Skip to comments.Fusion, anyone? Not quite yet, but researchers show just how close we've come (hot fusion, not cold)
Posted on 09/24/2013 8:56:27 PM PDT by LibWhacker
The dream of igniting a self-sustained fusion reaction with high yields of energy, a feat likened to creating a miniature star on Earth, is getting closer to becoming reality, according the authors of a new review article in the journal Physics of Plasmas.
Researchers at the National Ignition Facility (NIF) engaged in a collaborative project led by the Department of Energy's Lawrence Livermore National Laboratory, report that while there is at least one significant obstacle to overcome before achieving the highly stable, precisely directed implosion required for ignition, they have met many of the demanding challenges leading up to that goal since experiments began in 2010.
The project is a multi-institutional effort including partners from the University of Rochester's Laboratory for Laser Energetics, General Atomics, Los Alamos National Laboratory, Sandia National Laboratory, and the Massachusetts Institute of Technology.
To reach ignition (defined as the point at which the fusion reaction produces more energy than is needed to initiate it), the NIF focuses 192 laser beams simultaneously in billionth-of-a-second pulses inside a cryogenically cooled hohlraum (from the German word for "hollow room"), a hollow cylinder the size of a pencil eraser. Within the hohlraum is a ball-bearing-size capsule containing two hydrogen isotopes, deuterium and tritium (D-T). The unified lasers deliver 1.8 megajoules of energy and 500 terawatts of power1,000 times more than the United States uses at any one momentto the hohlraum creating an "X-ray oven" which implodes the D-T capsule to temperatures and pressures similar to those found at the center of the sun.
"What we want to do is use the X-rays to blast away the outer layer of the capsule in a very controlled manner, so that the D-T pellet is compressed to just the right conditions to initiate the fusion reaction," explained John Edwards, NIF associate director for inertial confinement fusion and high-energy-density science. "In our new review article, we report that the NIF has met many of the requirements believed necessary to achieve ignitionsufficient X-ray intensity in the hohlraum, accurate energy delivery to the target and desired levels of compressionbut that at least one major hurdle remains to be overcome, the premature breaking apart of the capsule."
In the article, Edwards and his colleagues discuss how they are using diagnostic tools developed at NIF to determine likely causes for the problem. "In some ignition tests, we measured the scattering of neutrons released and found different strength signals at different spots around the D-T capsule," Edwards said. "This indicates that the shell's surface is not uniformly smooth and that in some places, it's thinner and weaker than in others. In other tests, the spectrum of X-rays emitted indicated that the D-T fuel and capsule were mixing too muchthe results of hydrodynamic instabilityand that can quench the ignition process."
Edwards said that the team is concentrating its efforts on NIF to define the exact nature of the instability and use the knowledge gained to design an improved, sturdier capsule. Achieving that milestone, he said, should clear the path for further advances toward laboratory ignition.
Going to overextend myself here.
“Cold” fusion is real. But like solar, not economically viable for large scale power generation.
Functional “hot” fusion changes the world.
Given that Ford worked on direct gasoline injection combustion engines for >40 years before having them reach production (Yeah, M-B had done it in the 300SLs in the 50’s), Fusion might take a few more decades before reaching commercial success.
It seems that every article I've read on fusion since I was a teenager has said we're 20 years away from fusion.
Fusion at the solar center proceeds very slowly, as is evident from the several billion year lifetime of the sun. The sun's break-even time is tens of millions of years, corresponding to pre-nuclear-physics estimates of its lifetime, based on gravitational energy only.
Soooo, to break even in a few nanoseconds, one must naturally far exceed the pressure and temperature at the center of the sun.
... tell me where I'm wrong, and I'll listen.
LOL. My thought exactly -- 20 years and several billion tax dollars more to keep the researchers employed, pensioned and insured. Even if it became a reality the Greens would find some problem with it and kill it. Sorry for the cynicism but that seems to be the reality: deja vu all over again.
“In our new review article, we report that the NIF has met many of the requirements believed necessary to achieve ignitionsufficient X-ray intensity in the hohlraum, accurate energy delivery to the target and desired levels of compressionbut that at least one major hurdle remains to be overcome, the premature breaking apart of the capsule.”
Capsules? You’re working with capsules? You need dylithium crystals in a plasma containment system! Have you even invented transparent aluminum yet?
My God, man! Drilling holes in his head isn’t the answer! Now put away your butcher knives and let me save this patient before it’s too late!
