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I used to work in fusion, the engineering problems that need to be overcome before we have a working commercial reactor are tremendous. Also I tend to believe with some older critics that a tokamak will never be commercially viable:

http://www.askmar.com/Robert%2...

Computer modeling has been a tremendous help, but we do not have the capability to simulate a working tokamak reactor yet. We don't even have a complete understanding of plasma physics, for example modeling disruptions and ELMs in reactors can't yet be done to the best of my knowledge. Simulation generally needs very complex monte carlo models that simulate chemistry and nuclear interactions, magnetohydrodynamics (electric-magnetic "fluids"), etc.

Better magnets help shrink the size and may help reach new operational modes more easily, but this field is unbelievably slow. The current state of the art is Nb3Sn, and the material was discovered over 50 years ago. To get good magnets made from HT superconductors you're looking at a few more decades. This is one issue with the MIT arc design, the magnets required can't quite be made yet by the looks of it. Also the cables are tremendously expensive, Nb3Sn roughly $1k/m

Better materials help, but the radiation coming from a nuclear fusion reactor cannot be simulated offline to help develop new materials. Think an order of magnitude more nuetron flux than fission, but also proton bombardment and helium bubbles forming. Using a spallation neutron source may get the neutron flux, but not the proton flux etc. Best way is to try out new materials in the reactor...

We're nearing 100 years of trying to make fusion work, it's just the most difficult problem humanity has ever tried to solve. The first real attempt at building a fusion reactor was in 1938 by Kantrowitz. I am excited by these new companies in the US and UK that are going back the the drawing board and throwing out the tokamak, but I still don't see it happening in my lifetime.

The drawbacks you mention apply to rail guns, not Gaus guns. Gaus guns have serious problems of their own (most of the prototype designs aren't powerful enough, the only design I've read about that would probably have truly useful velocities requires superconducting magnets. If you read the wiki article, apparently there's serious problems with iron projectiles.)

http://en.wikipedia.org/wiki/Coilgun

http://en.wikipedia.org/wiki/Railgun

http://www.askmar.com/Massdrivers/Superconducting%20Quenchgun.pdf

On Page 6 it has an interesting table of the actual mass and physical dimensions of the accelerator. Note that muzzle energies far greater than proposed for the Navy's railgun project are possible (the smallest one is 1820 megajoule's, the navy wants a 64 megajoule railgun) but also notice the huge size and bulk of the launcher : 147 meters long.

But there's no arcing problem, and the proposed design is supposed to be reusable.

You must be talking about those EMC2 folks...

Unfortunatly, although the Navy continues to fund research into Polywell style fusion reactors, there are several big hurdles to overcome. The biggest ones (to me) are that the concept has unknown scaling constants (e.g, does a "big" version lose too much efficinecy), and they most expensive component (the magnets) are inside the reactor and get bombarded with radiation which creates and equally big material science headache as some of the alternate approaches.

Read more about it here...

Or we could just get Hydrogen-Boron fusion working, which runs at lower temperatures, and uses materials easily available on earth.

This is a killer and one of the big problems now for anything coming from space. Namely, why go to space to get something, if there's an easier, cheaper Earthside solution? I was under the impression that proton-boron fusion was harder than helium3-helium3 fusion, but that doesn't turn out to be the case (an interview with Richard Nebel on the Polywell fusion prototype project which he heads).

Question: Assuming a Polywell demonstrator works in say 3-10 years, would a developed reactor be able to burn 3He/3He, or does Polywell's performance "max out" with p/11B?

Answer: We looked at 3He/3He and concluded that the fusion reactivity was just too low. (The characteristics of 3He/3He (cross section, reactivity, Lawson criterion) are at least an order of magnitude below those for p/11B.)

You still have deuterium-helium3 which is easier (in terms of temperature and Lawson criterion), but that's less aneutronic than hydrogen-boron (due to the presence of deuterium-deuterium fusion which generates a neutron 50% of the time it occurs).

It did (more of a revival than revolution), and Dr. Bussard plans to use boron, not He-3...

Internal Electrostatic Confinement

For a non-maxwellian velocity distribution your problem is that even at optimal energies a collision is much more likely to scatter the ions than it is to cause fusion, and restoring the non-maxwellian velocity distribution will require energy (no, you don't get to violate the second law of thermodynamics I'm afraid ). For capturing X-rays your problem is to achieve a good enough conversion efficiency to make up for the dramatically increased X-ray losses.

With the exception of a few unconfirmed claims, nobody has been able to resolve the above problems (thou Bussard was quite vocal about his polywell device )


Bussard was more than vocal, his last experiments that the navy is now repeating where successful. Here's what Bussard himself had to say about the problem you mention:

Ions spend less than 1/1000 of their lifetime in the dense, high energy but low cross-section core region, and the ratio of Coulomb energy exchange cross-section to fusion cross-section is much less than this, thus thermalization (Maxwellianization) can not occur during a single pass of ions through the core. While some up- and down- scattering does occur in such a single pass, this is so small that edge region collisionality (where the ions are dense and "cold") anneals this out at each pass through the system, thus avoiding buildup of energy spreading in the ion population (Ref. 14).

