-Lab) which my bank calls "Doug Coulter DBA C-Lab. The key there was that it IS a real company with some history, a credit rating and so on, and I really did have those people on tap -- though they certainly don't work here full time. It may take a slight bit of imagination to fill out the forms, but shouldn't take any outright lies. Matheson gave me an open account, no sweat.
Part of it is just talking the talk like you're for real (this applies in a lot of things). You just need to sound like a normal purchasing agent, mainly.

For example, my "official" security arrangement is that I do employ a local deputy part time, as he's also a chemist and computer guy. My on call emergency response provider is a retired paramedic who lives next door and drops by from time to time (and who has pulled me out of the fires on more than one occasion in situations unrelated to this). And so on. It didn't seem to hurt to send a nice picture of the lab in full operation with the crew along with the forms when I sent them back -- sort of instant credibility.

Of course my "real" security arrangement is that I live in the boonies and am a gunsmith and competitive shooter, and no one in their right mind would come here to burgle me -- and in the boonies, everyone knows. Our real safety arrangement is more like "this stuff is so darn expensive you better believe we're not ever going to let it leak" and so on.

For guys who get to HEAS, there might be some of what I get available to forum members.
I'm hoping either myself or BillF will get there this time, bearing various goodies.

Mike:
I'll be posting as soon as I have some data I can back up with real measurements, probably on another thread dedicated to the topic of fuel purity. We did get some neutrons with the electrolyzed stuff, but even an optical spectroscope showed that we were losing most of the input energy to oddball stuff rather than just accelerating D. Getting those trusted measurements, and basic stability are the next goals, and I'm now testing a fast-fast neutron detector I designed which will be backed up and calibrated with the bubble detector and an old NATO "ball" type counter. A new main power supply is also going into operation, so there may be a few bugs to work out to get to really stable operation needed to make the measurements mean much, we shall see. I'm hoping I don't have to install and debug a mass flow controller, but gas flow vs pump rate has been an issue for stability here, as the main power supply croaks when overloaded due to a temporary higher gas pressure. We'll also be testing a comprehensive data acquisition system during this, so it will likely take awhile for trusted results to appear, but when we get them, they'll be good results, and include a lot of things most people don't measure (even ripple and stuff like that on the HV supply in realtime, instantaneous pressure and temperature of various things and so forth).

Our SWAG is that impurities open a lot of channels of loss, such as charge exchange, accelerating the wrong species, resonant energy exchange between impurity and fuel ions (ala how a HeNe laser pumps the Ne via the He) and so on, and even small amounts of impurity should contribute huge losses due to all these. But that's a "scientific wild a** guess", not an experimental result. The boys doing tokomaks have reported that small hi-Z impurities from sputtering have 100's of times the loss effect their percentage would indicate, which is what started me asking this question.

[Chris Seyfert]

Doug,

It sounds like you're paying through the nose for that 5N grade deuterium and associated quality fittings. On Cambridge Isotopes' website (www.isotope.com), they list 100L of 99.8% deuterium gas at $200, plus $200 for the "Code H-3" cylinder which comes with a standard CGA 350 fitting, which can fit a standard two-stage welding regulator. With your pseudo-company you might be able to order from them.

Also, the company that I work for just quoted deuterium from a local Airgas supplier - $500, including bottle, for 100L of CP grade (99.7%), plus delivery fees etc.

My two cents as far as the gas distribution - I've found that for short, low pressure runs from the flow control to vacuum chamber, 1/4" teflon tubing from McMaster-Carr works well, has low outgassing, and can be used with 1/4" compression / Swagelok connectors (usually with a compression insert). Probably only viable where the flexibility is really necessary, as the price ($2-3/ft) compares poorly with cleaned and capped soft copper refrigeration tubing.

[Richard Hull]

I would be stunned if absolute purity of internal product yielded one iota of improvement over a really crappy, junk loaded system. I would love to see the experiment run.

Richard Hull

[Carl Willis]

>I wish someone quoting these cheap prices for bottled D would say where they get it -- and how many years ago that price was valid, and how pure it was and how they checked that.

In the last month I got another 50-liter cylinder of D2 from Matheson, via their plant in Albuquerque, and posted details, including a breakdown of the $215.85 bill:

viewtopic.php?f=6&t=2944#p18178

This was CP-grade gas in a non-refillable lecture bottle. I don't have a business, I don't have a safety plan or any of that other hogwash, I walk in the door, the rep orders it without a hassle at all other than the ~2 week lead time and a sign-and-fax-in NRC compliance form; I go pick it up when it comes in, and pay cash. Price has not changed substantially since the last order I made, probably more than three years ago now (by the way, the old bottle is still over half full).