The greens and anybody else that's paying attention. A fusion reaction doesn't create radioactive products directly, but copious neutron radiation does. I recall slide presentations showing liquid sodium waterfalls absorbing the pulses created by the pellet "detonations". Everything around it gets "hot". It's a mess. Fortunately or unfortunately, an imaginary mess.
Particles can't tell time and have no memory. They only know the temperature and pressure they experience moment by moment. The sun converts 4 million tons of matter into pure energy every second and the density at the core is about 15 times that of lead.
The reaction at the sun’s core is the fusion of hydrogen-1, which in spite of the temperatures generated, is extremely slow. With conditions where the density is equivalent of a specific gravity of about 150, and temperatures in hundreds of Kelvins, the power density is only 275 watts per cubic meter. That’s really slower than mammalian metabolism, as a comparison. Much of this is due to the comparitive electrostatic repulsion to be overcome to slam protons together. Not so much for deuterons and tritons, which is also the fuel for thermonukes. The power density in a fusion weapon going off is far higher than the core of the sun. Another evidence of the lower energy threshold for D-T fusion is brown dwarf objects. While not massive enough to initiate P-P fusion (minimum mass is around 0.08 to 0.10 solar masses), if there are traces of deuterium or lithium, there would be short lived fusion reactions, although they will not last long at all on an astronomical timescale.
There is one problem with using laser based inertial confinement. After a pulse, the neodynium glass rods used by the lasers need to cool down. Even a speck of dust on the rods will cause them to shatter when the xenon flashtubes go off to pump the rods into lasing. Electron beams for internal confinement might work better, look up the “Z-Machine” in use at Sandia.
... That's a question.
There are two issues:
First, the efficiency of a particular reaction is entirely a function of nuclear reaction kinetics, so, you hit the temperature and pressure necessary to overcome the activation energy and you're good to go, regardless of whether that takes you a few nanoseconds or a few million years. It took a long time to get there in the sun because gravity is weak, and gravitational collapse takes a long time. But, once you get there, you're there. With lasers doing the inertial confinement you can get to temperature and pressure much faster.
If you think of it as nuclear chemistry, how you reach the threshold thermodynamic variables will not affect what values the state variables need to have to have enough free energy to push the reaction.
Second, far less importantly, AFAIK, nobody is going to try to recreate the P-P chain that goes on in the sun. It would be nice if we could, but the reason it proceeds so slowly is that the reaction kinetics for P-P fusion basically suck: it requires a weak interaction to stabilize the P-P fused nucleus. Most of the time the diproton (2He nucleus) is unstable and dissociates. An improbably weak decay flips a proton into a neutron in a very small number of cases. (I can't remember the number, but it's miniscule. This is why the sun is burning so "slowly.") The flipped neutron changes the diproton into deuterium, which is stable.
Most fusion researchers have been trying to do fusion with various combinations of deuterium, tritium, 3He, or even 3Li. These lead to more stable nuclei result products, with much more favorable reaction kinetics. Unfortunately, they also produce fast neutrons, which the P-P chain doesn't. As a result, there are radioactive byproducts our sun doesn't produce (in its primary reaction.)
So, to do fusion at achievable energies with decent Q's, we can't rely on the process used in the sun, anyway.
Yeah, my uncle stunned me with that one many years ago, "A human radiates more energy per unit mass than the sun." Along with the seemingly paradoxical fact, "A pinhead at the temperature of the center of the sun would kill a man a mile away." ( I still rely on my uncle's authority for that one! )
The answer is: it doesn’t matter because the energy needed is entirely a function of the temperature required to get two protons close enough for the strong nuclear force to overcome the coulomb barrier, and that is the same whether it is happening in a reactor the size of the sun’s core or a nanotubule.
/Sorry, Putin, Brussels, and Japan, that is the truth. (No others are in the running.)
The purpose of the NIF is to do nuclear weapons related testing and research. These stories about power production are a misdirection.
They will have it perfected in 30 years....
They just need more funding from fed gov....
Now the “Oak Ridge Boys” had a working LFTR reactor in the late 1960’s but we just sat on that and soon the Chinese will be selling LFTRs back to us....
Keep funding the Hot Fusion boondoggle while we have a viable alternative with less engineering problems than current nuclear reactors...
We're comparing steady state conditions over some period of time. The tens of millions of years I cited represents the length of time that the sun could shine on its energy of gravitational contraction, and I'm counting this total energy as the ( non-nuclear) ignition energy. So it takes that long for the sun to "break even" with radiation presumed to originate from fusion. So that's its break even confinement time.
