Is fusion inherently unstable? and should we be glad?!?!?

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
Todd Massure
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Is fusion inherently unstable? and should we be glad?!?!?

Post by Todd Massure » Thu Jan 20, 2005 11:35 pm

I've been thinking about the sun lately. It seems to me that fusion must be unstable even in the sun. If plasma fusion is really capable of a static self sutained "chain reaction" type burn wouldn't the sun be history long ago? I was thinking that what if the sun were a big ball of plutonium, instead of a big ball of primarily hydrogen? Wouldn't it have gone up in a huge blast rather quickly?
So it seems to me that maybe in the sun the fusion tends to lose the necessary pressure needed to maintain fusion (just like in man made plasmas) and must constantly move or expand outward in a shell to constantly find new areas where the conditions can be met, but only for a short time in each area. Or maybe it just dies out in one area and then is reborn in another area. If this is true, maybe it would mean that plasma fusion should be rethunk, maybe if the plasma were allowed to be more dynamic somehow, then possibly a sustained burn could finally be achieved.

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Adam Szendrey
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Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by Adam Szendrey » Fri Jan 21, 2005 12:01 am

In the core of the sun the pressure is tremendous . Fusion is driven by "gravitational confinement".
I looked up some numbers. The pressure in the core is somewhere between 2e11 and 3e11 atm. Aproximately 6e11 kg/s of hydrogen is consumed in the fusion process. The total mass of the sun is around 2e30 kg. If all of that would be fusion fuel , and all of it could be used up by the sun , it would last another 1e11 years.
But only 13 % of the avaliable hydrogen becomes fuel. The total percentage of hydrogen is 71 %.
From this the calculated lifetime is roughly 9.7e9 years, so the hydrogen percentage is probably meant at the creation of the sun. She's about 4.7 billion years old, so we can expect another 5 billion years, before our greatest source of energy, inflates and destroys life on Earth, which could never have existed without her...

Adam

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Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by ChrisSmolinski » Fri Jan 21, 2005 12:35 am

I am not sure if unstable is the word to use, I would use "inefficient", no "slow"
would be better. Fusion seems to be a process that just doesn't want to
happen. It takes a lot of pressure, literally, for those nuclei to fuse. And, as
you've said, that's a good thing, otherwise the Sun would have burned out
long ago.

Of course, in more massive stars, the fusion process does occur more
readily, hence they have a lifetime shorter than less massive stars.

Fusion requires economy of scale to operate. If you have say a few hundred
solar masses, you can really get it cooking; you can burn through that in
millions of years. A solar mass, on the other hand, takes ten billion, plus or
minus. We can add a few more datapoints into the curve from stars of other
masses (all with lots of guesses since it is rather presumptuous to estimate a
process that takes 10 billion years, based on a century or two of data). Now
extrapolate out to the incredibly puny quantities of hydrogen we have to play
with. We humans even cheat using deuterium and tritium.

The obvious factor changing in stars is the gravitational force, compressing
the material. Nature gets this for free in stars. We've found that we can do it
too, using a fission device to apply some pressure. For a few milliseconds
anyway.

I came to this forum a few years ago convinced that fusion power was "just
around the corner". Heck, even hobbyists were doing fusion in their
basement, we must be close. Now I am convinced, even though it is poor
scientific form to say so, that man will not be able to harness usable energy
from fusion.

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Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by dlsworks » Fri Jan 21, 2005 1:44 am

I like the "unstable" angle myself. But it should be noted that, the sun actually consumes it's ability to produce fusion, as it grows. This would explain a temporal conservation path of the nature of the sun.
But getting back to the "unstable" model for fusion, or rather, that is what I would like to deem my concept. Was that, in the notion that if we cannot preserve the natural artifices of the sun, then we will not beable to produce the desired result. Consider a translation, that the term "unstable" be traded with the term to "change with intent of original concept". That is to "redirect forces" that would otherwise be kept into check. To produce a stable product, but with an unstable action. To redirect, by means of carriers or clever structural redirection. (eg. from otto cycle to wankle cycle). What can be said about the following idea. (originally submitted to Larry Leins, regarding his LINAC orientation) It's not unusually, novel, but perhaps it will give someone an idea.

Larry,
So how's this on for size. Consider a concentric focus system of 4 of your bad-boys. Then add close proximity superconducting electromagnets to fill in the ansitropic arrangment of the LINAC's. Then inject deuterium and tritium in ultra minute amounts in a primary phase. Then a relatively large amount of aneutronic fuel in a secondary phase. The first fuel is accelerated. Immediatly behind it, the aneutronic fuel is in hot pursuit. Finally they converge where they nearly meet, at proposed incedent geometry (tetrahedral) of said LINAC arrangment. At said point, prior to convergence. Magnetic field is induced such that it is out of phase of first fuel , by convergence of peak pulse, but in phase will secondary fuel. Primary fuel is ingnited as per LINAC energy and non-peaking magnetic compression (out of phase as described) to fill the asymmetrical compression induced by the LINAC geometry. At which point the aneutronic fuel is acclerated in.. even faster. Within the next few moments, the peak magnetic compression pulse coincides, with lateral coverage, with that of the secondary fuel charge, filling in the assymtries. The deuterium-tritium provides a seeding energy, as well as an expanding spherical wavefront topology to the anuetronic fuel. The aneutronic fuel should thereby undergo some conversion effeciency to the fusion process. But wait, it get's some interesting from here.
The magnetic compression wavefront should lag the exapanding fusion derived topology wavefront and induce another assymetry. The inverse of the the assymetric cojugate. There by deflecting the resultants of the fusion process back up through the long drift tubes(such as a cherry pit through the fingers). Wherby, the energies can be extracted effeciently. There after the process is repeated, at a good frequency.
The whole electrical extraction system should be of superconducting storage type, of which net energy can be extracted for both use and of powering the system entirely.
I think this solves many issues of ignition, symmetrical compressibilty as well as expansion and effecient extraction.

