H-B11 inertial fusion: LENR that maybe works :)

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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tomclarke
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H-B11 inertial fusion: LENR that maybe works :)

Postby tomclarke » Tue May 10, 2016 2:59 pm

So this is of course not LENR, except technically because the energy needed for ignition is only 30kJ. It has G. Miley as co-author on some of the papers which I find worrying, but it is such a very very neat idea, and breaks no normal physics, I'd like to find a serious critique of it.

Apologies if it has been discussed here before (I bet it has) but I could not find it.

The person doing this is Hora, and there are several papers which do get eventually published - the journal I note is CUP (good) impact factor 1.3 (less good) but then for something so speculative you maybe don't get a lot of mention in Nature.

https://arxiv.org/ftp/arxiv/papers/1510/1510.02465.pdf

Let me summarise the elements of this claim:
(1) H-B11 fusion when intertially induced from ultra-short laser pulses has a much higher cross section than would be expected
(2) The reason for this is additional reactions caused by the emitted alphas adding energy to nuclei, when this happens multiple times it can dramatically increase the chances of additional fusions. An avalance effect.
(3) high power petaWatt ps lasers are now available to drive the initial fusion
(4) nW lasers can be used to make of order 10kT transient magnetic fields
(5) If the above inertially induced H-B reaction happens in 10kT the fusion product alphas are contained by the magnetic field (small gyroradii) in a small enough volume to turn the avalanche effect into effectively a chain reaction (for the time that the magnetic field exists)
(6) End result: 30kJ ps laser energy in => GJ energy out from a cylindrical H/B11 sample. Aneutronic (obviously). Could be pulsed at 1 per second etc.

Anyone else think this idea, whether it works or no, is very very cool?

Crawdaddy
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Re: H-B11 inertial fusion: LENR that maybe works :)

Postby Crawdaddy » Tue May 10, 2016 4:23 pm

The first author is also a cold fusion guy.

tomclarke
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Re: H-B11 inertial fusion: LENR that maybe works :)

Postby tomclarke » Tue May 10, 2016 4:28 pm

That is more worrying - but it is not exactly cold! PetaWatt lasers certainly induce fusion, the issue is whether this avalanche effect is real an large enough.

Crawdaddy
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Re: H-B11 inertial fusion: LENR that maybe works :)

Postby Crawdaddy » Tue May 10, 2016 5:52 pm

tomclarke wrote:That is more worrying - but it is not exactly cold! PetaWatt lasers certainly induce fusion, the issue is whether this avalanche effect is real an large enough.


This is all well and good.

The technical challenges of this design are pretty significant. The alignment, laser efficiency, and contamination problems of the NIF are inherent in this proposal.

One thing you do not want to do inside an optical instrument is vaporize a target (such as the magnetic field generating plate assembly in the document) once a second.

I think the tri-alpha strategy is probably better. Especially if they have found some low energy peaks in the cross section data that isn't in the existing low resolution literature.

PNeilson10
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Re: H-B11 inertial fusion: LENR that maybe works :)

Postby PNeilson10 » Thu May 12, 2016 12:06 pm

Fusion chain reactions are cool and change the assumptions.

The overall reaction rate is no longer determined by simple cross sections. Its determined by the chain reaction rate.

This would be the case for all variations of the so called LENR reactions. They are not LENR at all. No low energy anywhere. Just standard energy, low probability reactions. Taking place in the solid state plasma in the lattice. Once the low probability event occurs you then have a standard chain reaction. If the lattice is well prepared, the chain reaction is sustained. With sustained chain reactions you get a large over all reaction rate from a low energy input.

Maintaining the chain reaction is more important than the initiation of the chain.

Boron + p yields three alphas splitting up 8.7 MeV for 2.9 MeV each

Lithium 7 + p yields two alphas splitting 17.2 MeV for 8.6 MeV each

Fewer higher energy alphas vs 50 % more but lower energy alphas. Which yields the better chain reaction rate? How do you prepare the lattice to best sustain the chain reaction? Which reaction is easier to initiate at low probability energies?

D Tibbets
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Re: H-B11 inertial fusion: LENR that maybe works :)

Postby D Tibbets » Thu May 12, 2016 12:55 pm

Very quick compression of a fusion substrate may produce a plasma of such density that the few alphas produced would not escape but thermalize with the fuel and drive a progressive heating of the plasma till the fuel was depleted (or some useful subset). This chain reaction concept seems simple. George Miley has lent his name to a lot of fusion papers. He may promote somewhat optimistic schemes, but I have never heard of him making fraudulent or unknown physics claims to promote his ideas.

Very fast laser pulses could quickly compress a plasma, perhaps much better than a sluggish NIF type laser compression. It seems some European effort was directed at using faster laser pulses in a NIF type compression and heating scheme that at least in theory would require substantially less laser power. I don't know the status of this effort.

A possible complicating factor is the symmetry of the compression. In the DPF theta pinch the compressed plasma is in the form of a magnetic plasmoid that quickly generates opposing positive ion and negative electron flows in opposite directions that exits the plasmoid. This presents opportunities for energy harvesting, but also limits the fusion product thermalization with the plasma. The balance of the often competing effects governs the system. Until these processes are understood and successfully harvested/ worked around, it is difficult to predict success. I think any magnetic field generated would not be a monopole (obvously), so there has to be some non spherical deviations that may be small but very important for containment issues.

Also, even with particle containment, energy loss through radiation may be daunting- Bremsstrulung X rays, gyrotron x-ray radiation (may be more profound than Bremmstruhlung at those B field strengths) and side reaction gammas (in p- B11 fusion) may limit heating to a modest to profound degree.

Dan Tibbets
To error is human... and I'm very human.

tomclarke
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Re: H-B11 inertial fusion: LENR that maybe works :)

Postby tomclarke » Wed May 18, 2016 5:39 pm

I've looked a bit more at this idea. I still think it is very cool. It is the sort of thing that might just work - new tech because we have not had petawatt lasers for very long.

But the evidence for two of these steps is a bit dubious:

(1) the avalanche effect. It seems that ns lasers (much lower power) can provide more avalance than petawatt ps lasers. This breaks the proposed mechanism and makes it more likely this is something else rather than fusion chain reaction. Still, worth following.

(2) the cited evidence for ultra-high laser-induced magnetic fields is very poor. The authors themselves agree the (indirect) calculation of very high fields is not consistent with other evidence. But, ultra-high fields are obtainable via pinches, so maybe...

Tom

PNeilson10
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Re: H-B11 inertial fusion: LENR that maybe works :)

Postby PNeilson10 » Wed May 18, 2016 6:18 pm

Too much gas plasma thinking vs. too little solid state plasma work has been done.

In a gas plasma - particle trajectories are random

In a particle beam impacting a solid target experiment that measures the reaction cross section, the particle beam is unaligned with the solid lattice.

In a solid state plasma - the reaction take place in the regular and repeating field structure created by the lattice. The product of a reaction deep in the lattice may have a non-random trajectory due to the structure of the fields surrounding the reactants. Furthermore, the ponderomotive force may be channeled by the lattice. Any non-random trajectory will yield a cross section that is different than a particle beam cross section. If some sort of strong self alignment is created in the lattice the reaction cross section may be much higher (or lower) depending on the lattice material.

I wonder how long it will be before any experiments look for this potential effect.


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