When it comes to radical energy solutions, an extreme long shot is a nuclear power scheme that would combine fusion and fission. Existing nuclear plants all run on fission, the splitting of heavy nuclei such as uranium, to produce power—not to mention tons of hazardous waste. Fusion joins together light nuclei, as occurs in stars and hydrogen bombs, but practical fusion-power generation has yet to be demonstrated despite decades of research. One of the newest ideas is a hybrid plant in which fusion would trigger atom splitting in spent nuclear fuel, boosting the energy output and "burning up" the waste.

Yet that hybrid approach looks positively mainstream alongside some other speculative fusion work that has recently attracted attention and venture capital. Online chatter about alternative fusion research reignited this month when the ambitiously named General Fusion announced it had raised $19.5 million from investors including Amazon.com's founder Jeff Bezos. General Fusion's planned machine would look right at home illustrating a steampunk novel

Compared with the billions that governments are sinking into projects such as the National Ignition Facility (NIF) and ITER, $20-or-so million is a pretty cheap lottery ticket. But is there really any chance of a payoff? Is any concrete progress getting reported? Here's a quick snapshot of three of the projects.

General Fusion

* Technology: Magnetized target fusion. In General Fusion's design, liquid metal (lithium and lead) spins inside a spherical tank, leaving a cylindrical cavity at its core. Puffs of deuterium and tritium (heavy isotopes of hydrogen) injected at each end meet at the center of this vortex cavity where magnetic fields trap them for a few hundred microseconds. About 200 pneumatic pistons slam the tank from all directions, sending an acoustic shock wave through the molten metal. The wave converges on the target, collapsing the vortex and generating fusion. Repeat, perhaps once a second.

* History: Researchers have studied magnetized target fusion since the 1970s. Early designs similar to General Fusion's were stymied by inadequate technology to compress the fuel evenly before it dispersed. Another variant, currently pursued by researchers at Los Alamos National Laboratory, eschews the liquid metal and mechanical compressors, instead using a magnetic pulse to implode a metal cylinder.

* Published results: Some papers in the Journal of Fusion Energy in 2008 reported General Fusion's first work on developing a piston and designing a plasma accelerator (for injecting the deuterium). A "proof-of-principle" experiment conducted in 2006 compressed deuterium gas with an acoustic shock wave and produced some neutrons (a fusion by-product), but that work involved no spinning molten metal, pistons or plasma injection.

* Status: General Fusion's vice president of business development, Michael Delage, says the company has since demonstrated the desired high-precision servo-control of a piston (timing the impacts to within eight microseconds) and are using another full-scale piston to study how acoustic waves propagate in molten lead–lithium. The first plasma injector began operating a year ago. A talk at the Canadian Nuclear Society's annual meeting next month will outline this work and the next steps.

Energy/Matter Conversion Corporation (EMC2)

* Technology: Polywell plasma confinement. A polyhedral arrangement of electromagnetic coils traps electrons at its center, producing a potential well for positively charged ions such as deuterium. The positive ions accelerate toward the center of the well, where some of them collide violently enough to fuse.

* History: Championed by Robert W. Bussard, the polywell is a variant of an older method, inertial electrostatic confinement, which enthusiasts have used to construct tabletop fusors. Bussard formed EMC2 in the early 1980s to pursue inertial electrostatic confinement fusion to generate power. Theorists have argued that these schemes will inevitably suffer excessive particle and energy losses (for example, see here and here). Bussard claimed (pdf here) to have found a way around the problems with his last polywell device, "Wiffleball 6," shortly before the device broke down and his funding (from the U.S. Navy) ran out. Don't try telling a story line like that to a skeptic. Bussard died in 2007.





* Recent work: With resumed Navy funding, EMC2 built "Wiffleball 7" to examine the claims made for WB-6. The results have not been published outside of an internal report, apparently in line with funding contract provisions limiting disclosures. Still, the Navy saw fit to award EMC2 a further $7.9-million contract in 2009 to build WB-8, with magnetic fields eight times stronger than WB-7, to test how well the performance scales up.

* Status: A terse quarterly report at recovery.gov indicates WB-8 has been built, "operates as designed," and "is generating positive results," with up to a year of further experiments ahead. In the absence of published peer-reviewed results only the Navy can know if it is getting value for its money after all these years.

Tri Alpha Energy

* Technology: Plasma electric power generation. The plasma is confined magnetically. By fusing boron and hydrogen (not deuterium and tritium), each reaction produces three alpha particles (helium nuclei) and releases no neutrons. The energy can be extracted as electricity from these charged particles more directly than the usual approach of heating steam to drive a turbine. (EMC2 is also interested in this "aneutronic" route—that would be Wiffleball 8.1.)

* History: Norman Rostoker and two colleagues proposed, essentially, this reactor in 1997 (also available here). Rostoker, an emeritus professor of physics at the University of California, Irvine, went on to co-found Tri Alpha Energy. In recent years Tri Alpha has reportedly gathered roughly $100 million in funding from investors such as Microsoft co-founder Paul Allen.

* Published results: Tri Alpha Energy has a reputation for operating in stealth mode, and yet Rostoker and other Tri Alpha scientists are regularly filing updated patent applications and presenting research results at conferences (an invited talk and 15 poster presentations at a November 2010 plasma physics conference alone). A study of plasma behavior in their latest device ("C-2") appeared in the leading physics journal, Physical Review Letters, last July.

It is a safe bet that none of these projects will be producing copious quantities of fusion anytime soon. General Fusion has barely gotten started, and Tri Alpha's research output illustrates how much can remain unfathomed after decades of serious work. If a group does eventually strike the scientific jackpot, that program will still face a long and expensive development path littered with potentially showstopping technical obstacles as challenging as those that vex the mainstream approaches of NIF and ITER. For an investor a winning lottery ticket would just offer a seat in a real game.