The problem isn't that scientists can't produce fusion reactions; even amateurs have done it. It's that all discovered fusion processes consume more energy than they produce. (The similarity of the terms can be confusing, so it's worth a reminder that nuclear fission, in which atoms split, is the well-known technology that already keeps lights on in some homes.)
But attention is particularly focused on fusion right now because of an unexpected breakthrough at the National Ignition Facility, and another at the Massachusetts Institute of Technology, both in the United States.
The aim of the NIF is to create fusion reactions by focusing almost 200 laser beams on a precise point. Although the facility just began testing, it just created waves by succeeding in creating a stable plasma and setting a record for the energy content of its laser beams. And at MIT, the Levitated Dipole Experiment unexpectedly showed that it can concentrate turbulent plasma in its reaction chamber.
Besides the NIF, there are fusion projects going on around the world. All have two things in common: they're still at an experimental stage, and they've all been derided by critics at one point or another. But by looking at the pedigree, breakthroughs and financial support of projects, I've come up with a set of TKTK projects that, like the NIF, could someday give the world a cheap new energy source.
I've tried to roughly rank them by their apparent prospects. By necessity the descriptions are pretty short, but you can Google any for more; also, look up the Lawson criterion, which sets the requirements for the sort of self-powered fusion reactions that would be required for any of the below projects to be successful. Here they are:
- The National Ignition Facility (USA) -- With its initial proof of the viability of using lasers to create fusion, the NIF has become the world's most watched fusion project. The ful name of the technology is laser-based inertial confinement fusion; the basic concept is firing 192 separate lasers to rapidly compress a tiny fuel pellet, which will (hopefully)undergo fusion at its core. Experiments around the idea began in the late 1970s, and following a series of cost overruns, the $3.5 billion NIF opened last year.
- ITER and DEMO (France) -- The International Thermonuclear Experimental Reactor is planned for France, but ultimately funded by seven countries, if you count the European Union as a single member. Building on the work of numerous other projects, like the Joint European Torus, China's EAST and South Korea's KSTAR, it would be proper to call ITER the grandfather of fusion research -- though the facility won't actually be complete until 2018. ITER is based on a tokamak, a circular (toroidal) magnetic chamber that compresses atoms to achieve fusion. If ITER works out perfectly, construction could begin on DEMO, a Demonstration Power Plant intended to produce usable amounts of electricity.
- LDX (USA) -- The Levitating Dipole Experiment, also mentioned above, is MIT's attempt to create a new design for fusion reactors. While shaped like a tokamak, which uses external magnets, the LDX brings the magnetic field inside its chamber, allowing different interactions with the plasma inside, including an unexpected density from turbulence. And, as the name suggests, the chamber levitates.
- HiPER (Europe) -- The High Power Laser Energy Research facility is supposed to be something of an improvement on the NIF's design, using a "fast ignition" approach that shrinks the size and output of the lasers to save on energy costs. Needless to say, HiPER got a boost from the NIF's early success, but the initial design and construction work isn't planned to begin for another year or two.
- Z-IFE (USA) -- A device at Sandia National Laboratory called the Z machine has proven capable of reaching extremely high temperatures (in the billions of Kelvins) and causing fusion with X-rays. Sandia has already upgraded the Z machine once, and through a series of further upgrades plans to reach the Z-inertial fusion energy (ZIFE) power plant and work up to creating a fairly continuous stream of fusion energy. The trick, as with all of these projects, will be achieving a positive energy output.
- General Fusion (Canada) -- This is a Canadian startup working on something they call "acoustically driven magnetized target fusion". Much like the NIF's laser fusion, General Fusion plans to use many pressure points to cause fusion in a central pellet; but unlike NIF, the company's design uses phsyical rams that transmit shock waves to compress the material. It's funded with a few million dollars, versus the billions governments have put into projects like NIF and ITER, but General Fusion can at least claim a unique design, which it says is superior because of modern computer controls.
- Lawrenceville Plasma Physics (USA) -- Another private company, LPP is working with even less funding than General Fusion, for the moment. LPP, run by a researcher who started off with NASA grants, plans to use a "dense plasma focus" device that creates magnetic fields with electricity and uses them to focus matter into a plasmoid. While similar to ITER, one of its advantages would be a lack of external magnets (like the LDX); another, its much lower cost to prototype and smaller scale overall.
- FRX-L (USA) -- Under study at the Los Alamos National Laboratory and the Air Force Research Laboratory, the FRX-L uses magnetized target fusion, which is much like General Fusion's approach, above. Unlike General Fusion, the researchers using FRX-L aren't driven by the imperative of finding success within a few short years or being shut down.
- Wendelstein 7-X (Germany) -- Another pilot project intended only to evaluate the potential of fusion energy, the Wendelstein 7-X is, like ITER, based on a toroidal design. The 7-X will be a replacement for the previous 7-AS unit at Germany's Max Planck Institute when it's completed in 2015; the aim is for the unit to be able to operate for 30 minutes continuously, proving that fusion could be used in power plants.
- Sonofusion (USA) -- Also called bubble fusion, this technique can supposedly use sound waves to compress matter for fusion. It's also in the scientific doghouse, following a scandal in which the students of a researcher who initially claimed to have achieved sonofusion wrote a paper supporting his results. You can find a long technical paper on it here, and there's also a startup called Impulse Devices working on sonofusion.