Fusion Will Never Work

[MSimon]

Next, boron fusion will produce enough neutrons to activate its structural material

Milli-curies vs curies. The danger is in the dose.

[alexjrgreen]

I'm describing what I can see in the WB7 photo...

PLEASE remember that the WB7 photo on the EMC2FDC site is a DIAGNOSTIC run. There is no fuel, only electrons and neutral He gas which gets locally excited and then radiates where it gets hit by electrons.
The glow pattern you are seeing simply tells you where the electrons go, not where the fuel goes. There is no fuel there. Glow outside the MaGrid is due to electrons impacting neutral He outside the MaGrid, not fuel ions exiting a cusp and radiating outside the MaGrid. Nothing can be learned about the behavior of the fuel from that picture.

Tom Ligon pointed out that the Helium doubly-ionizes, so there will be some ions influencing what we can see.

But assume that the photo shows us the electrons, a bit like this:



except that the electron density will be lower where the electrons accelerate near the magrid.

If an ion escapes from a central cusp, what path will it take?

[chrismb]

If an ion escapes from a central cusp, what path will it take?

The phraseology makes me think of the 'does a falling tree make a sound if no-one is in the forest to hear it?'

I guess the equivalent is "does a Polywell ion ever leave a wiffleball if there are no diagnostics to monitor it?".

[alexjrgreen]

If an ion escapes from a central cusp, what path will it take?

The phraseology makes me think of the 'does a falling tree make a sound if no-one is in the forest to hear it?'

I guess the equivalent is "does a Polywell ion ever leave a wiffleball if there are no diagnostics to monitor it?".

Art Carlson says so...

[KitemanSA]

If an ion escapes from a central cusp, what path will it take?

Straight to the chamber wall.

[Art Carlson]

I finally got time to look at the article that started this thread. The statement that caught my attention was "A self-sustained tritium fusion chain appears to be not simply problematic but absolutely impossible.", so I concentrated on Section 5.2, "The illusions of tritium self-sufficiency".

I was troubled at the outset with a number of statements that seemed to be sloppy, mostly when he introduced the tritium question as Point 4 in Sec. 5.1. For example, he seems to think that the neutrons must be thermalized before they undergo the breeding reaction. AFAIK, the breeding reactions are expected to occur with fast neutrons, not thermalized neutrons. In particular, if you are worried about boosting your breeding ratio, you should be interested in the reaction Li7 + n -> T + alpha + n, which does not consume the neutron, but is endothermic so only occurs with fast neutrons.

Looking at the substance of his argument in Sec. 5.2, it seems he is taking essentially all his information from "Prof. Abdou from UCLA, one of the world's leading experts on tritium breeding" (an assessment I am willing to accept until I have reason to think otherwise). It seems, though, that Abdou's stated conclusion is that "a small window for tritium self-sufficiency still exists theoretically" (in Dittmar's words), but Dittmar then turns around and tells us what the "correct interpretation" would have been. My conclusion on this point is that the situation is more difficult than I realized, but that there is no reason at this time to conclude that a solution is "absolutely impossible". In particular, my understanding is that if you really get into trouble, you can always add neutron multipliers like Be and Pb to get back into the green zone.

Backing up to the other three "major scientific breakthroughs" required according to Sec. 5.1, these are

• steady-state operation
• the materials problem, especially the neutron flux to the first wall
• tritium containment in light of radiation hazards and proliferation risks

Here as well, Dittmar tends to be polemic and imprecise. What he cites are real problems, but he doesn't contribute any new data or insight, and I think his summary is not even especially helpful. I short, I haven't learned anything new (except perhaps to keep a closer eye on tritium breeding).

[Axil]

Fusion and fission make a good couple; together they fill each others gaps.

Fusion-fission hybrid reactors can be viewed as sub-critical nuclear fission reactors driven and controlled by an internal high energy neutron source; the fusion reactor. Such hybrids combine the natural neutron richness of the fusion power source with the power richness of the fission source, thereby eliminating the intrinsic power poverty and neutron deficiency of these respective reactor types. Also eliminated is the somewhat marginal specific tritium breeding rates of fusion power reactor designs, the low specific fissile material breeding rates of conventional fast breeder fission reactors, and the criticality control problems of fast breeder reactors.

Specifically, the fission process produces tritium in significant amounts. There is a wide variety of light element reactions that produce a tritium byproduct. These reactions include those of oxygen, lithium, carbon, nitrogen, beryllium, hydrogen, and boron to name just a few.

The cross sections of these reactions are optimized in a liquid blanket. As the high neutron energy levels of fusion gradually decrease in the neutron thermalization process within a liquid blanket, these thermalizing neutrons will eventually hit their optimum cross section for tritium production in a constantly evolving soup of transmuting isotopes.

Because the Fusion-fission hybrid reactor is self sufficient in tritium production, any proliferation risk is eliminated. Tritium is never stored on a long term basis or leaves the reactor site and is consumed apace in the fusion reaction.

In a fission reactor, tritium production is its biggest radiation release risk. In a fusion-fission hybrid, it is its biggest advantage.

[Art Carlson]

The ultimate Q for pB11 at the resonance peak is about 22. At the cross section peak around 8.

Where does this number come from? (Not trying to make trouble, just meekly seeking information.) I suppose the fusion reactivity is for a p-beam streaming against a B11-beam (but it could possibly be for monoenergetic but isotropic distributions, or even <shudder> Maxwellian distributions). I can't imagine what you would take for the loss term (the denominator of Q) if not bremsstrahlung, but what assumption will land you at Q = 22 (or ?

It is for a no loss device only considering the acceleration energy. Beam-Beam interactions. In other words the Carnot calculation for an ideal Polywell. Reality is likely to be somewhat different.

I see.

That's not a very exciting value for Q. For example, if you can convert fusion energy to electricity with 40% efficiency, you are willing to recirculate 20% of the electricity you produce, and you can convert electricity to the energy form needed to drive your plasma with 90% efficiency, then you need a Q of at least 1/(0.9*0.2*0.4) = 14. An "ultimate Q" of 22 doesn't give you as much room to play with as you would certainly like.

While it is certainly accurate to to say that 22 is the "ultimate Q" in the sense of a strict upper limit, it does sweep an awful lot under the rug, not just bremsstrahlung. To get the full resonance cross section, you need counter-streaming p and B11 beams, but both the isotropization time and the slowing down time are shorter than the fusion time. These are classical collision processes that are easy to calculate with a mono-energetic distribution and really cannot be avoided. Next would come thermalization, but then we are quickly back to Rider's conclusion that you need some mechanism that allows you to recirculate energy between different groups of ions with a very high efficiency. If you had that - any nobody has any idea what that mechanism might possibly be - then and only then would the "ultimate Q" possibly be as high as 22.

[rcain]

just to get back to the question of 'which regime' briefly, it strikes me that both waste disposal and plant decommisioning are big items of cost and risk to factor in. i'm sure MSimon has some figuires off the top of his head. They are certainly factors that scare investors and the public alike.

So for my money, I would favour any technology that focussed on these. Notwithstanding optimal decisions on build cost, operating cost and (generating) efficiency. Oh, and we need to start building them next year, whatever they are.

What would the optimal approach/technology be, if these were the priorities?