Talk:Polywell

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Contents 1 Key to the design / merge 2 Bussard's polywell and lecture 3 Images from the paper 4 Losses 5 Magnet arrangement? 6 Seventh power? 7 Lawson criterion 8 Award 9 What gives?

[edit] Key to the design / merge

If I understand correctly, the key to this design is the relative weights, charges, and sizes of the different particles involved. The electrons weigh much less than the ions, and so are carried around in circulation by the magnetic field in a way that forms a quasi-spherical shell inside the device. The ions are much heavier and have more inertia, so they rarely collide with the tiny electrons and aren't affected by the magnetic field, but are attracted to the electrons en masse and crash together after passing through the shell and going towards the center. — Omegatron 22:02, 27 November 2006 (UTC)

Correct.

As for the proposed merger, I would disagree. The Farnsworth fusor has its own article (it's a specific type of inertial electrostatic confinement). Why shouldn't this one? -- Rei 06:16, 28 November 2006 (UTC)

Fusor should be merged, too. If not, all three have redundant content which needs to be split. — Omegatron 13:15, 28 November 2006 (UTC)

Every type of fusor already has their own articles. Why shouldn't this be the case? Why should we jam all of this technical detail, history, etc, for each into a single article? That would be like insisting that mice, rats, gerbils, etc all get grouped into the "Rodent" article.

Polywell is a very different beast than a Farnsworth-Hirsch fusor, even though they're both IEC fusion devices. The physics behind it is very different. It's wrong to shove them together as though they're minor variants on the same design. In short, I stridently object. -- Rei 20:10, 28 November 2006 (UTC)

I have a problem, I read the article, and I still don't understand how it works. I think this could use another section before design of "Theory". I just want to see something in there about how it confines the fuel like we're talking about here. Even after reading the entire article, reading all seemingly related articles, and reading your posts, I still don't understand what the deal is. How do they confine the electrons to the center with a magnetic field? I read one thing that says it's kind of similar to a Penning Trap, but if I'm not mistaken, that's only for one charge of particle. Plus, I see nothing in this polywell design that looks like a large electric field being generated. It's all done with a magnetic field right? wrong? If it is, how can this design confine them in a sphere when the Tokomak has to spin them in a toroidal design? Is that because this design is only confining negative charges as opposed to positive charges? That would make sense to me, but I am seriously lacking an authoritative explanation on this. But even so, how does it confine the electrons with just a magnetic field in a sphere. That is what I would like to see from an added section to this article.

Also, there is talk about a "grid", but I would like to see a more direct description of what other designs it is used in. Most people reading I think are going to have no clue what you mean by a grid.theanphibian 18:26, 16 February 2007 (UTC)

Sorry for being so annoying, I have another question! The first line of the article states that this is "a gridless inertial electrostatic confinement fusion process". Now, the last 2 paragraphs I wrote were in reference to the magnetic mirror (wanting more information), but I also want to pick about the "inertial electrostatic confinement" part. Is this really inertial? For that to be the case, shouldn't you be throwing fuel into the reactor as it fusions to have it accelerated by the electric field created by the negative charges? My impressions up to this point was that this is not the case. Take a Tokomak for instance, there is much more fuel present than what is fissioning at any given time. It just bounces around until two particles "hit". Is that not the case with the polywell? If you say "inertial", you are suggesting the opposite, that fuel ions are accelerated and fissioned in a continuous stream injected into the core. To tell you the truth, I just don't know which way it is. And YES I watched the google video of this.theanphibian 18:58, 16 February 2007 (UTC)

[edit] Bussard's polywell and lecture

Bussard says a lot, and he says it fast. I'm just an engineer, so I don't know what a lot of these terms mean, but here's my summary of notes from watching the Google lecture. We should cover a lot of this stuff:

Research timeline

• Has been working on fusors for the past 11 years with his company EMC²
  • Team of 5-10 people for 12 years
  • Funded by DOD/DARPA, so results have been classified. "Embargo" on publishing papers for 11 years.
    • Claims only reason for lack of money is because DOE has charter to research fusion with tokomaks and won't fund other fusion research
• First test September 1994
• Now that contract is over? he plans to write papers about the results.
  • First summary paper should be online soon, was published in October in proceedings submitted to the 57th International Astronautical Conference in Valencia, Spain
    • Bussard is a fellow of International Academy of Astronautics
    • Can't go to Valencia to present it because of medical limitations
  • Then hopes to write a 120 page or so paper to explain everything for a bigger journal like Fusion Technology
• Funding ran out in 2005, "saved" by "Admiral Cohen" to get through 2006 just long enough to get these results
  • • Was funding cut? Mentioned being under "Advanced Energy Development" "line item" in Navy's budget, which was killed to make room for Iraq? Or was the budgeted money all used up? Or contract expired?
• Closed the lab down on 1st November 2005?
  • SpaceDev (SpaceShipOne, James Benson) is interested in fusors for space engines
    • Moved one million dollars of Navy equipment to SpaceDev
    • SpaceDev hired the three best lab people to continue research
  • "Or maybe Google" could fund it, says that he ended up giving the speech there 'by accident', but they do happen to have a lot of money...

