Review article on beam/accelerator driven fusion?

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Sven Andersson
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Review article on beam/accelerator driven fusion?

Post by Sven Andersson » Sun Jan 29, 2017 8:19 pm

You can accelerate nuclei of any light element and direct it to a target, that is usually solid. The first experiment of such a kind, was done with accelerated protons against a lithium target, I think. Thousands (or perhaps even tens of thousands) of such experiments have been done.

The result of the experiment is a curve of the number of fusion reactions (or the cross section of the reaction) as a function of energy of the incident particles.

I'm looking for some sort of review article on this. Or perhaps a monograph. Old or new doesn't matter.

This info may exist in data bases at IAEA's site, but how do you read them? I prefer to read what someone in the know, has written.

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Re: Review article on beam/accelerator driven fusion?

Post by Grigory_Heaton » Sun Jan 29, 2017 9:29 pm

I use this, shown to me by someone on this forum a little while back:

https://www-nds.iaea.org/exfor/endf.htm

It's not perfect but it's the best I've seen so far. You can search for a given reaction (say for the 700 kV Cockcroft and Walton experiment you mentioned, you would do Target: Li-7, Reaction: p,g). My biggest issue with it is that almost all reactions except D,T and D,D have almost no data at energies less than 0.5 MeV. Once you search a reaction you can plot the data, usually cross section vs. energy.

Is that what you were looking for?

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Re: Review article on beam/accelerator driven fusion?

Post by Richard Hull » Sun Jan 29, 2017 9:43 pm

Mark Oliphant is generally credited with discovering fusion via experiemnt in the 1932-33 time frame. Hahn and Strasserman discovered fission in 1938, again, by experiment.
Both Oliphant and Hahn-Strasserman failed to figure out what they had done or its ramifications. This is similar to Bequerel and Roentgen who made disoveries. They failed to fully appreciate or explain the physics behind what they discovered.

Lucky donkeys make discoveries.
Technology make those discoveries useful.
Physicists figure out the how and why of the mechanism, often long after the discovery and often long after technology has made the discoveries useful. (X-rays is a stunning example)

Some discoveries are figured out and developed rapidly via both physics and technology. (X-rays and fission)

Other disoveries languish once discovered and are fully explained and reproducible. Yet, they fail to develop a promise of major benefit to man (Fusion)

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Sven Andersson
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Re: Review article on beam/accelerator driven fusion?

Post by Sven Andersson » Tue Jan 31, 2017 5:24 pm

Grigory_Heaton wrote:Is that what you were looking for?
Not quite; I want the whole story. What happens at low energies is particularly important. I also have difficulties understanding that database. But, thanks for your reply anyway!

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Re: Review article on beam/accelerator driven fusion?

Post by Sven Andersson » Tue Jan 31, 2017 5:34 pm

Richard Hull wrote:Mark Oliphant is generally credited with discovering fusion via experiemnt in the 1932-33 time frame.
The reason I pursue this is that I suspect that the nuclei, when they fuse in a beam fusion experiment are actually standing still relative to one another. The projectile nucleus gives up all or almost all of it's kinetic energy as bremsstrahlung. Then it is near the target nucleus and both are very close in both position space and momentum space and undergo nuclear fusion. How do you prove this? Measure the bremsstrahlung? Perhaps there are some clues in the graphs of cross sections plotted against kinetic energy?

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Re: Review article on beam/accelerator driven fusion?

Post by Grigory_Heaton » Tue Jan 31, 2017 7:46 pm

Most reactions have no data at low energies because the output would be so tremendously low. Fusion is a tunneling process so it depends on particle energy and the width of the potential barrier. For example, proton-proton fusion could technically take place in water but the probability of this occurring at room temperature means that it is almost certain it has never happened in the history of the universe, and likely never will. Now something easier, for example p-B11 fusion at 3 keV, might technically be possible but would be essentially impossible to measure. That reactions just produces a bunch of alphas, so it would be incredibly difficult to see reactions if they are happening at an incredibly low rate. That's why you don't see a lot of low energy data there.


