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 power—1,000 times more than the United States uses at any one moment—to 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 ignition—sufficient X-ray intensity in the hohlraum, accurate energy delivery to the target and desired levels of compression—but 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 much—the results of hydrodynamic instability—and 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 ignition—sufficient X-ray intensity in the hohlraum, accurate energy delivery to the target and desired levels of compression—but 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.
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