Research results

• Says tokomaks will never work, Bussard was one of the people who got them started
  • "Stars aren't toroidal", "billions of dollars to discover that it's not any damn good", and other choice quotes
  • Better to simulate center-pointing force like gravity in stars; uses electric fields to push towards the center instead of a toroid
• Says "like marbles in a well", so my wanting to mention an analogy to "marbles in a bowl" is not a half bad idea, is it?
• Mentions burning nuclear waste from fission reactors with a D-T system while simultaneously producing power, to drop nuclear waste storage time from 4000-9000 years to 40-90 years
• Older designs are IXL or EXL
  • IXL (ion acceleration) energy's lost and grid melts. 90-95% transparency is the best they can get, but no grid is transparent enough.
  • EXL (electron acceleration, two guns) inversion of IXL. Gets rid of electron interception but replaces it with ion interception
  • Hirsch has on his desk the prototype that reached 10^10 fusion reactions (per second?) on D-T
    • Ion guns facing each other
    • Drive voltage probably in excess of -150 kV --Tom Ligon162.84.67.130 23:30, 11 January 2007 (UTC)
    • 10^-6 total energy gain, due to grid loss problem and collision with walls
  • quasi-spherical magnetic fields
    • trap injected energetic electrons to form spherical negative potential well
  • There are no magnetic monopoles. Bussard patented a device in which the magnetic fields are on the edges of a polyhedron with an even number of faces around every vertex so alternate faces are north-south
  • Electrons are trapped by polyhedral magnetic field in a spherical configuration, ions are dropped into electron shell and trapped by electrons. Has to do with weight difference of electrons and ions?
  • fusion ions trapped in this spherical well
    • focussed through central region (1/r^2)
    • oscillate across core until reacted
• Previous designs like two magnets facing each other had line cusps around the edge, with two magnets facing each other there's an equator of loss
  • Alternating polyhedra design has lots of point cusps instead of line cusps, which have lower losses. "Polywell" magnetic polyhedral grid
  • System acts like a spherical colliding-beam device
  • Fuel gas is input at potential well edge
  • Fusion products escape to system walls
• Maxwellian distribution problem
  • His fusors do not use a Maxwellian distribution. Not maxwellian equilibrium plasmas like Tokomak
  • Non-local thermodynamic equilibrium
• Boron with a charge of +5 falling into a 100 kV well will reach 500 kV; doesn't need a 500 kV well
• Needs to be slightly ion-rich to create a virtual anode instead of a neutral core
  • There's significant wiggle room between ion-rich enough to create fusion and too ion-rich that it 'blows the well'
• The major problem they were facing is electrons striking the apparatus without a magnetic shield. they solved this a year ago.
• Another problem is arcing
• Neutrals can be ionized with microwaves and "gauss lines"? (used a modified consumer microwave oven) to allow them to be controlled
  • • Ha! Yes! I pulled apart an old microwave and found the magnetron could be rigged to seal a vacuum if we adapted it to a modified CF plate. We mounted it on PXL-1, and demonstrated it would light off copious ionization in that device. This is Electron Cylotron Resonance (ECR), the same thing that makes the magnetron work. Microwaves at 2.45 GHz cause electrons in a 875 G magnetic field to resonate, and any neutral hitting that zone gets zapped fast. PXL-1 had an 875 G topology not too far from its walls, and a pretty blue glow showed up there. When that magnetron burned out, we found an identical oven at one our favorite science supply houses (a plumbing supply store) and swapped them a new oven for it.
    • But for stronger magnets, higher frequencies are needed to place ECR near the walls. And that's not a $100 problem. Tom Ligon 162.84.67.130 01:11, 12 January 2007 (UTC)
• Without big enough power supplies, used capacitor bank to run wb4 for a few milliseconds
  • in 2005
  • 12 kV drive, 10 kv well depth, D-D fusion 10 kv
  • Achieved 10^9 fusions/second for a quarter of a millisecond, based on count of three neutrons
    • 100,000 times higher than farnsworth or hirsch (though Hirsch apparently reached 2×10¹⁰ neutrons/s in the 1960s)
• Things they know it needs:
  • No metal surfaces open to the electrons
  • Needs to be recirculating
  • All coil containers need to be conformal to magnetic field shape, so electrons are not striking the magnets, need gaps between magnets