Darius

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Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by walter_b_marvin » Fri Jan 21, 2005 3:39 am

Never give up on man's enginuity. Electricity was an egg-head fad in the 17 and 1800's you know

walter_b_marvin

Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by walter_b_marvin » Fri Jan 21, 2005 3:48 am

The basic problem is not extraction but ignition. If one can get more out than in, who cares about the effeciency of the process? The most basic extractor would be a water to moderator water heat exchanger and steam turbine. But one has to get about 2 for 1 raw output to ignition input for this to work. Note that for gasoline the inigition energy to output energy is of the order of 1 to 100. Given this analysis, let me pose a question to the group:

Most fusion has bee tried with the simplist reactions. Are there more exotic reactions, including intermediatry short lived particles or antimatter that even though they might require an even higher ignition input energy, nevertheless produce a better ignition to raw output ratio?
Afer all, we really don't want the sun for a next door neighbor, do we?

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Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by Richard Hull » Fri Jan 21, 2005 5:16 pm

The sun can do fusion only because of a perpetual, inexhaustable, gravitational confinement assist.

The Sun is, volumetrically, very, very lousy at doing fusion averaging only a few fusions/ sec/ cu meter. The sun has not sustained ignition. Our fusors can far exceed average solar FUSION power densities!........AS long as we keep pouring energy into the system.

The sun is self sustaining, but there is no fusion ignition there. Only perpetual potential enegy conversion, gravity to fusion. It is in a form of stasis between radiation pressure due to fusion plasmas wanting to expand and blow off the gas mantle and the crushing force of gravity. Gravitational potential energy is the virtually unlimited energy source in all stars.

In our fusors, we rely on a wall outlet and pay for every watt needed to do fusion.

I feel that continuous confinement of plasmas to do fusion WITHOUT GRAVITY for net power gain is an impossibility. Thus, I feel all earth bound continuous functioning plasma schemes to do power ready fusion are doomed to failure.

We have just not realized that stars do fusion only because of gravity, or, it just hasn't sunk in deep enough yet. We are beguiled and led to the "plasma trough" to drink up fusion, as we see the sun doing fusion with it. A second point is that with the right materials, we find that we, too, can easily do fusion here on earth with plasmas....And, damned cheap too; compared to solar energy densities. Unfortunately, at every turn, the confinement leaks or uses 100,000 times the energy we get back in fusion.

I still purport that fusion dreams involving plasmas are not far removed from someone feeling that with only one more magnet or just the right offset on his wheelwork, he will have a perpetual motion machine.

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: Is fusion inherently unstable? and should we be glad?!?!?

Post by walter_b_marvin » Sat Jan 22, 2005 1:50 am

My very point richard. If you want to fet energy out of fusion on earth, the sun's way is not it. but a perpetual motion machine fusion is not. fusion reaction DO release more energy that they consume for ignition. What is required is someone clever enough to light the match and get the tinder going etc.

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Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by Alex Aitken » Sat Jan 22, 2005 2:05 pm

Richard,

"Only perpetual potential enegy conversion, gravity to fusion. "

This makes no sense gravitational potential energy is not converted and fusion potential energy isnt increased - its converted to heat and light, if you argue the sun is a source of perpetual free confinement, I'll agree with you and this is the secret to its abilities of a power source, it takes no energy to confine the hydrogen so any fusion is a positive gain.

The sun may have lousey power densities but it isnt trying to make massive amounts of helium or power, its doing just enough fusion to prevent its collapse. If fusion of hydrogen were more difficult to do the sun would shrink until the amount of fusion balenced gravity again. If you added some sort of fusion catalyst to the core the density of power would increase, the core would expand and the temperature drop and the density of fusion would be decreased.

I dont think its fair to call fusion unstable, in the same way fission inherently isnt. You start throwing reactor grade plutonium into a hole in the ground and at no point will get a big bang, fission will start with a flash of neutrons/other radation, things will melt and start to boil and the molten mass will start to melt its way through the earth but no bang. If you had a cauldron with a high enough melting point it could be sustained like a log fire. Its getting a bit dim throw in another chunk..... (with only the vapour of plutonium/waste and intense radiation to spoil the view).

Fusion density in the sun is very low because gravity is a very weak force. You need huge amounts of material to get a confining field. Electricity and magnetism are vastly stronger. Even if they require power to maintain the field (avoiding superconductors for example) as the confining volume goes up the cost to maintain the field per unit volume drops, so its only a question of how big a reactor needs to be to breakeven, everything else is engineering and economics.

walter_b_marvin

Re: Is fusion inherently unstable? and should we be glad?!?!?

Post by walter_b_marvin » Sat Jan 22, 2005 8:12 pm

I agree but go one step futher..... At hight energies the strong, weak and electromagnetic fources are of comparable strengths. In fact the electromagnetic and weak forces have been "unified". In or fusors we use only electromagnetic forces for confinement. The strong force does not have a long range. but the weak force in combination with the electromagnetic force might find a confinement scenario

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