Alternative Nuclear fusion projects Tri-alpha Energy, General Fusion and Helion Energy featured in Nature

Tri Alpha is testing a linear reactor that it claims will be smaller, simpler and cheaper — and will lead to commercial fusion power in little more than a decade, far ahead of the 30 to 50 years often quoted for tokamaks.

The ITER tokamak is mired in delays and cost overruns. The facility, being built in Cadarache, France, is expected to be the first fusion reactor capable of generating an excess of energy from a sustained burn of its plasma fuel. But it looks set to cost as much as US$50 billion — about 10 times the original estimate — and will not begin its first fuelled experiments before 2027, 11 years behind schedule.

Over the past decade and a half, mavericks have launched at least half a dozen companies to pursue alternative designs for fusion reactors. Some are reporting encouraging results, not to mention attracting sizeable investments. Tri Alpha itself has raised $150 million from the likes of Microsoft co-founder Paul Allen and the Russian government’s venture-capital firm, Rusnano.

Tri-alpha Energy has started to let its employees publish results and present at conferences. With its current test machine, a 10-metre device called the C-2, Tri Alpha has shown that the colliding plasmoids merge as expected, and that the fireball can sustain itself for up to 4 milliseconds — impressively long by plasma-physics standards — as long as fuel beams are being injected. Last year, Tri Alpha researcher Houyang Guo announced at a plasma conference in Fort Worth, Texas, that the burn duration had increased to 5 milliseconds. The company is now looking for cash to build a larger machine.

As a science programme, it’s been highly successful,” says Hoffman, who reviewed the work for Allen when the billionaire was deciding whether to invest. “But it’s not p–11B.” So far, he says, Tri Alpha has run its C-2 only with deuterium, and it is a long way from achieving the extreme plasma conditions needed to burn its ultimate fuel.

Nor has Tri Alpha demonstrated direct conversion of α-particles to electricity. “I haven’t seen any schemes that would actually work in practice,” says Martin Greenwald, an MIT physicist and former chair of the energy department’s fusion-energy advisory committee. Indeed, Tri Alpha is planning that its first-generation power reactor would use a more conventional steam-turbine system. Other fusion entrepreneurs will have to tackle similar challenges, but that has not deterred them. Slough is chief scientific officer at Helion Energy in Redmond, Washington, which is developing a linear colliding-beam reactor that would be small enough to be carried on the back of a large truck. The Helion reactor will fire a steady stream of plasmoids from each side into a chamber, where the fuel is crushed by magnetic fields until fusion begins. Within one second, the fusion products are channelled away just as the next pair of plasmoids hurtles in. “The analogy we like to make is to a diesel engine,” says the company’s chief executive, David Kirtley. “On each stroke you inject the fuel, compress it with the piston it until it ignites without needing a spark, and the explosion pushes back on the piston.”

Helion has demonstrated the concept in a D–D reactor with plasmoids that fire once every three minutes, and it is now seeking $15 million in private financing over the next five years to develop a full-scale machine that could use D–T fuel to reach the break-even point, when it generates as much energy as it takes to run. The company hopes that its reactor could eventually reach the hotter conditions needed to fuse deuterium with helium-3, another combination that produces only α-particles and protons, with no neutron by-products.

Kirtley is optimistic about the money. “There is a giant market need for low-cost, safe, clean power,” he says. “So we’re seeing a big push in the private investment community to fund alternative ways to generate it.” And if the fund-raising is successful, says Kirtley, “our plan is to have our pilot power plant come online in six years.

General Fusion has demonstrated the idea with a small-scale device, using pistons driven by explosives, and has raised about $50 million from venture capitalists and the Canadian government. If the company can win another $25 million or so, Laberge says, it will build a beefier implosion system that can compress the plasma to the levels needed for fusion — perhaps within the next two years.

Despite such optimism, Dean estimates that it will be at least a decade, maybe a lot longer, before any alternative fusion company produces a working power plant.

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