Future research

• SpaceDev
• Also considering easier to build neutron-emitting systems to retrofit existing fossil fuel plants
• Navy is interested in p-11B for electric submarines
• Proposed project is estimated at 150 (D-D) to 200 million (pB11), five years to complete a working reactor
• Size would be 1.5-2 m for D-T, 2-2.5 m for p-B11, no larger needed
• Physics problems are gone, engineering problems and money are the only things left to deal with, though engineering is 10 times as expensive as physics
  • "2 megavolt output"
  • "200 kV standoffs"
  • Future devices will not be circular coils, but will be optimized for the shape of the magnetic field?
• Would first spend $2M?:
  • creating two more small machines like the last one created (WB6?)
    • First a truncated cube
    • Then a truncated dodecahedron
  • Then run those results by a review panel before proceeding to the rest of the $200M?

Others working on fusors:

• George Miley of the University of Illinois, working with grid-based fusors
• Gerry Kulcinski and John Santarius of University of Wisconsin also working with grids, trying to improve Farnsworth's design
  • (I notice they claim 1.1x10^8 neutrons/sec with D-D)
    • That reference cites operation at 130 kV. The WB-6 tests were at 12.5 kV drive, 10 kV well depth, conditions under which conventional IEC machines make so few neutrons as to be difficult to detect. Tom Ligon 162.84.67.130 19:57, 23 January 2007 (UTC)

There are also letters online ostensibly written by him: [1] [2] — Omegatron 20:31, 29 November 2006 (UTC)

Thank you for the summary. I am listening to the lecture now. Two things jump out. First, Achieved 10^9 fusions/second for a quarter of a millisecond, based on count of three neutrons. Isn't this a bit of an extrapolation? Second, if they really have something, why don't they have a website? None of the charts in the video are legible. Paul Studier 23:14, 29 November 2006 (UTC)

Websites concerning products are for trying to sell them. Bussard is trying to raise funders, which isn't quite the same thing. A quick google search looking for scientific review of Polywell shows what little is out there so far as being favorable.[3]. As for the neutron count, I'd have to listen to the talk again. That doesn't sound right -- 10e9 fusions/second for a quarter millisecond would mean the release of 2.5 million neutrons. Surely their detection rate couldn't be that low, could it? -- Rei 00:15, 30 November 2006 (UTC)

Well, seeking funders is the same as advertising. I would like to just see the charts he put up in the video. As for 3 neutrons, Bussard mentioned that the detectors were several feet away, the fusion event was short and it generally takes several cm of solid material to stop a neutron. If I recall correctly, neutron detectors have a couple cm of area and contain gaseous boron trifluoride, which is not very dense. So the conversion factor is plausible. However, 3 neutrons from one event is not enough to convince me. Still this justifies an article because I believe that even hoaxes should be documented. Paul Studier 04:46, 30 November 2006 (UTC)

First, Achieved 10^9 fusions/second for a quarter of a millisecond, based on count of three neutrons. Isn't this a bit of an extrapolation? As for the neutron count, I'd have to listen to the talk again. That doesn't sound right -- 10e9 fusions/second for a quarter millisecond would mean the release of 2.5 million neutrons. Surely their detection rate couldn't be that low, could it?

Sounds like a very ballpark estimate to me. He said the detector was on the other side of the room, so it's only going to intercept a portion of the neutrons produced, but a count of 3 seems like not enough data points to accurately measure anything. Could neutrons prefer to shoot off in certain directions if the plasma is not perfectly spherical, or are they completely unimpeded by everything?

Also, he says his fusors had 100,000 times as many fusions as Farnsworth or Hirsch, yet it doesn't seem to be that high, and even if it is, others have reached higher numbers since.

'“Just plugging it into the wall, I think I produced 105 neutrons per second,” Hirsch recalls. (His more carefully controlled trials in 1967 yielded more than 1010 neutrons per second, a benchmark that has yet to be beaten by the modern versions of this device.)'

"New fusors based on Hirsch's design were first constructed in the later 1960s. Even the first test models demonstrated that the design was a "winner", and soon they were producing production rates of up to a billion per second, and has been reported to have observed rates of up to a trillion per second."

Here's some info on measurements and calculations.

I've had to mention this many times already, but I guess that I have to mention it again. Bussard claimed 100,000 times the neutron production rate under the same well depth and driving conditions as Farnsworth. Sure, one can build a bigger fusor or put more current into it to get a higher neutron production rate, but that's not an apples to apples comparison.

