Oppenheimer-Phillips, and a guarantee of overcoming Coulomb?

Discuss how polywell fusion works; share theoretical questions and answers.

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chrismb
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Oppenheimer-Phillips, and a guarantee of overcoming Coulomb?

Post by chrismb »

At the risk of countering my departure message of yesterday, there is one point of issue that I feel I should 'put to bed' before deleteing 'talk-polywell' in my shorcuts, else any newbs (or those uneducated in such matters who look these things up here) might be a bit bewildered, due to the writings of a clown who wrote;
Joseph Chikva wrote:So, one beam of particles should transit through another beam and their relative speed (velocity) should be sufficient for that the majority of particles could overcome the Coulomb barrier between the reacting particles.
to which I replied
... points to note;
...

... the required energy to overcome the Coulomb barrier is many MeV of energy. At this level ['many MeV'], if such particles meet they simply destroy themselves in a process called 'Oppenheimer-Phillips stripping'. There is no energy to be gained by this process, but if your objective is to get a pile of nuclear particles then it does that.

... At energies below O-P, energy-releasing fusion doesn't occur just because you get two nuclei to a high energy. The nucleii must undergo tunnelling. This is a probabilisitic process. Only one in a million of any such reactions would end in fusion - even if they were spot-on, head-to-head.
(new highlights/parentheses are mine)

The peak cross-section for, example, D-T is around 64keV. But the Coulomb Barrier is around 1 MeV (I think the exact figure is ~500keV, but I'm talking oom here for light particles). This is because when fusion fuel nucleii meet, they play a sort of lottery game in which they decide whether to fuse. Most don't and bounce away in a Coulomb scatter.

The way in which fusion nucelii fuse is not by overcoming the Coulomb barrier, which is ~1 MeV high for light nucleii fusion, but by digging a tunnel underneath that very high hill of energy.

So you might think [just like the clown above has posited] 'Ah! So if you want ALL your nucleii to fuse, then just drive your nucleii to an energy ABOVE that hill, and truly overcome it!"

Unfortunately not, because light nucleii have very low binding energies and in nuclear terms they are 'weakly bound'. If you pick 1MeV as the collision energy, sure some may fuse, but another reaction begins to dominate for deuterium called Oppenheimer-Phillips, which simply knocks off neutrons like a marble game.

This is why you can never have any sort of certainty [like 'the majority of particles'] that fusion will occur between any two particular nucleii. It is a random game you are unlikely to win, and your game is either the lottery or marbles. The fusion we see in fusion reactors, be it thermal tokamaks or electric-fusion fusors, is just a statistically anomalous tail-end of unlikely reactions that occasionally occurs, instead of the expected Coulomb scattering. The only reason we see fusion is because there are trillions of trillions of collisions, and so we see the millions of fusion reactions. Just like if you bought trillions of lottery tickets, you might expect a few wins out of so many tickets.

The clown has misunderstood that the 'peak cross-section' for fusion is a much lower level than the Coulomb Barrier. In part, this is because he appears to have stated a strange view that there is no such thing as quantum effects in fusion.

In historic terms, it may be interesting to note that when Rutherford set his lab, the Cavendish, on course to split the atom, the idea that all at the time had was that it would take MeV levels of acceleration - because that was known to be the Colulomb barrier height. It was Gamow who visited the Cavendish who came up with tunneling theory and gave hope to Cockroft and Walton to get on with as much acceleration voltage as they could manage to generate. As soon as they accelerated protons into lithium at 100keV, way way below the level expected, that they got strong helium emissions - they'd split the atom with tunelling! It is historically noteworthy that many research labs around the world at that time could have already accelerated to those levels with relative ease, but no-one bothered looking because everyone saw the 'Coulomb barrier' height to be the accelerators' target, and it was, in effect, Rutherford accepting Gamow's work (that few else accepted at the time - and seemingly some still don't) that lead them to running the experiment anyway, in case he was right. It paid off, and all involved got their Nobel prizes.

Joseph Chikva
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Re: Oppenheimer-Phillips, and a guarantee of overcoming Coul

Post by Joseph Chikva »

chrismb wrote:The peak cross-section for, example, D-T is around 64keV. But the Coulomb Barrier is around 1 MeV (I think the exact figure is ~500keV, but I'm talking oom here for light particles).
Dr. Norman Rostoker (irvine University, Tri-Alpha company)
Patent application.
Background of invention.
Because atomic nuclei are positively charged--due to the protons contained therein--there is a repulsive electrostatic, or Coulomb, force between them. For two nuclei to fuse, this repulsive barrier must be overcome, which occurs when two nuclei are brought close enough together where the short-range nuclear forces become strong enough to overcome the Coulomb force and fuse the nuclei. The energy necessary for the nuclei to overcome the Coulomb barrier is provided by their thermal energies, which must be very high. For example, the fusion rate can be appreciable if the temperature is at least of the order of 104 eV--corresponding roughly to 100 million degrees Kelvin. The rate of a fusion reaction is a function of the temperature, and it is characterized by a quantity called reactivity. The reactivity of a D-T reaction, for example, has a broad peak between 30 keV and 100 keV.
Where are here 500keV, 1MeV, many MeVs?
So, crismb invented a new terminology. As do not like existing.

