Muon Fusion?

[joedead]

Japan Working on Muon Catalyzed Fusion and Have Plans for Achieving Advances to Commercial Power Generation....

http://nextbigfuture.com/2009/09/japan- ... usion.html






Seems like they have a long way to go, but interesting none-the-less!

[Helius]

I must be missing something. A Q=.4 would mean a tremendous boost for a fission reactor, as an Energy multiplier, and we should be falling all over this.

Why in Good's name do so many think a Q>1 is the all or nothing goal?

[chrismb]

Q=0.4 would be good, but that this is, I suspect, the 'theoretical' energy balance so far. This is the calculation based on the outright energy of the muons put into the process, not in the production of the muons. A bit like JET claiming near Q=1 for their 20MJ output per pulse, but happen to forget the 1000MJ that needs to go into creating the magnetic field.

But muon fusion research is a truly legitimate branch and is well worth further support, and monitoring. As you say, if you could make a near 100% efficient muon generator, then we're looking at a neutron generator system at 40% efficiency, which could be plenty useful enough.

[D Tibbets]

As chrismb mentioned, my very limited understanding of muon assisted fusion is the cost of the muons. They have a very short half life so can only assist in or catalize a limited number or reactions before it decays. Of course if the decay products end up producing heat at least some of the energy could be recovered in a thermal generation cycle.

How much energy does it take to make a muon? I recall ~40 MeV (though if it weighs 200 times as much as an electron I would expect a minimum of ~ 100MeV). It would have to be made in a particle accelerator. How much energy would have to be pumped into the accelerator - to produce one muon along with all the other waste (?) collision products?


Dan Tibbets

[chrismb]

Of course if the decay products end up producing heat at least some of the energy could be recovered in a thermal generation cycle.

Unfortunately, unlikely because the muons are injected into liquid or solid D or T - viz. is an operation performed at very low temperatures.

I would be curious to know, however, if higher densities could be achieved with D and T by exceeding the critical conditions (33K/14atm) and whether it is then mechanically possible to cause higher densities than otherwise occur in the liquid states. Density is one of the limiting factors, for muon reaction efficiency, because if you increase the chance of the muon interacting with [further] D and T then so you increase its capacity to fulfil its full potential in its short life. So, figure out a way to get really high denisty deuterium (without ionisation, i.e. not a plasma), and muon injection suddenly becomes a very interesting option indeed.

[Skipjack]

I was thinking about posting this her. But then I did not think it was thaaaat great an idea for the problems mentioned by some here.
I just cant see how this could ever be efficient.

[kunkmiester]

They do thermal cycles at lower temperature--there's a thing that runs on the ocean, pumps propane or something down a hundred feet or so to the colder section. You really just need enough temp difference. I'm not sure a cryogenic thermal cycle would be feasible.

[chrismb]

They do thermal cycles at lower temperature--there's a thing that runs on the ocean, pumps propane or something down a hundred feet or so to the colder section. You really just need enough temp difference. I'm not sure a cryogenic thermal cycle would be feasible.

that is true, but in this case the refridgerated deuterium is there by mechanical (energy-input) means. We've got plenty that is 'hotter' than liquid deuterium, there's no work benefit that can be recovered from this situation.

[D Tibbets]

Shows graph of muon catalyzed reaction rates:

http://www.muonfusion.com/


And, the wikipedia article mentions the energy cost of the muons, along with time scales, muons sticking to helium nuclei problems, etc.


http://en.wikipedia.org/wiki/Muon-catalyzed_fusion

The picture in the Japanese research shows the muons being recovered from the alpha/ helium nuclei and recycled. How they plan to do this in the timeframe ( a few microseconds) of the muons lifetime would be challenging. If the muons are not recovered, they are lost at about the same rate as the decay half life. One muon might catalyze 100 D-T fusions (at liquid hydrogen temperatures) before decaying, and helium absorption might remove the muons at the same rate, thus allowing only ~ 50 fusions per muon. Recovering the muons would restore the fusion rate to ~ 100 per muon, but again how can this be done in short timeframes? Presumably the alphas produced would tend to remain in the liquid hydrogen mix, unless the volume of the liquid was so small that the alpha could escape before being cooled or otherwise tied up in the liquid hydrogen mix. The helium absorption of the muons would presumably be dependant on the concentration of the helium nuclei/ alpha particles present, and this would presumably be dependant mostly on the fusion rate. I would think that the numbers of alphas present would be extremely smaller than the hydrogen (D,T) unless the fusion rate was so high that the liquid hydrogen would quickly vaporize unless under tremendous pressure (and cooling input). I assume the alpha particles must have a tremendous appetite for stealing electrons/ muons in this very cold liquid medium.

I could see the neutrons produced escaping the local liquid hydrogen medium, then being captured in a neutron absorbing blanket to produce useful heat. But if you are getting a few megawatts of heating energy from the neutrons, you are also getting ~ a few hundred thousand watts of alpha heating energy deposited locally. How do you keep the hydrogen chilled? Even if you used tiny capillaries with thin walls so that most of the alphas escaped the liquid hydrogen medium before being absorbed, the energy would be deposited in the nearby structure/ insulating layers/ cooling helium, etc. If a vacuum surrounds the hydrogen filled capillary tubes, the nearby heating might be decreased, but any alpha heating of the liquid hydrogen (even if it is only 1 % of the alphas) would then be harder to extract due to the vacuum layer.

For that matter, how do you prevent excessive heating of the liquid hydrogen with the born hot muons? Any cooling of the muons would presumable eat into their aviable lifetimes. I could see the hot muons not being a problem for laboratory tests, but at the densities needed for practical power production, the introduced heat might be a show stopper (?).

