The past few months have proved that hope for nuclear fusion as the ultimate clean and nonpolluting energy source springs eternal. One reactor plan projects a tantalizing gigawatt-year net energy out of its still-on-the-drawing-board idea. Another scheme uses the same reaction as the first but seeks smaller-scale reactors. A third uses the familiar “heavy hydrogen” reactions of decades past—deuterium and tritium hydrogen isotopes combining to create helium, neutrons, and energy—but relies on possibly transformative design changes enabled by using the latest superconducting magnets.
To be clear, unexpected errors or oversights could still ground one or all of these efforts. But when so much of the research world is depending on the overdue and overbudget US $20 billion ITER project, each of these efforts counteracts the monoculture mind-set in fusion research that has been the subject of some industry questioning and criticism.
“There’s inertia in having the established magnetic [fusion reactors], and it’s a mature technology that’s being used,” says Dennis Whyte, director of MIT’s Plasma Science and Fusion Center. “But the new superconducting technology has improved over even the last three to four years. Even since we started the project, the capability of the technology has improved.”
The new reactor design Whyte now touts is a familiar torus-shaped tokamak—much like the current generation of doughnut-shaped plasma fusion reactors such as NSTX in Princeton, N.J.; ST25 in Milton Park, England; and the projected ITER project in France. But unlike the existing tokamaks, this one is smaller and has more powerful magnets. The magnets’ power comes from a second-generation breed of superconductor made with rare-earth barium copper oxides. REBCOs, as they’re called, can continue functioning at higher
temperatures and magnetic-field strengths than most other superconductors today. For instance, compared with ITER, Whyte’s “affordable, robust, compact” (ARC) reactor nearly doubles the magnetic field strength, from ITER’s peak strength of 13 teslas to an ARC peak magnetic field of 23 T. That’s important because the potential power that can be extracted from a reactor scales as the magnetic field to the fourth power.
ARC began as a class project at MIT, Whyte says. And now it’s seeking partners to bring its drawing-board design to life. Plus, Whyte says, students are still adding new innovations—like high-temperature alloys, modular 3-D–printed core designs, and clever thermal cooling fins that could offer twice the cooling capability. “This is technology that is just ready to blossom,” Whyte says. “This is an incredibly exciting time to be in engineering.”
Lawrenceville Plasma Physics’ Focus Fusion device is in the advanced research phase, says LPP president and chief scientist, Eric Lerner. It has now had 12 test runs using a heavy-hydrogen mix like the plasma soup that fuels tokamak reactors. But, says Lerner, these preliminary reactions are just to test the system. Ultimately the “dense plasma focus” device is designed to combine protons with boron atoms to generate three helium atoms plus energy—and crucially no neutrons that can contaminate other nearby atoms in the fuel or reactor and turn them radioactive.
According to the LPP website, the device consists of two coaxial cylindrical metal electrodes sandwiching a low-pressure gas. A mega-ampere-scale capacitor bank discharges millionth-of-a-second bursts of power that induce a current and a megagauss magnetic field. The device, LPP says, can get the gas up to billions of degrees Celsius for billionths of a second. The company’s calculations suggest these conditions could ultimately be sufficient to spark proton-boron fusion.
Lerner says his group, based in Middlesex, N.J., is now trying to get atomic impurities out of the plasma, because fusion reactions are extremely sensitive to foreign atoms in the mix. But he says he expects to be testing his device on proton-boron mixtures within the next year.
“I find their results interesting but preliminary,” says Robert Hirsch, who from 1972 through 1976 directed fusion research for the U.S. Atomic Energy Commission and Energy Research and Development Administration. Hirsch also chaired an independent review panel of the dense-plasma-focus device last year. “There is simply too much happening in these experiments to draw conclusions early on.”
Another promising unorthodox fusion reactor design was announced this year. It too proposes to fuse protons and borons to create energy plus innocuous helium as its ash. But instead of large, high-strength magnets, it would use some of the shortest and most powerful laser pulses in the world today to produce short bursts of high-strength magnetic field.
Heinrich Hora, emeritus professor of theoretical physics at the University of New South Wales, in Australia, says a spate of recent experiments in Europe have led his group to conclude that an “avalanche” fusion reaction could be triggered at the trillionth-of-a-second timescales of a petawatt-scale laser pulse—whose brief bursts pack a quadrillion watts of power. If scientists could exploit the avalanche correctly, he says, it could lead to a breakthrough in proton-boron fusion.
“You put in 30 kilojoules and get 1 billion joules out,” Hora says of his team’s preliminary calculations. “The whole avalanche process is a state of plasma that’s very much unexplored. More experiments are now necessary.”
His group’s conceptual reactor design was published in July in the journal Laser and Particle Beams. And Hora along with collaborators in the United States and Europe presented separate papers outlining their research in September at the Inertial Fusion Sciences and Applications conference in Seattle.
“How can we afford not to be doing this?” Whyte says of the smaller and cheaper unorthodox approaches to finding nuclear energy’s holy grail. “Fusion is hard. But it’s worthwhile.”
This article originally appeared in print as “Alternative Fusion Projects Warm Up.”
A correction to this article was made on 23 November 2015.