Slashdot Mirror
Green Light For ITER Fusion Project
brian0918 writes, "A seven-member international consortium has signed a formal agreement to build the $12.8 billion International Thermonuclear Experimental Reactor (ITER). From the article: 'Representatives from China, the European Union, India, Japan, Russia, South Korea, and the United States signed the pact, sealing a decade of negotiations. The project aims to research a clean and limitless alternative to dwindling fossil fuel reserves, although nuclear fusion remains an unproven technology.' ITER will be built 'in Cadarache, southern France, over the course of a decade, starting in 2008.'" If ITER is successful, a commercial reactor could be built by 2040. Funny, I seem to remember fusion researchers from Livermore in the 70s say that commercial power was 20 years away...
I worked at D3D 'way back in the 1980s, when people thought breakeven would be achieved before the turn of the millennium. If as much effort were put into electrostatic confinement (the Farnsworth fusor we keep hearing so much about) that might have actually happened. The advantage of the Farnsworth fusor is that it uses a confinement field with a divergence term!
The magnetic field has no divergence (there are no magnetic monopoles) so it is extremely difficult to confine anything -- you can only slow down the leakage. That comes with some problems -- for example, it's very hard to get anything into or out of a magnetic bottle (as in a Tokamak) unless it is electrically neutral. Accelerating and heating the plasma are hard because the energy sources you can use (manipulation of the magnetic field itself, either at radiofrequency (RF heating) or near DC (betatron heating), themselves destabilize the confinement.
D3D used the innovation of firing neutral atoms in through the magnetic bottle, which provides material and heat into the plasma (the atoms generally ionize once they get in -- and then they're trapped like the rest of the plasma). The problem there is that we have no technology to accelerate neutral particles -- so they had these little tiny particle accelerators that fired their beams through GIANT TANKS of reactant that was intended to neutralize the input beams on-the-fly. Some small percentage of the particles got neutralized, and the rest bounced off the outside of the magnetic bottle into a beam dump. Seeing the size of the equipment made me realize that tokamak fusion is probably a dead end for power generation -- if it can be made to work at all (in the sense of achieving, say, 10x heat gain), the ancillary equipment is HUGE and it's not at all clear that economies of scale are enough to make it worthwhile.
The Farnsworth-Hirsch type fusors have the advantage that you can fire in charged particles -- they rattle around and lose some of their kinetic energy, and after that they're trapped in a normal potential well. Like muon-catalyzed fusion machines, the Farnsworth fusor is in a race to get the energy out of a fusible nucleus before it leaks away -- but fresh hydrogen or deuterium ions are much, much cheaper than muons, and it seems to have a better chance of working.
(Remember muon-catalyzed fusion? Muons act like electrons, only more massive -- so atoms that have an electron replaced with a muon get smaller [it's a quantum thing], bringing the nuclei closer together and boosting the fusion rate. You can get a pretty high fusion rate (a few fusions per muon per microsecond) at close to room temperature in pretty tame materials. The problem is that muons only last about two microseconds before decaying into energy, neutrinos, and electrons -- so you have to make several hundred fusions per microsecond, to make the energy worth the effort of making a muon in the first place. Nobody was able to make it pay off.)