With inertial confinement, the laser blast inputs a certain energy, and the confinement must be long enough so that the fusion reaction generates an equal amount of energy.
Well ... I guess this makes for a difficult comparison, since the laser energy input ( presumed instantaneous ) is arbitrary, whereas the sun's gravitational self-energy is a function of its mass and radius. It follows that my inference that the P-T conditions must "greatly" exceed the solar center had no basis. So I was RRRRRR .... RRRRRR ...., well, you know.
I believe you will find this is factually incorrect.
The reason for using neutron-rich reactants is that the comparatively neutron-rich result products are better stabilized by the strong nuclear force. The P-P reaction is not slower because of Coulomb interaction, but because the diproton nucleus is unstable, it decays too quickly; there is no binding, and no binding energy is released as a result. P-P stabilization is achieved through the intermediary of a weak interaction which flips one of the up-quarks in one of the protons into a down quark. The result is a neutron, a positron, and a neutrino. The nuclear result product changes from an unstable He isotope (diproton) into deuterium, which is stable. However, this weak interaction is quite rare. As a result, most P-P reactions actually fail, even in the center of the sun. This is why the sun burns "slowly."
Neutrons do not "shield" protons at the internuclear distances required to ignite fusion; they simply add additional binding energy via the strong nuclear force. For all practical purposes, the Coulomb repulsion of two deuterons or two tritons or two protons (or any other combination thereof) is identical to the Coulomb repulsion of two bare protons.
If neutrons could effectively shield the electromagnetic force, they would also shield an atom's own electrons from its protons, changing the atomic orbitals of isotopes, and the chemical properties of isotopes would be different (17O and 18O would be less oxidizing than 16O, for example.) But the chemical properties of isotopes are not different, because neutrons do not have this capability.
It’s an easy mistake to make. The key thing is that the protons don’t care about where they are. They’re just not that smart. Classically, all they need is enough kinetic energy to get close enough to overcome the Coulomb barrier. Quantum mechanically, they don’t need quite that much energy, just enough for their proximity to be close enough that their wave functions have significant overlap (or equivalently, that their KE can “tunnel” through the Coulomb Barrier.)
And this happens at the same energy whether the impetus is gravity, lasers, or Maxwell’s Demons.
That's nowhere near "ignition", which is being sought in the ICF experiments. I only recently learned of a type of supernova caused by "pair production instability" which does actually represent a star exploding like an H-bomb, with near 100% efficiency due to its size. Mind-boggling.
This is exactly right. We are no closer to fusion today then we were 30 years ago. The problem is and always has been containment — or how not to melt a hole through the Earth. I don’t think actual ignition has ever been the hard part of the problem.
We’ll probably be building non-orbiting stationary power generation factories in space and beaming the power down well before they solve the fusion puzzle.
And cold fusion? Cold fusion is a myth, it’s not fusion at all, it’s a chemical reactor.
Massive stars that can undergo pair production instability are not using fusion mechanisms that are envisaged in the ICF. These stars, I believe, are triple-alpha-cycle degenerating stars. At the very least they are carbon-cycle stars. Their energy is not coming from the fusion of isotopes of hydrogen.
This is correct.
The problem is and always has been containment or how not to melt a hole through the Earth.
This is not correct.
I dont think actual ignition has ever been the hard part of the problem.
This is also not correct.
There is no "containment" issue. "Confinement" refers to the issue of confining sufficient fusion material for sufficient time in a small-enough region at sufficient temperature to maintain a self-sustaining fusion reaction -- achieving what is colloquially referred to as "ignition." It is the only issue there has ever been. And we are not much closer to doing it than we were in the 1950's; we only know more things that don't work.
Re: “It seems that every article I’ve read on fusion since I was a teenager has said we’re 20 years away from fusion.”
Europe, Russia, and the USA have been doing commercial fusion research since at least 1960.
It would not surprise me if the world wide price tag for this technology has reached $100 billion.
If we had put that money into photovoltaic, battery, and hydrogen research instead, I think we might be at break even or better on those three technologies.
6: Fryer, C.L.; Woosley, S. E.; Heger, A. (2001). "Pair-Instability Supernovae, Gravity Waves, and Gamma-Ray Transients". The Astrophysical Journal 550 (1). arXiv:astro-ph/0007176. Bibcode:2001ApJ...550..372F. doi:10.1086/319719
But my point was, it's not a nuclear fusion from what are ordinarily considered nuclear reactant candidates in terrestrial fusion projects.
