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Two-Laser Boron Fusion Lights the Way To Radiation-Free Energy
ananyo writes "Fusion unleashes vast amounts of energy that might one day be used to power giant electrical grids. But the laboratory systems that seem most promising produce radiation in the form of fast-moving neutrons, and these present a health hazard that requires heavy shielding and even degrades the walls of the fusion reactor. Physicists have now produced fusion at an accelerated rate in the laboratory without generating harmful neutrons (abstract). A team led by Christine Labaune, research director of the CNRS Laboratory for the Use of Intense Lasers at the Ecole Polytechnique in Palaiseau, France, used a two-laser system to fuse protons and boron-11 nuclei. One laser created a short-lived plasma, or highly ionized gas of boron nuclei, by heating boron atoms; the other laser generated a beam of protons that smashed into the boron nuclei, releasing slow-moving helium particles but no neutrons. Previous laser experiments that generated boron fusion aimed the laser at a boron target to initiate the reaction. In the new experiment, the laser-generated proton beam produces a tenfold increase of boron fusion because protons and boron nuclei are instead collided together directly."
The Earth's crust contains about 5x as much Boron as Uranium, but we already use quite a lot of it for other applications and are extracting it at almost seventy times the rate.
However, 80% of extracted Boron is B-11, whereas only 0.7% of naturally occurring Uranium is U-235.
If I'm crunching the numbers correctly, 1 gram of Boron produces 25,000 kWh of electricity - assuming perfect capture, 100% boron-11 and no other loses. (Granted, all unrealistic assumptions, but it's a starting point.)
If we replaced all electric generation on the planet (about 20 trillion kWh / year) it would take 800 tonnes of boron per year.
Turkey has the largest known Boron deposits at over a million tonnes or 1,200 years worth. And there are several other countries with large (thousands of tonnes) deposits as well, and that's just the Boron we know about.
All really rough estimates, but I don't think will run out of Boron fuel any time soon.
For anyone that wonders: french research agency CNRS has thousands of small research teams, which are each commonly led by a research director. A CNRS research director is like a university professor, except he/she is not in charge of any teaching.
It's not a problem, it's an advantage.
You get a 3X +2 Helium nucleus (aka alpha) at 8.7 GeV. Since the particles are charged, you can convert their energy to a usable electrical current directly. (Think field windings of a generator, except there is no winding, just a moving charge.) Neutrons have the disadvantage of _requiring_ a thermalization process to capture their energy.
The disadvantage of the alpha is that it is _easily_ thermalized. You need to keep everything out of it's way until you can extract its energy. This implies super deep vacuum, or a super tiny machine so that the energy conversion device is within the slowing down length of the alpha. The slowing down length of an alpha in air is on the order of a centimeter, IIRC.
Of course, I'm assuming that direct conversion is superior to thermal conversion. If thermal conversion is superior, then just thermalize the alpha just like a neutron, in a big tub of water. Just make sure your tub is grounded to prevent charge buildup.