As for a count of 3, yes, you'll have a very wide confidence interval, but it is statistically meaningful. If I interviewed a a million people and three reported that that they had Condition X, I could conclude with a good degree of confidence that Condition X was not a one-in-a-billion event. -- Rei 16:41, 30 November 2006 (UTC)

Aha! — Omegatron 21:23, 30 November 2006 (UTC)

I think that's a pretty decent layman's description there. I'm not a fusion expert, but I do have a background in radiation detection. The 3 neutrons seemed odd to me as well, but then I reconsidered the type of experiment they were doing. I think fusion only actually happened over a very small time interval. Now, if you know anything about detectors, you should know that this isn't going to be easy to detect. They have 'dead time' on the order of milliseconds, so the best a detector could do is find one neutron over this short time period. It might have gotten 5 million, but you can only count one. Furthermore, I expect that they did have multiple detectors and all at a considerable distance. Let's say they had 3 detectors that could detect one neutron each, this indicates a fusion rate of some certain value or above. The exact reverse calculations of figuring how many neutrons were ejected for those 3 detected neutrons would be a nightmare, but I imagine they did it.

None of the charts in the video are legible. I would like to just see the charts he put up in the video.

I already wrote to the address listed on fusor.net and asked for copies of the slides or images. No response.

I guess we have to wait for the papers to be published, though he said he already published a summary for the International Astronautical Conference proceedings. Why can't I find it?

The abstract is available at http://www.iac-paper.org/user/download.php?id=4338&type=abstract&section=congressbrowser Chandon 06:09, 4 December 2006 (UTC)

Still this justifies an article because I believe that even hoaxes should be documented.

It's our duty to report neutrally on anything notable, regardless of whether it really works, is a hoax, or is a good idea that fails to produce good results. — Omegatron 13:51, 30 November 2006 (UTC)

If I were going do a hoax, I wouldn't say I got four tests each with just a few neutron counts over less than a millisecond each. I'd say I ran ten seconds, and got enough counts to be scarry. And I wouldn't stick hard-to-read scanned paper plots in my report, I'd dummy-up some nice looking plots with Excel. Bussard has laid out the truth, in admitedly hard-to-read-form, as to just what data those runs produced. And the man was born in 1923 ... he's not trying to get rich, he just wants to be sure this thing is on track to get built while he is still around. He would be happy to turn the thing over to someone both qualified and committed to it. I worked on the project for over 5 years. Tom Ligon 162.84.67.130 21:20, 11 January 2007 (UTC)

From [4] Neutrons produced from the D-T reaction are emitted isotropicly (uniformly in all directions) from the target. Neutron emission from the D-D reaction is slightly peaked in the forward (along the axis of the ion beam) direction. The source described here is a commercial neutron source that accelerates ions which hit a solid target. Since the ions in the fusor are pretty much going in all directions then the distribution should be isotropic even if the plasma itself is not symmetrical. Paul Studier 20:47, 30 November 2006 (UTC)

As for 3 neutrons being significant, I would have to know the details of the detector. Did they detect the neutrons only during the quarter millisecond that the plasma was operating, or over a much longer time period? What is the background rate from cosmic rays, etc. for the time period? As I recall, neutron detection was controversial with both cold fusion and bubble fusion. This thing is smelling like a hoax to me. I would be very interested in seeing the slides. Paul Studier 20:56, 30 November 2006 (UTC)

The few neutrons in each of the four tests were all detected during the sub-millisecond period when the remaining instruments show a deep potential well exists. As the background count of the counters was down to a few counts per minute, consistently getting several counts per test on four tests in a row, is highly significant. The counters would have been over a meter from "the action" due to chamber diameter. If he used the counters I set up, I went to exceptional lengths to shield them against stray counts due to electrical discharges. -- Tom Ligon

changing from a cubic construction to a polyhedral one.

A cube is a polyhedron... — Omegatron 10:39, 3 December 2006 (UTC)

More references:

Bussard, R. (1991). Some Physics Considerations of Magnetic Inertial-Electrostatic Confinement: A New Concept for Spherical Converging-Flow Fusion. Fusion Technology, 19(2), 273-293.

KRALL, N. (1992). The polywell™: a spherically convergent ion focus concept. Fusion technology, 22(1), 42-49.

Robert W. Bussard's Legislative Proposal to Congress

[edit] Images from the paper

These are covered under fair use.

(Images placed in article.)

The diagrams in the paper, are, unfortunately, completely illegible. I'm not sure what I think about that... — Omegatron 20:26, 14 December 2006 (UTC)

Dr. Bussard no longer has an office staff to help him make pretty reports. He still tends to be an overhead-projector/photocopier kind of guy, and may not tend to use the latest and greatest computer graphics. But the data presented are shots of fairly raw material. If he were faking this, he'd have claimed 10-second runs with 10 billion fusions detected, and we would be wondering why nobody was killed. -- Tom Ligon

[edit] Losses

For the fusor: "Without the motion of electrons and magnetic fields, there are no synchrotron losses and low levels of bremsstrahlung radiation."