Doug, I'm inclined to agree with Chris that at $1600 you are spending profligately on a high-purity regulator and research-purity gas, and I have no idea why you had to suffer through all the regulatory song-and-dance you reported unless it had to do with the sheer quantity you bought. Of course, you plan to do an experiment where purity is a variable and given that specific interest you probably came out OK on the price. But for the average hobbyist getting into this game, more interested in budget neutrons than purity studies, Richard's cost estimates in the FAQ for regulators and gas are still accurate according to my own experience.

Nathaniel, here's another shot at your question if you're still around: capillary is usually 1/16" OD, a manageable size for brazing into something larger. I now prefer laser-drilled apertures to capillary. They are conveniently sold pre-mounted in an NPT fitting. At ~$40 apiece from DayStar for an uncalibrated 4 micron hole, they're comparable in price to the equivalent conductance in standard capillary and you won't be hassled by cutting capillary (annoying) or brazing it (not difficult but you need the supplies and a little practice).

-Carl

[Tyler Christensen]

You don't need a pre-certified account or anything? There are local Matheson distributors, maybe I'd have better luck walking in rather than calling if they operate the same as your local distributor

[Doug Coulter]

I dunno why the regulatory stuff, maybe it's new -- it was DHS which are new themselves, and can be as annoying as the TSA. The rep said it was for any quantity, and it really wasn't terrible since I could meet the requirements. But if you're a kid trying to buy this stuff, well...

Richard, you're invited here anytime to see any experiment run. We'd love to show you our dog and pony show in return for the time you graciously showed us yours with almost no warning on our way back here from DC. Kind of a long drive, maybe BillF will fly you sometime.

Carl, I dunno if this was profligate or not until I do the experiments. Soon!

I do know that H (or D) is pretty leaky stuff, and I'd not modify some other regulator to take it, fearing that alone, not to mention contamination of the product. Same goes with valves, we got real H valves for our lecture bottles we're going to put this in, and have outgassed them already (a week at e-8 mbar with baking at 150c or so). YMMV of course.

ChrisB helped do one computation of the difference between clean and impure D, and he came up with factor of a couple hundred worse for contaminated. At that, he left out the energy exchange losses with other ions which can be huge by themselves. As I was unable to reproduce some of the pure D results with the electrolyzed D, not even close, I decided to study the subject some more and do the experiments needed. With impure D I got maybe 1% of the neutrons others report with reasonably pure stuff.

Getting the power input levels down is a big deal for me -- efficiency is my bag running on solar panels, and in tests of another prediction of ChrisB's I found a tungsten rod 1/16" diameter and 6" long replacing a grid gets white hot at 43 watts DC input....This was to test the voltage threshold for neutron production when there was basically no chance for fast on fast, and BTW, Chris was correct.
Basically, no detectable neutrons until about 20kv, whereas with fast on fast you'd see a resonance peak at about 12kv (square root more or less of the 125kv peak for beam on target).

Considering the total amount of money I have in this game already (two brand new oil free turbo systems, mass spec etc etc), the price wasn't that bad, just offensive to an old Scottish scrounger. It's less than I pay one lab grunt in a month. I'm lucky to have the bucks, unlucky not to have more time for doing things on the cheap which is truly more fun than making the bucks. On the other hand, having new stuff that works reliably is pretty nice too.

And if Richard is right -- well, we'll know for sure soon, I will post at what point what type of impurity starts degrading results vs power input and how much. Easy to make muddy water from pure, harder to go the other way! If really dirty works fine (though it doesn't here) then everyone else can save money and I've helped us out. If the pure stuff does no better with the same everything else, I'll tell all.

Does anyone know what the main impurities are in the CP grade you've been getting?

[Carl Willis]

Hi Doug,

>ChrisB helped do one computation of the difference between clean and impure D, and he came up with factor of a couple hundred worse for contaminated.

Contaminated at what level, and with what? CP grade is 99.7% D2, according to my Certificate of Analysis. It lists no details about the contaminants, but the largest would be H for sure.

Was there a thread about this particular calculation you referenced that led you off on the purity stint? Because I think it's suspect: It would seem to be predicated on having an accurate and comprehensive model for the atomic and nuclear processes in the Hirsch-type fusor with assumed-pure fuels--and then adjusting such a model to account for differences in fuel purity! If such a model exists, and it has predictive value that would make a compelling case for UHP gas, it's news to me.

Conventional yield calculations and experimental data for monoenergetic beam-on-dilute-target situations like neutron tubes do not indicate differences in yield of a hundredfold for 3000 ppm of diluents.