My understanding is that pair-production collapse only occurs in post-Helium stars. A citation by two of the same investigators of more recent vintage, I believe, says oxygen fusion chain reactants are in play at this point in the star's life:
a b Kasen, D.; Woosley, S. E.; Heger, A. (2011). "Pair Instability Supernovae: Light Curves, Spectra, and Shock Breakout" (pdf). The Astrophysical Journal 734 (2): 102. arXiv:1101.3336. Bibcode:2011ApJ...734..102K.
He proposed that it might be possible through a staging process similar to a thermonuclear weapon, where about 30-65% of the energy came from fusion and other 70 to 35% came from the fission used to initiate the staging reaction. Of course, that type of fusion wouldn't satisfy the Enviro-Nazis, and that kind of reactor -- to my knowledge, and I am no expert -- has never been significantly researched.
As for the other kind of fusion? "It might happen," he said, looking around the seminar room, "within the lifetimes of a few of the people in this room." I was then one of the youngest grads in the room, a 26 year old. 30+ years have passed since then. I believe Teller's prediction might have very well be too optimistic.
OK, but MY point was that the "ignition" being referred to in ICF is a chain reaction, and not just "burning" at some low rate of consumption, as in the sun:
The energy released by these reactions will then heat the surrounding fuel, and if the heating is strong enough this could also begin to undergo fusion.The aim of ICF is to produce a condition known as "ignition", where this heating process causes a chain reaction that burns a significant portion of the fuel.
"These reactions" refers to the fusion caused by the laser heating, which plays the role of the fission "trigger" in an H-bomb, as I understand it. This is thermonuclear ignition, like an H-bomb, and like a pair instability supernova, but not like the sun.
Your body actually generates more heat per cubic inch than the sun.
Simply because only ~300W/m^3 are being produced, that doesn't mean the reaction is not sustaining itself! Remember even though only ~300W/m^3 are produced per second, a cubic meter of matter in the center of the sun has an energy density of around 10^16 J/m^3. That's ignited plasma, no question about it.
And keep in mind, when you consider the 'Q' that various projects are envisioning, fusion reactors will be using most of their energy to maintain confinement (fed back into the lasers or magnetic fields); they are not going to be exploding like a thermonuclear weapon. They will have many times better yields than the P-P fusion chain, but the definition of ignition doesn't change. It's just the difference between burning incense or gasoline. At some point, either fuel "catches" and the oxidation becomes hot enough to maintain the kindling temperature for more oxidation to occur. Only difference is, it's nuclear chemistry instead of atomic chemistry.
This isn't right. A thermonuclear reaction is unstable, the reaction rate accelerates explosively as result of the heat it is generating.
The sun is like a furnace held together by gravity. Its stability is in stark contrast to a pair instability supernova, which consumes its fuel on a time scale of seconds.
I know in astronomy they refer to Hydrogen ignition and Helium ignition for the beginning of the different burning phases, but the ICF article puts "ignition" in quotes and carefully explains the positive feedback they are looking for. They have a link for "chain reaction" where the definition is given: "A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events."
Note: "self-amplifying", i.e. a runaway reaction.
“Cold fusion is real”
So far no one has produced a cold fusion system. Every last one claimed to work has been a scam.
Sorry, but this isn't correct. There's no more "instability" in the ignition of a thermonuclear weapon than there is in the sun. The reaction kinetics are different because the reactants and confinement mechanisms are different. That's all. There is nothing fundamentally different about the physics which involves a release of binding energy from the strong nuclear force. The criticality, or runaway, reaction is entirely in the fission part of the bomb.
The "instability" in all the cases you're talking about is all about the containment's ability to confine fuel long enough to fuse; that's all. In a PPI supernova, most of the fuel is not instantaneously consumed by some sort of "instability." In fact, most of the fuel isn't consumed at all. The core is entirely consumed and blows most of the hydrogen/helium atmosphere (about 75% of the star) off into space. The same thing happens in a thermonuclear device. Ablation of the shell and x-ray pressure confines the reactants long enough for significant consumption of the reactants, but there isn't any special magic sauce there that isn't present in the sun. It's just a more energetic reaction because it isn't the P-P chain.
Like I said, not viable. Ok maybe should have said for even small power gen, too...
No magic sauce, just feedback. It’s a very general concept, epitomized by the HS auditorium audio feedback, heard as an earsplitting screech. It accounts for supernovae of all sorts, I believe.
As I read the LHC wiki article, this is what they’re trying to achieve, but they’re having trouble getting the microphone close enough to the speakers :-)
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