But... the polywell uses magnetic fields to redirect electrons. So wouldn't it suffer from these losses? — Omegatron 15:23, 18 December 2006 (UTC)

There are few that doubts that these devices do fusion, resulting in production of a lot of neutrons, but we have had that on some level for many years. What miss are the principles and math (rather than just the pictures, remember Lord Kelvin on numbers....) to show how they plan to meet the Lawson criterion and represent a leap change in sustainable net energy output. If not it is just a better "steam engine". The polywell seems to have some potiential in the area of recirculation. But unless they have some novel underlying theory; bremsstrahlung will still drain the energy of the fuel and ash ions. Somewhat simplified bremsstrahlung happens as moving charged particles form dipoles that change orientation and length which results in the emission of electromagnetic radiation. Unfortunately it does not matter what particles move as long as there are relative speeds. At fusor energy levels, heavy ions are not a problem in themselves, but electrons are a real pain. As an p-¹¹B enthusiast myself it would interrest me immensely e.g. to see some novel electron draining or shielding principles, rather than the plumbing equipment and the conspiration that is hinted here.Haade 15:41, 26 December 2006 (UTC)

[edit] Magnet arrangement?

The article notes "Later designs began spacing electromagnets, reducing the metal surface area, and most critically, changing from a cubic construction to a polyhedral one.". When I look at the images of the devices, even the modern ones, they all seem to have a cubical arrangement. What's the story here? Maury 13:32, 5 January 2007 (UTC)

Having built and run a couple of them for Bussard, I can tell you why they are cubes: Cheap, compact, and good enough. He would like to build WB-8 as a higher order, which I believe is a dodecahedron, or more specifically a truncated dodecahedron. All of the magnets face the same pole in in all forms of the Polywell (r). That essentially means the field direction on all faces are in, and all corners are out, and this constrains the valid configurations. I have corrected this and a few other points in the main WIKI.Tom Ligon

Ok, well if they are all cubes, which I think is what you're saying, why does the quote state they aren't? Is there another version of the device that was built that is not referenced in the article? If so, we should add it! Maury 20:26, 11 January 2007 (UTC)

Why did he say it needed an even number of faces? — Omegatron 18:43, 11 January 2007 (UTC)

Must be a mis-quote. I can guarantee you that ever single Polywell (r) built so far is a cube, from HEPS to WB6, there are photos of most of these in the Google talk and his October paper, and I've never seen anything to the contrary. When I first read the Polywell Wiki, it definitely had the error, plus a few other minor glitches, which I've corrected. The reason he wants to build WB7 and WB8 is to compare two comparably-sized machines, one a cube, one a dodecahedron, to determine if the higher order (and presumably more spherical) machine works enough better to mess with it. He did discuss possibly making a MPG machine as a dodecahedron, and I built a paper model to look at the idea, but I see no evidence it was ever built.

As for the geometry, think of these donut magnets ... each a copper coil, with a particular direction of magnetic field thru the hole in the middle. Assemble all of these into a regular polyhedron, each with the field in the hole pointed the same direction, let's say all with N in. The fields encircle these toroids, so around the periphery of the magnets, N points OUT. The working geometries are all forms in which the central holes are IN, the truncated corners are OUT. So if you inject electrons on one face hole, they'll circulate to go IN face holes, OUT corners. I have not personally worked out all the geometries that will do this, but the truncated form of the equilateral pyramid, the cube, and the dodecahedron definitely do it neatly. --Tom Ligon 162.84.67.130 00:01, 12 January 2007 (UTC)

[edit] Seventh power?

Has Bussard rigorously establshed that holds valid all the way to power outputs 10^7 times greater than are seen in the polywell models tested so far?--207.245.10.222 23:41, 7 January 2007 (UTC)

The actual model is B^4R^3 for rate of fusion, and B^4R for power gain. (and if someone wants to clean up my math coding, be my guest). He presumes, based on his design experience, that B will also increase with R. In fact, once he gets up to magnets of 1.5 meter radius or so, liquid helium superconductors become a viable option, and at that point the scaling may get a LOT better. Tom Ligon 162.84.67.130 00:01, 12 January 2007 (UTC)

I assume that when density is high you can do a lot in a small volume, is this part of what drives the high ratio as well?