>Basically, no detectable neutrons until about 20kv, whereas with fast on fast you'd see a resonance peak at about 12kv (square root more or less of the 125kv peak for beam on target).

I don't understand the conceptual approach underlying the above statement.

Good for you for putting your money on an idea and trying it, though.

-Carl

[Chris Bradley]

Carl Willis wrote:
> Contaminated at what level, and with what? CP grade is 99.7% D2, according to my Certificate of Analysis. It lists no details about the contaminants, but the largest would be H for sure.
> Was there a thread about this particular calculation you referenced that led you off on the purity stint?
It was related to an off-line discussion about using D2O as the source of D. What the effect of these 99** purity levels is, I wouldn't want to say as I would guess much would then be to do with other contaminations getting into the process during running, particularly shell sputtering of heavier elements with bags of electrons.

But purity of D clearly is 'a factor', and Doug is on a mission for optimum performance so has taken that to the extent of its logical conclusion. Good for him! As you say, we're all grateful that people put their own good money forward to experiment with these things and report back.

[Doug Coulter]

Sorry all about this getting so off topic from Richard's treatise on gas handling, which pretty much says it all, much of it directly verified here by experiments attempting to do it on the cheap and finding out which things matter. We did find that a tiny needle valve from McMaster (about 20 bucks) followed by a couple inches of .005 capillary tube worked pretty well for controlling small gas flows from stp to vacuum, if all was soldered or brazed, and the valve parts polished internally so it sealed well when shut. Doing this left the stem seal above stp by about an inch of H2O, so it didn't leak air into the system. Works well until you accidentally allow some electrolyte to get into that cap tube and plug it up with dried carbonate.

I got my ideas on purity from two sources, actual experiments with impure gas that couldn't replicate results reported here (by factor roughly 100), with all else the same as I could make it, and a report by one of the university (Princeton?) tokomak groups who found that even a tiny amount of sputtering off a tungsten beam stop increased losses roughly a hundred fold, as reported in an older Physics Today I can't easily put my hands on just now (hundreds to look through to find it again), so I hope you'll trust my memory. They changed the tungsten for carbon and got a large improvement, but still had losses due to the carbon in diagnostic tests. They reported that it only took minute amounts (PPM) of impurity to vastly increase losses. When two substances share what amounts to a close spectral line (or difference between two energy levels) it becomes very easy for one to give up energy to the other, and the other one may then radiate this energy easily as photons, depending on various selection rules.

This is the principle of the HeNe laser. It's the Ne that lases, but it's pumped by energy transfer from the He, for which I could quote many many sources -- a good one is "Molecular Engineering" by Henry A. McGee, Jr.. Transfer from the He to the Ne is very efficient, and in this case, desired.

In general, it seems that higher atomic number atoms are worse for this, having many possible energy levels compared to lighter atoms, so more chances of a resonant exchange. This is just one loss mechanism that is possible -- for example, a heavy ion can get a multiple charge and act like a disproportionate space charge for the amount of them, which will repel the lighter ions away from the intended trajectory easily -- bb bouncing off a bowling ball. Obviously, energy is required to accelerate any ion, and any ion will be accelerated in the fields, which is probably a secondary effect compared to resonant energy exchange. But these ions will be in general slower moving, and may be impacted by lighter ones, which also wastes the energy put into those. We are, after all, trying to create collisions here, and our systems don't discriminate too much based on A or Z, at least until we start paying attention to electrostatic focus conditions.

Carl is right for monoenergetic beam-on-target situations, but that's not what we have in a fusor; in general we have an amorphous (heterogeneous in several parameters?) plasma, on which many lifetimes of work have been done, a lot of it for the laser world. There, the effect of tiny impurities on energy transfers and (meta)stable states is profound and well documented. I think it pays to look at work done by others in somewhat related fields and maybe learn something. There is also substantial work in Q machines on impurities, and the word from that is -- they're very bad.

Chris had asserted that we have mainly fast on slow collisions, so I did a test of this. Most beam on target tubes (which sadly do much better than most fusors re power in per neutron out) run in the 125kv region, which seems to give about the max cross section for this reaction. As the particles are same weight, the center-mass collision energy in this case is the square root of the energy of the moving particle (I think you can ignore any chemical binding energy in the single digit ev here), so they are creating the same center mass energy you'd have for head on collisions at ~11 kv or so.
(The more general case is the geometric mean which reduces to square root for identical particles, so light on heavy gives better results when the heavy one is stopped in the lab frame)

Therefore, if fast on stopped is best at 125kv, we can assume that head on collisions ought to be best at about 11kv -- this principle is used in all modern high energy accelerators for quite awhile now to get higher center-mass-energy collisions. There are a lot of obvious reasons it would be better to be able to run at the lower voltages.