TDPerk
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Post by TDPerk »

"At the risk of countering my departure message of yesterday,"

Yes, please get your trash out of here. You emitted far more smoke than even heat, let alone light.
molon labe
montani semper liberi
para fides paternae patria

chrismb
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Post by chrismb »

TDPerk wrote:"At the risk of countering my departure message of yesterday,"

Yes, please get your trash out of here. You emitted far more smoke than even heat, let alone light.
Your post makes it look like there are now even more clowns on this forum who don't want to hear that fusion is by quantum tunnelling, or read anything about the history of science and understand how and why we've got to where we have got to in fusion, possibly for love of all the unfounded LENR pontificating?

..and, so, by these 'democratic' means in which every clown has to be allowed to have their say, therein lies the origin of dumbing down.

You have done no less than cement in my mind that this is, indeed, the correct moment in this forum's trajectory to pull hard on the T-handle.

Joseph Chikva
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Post by Joseph Chikva »

chrismb wrote:Your post makes it look like there are now even more clowns on this forum who don't want to hear that fusion is by quantum tunnelling,...
Mr. Oppenheimer-Phillips,
And why not by Higgs Boson?
Or would you not like to explain why tunneling occur?

KitemanSA
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Re: Oppenheimer-Phillips, and a guarantee of overcoming Coul

Post by KitemanSA »

Joseph Chikva wrote:
chrismb wrote:The peak cross-section for, example, D-T is around 64keV. But the Coulomb Barrier is around 1 MeV (I think the exact figure is ~500keV, but I'm talking oom here for light particles).
Dr. Norman Rostoker (irvine University, Tri-Alpha company)
Patent application.
Background of invention.
Because atomic nuclei are positively charged--due to the protons contained therein--there is a repulsive electrostatic, or Coulomb, force between them. For two nuclei to fuse, this repulsive barrier must be overcome, which occurs when two nuclei are brought close enough together where the short-range nuclear forces become strong enough to overcome the Coulomb force and fuse the nuclei. The energy necessary for the nuclei to overcome the Coulomb barrier is provided by their thermal energies, which must be very high. For example, the fusion rate can be appreciable if the temperature is at least of the order of 104 eV--corresponding roughly to 100 million degrees Kelvin. The rate of a fusion reaction is a function of the temperature, and it is characterized by a quantity called reactivity. The reactivity of a D-T reaction, for example, has a broad peak between 30 keV and 100 keV.
Where are here 500keV, 1MeV, many MeVs?
So, crismb invented a new terminology. As do not like existing.
By the semi-empirical binding energy formula, the D-T reaction must overcome a coulomb repulsion of about 1.47MeV. In the Rostaker quote, it seems almost absolute that he has used the common, but technically incorrect, short hand of "overcoming" being equal to "getting close enough for tunneling to work". 10s of keV gets you close enough to fuse a SMALL percentage of the instances where they get that close. 1.4MeV should provide so much energy that many will "fuse" but most will blow apart again.

I guess the point is that with the 10s of keV, the ions get close enough for the saturation binding energy to provide the rest of the energy to OVERCOME the coulomb repulsion! 30keV to 100keV gets you closer (more fuse), more than that you start blowing apart more and more of them.

Fun, no?

Chris, what is the x-section of D-T at 1.4MeV?

KitemanSA
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Post by KitemanSA »

Chris,
Never mind, I looked it up myself.
The x-section for D-T at 10keV is ~200 mbarn. At 1.4Mev it is back down to about 110 mbarn. At that point it is still reducing with added energy.

Joseph Chikva
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Re: Oppenheimer-Phillips, and a guarantee of overcoming Coul

Post by Joseph Chikva »

KitemanSA wrote:In the Rostaker quote, it seems almost absolute that he has used the common, but technically incorrect,...
Now Mr. "I Yesterday Have Read in Wiki and Today Postulate" says that the person who was financed with 100 millions for experiment understands nothing?
Certainly, one of friends claims that understands fusion even better than leader of Soviet fusion program!
So, the second will teach Rostoker how he should explain his invention.

What heck "semi-empiric formula of binding energy" Mr. "I Estimate Steam Flow from Computer Monitor"?
There is a graph showing dependence of fusion cross section on collision cross section in center-of-mass frame or graph of fusion cross section on temperature.