This is getting a little out of my depth. I watched him do the calculations a few times, but the only way I could honestly say I could totally follow them is if I videotaped these sessions and then studied them for hours or days. There are a few references associated with this Wiki to papers before the publication blackout was imposed that may shed some light. I've not gone into the math-heavy ones myself because I really don't have the skills in that area, but papers on the subject by Nick Krall, one of the best plasma physicists who ever walked or breathed, may be enlightening. If, in fact, Dr. Bussard does finish that big paper someone discussed, 150 pages or so, it will be intended for peer review and should pretty rigorously detail the scaling issue, and answer other questions.

I can say with high confidence that none of the math involved is some kind of wierd physics. Its all straightforward stuff, most of it found in the NRL Plasma Formulary, a favorite reference of plasma physicists. I could recognize all the formulae, but I doubt I could reconstruct the system on my own. A good plasma physicist, taking a perhaps skeptical but honest look at the problem, could likely reconstruct the models, in time. This might take years of work to get all the details, though, and I hope the detailed work is presented before then. Tom Ligon 71.114.3.132 17:04, 13 January 2007 (UTC)

Years? If the physics is truly that complicated, how can anyone be certain that unforeseen complications do not occur somewhere between the existing models and energy break-even? --216.13.72.151 23:07, 15 January 2007 (UTC)

The only way to know for sure is to build it. Tom Ligon Tomligon 23:00, 16 January 2007 (UTC)

[edit] Lawson criterion

Has Bussard mentioned confinement time for either electrons or ions or energy? Has he mentioned the density or temperatures? How close is he to the Lawson Criteria? It would seem to me that the triple product n_eTτ_E would not improve with size because the electrons escape as they change direction. This is why mirror machines fell from favor decades ago. Paul Studier 00:11, 16 January 2007 (UTC)

A Polywell MaGrid will beat the pants off any simple mag mirror, although they do have things in common. Mag mirrors have horrid cusp losses, and the MaGrid recirculates any electrons lost to the cusps. And the magnetic confinement is electrons, not ions (which would be enormously harder). The MaGrid is the anode of a diode, with the electron emitters at about the potential of the outer walls of the machine. The electrons only want to hit the MaGrid, and the magnetic field greatly delays that. The grid behavior makes recirculation possible, the WiffleBall factor makes it trap sort of like a mag mirror but better. I can tell you that WB-6 is estimated to hold on to the electrons for on the order of 100,000 transits of the machine, and they stay at very high kinetic energy (which makes them make a potential well for the ions).

I have not seen the ion lifetimes but it is probably surprisingly high. That will depend on the density. Too high, you swamp out the ability to drive the machine and have excessive unproductive collisions, too low and the fusion rate drops (although ion lifetime is higher at low density, as this gridless electrodynamic potential well is nearly ideal for confining them). However, the fact he got it to run with such a simple puff-gas system to inject deuterium suggests the "sweet spot" is pretty large. I have little to offer that would apply directly to Lawson's criteria of temperature, density, and confinement time in a plasma in thermal equilibrium. That's not what Bussard's machine does. Something more or less equivalent goes on ... long ion trapping in a deep potential well, maintaining high peak kinetic energy as they dynamically recirculate, and high density at the point of highest, or nearly the highest, kinetic energy. That's supposed to be the easy part in this device, once the cost of hanging on to high energy electrons is dealt with.

WB-6 was no-where close to breakeven. You can get a hint of how far off by realizing the WB-6 radius was around 0.15 meters and he thinks he needs 1.5 meters to hit breakeven. While the actual output scaling is B^4R^3, his working assumption is evidently that B will rise in proportion to R, so he generally expects the fusion produced to go up as R^7, and power gain to go up as R^5. From that, I leave you to whip out the calculator (or a napkin to count the zeros, actually) and draw your own conclusions. But the point is, he doesn't think we need to sneak up on this by building 10 machines over the next 40 years, trying to marginally improve each one with theta pinches, etc. He thinks we can go straight to the proper size and it will either work or come darned close to it. And if it comes up short, a very little additional scaling up ought to work. The great thing is, this doesn't make some open-ended project that goes on for half a century. The cost of the full-sized machines is, frankly, cheap if they have any significant chance at all of working, and it should not take very long to build one at the required size. The thing would be far smaller and simpler than ITER. Frankly, I see no reason we can't support ITER and this too. Why should ITER feel threatened? Would they be afraid of it succeeding? They should be overjoyed. All those guys have the skills (after dethermalizing their fusion education) to build these things. They wouldn't be out of jobs.