So, it appeared obvious to me to set up an experiment to test this as well as I easily could.
I am doing cylindrical grids for mostly mechanical reasons here, so all this is in that model.
I kind of doubt the geometry makes a big difference to this for this case.

With an "open" grid, the possibility of fast on fast at least exists inside the grid. With a rod replacing that, that possibility is minimal as all the ions are accelerated into the rod and not really towards one another. Ones coming from opposite directions hit the rod instead -- which may or may not have some D embedded in it like a borehole tube target, at least until it heats up, which happens very quickly. So with the rod, you get primarily fast on slow (or stopped) type collisions with neutrals that have become neutral/stopped from hitting the rod. The density of neutrals around the rod is in general higher than the average gas density, as this has sort of a compression ratio, which I noted in another experiment with an open ended cylindrical grid spewing ions out of the open end. This one I have pictures of, it's pretty but not useful unless you're making an ion source this way. The space charge blows the particles out of the end quite nicely against the main field gradient. Which leads to some other issues worthy of discussion, but not on this thread which is already getting far afield.

In this test, we got neutrons from a grid (not a ton, but a definite signal and bubbles) at voltages where we got exactly zero to our limits of measurements on several detectors with a rod, at voltages up to about 19kv. Above this we started seeing some neutrons from the rod too, but never close to as many as from a grid designed to reach electrostatic focus in that voltage range and at low space charge levels (space charge disturbs the focus conditions and has to be designed around). We were running with an ion source for all these, to keep the ion/neutral ratio good, and to allow working at lower pressures, currents, and space-charge densities.

All these tests were done with the impure D, which is all we had at the time. We saw optical evidence of the impurities on a small optical monochromator, and a *lot* more photons on non-D lines than on the D lines. This made me move the D source to the tank with the mass spec and find out the ugly truth about it.

Back to SWAG for a moment. No one really appreciated the semiconductor usefulness of either Ge or especially Si until they were prepared far more pure than had ever been done before, and in retrospect the reasons were obvious -- it only takes a tiny amount of doping to radically change their properties. Could this sort of thing apply here? How would we know? No one's tried it as far as I can find, here or elsewhere (including the big labs), and even with a pure D source, it won't exactly be easy, as there is the tank outgassing and many other possible problems in getting to real purity. What we do have is plenty of reports from plasma related fields that tiny amounts of impurities really mess things up (compared to theory for pure), especially heavy impurities.

So, that led to "why guess when you can know?", one of our mantras, and we're going to do our best to find out, instead of guessing (gassing? Pontificating?). I figure this is just one of a lot of "baby steps" to really getting this done right. Others include focus, time-space bunching and transit-time resonances, and handling space charge effects on the rest, and probably a few I'm forgetting just now.

Carl is probably right that there's no comprehensive model for this. I asked the guys at SIMION if their product could really handle a simple case for a fusor, and the answer (nice of them to be honest and save me the time and money) was nope, even for pure gas/ions. There's just too much going on for that program to take it all into account in a realizable computer system. Though I am a competent programmer and own a teraflop machine, I just don't think it's the best use of the next few years to tackle this one myself.

If they run that CP D through a purifier, I'd expect that the main impurity is indeed H, as those get to PPB levels when used on H, and as far as they're concerned, D is the same stuff. So that other junk is likely from the cylinder outgassing into the pretty pure gas they probably put in there, so you'd expect some air components, and water (anyone who wants to send me a sample to measure on the mass spec is welcome to do so ;~). From my UHV experience, I'd guess that getting those tanks really clean inside is the major expense here, and the bill from Matheson seems to say that as well -- the empty tank cost nearly as much as the contents. Must be nice to be able to walk in and make a deal, I got mine from Pennsylvania, quite a long drive from SW Virginia, out of the range of a day trip for me (heck, it's 4-5 hours to Richard's from here, and he's in the same half of the same state). They said that was the closest to me and I was in that sales-turf, so that's what I did. My local gas supplier for welding sorts of things couldn't even order regular hydrogen due to the new "safety" regulations.

Attached is a sort of lousy picture of the space charge accelerate stream of ions from the center of a cylindrical grid, going *against* the main E field, no sweat. Space charge is a much larger effect here than most seem to want to admit, and one for which I'm working up the math for the fusor situation.
Gratuitously attached also find a picture of the glow from a two grid system designed for focus (running in helium at the time), taken a few seconds earlier under the same conditions, so you can better see the overall apparatus we used (BillF's system, diff pumped). The lamp glowing in the picture is the HV supply ballast. The scope was looking at the raw output of a gamma spec head, and a neutron counter -- no counts on He, of course.