If the system could operate in a warmer, very dense hydrogen gas (but below ionization temperatures) I could see some of the thermal conflicts being resolved. If the system worked in a plasma, it would be even easier, and also benefit from significantly higher fusion cross sections. The lower aviable densities in a plasma my also be a show stopper( it takes the muons too long to get from one hydrogen molecule/ ion to the next). Some of the muons would be free, but would the close approaches to D or T ions provide some benefit compared to the muons being tied up in D,T atoms, or D-T molecules? Also, in some Fusors the neutral gas content might be in the majority, and fusions would be dominated by ion- neutral collisions. Would this provide enough boosting to make muon production and recycling practical? The muon loaded hydrogen gas would have to be made and injected very fast before the muons decayed. Or perhaps the muons would be injected, and recombinations could provide the target neutral atoms (or self fusing D-D or D-T muonic molecules). Again, the recombinations would have to occur very fast, before the muons were lost.

Dan Tibbets

[chrismb]

There seem to be a few misunderstandings there, Dan. Muon lifetime is not affected by their 'temperature' (whch is a bulk property) and the idea would have to be to get the fast particles (neutrons and alphas) out to generate a thermal high somewhere other than the reaction mass.

As I mentioned, you cannot make a 'plasma' out of muon atoms, it's non-sensical. A plasma is the ionisation of atoms, but the idea with muon fusion is that you are forming atoms.

[MirariNefas]

About 10,000 muons reach every square meter of the earth's surface a minute; these charged particles form as by-products of cosmic rays colliding with molecules in the upper atmosphere. Traveling at relativistic speeds, muons can penetrate tens of meters into rocks and other matter before attenuating as a result of absorption or deflection by other atoms.

—Mark Wolvertron, science writer, Scientific American magazine, September 2007, page 26 "Muons for Peace"

Okay, forget solar panels, cosmic rays are where it's really out. We'll build muon catalyzed fusion surfaces, and we'll call them cosmic panels.

[D Tibbets]

There seem to be a few misunderstandings there, Dan. Muon lifetime is not affected by their 'temperature' (whch is a bulk property) and the idea would have to be to get the fast particles (neutrons and alphas) out to generate a thermal high somewhere other than the reaction mass.

As I mentioned, you cannot make a 'plasma' out of muon atoms, it's non-sensical. A plasma is the ionisation of atoms, but the idea with muon fusion is that you are forming atoms.

I'm not claiming that temperature effects the muon halflife. What I'm speculating on is that the muons, once produced are traveling at millions of eV speeds, and will have to be cooled both to prevent then from heating the liquid hydrogen, and because they will have to be slowed before they have a chance to be captured into an atom. This will require some finite amout of time to do, and this could decrease the time they are aviable in the hydrogen soup before they disapear.

In a plasma the muons would be free flying. Do to their semirandom motions in the plasma (free ions, electrons, and muons) occasionally they will pass very close to the nucleus of an ion( maby even completing half an orbit before departing if the plasma is cool enough). Compared to a muonic atom, the time spent in this neighborhood would be much less, but the temperature dependant fusion crossection would be much greater. What I was wondering was if the balance would come close to the reaction rate in the cold liquid hydrogen. In a Polywell type reactor, the muons would be spending most of their time near the center (because they are slow here, they may be even more concentrated in the center compared to electrons due to thier greater inertia). Meanwhile, due to confluence, the ion density would also be greater in the center. So the chances of the muon passing very close to a nuclei would be significantly greater than in a thermalized plasma like a Tokamak. Also, the hot ions would be approaching each other much more frequently, so that if a muon happens to intervene, there could be a lot more oppertunities for fusion. This assumes the increased speed of the ions compensates for the increased density of the sluggushly moving liquid hydrogen molecules. If the formation of muonic D-T or D-D molecules is required for most of the reactions as opposed to a muonic molecule coming close to a different molecule. then my speculations about plasmas are moot.
Mouns in a Polywell would not be contained as well, but since thier halflife is only a few dozen transits it would be irrelavent. Also, the problem of alpha's capuring a muon would be reduced.

Dan Tibbets

[D Tibbets]

About 10,000 muons reach every square meter of the earth's surface a minute; these charged particles form as by-products of cosmic rays colliding with molecules in the upper atmosphere. Traveling at relativistic speeds, muons can penetrate tens of meters into rocks and other matter before attenuating as a result of absorption or deflection by other atoms.

—Mark Wolvertron, science writer, Scientific American magazine, September 2007, page 26 "Muons for Peace"

Okay, forget solar panels, cosmic rays are where it's really out. We'll build muon catalyzed fusion surfaces, and we'll call them cosmic panels.

Problem with this is that if a square meter of material is loaded with deuterium and or tritium and then almost all of the muons are captured and quickly transferred to subsequent hydrogens as the fusion progresses, each muon would ideally result in perhaps 200 fusions. If 10,000 muons per min ( ~ 160 muons per second) hit your 1 M^2 target, you could get ~ 30,000 fusions per second. You need about 1 trillion fusions per second to get 1 Watt of power. So your 1 M^2 panel would be delivering ~ 0.00000003 Watts of power. This is a little less than the output from a solar panel

Dan Tibbets

[Art Carlson]

In a plasma the muons would be free flying. Do to their semirandom motions in the plasma (free ions, electrons, and muons) occasionally they will pass very close to the nucleus of an ion( maby even completing half an orbit before departing if the plasma is cool enough). Compared to a muonic atom, the time spent in this neighborhood would be much less, but the temperature dependant fusion crossection would be much greater. ...

Are you talking about a three-body reaction?! You can wait forever for that to happen.

(edit: repaired broken quote)

[chrismb]

? I think that's Dan's quote...