We tend not to think so much of "temperature" in IEC machines, but the drive volts were 12.5 kV and the well depth about 10 kV on WB-6. That puts the kinetic energy of the deuterons at up to 10 keV (11604 K/ev x 10000 eV, or on the order of 110-120 million degrees K). But remember that this is no Maxwellianized thermal machine. Virtually all the deuts meeting in the middle are at the same kinetic energy, instead of just a few at the tail of a distribution, and there are a lot of head-on, or close to head-on, collisions possible. Also remember, it is velocity, not KE, that actually figures in rate of fusion, and head-on collisions hit like 4x the kinetic energy (i.e. twice the velocity, and KE goes as 1/2 m v^2) of either particle would do against a stationary target, as far as rate of reaction goes. BTW, that's not a violation of conservation of energy, its just that KE (moving to stationary frame) is the lookup-value for fusion cross-sections. Tom Ligon Tomligon 02:11, 16 January 2007 (UTC)

I think what most of us would like to know is some general explanation how you keep those atoms at the same kinetic energy. Even for reactions with a large cross section, shouldn't off-target collisions dehomogenize the kinetic energy levels and flush efficiency down the toilet? How do you get those atoms out of the reactor without losing too much energy? You don't have to give us nobel prize worthy answer, we'd just like to have *some* idea how this concern is addressed. 82.135.66.148 11:24, 6 February 2007 (UTC)

On each pass, as the ions approach the MaGrid, their kinetic energy and velocity drop to near zero. This makes them bunch up. In a properly-run machine, this is the only zone where the fuel ions have a condition of thermal equilibrium. In this zone, they Maxwellianize back to a low average kinetic energy. The collision crossection for this is supposedly quite high in this region, and they equalize back out on every pass. I belive Bussard mentions this in both the Google talk and the October 2006 paper, "The Advent of Clean Nuclear Fusion", page 13, second paragraph.

As soon as they leave this region, they accelerate back toward the center of the machine, a zone where density is low. As they approach the center, the odds of a head-on high energy collision go up dramatically (optimum for fusion). In the very center, collisions are from all angles, but at high energy, and high density. The ions spend about 1/1000th of their time in this high-density region, and generally don't experience enough scattering that the mechanism above can't "anneal" it out. Tom Ligon 162.84.67.130 18:33, 6 February 2007 (UTC)

[edit] Award

Looks like Bussard has won an award for the Polywell from the International Academy of Science! I have added the reference to the article.JulesVerne 13:30, 5 March 2007 (GMT)

There are several organizations with the same name, and the consensus around here seems to be that this award is not very important. See Talk:Robert W. Bussard#Outstanding Technology of the Year Award - 2006. — Omegatron 19:24, 6 April 2007 (UTC)

[edit] What gives?

It sounds like he has given a talk at Google, and also says, "We are probably the only people on the planet who know how to make a real net power clean fusion system, and we are out of support!" [5] So why is this not being funded? Perhaps this discrepancy should be noted in the article. --Remi0o 12:33, 7 April 2007 (UTC)

Because it is basically a Magnetic mirror machine. The concept was eventually abandoned because it proved to be impractical to maintain the necessary non-Maxwellian velocity distribution. I am tempted to add the category Pseudophysics. Paul Studier 22:21, 7 April 2007 (UTC)

Saying that the polywell, whose configuration and principle of operation is very different from a magnetic mirror, is a magnetic mirror, and then saying that, because you said they are the same, it's fringe science, even though magnetic mirrors aren't fringe science, is, at best, original research. Removing category. Kevin Baas^talk 22:49, 7 April 2007 (UTC)

How about the quote from the article "We are probably the only people on the planet who know how to make a real net power clean fusion system, and we are out of support!" So he knows more than all of the people at the big fusion experiments including the folks building ITER. Certainly sounds like someone out of the mainstream of science to me. Personally I think it deserves a pseudophysics category, but I will only put back the Fringe science category. Paul Studier 23:23, 7 April 2007 (UTC)

"Fringe science is a phrase used to describe scientific inquiry in an established field that departs significantly from mainstream or orthodox theories." -The Polywell, besides not being science (it's engineering), is based off of mainstream scientific theories. The polywell is engineering, not science. And that's what he's talking about when he says they know how to do it.

Regarding Maxwellianization, this is how i see it: the well establishes a relationship between the ions distance from the center and it's radial velocity. It's velocity perpendicular to it's radial velocity is essentially an angular velocity. So let's split this up into radial and angular velocities:

angular velocity: Assuming for a moment that the angular veocity for each ion is mantained (inertial), as the ion gets closer to the center the angular velocity's contribution to the kinetic energy decreases, such that when it's in the center it is exactly zero. (because a ball traveling in a circle of radius r at angular velocity 2pi is traveling with linear velocity 2pi*r.) So as ions approach the center, their angular velocity components become non-maxwellian, such that at the center they are all exactly the same: 0.