In layman's terms, the Polywell design fuses ions faster than they maxwellianize, thanks to the ratio of time in core to time in edge. The full high level paper from Bussard can be found here.

Your comment that restoring the non-maxwellian velocity distribution will require energy is oversimplified. You only need to maintain the non-maxwellian distribution long enough for the ions to fuse before they maxwellianize. Thermalization in the outer edge dominates the coulomb interactions from the core more than the collisions dominate the fusion rates. Those are the conditions that allow fusion to occur faster than maxwellianization. No magic, no violation of physics, just a beneficial design that Rider and Nevins both overlooked in their assumptions.

Polywell Fusion is the future.

http://en.wikipedia.org/wiki/Polywell
http://askmar.com/ConferenceNotes/Should%20Google% 20Go%20Nuclear.pdf
http://www.youtube.com/watch?v=jmp1cg3-WDY
http://video.google.com/videoplay?docid=1996321846 673788606

Can you hold your breath for 5-10 years? That is about about how far away we are from nuclear waste free p + B-11 inertial electrostatic confinement fusion. http://en.wikipedia.org/wiki/Robert_W._Bussard http://www.askmar.com/Fusion.html It is clear to me that Bussard is the most important man on the planet at the moment. Anyone got $200 million for him to build a full size prototype? Do yourself (and the rest of us) a favour and check out his research. ps. with low cost energy you can make ethanol from low value sugar cane for 35c / litre. (if you are stuck on combustion, :-P)

is the work (also funded by the navy) undertaken by Dr. Bussard (of interstellar spaceship fame). His design for an electrostatic inertial confinement machine shows more promise than the heavy, expensive tokamak prefered by the internatinal ITER project, and has been built and tested in the lab, but not yet to an energy-return scale. The work was kept secret due to the source of funding, for the last 12 years, so it is only now that we're hearing aboutu it. http://video.google.com/videoplay?docid=1996321846 673788606 - Lecture given by Bussard at google, giving an overview of the project. 1:30 long, so if you don't have time, read: http://www.askmar.com/ConferenceNotes/2006-9%20IAC %20Paper.pdf - Summary paper, outlining the research and results so far. The real research paper is yet to be published, but that's what he's working on now.

I wouldn't be too worried about this as there are some serious national security issues that are around with more than half of all oil used in the USA coming from abroad. In this situation the U.S. Navy is one who would want to be explicitly involved with the development of a fuel source they could use for their own ships and be able to continue to fight without having to invade an oil producing country in order to merely maintain their own ships.

A major world conflict involving the USA (Iraq is not a major world conflict from this viewpoint) could easily cut off needed petroleum reserves and nearly kill off the U.S. ability to fight.

And as I pointed out, the Navy is also very interested if this might become a replacement for their own nuclear fission plants, which have been nearly the only new construction of nuclear power of any kind in the USA over the past 30 years. If Bussard's research is accurate and can achieve the real breakthroughs he is suggesting, putting one of these on board a submarine is nearly a no-brainer. That just doesn't seem to even be a remote possibility if the Tokamak design even reaches the break-through numbers that are being claimed with that design.

Also, if there is even a marginal improvement over the Farnsworth/Hirsh Fusor technology (as it seems some huge gains have indeed been made over that design), there are already practical commercial applications for even that sort of technology. The ability to create a strong source of neutrons that can be controlled with a simple electronic switch may even be useful to enhance a fission reactor if nothing else. This as a radiation source for cancer treatment may be another huge application that has nothing to do with the ability to actually "break even" and actually generate power. Current sources of neutrons tend to be spent nuclear fission reactor fuel or other radioactive substances.

The information about these reactors is already "out there", so trying to bury the information is not going to do much good. The real issue is trying to convince prominent physicists that Bussard isn't off his rocker and to critically but fairly review the existing papers that have been published about the topic. Several have been published, including this article that was peer-reviewed and published in a respected international physics journal. The references in this paper alone are sufficient to request "Freedom of Information Act" request for the rest of the research if you really want to dig into it, as well as to dig up the patents that have been filed on behalf of this fusion method.

BTW, Breeder reactor technology does work and a working plant is just 200 miles north of where I'm at (in the Idaho National Engineering Lab). The problem with breeder reactors (and finally mentioned on the CBS - 60 minutes TV "newsmagazine" about nuclear power plants) is that they produce large quantities of Plutonium at concentrations that are sufficient to build nuclear bombs with the material. Bomb grade Plutonium works just fine in a nuclear reactor, but it is so easy to "accidentally" pull some out and build the bomb that the major nuclear powers don't want to see the technology be widespread among countries that currently don't have nuclear bomb programs of their own. This is also how North Korea got its bomb material in the first place. This gets rid of nuclear waste, but that is one heck of a social cost to worry about instead that General Electric can have their own private arsenal of nukes if they wanted them and had these sort of breeder reactors. That knowledge is enough to put your tin hat back on again.