And let Chris say where I can find the graph of dependence Oppenheimer-Phillips reaction for different reactants: D-T, D-He3, etc.

Ivy Matt
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Never tell me the odds!

Post by Ivy Matt »

Oh, is that why those fusion reaction rate graphs don't go up infinitely with increased energy? And why you don't want your p+B11 fuel to get any "hotter" than about 600 keV? I guess I sort of knew that already, although I hadn't thought much about why it was so.

I'm on firmer ground with the history, and I'd say Chris has it right, but I think I'll defer to CERN.
Temperature, density, confinement time: pick any two.

KitemanSA
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Re: Oppenheimer-Phillips, and a guarantee of overcoming Coul

Post by KitemanSA »

Joseph Chikva wrote:
KitemanSA wrote:In the Rostaker quote, it seems almost absolute that he has used the common, but technically incorrect,...
Now Mr. "I Yesterday Have Read in Wiki and Today Postulate" says that the person who was financed with 100 millions for experiment understands nothing?
??? Does anyone ELSE see where I state or even IMPLY that Rostaker understands nothing, or is the lack of understanding solely by civil Mr Chitva here?
Joseph Chikva wrote: Certainly, one of friends claims that understands fusion even better than leader of Soviet fusion program!
If I recall correctly, he claimed to understand it better than a corpse. He was having a joke at your expense. He was not saying much there as it is VERY easy to know more than a corpse! :)
Joseph Chikva wrote: So, the second will teach Rostoker how he should explain his invention.
Nope, just explaining to a non-English speaker the propensity of English speakers to use verbal short hand. For instance, "overcome" can have MANY meanings. That is the beauty and the beastliness that is English. It also leads non-English speakers to screw up frequently! ;)
Joseph Chikva wrote: What heck "semi-empiric formula of binding energy" Mr. "I Estimate Steam Flow from Computer Monitor"?
FYI, Mr "I make up non-sensical names for people I know nothing about". :lol: http://en.wikipedia.org/wiki/Nuclear_bi ... iempirical formula for nuclear binding energy
Joseph Chikva wrote:There is a graph showing dependence of fusion cross section on collision cross section in center-of-mass frame or graph of fusion cross section on temperature.
True, and at the full coulomb repulsion energy value, the cross-section is SMALLER than at a much lower value.
Joseph Chikva wrote: And let Chris say where I can find the graph of dependence Oppenheimer-Phillips reaction for different reactants: D-T, D-He3, etc.
I am still not sure what you think HE thinks you think he said.

hanelyp
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Post by hanelyp »

fusion cross section is one factor in selecting plasma energy. Electromagnetic radiation from the plasma is another. You want a high fusion cross section in relation to losses, and losses climb very fast with plasma energy.

Joseph Chikva
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Re: Oppenheimer-Phillips, and a guarantee of overcoming Coul

Post by Joseph Chikva »

KitemanSA wrote:
Joseph Chikva wrote: And let Chris say where I can find the graph of dependence Oppenheimer-Phillips reaction for different reactants: D-T, D-He3, etc.
I am still not sure what you think HE thinks you think he said.
He said the following:
chrismb wrote:If you pick 1MeV as the collision energy, sure some may fuse, but another reaction begins to dominate for deuterium called Oppenheimer-Phillips, which simply knocks off neutrons like a marble game.
And I am very much intsrested in cross section.

And you are right, may be "overcome" has many meanings.
But what means "overcome of Coulomb barrier" in Rostoker's text and not mine?

Joseph Chikva
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Re: Never tell me the odds!

Post by Joseph Chikva »

Ivy Matt wrote:I'm on firmer ground with the history, and I'd say Chris has it right, but I think I'll defer to CERN.
In what Chris is right?
Do you too state that if accelerating and then colliding Deuterium and Tritium beams you will get something else than He4 and neutrons?
Even if center-of-mass collision energy would reach 1MeV.
Who can say that the birth of H4 isotope is the most probable process? The main process as Chris states!

Ok, how looks Oppenheimer-Phillips reaction for D-He3?
Not target reaction?

For p-B11 that is not imaginable at all.
Please explain.

rcain
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Post by rcain »

not that i am really qualified to join in here, but an interesting looking treatment of Oppenheimer-Phillips in the raw by Ragheb & Miley (1990) - here: http://www.springerlink.com/content/u87311484300658g/

Joseph Chikva
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Post by Joseph Chikva »

rcain wrote:not that i am really qualified to join in here, but an interesting looking treatment of Oppenheimer-Phillips in the raw by Ragheb & Miley (1990) - here: http://www.springerlink.com/content/u87311484300658g/
Cross-section?
Conditions?

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