Now, dropping that assumption, the rule still applies, because it's a law of geometry (translation of coordinate systems). However, we add in maxwellianization of the angular velocity, which will make their angular velocities approach an average, with a normal distribution. That average, since as many will be going clockwise as counterclockwise, is zero. It is only a matter of what the standard deviation of the normal distribution is. Or, more precisely, how fast the standard deviation increases or decreases with respect to the distance from the center. (This is really a crude model, because they do not actually linear velocity perpendicular to their radial velocity as they go away from the center. their angular velocity decreases. the trajectory (in two dimensions) would look more like a polar rose or trefoil knot.) in any case, it seems to me that maxwellianization will tend to reduce the standard deviation of their angular velocities, leading to better focus.

radial velocity: Again, starting with the simpler non-maxwellian case: because of the radial electrostatic gradient, the radial velocity of an ion will be a function of its initial radial velocity and distance from the center. To simplify this, one can combine initial distance from center and radial velocity by finding the distance from the center in which the radial velocity is zero. Thus, if they all start from the same distance from the center at wich the radial velocity is zero (disregarding that this is quasi-spherical rather than spherical), they will all have the same radial velocity at any given distance from the center.

Ideally, they all have zero radial velocity at the very outer edge of the sphere, thus giving them maximum kinetic energy at the center. this is what the polywell attempts to do by using microwaves to ionize the gas. according to mainstream scientific theory, the ionization rate will depend largely on how well matched the magnetic field strength at the point of ionization is to the frequency of the microwave radiation. Thus, since the magnetic field strength decreases as one goes towards the center, one can set the microwave frequency such that it ionizes the most at the very edge of the sphere.

So now lets take into account maxwellianization of the radial velocity component. And here is the key: potential energy does not maxwellianize. Sure, they will maxwellianize on the outside, all to the same low average velocity (and thus low standard deviation (i.e. "temperature"). But, since their initial distance from the center of the ions is all about the same (the very edge, where the gas is ionized), and their velocities (KE) are relatively low in comparison to their potential energy (the huge voltage gradient between the center and the outside), as they go toward the center they will be accelerated at the same rate, and thus their radial velocities relative to each other will stay the same. since maxwellianization is a function of velocities relative to each other, and not absolute velocities^{(throwing ice in space won't make it melt)}, maxwellianization will occur at the same rate, and their standard deviation ("temperature") will not increase as they go towards the center, even though their average KE gets much higher.

Now this doesn't take into account the fact that as ions are going towards the center, the same number of ions are going away from the center, at the same average radial velocity. So you have two sets of ions whose relative radial velocities are higher and higher as you approach the center. That is a possible source of additional maxwellianization. As I understand it, if they are flying past each other very fast, the ions going in opposite directions spend so little time at any distance from each other where inter-atomic forces would be significant that tehy don't really affect each other. So maxwellianization between inbound and outbound ions would occur at a higher rate as you get further from the center. - a maxwellianization that leads to zero average radial velocity. This causes the ions' "distance from the center at which their radial velocity is zero" to approach "far from the center" quicker than it approaches "close to the center". Leading towards the ideal condition mentioned earlier.

That's all very rough. Forgive me: I don't really know what I'm talking about. 69.131.30.74 00:59, 8 April 2007 (UTC)

I don't quite follow all of this but I will think about it. Whether it is true or not, and whether this is how Polywell is really supposed to work, it is science that is quite a bit different than the mainstream science that led to the abandonment of mirrors and the move to tokamaks. That alone should qualify it as fringe science, whether or not the thing works. Paul Studier 01:54, 8 April 2007 (UTC)

• This is not a magnetic mirror.
• Bussard was Assistant Director under Director Robert Hirsch at the Controlled Thermonuclear Reaction Division of what was then known as the Atomic Energy Commission.
• They founded the mainline fusion program for the United States: the Tokamak. Bussard later abandoned this approach in favor of the Polywell approach.
• And was funded by the Department of Defense.
• And later granted an award for it by the National Academy of Science. [6]
• They abandoned ICF as a road to fusion power as well, but the HiPER isn't considered fringe science.

Kevin Baas^talk 02:28, 8 April 2007 (UTC)

How is this not a mirror? One could travel through the exact center of the face of the truncated cube and ones motion would be parallel to the magnetic field lines. See page 16 of [7]. Any electron that starts in the center and goes towards the center of the face will escape. If there is something that prevents this, then this is new science not generally accepted by the plasma physics community. Paul Studier 04:36, 8 April 2007 (UTC)

And later granted an award for it by the National Academy of Science. [8]

That appears to be an inconsequential organization. Otherwise good, though.

Lots of non-Tokamak fusion devices have been proposed, built, and abandoned, but that doesn't make them pseudoscience. Be skeptical, but not pathologically skeptical. — Omegatron 21:15, 8 April 2007 (UTC)