[Carl Willis]

>the center-mass collision energy in this case is the square root of the energy of the moving particle [...] so they are creating the same center mass energy you'd have for head on collisions at ~11 kv or so

It was mostly this little nugget that clashed with my conventional physics education. Correct calculations abound in the archives because the kinematics of the DD reaction happens to be a dead horse that gets beat regularly. Though the math of converting energy in the center of mass frame to energy in one particle's frame is simple, so many who are so sure of themselves curiously don't get it anywhere close to correct! I don't know why that is....

Anyway, here's one post (of probably dozens) where I do the math. No terms of SQRT(E) show up at all. (For one thing, that would be dimensionally incorrect.)

viewtopic.php?f=14&t=6798#p46791

>With an "open" grid, the possibility of fast on fast at least exists inside the grid. With a rod replacing that, that possibility is minimal as all the ions are accelerated into the rod and not really towards one another.

Why do you assume the possibility is "minimal?"

Non-radial particle orbits with angular momentum exist. Just like planets orbit a star with elliptical trajectories, particles can orbit the cathode in a fusor with elliptical trajectories. They can run right into each other at high energy outside the cathode. The solid-cathode experiment does not preclude that.

>The density of neutrals around the rod is in general higher than the average gas density, as this has sort of a compression ratio, which I noted in another experiment with an open ended cylindrical grid spewing ions out of the open end.

The density of neutrals is generally higher? Really?

I think when you put the opened-up tube in there you get a hollow-cathode discharge inside. Maybe my reasoning is too conventional.

-Carl

[Dustinit]

Why do you assume the possibility is "minimal?"

Non-radial particle orbits with angular momentum exist. Just like planets orbit a star with elliptical trajectories, particles can orbit the cathode in a fusor with elliptical trajectories. They can run right into each other at high energy outside the cathode. The solid-cathode experiment does not preclude that.

>The density of neutrals around the rod is in general higher than the average gas density, as this has sort of a compression ratio, which I noted in another experiment with an open ended cylindrical grid spewing ions out of the open end.


The density of neutrals is generally higher? Really?

I think when you put the opened-up tube in there you get a hollow-cathode discharge inside. Maybe my reasoning is too conventional.

-Carl

I see nothing wrong in the conclusions drawn Carl. "Minimal" doesn't exclude other orbitals but does exclude all fast on fast at the focii which now inside the rod and beam paths through the grids which centre on the rods.
Ions colliding with the rods and neutralising or bouncing will have lower energy and diffuse away and thus create a pressure gradient. This also follows for hollow cathode discharge.
I think you are being argumentative.
Just my opinion.
Dustin.

[Carl Willis]

Hi Dustin,

I said what I said because I don't think those two conclusions follow from the experiments offered in evidence. They may be correct. They may not be. Either way I think they are speculative. Hence my argument.

About the neutrals and whatnot....I can make an argument that more are formed near the outer wall. How's that? Ion energies are lower there. Stopping power in the residual gas is higher. Who's correct? We don't know. The experiment offered didn't test that question directly.

-Carl

[Dustinit]

About the neutrals and whatnot....I can make an argument that more are formed near the outer wall. How's that? Ion energies are lower there. Stopping power in the residual gas is higher. Who's correct? We don't know. The experiment offered didn't test that question directly.

I myself have made that argument before as secondary electrons created would probably neutralise ions at their low kinetic energies near the shell.
Of course, diffinitive proof of any logical argument is required to accept it as fact.
All else is speculation an inference.
Dustin.

[Richard Hull]

One thing is, and probably will always remain in effect: This system, due to its simplistic operation, lack of controls over vast ranges of operation, is so complex as to virtually defy analysis at anyhting like a comprehensible level to the amateur and of little useful value, if pinned down, to the professional.

We can speak and experiment on zones of special interest, ion production, massive recombination, electron losses, deuterium purity, grid geometry, etc. In the end, there will be little if any advance in fusor system output without a correspnding increase in complexity and cost. Thus, pushing this device ever closer to mimicing the costly and oversized fusion debacles already extant.

It will apparently always be possible to muse, cogitate, and spend time and treasure chasing an amateur illusion to useful fusion.

Take heart though, We only have a 10e9 to 10e11 improvement factor to go. Certainly, it is just a matter of money and engineering.

Richard Hull