As for interpreting the graphs, cross section is the "area" of the target particle that can allow the reaction to take place. Think of it as probability. Higher cross section means better chance of fusion. So the cross section vs. energy chart just shows you what chance of fusion you can expect given a particle kinetic energy. To get a feel for what a certain cross section value "means", look at the successful fusion devices on this forum, find out what voltage they used, then use the equivelant electronvolt kinetic energy value and look at the cross section on the charts for D-D fusion.

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Re: Review article on beam/accelerator driven fusion?

Post by Dennis P Brown » Wed Feb 01, 2017 10:17 pm

When you say
The projectile nucleus gives up all or almost all of it's kinetic energy as bremsstrahlung.
No, it doesn't. Nor do you really get what that process is if you think MeV protons just slow/stop because of a similar positive force.

Also, if a proton or other large nucli did what you said, then powerful gamma rays would be produced and seen with a characteristic spectrum that is easily identified - no such results, to my knowledge have ever been published and that would be an important discovery; so, no, unless you show otherwise, nuclei do not stop and fuse in that manner.

Further, in high speed fusion collisions do not need to tunnel since in the high MeV range, the Coulomb force can be over come so the strong force takes over leading to fusion.

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Re: Review article on beam/accelerator driven fusion?

Post by Richard Hull » Thu Feb 02, 2017 5:32 am

Yes, super high energy reactions don't need to tunnel, but at some point they kill fusion as well and head toward spallation. Ripping atoms apart without fusing at all. This depends on a number of factors. We fusioneers absolutely rely on Quantum Tunneling at our low energies. This yield abysmal results, but result quite usale and satisfactory to the amateur community.

The reason fusion cross section have a fall off at higher energies in collisions in low Z nuclei is due to spallation. D-D is a prime example. At about 1 mev in D-D fusion the Oppenheimer-Philips reaction starts to become favored. Neutrons are ripped from their deuterons with fusion falling off fast with increasing energy.

In the end, you can't win for losing.

Dennis is correct, if you fuse D-D in our two most favored reactions there are no photons due to bremsstralung during the act of fusion.... Maybe when the Tritons and Protons slam into the shell, yes, but not at the time of fusion.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Review article on beam/accelerator driven fusion?

Post by Sven Andersson » Mon Feb 06, 2017 3:57 pm

Dennis P Brown wrote:No, it doesn't. Nor do you really get what that process is if you think MeV protons just slow/stop because of a similar positive force.
If the projectile nucleus travels exactly on a trajectory that aims it towards a target nucleus, and if it has lost little or no kinetic energy from previous deflections, then the only outcome is that all or almost all of the kinetic energy is transformed into bremsstrahlung. Then the two nuclei both stand still and are very close to one another (the electrons that hold the crystal together are much further away) and fuse.
Dennis P Brown wrote:Also, if a proton or other large nucli did what you said, then powerful gamma rays would be produced and seen with a characteristic spectrum that is easily identified - no such results, to my knowledge have ever been published and that would be an important discovery; so, no, unless you show otherwise, nuclei do not stop and fuse in that manner.
Fusion in these beam fusion experiments is a rare event; about one projectile nucleus in 100 000 or one in a million or less fuse with a target nucleus. Meaning that the bremsstrahlung gamma rays produced are also rare and can be missed by investigators or confused with gamma rays from the fusion event itself. I'm sure that if a systematic search were made for this radiation then it would be detected. May have been mentioned en passant in some article sometime. Buried deep in the scientific/technical literature.

This is Charles S. Cagle's fusion, BTW.

http://adsabs.harvard.edu/abs/1990STIN...9113238B <---- Is this a book, or a data base or a report? How/where can I read it?

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Re: Review article on beam/accelerator driven fusion?

Post by John Futter » Mon Feb 06, 2017 6:02 pm

Sven
I cannot think how you would measure your "gamma bremsstrahlung" in amonst a ton of x-ray bremsstrahlung as the detector cannot distinguish whether the energy recieved is gamma or x-ray

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