Experimental polywell reactor (outside of its vacuum chamber)
Polywell (polyhedral potential well) is an IEC (inertial electrostatic containment) reactor design. Polywell is really clever since it doesn't try to directly contain the reacting plasma. The six electromagnets are used to contain a high energy electron cloud in the center. The electron cloud is contained by the magnetic fields and energized by microwave radiation, and by fiddling with the magnetic field strength and the microwave strength it's possible to precisely control the energy distribution within the core. Then you inject low energy hydrogen and boron ions into the reactor. They're positively charged and the core is negatively charged, so they're accelerated into the centre of the reactor (the potential well) to very high energies. Since they're being accelerated by electrostatic attraction rather than by heating they accelerate to a fairly uniform energy level, so almost all your ions have potential for fusion. So there's no slow ions that are bleeding away your energy, like in a tokamak. The other cool thing is that if the particles don't fuse, they pass through the core and then stop and are pulled back in from the other side. It still might take 1000 tries before a fusion occurs, but there's almost no energy loss from failed interactions.
The really cool part is that the fusion reactions occur in the centre of the core, in the middle of the electron cloud. The reaction is a boron-proton reaction which is an unusual fusion-fission reaction (boron-11 and the proton form super-energized carbon-12, which rapidly decomposes into helium-4, releasing more energy), which produces no radiation at all. Unlike a tokamak you can actually do boron-proton in a polywell since it has precise control over the energy distribution of particles inside it. Most of the energy from the reaction is captured by the electron cloud. There's a certain amount of physics in this next step I don't understand, but from what I've been told there's a process to extract electrical current directly from the cloud, so there's no thermal energy losses. A full sized reactor is estimated to produce 2,000,000 volts of DC electricity, and about 120GW of power. Ten full sized polywells could power the entire continental USA, and since it's not a thermal plant you don't need millions of gallons of water to cool it.
It was invented by Robert Bussard, one of the pioneers of fusion research, who unfortunately died of cancer last year. :-(