Plans unveiled for private U.K. fusion reactor powered by ‘smoke rings’ and pneumatic pistons | Science

Plans unveiled for private U.K. fusion reactor powered by ‘smoke rings’ and pneumatic pistons | Science

Hundreds of pistons would compress a ring of plasma inside General Fusion’s pilot fusion plant.

General Fusion

A Canadian company, one of several betting on alternative approaches to fusion energy, announced today it will begin to build a pilot power plant next year in the United Kingdom. The plant, financially backed by the U.K. government and 70% of the size needed for a commercial power plant, will not generate energy, but rather will demonstrate the viability of the company’s fusion approach after it fires up in 2025, says Christofer Mowry, CEO of Vancouver-based General Fusion. “This is the first substantial public-private partnership in fusion,” Mowry says.  

The pilot plant will cost several hundred million dollars and will be built at the UK Atomic Energy Authority’s campus outside Oxford, also home to the Culham Centre for Fusion Energy, which operates the Joint European Torus—the world’s largest working fusion reactor—and the United Kingdom’s Mega Amp Spherical Tokamak Upgrade reactor.

Fusion advocates cheered the announcement from the 19-year-old company, which has raised $300 million from a mix of public and private sources. “General Fusion is a key player in the growing fusion industry,” says Melanie Windridge, U.K. director of the Fusion Industry Association. “They’ve raised significant investment for their magnetized target fusion concept, and we look forward to seeing their fusion demonstration plant come to life.” 

For decades, fusion, the power source of the stars, has lured researchers and investors with the promise of carbon-free energy made with abundant fuels. The problem is that it requires immense temperatures and pressures to coax hydrogen nuclei to overcome their mutual repulsion and fuse into helium in a reaction that releases energy. No fusion reactor has yet run long enough or efficiently enough to produce more energy than it consumes to sustain the reaction.  

ITER, the giant international reactor project in France, is supposed to get to this energy “gain” first. The device relies on enormous superconducting magnets to hold the ionized gas, or plasma, in a doughnut-shaped vessel while it is heated with microwaves and particle beams. But the more than $20 billion project has moved at a glacierlike pace: It is scheduled to turn on in 2025, but a demonstration of energy gain isn’t expected until after 2035. That has opened space for nimble startups to try to get there quicker with other techniques.

General Fusion uses an approach called magnetized target fusion. An injector generates a loop of plasma, like a cigarette smoke ring, which, through its swirling motion, creates a magnetic field that holds the cloud of particles together. During the plasma ring’s brief lifetime, it is compressed to temperatures and pressures where fusion should ignite.

The company has been fine-tuning its plasma injector for years and says it can now spit out rings that last several tens of milliseconds—an eon for such particle clouds and more than long enough for fusion to occur. “We can make the best self-contained plasma in the world,” Mowry boasts. Rival company TAE Technologies also relies on plasma rings and can sustain them for a similar length of time. But instead of compressing its rings, TAE sustains and heats them with particle beams.

With the pilot plant, General Fusion wants to demonstrate the advantages of its compression-based approach. The plasma ring is fired into a chamber lined with a layer of spinning liquid lithium, used to absorb high-energy particles kicked out by fusion that could otherwise damage the reactor. When the plasma reaches the chamber’s center, hundreds of pneumatic pistons pound the outside of the reactor wall in carefully timed pulses that push the lithium inward and spherically compress the plasma to the point of ignition. A commercial reactor would have to squeeze fresh plasma rings with pulses every few seconds to produce economic quantities of power.

The aim of the pilot plant, Mowry says, is to reach a fusion-relevant temperature of more than 100 million degrees Celsius and show that the whole process could be economical. It will use a relatively unreactive fuel of pure deuterium, a hydrogen isotope with one neutron, instead of the deuterium-tritium (D-T) mix a full-size commercial power reactor would use. That lets the pilot project avoid having to source rare, radioactive tritium and deal with the excess heat and generated radioactivity. A working reactor would breed its own tritium by using the radiation produced by the fusion reaction to break down the some of the lithium liner.

If the pilot plant can squeeze plasma to 100 million degrees Celsius for long enough and with sufficient density, then D-T fusion would work because the theory has already been demonstrated by public fusion efforts, Mowry says. “We’re inside the envelope of the knowledge base,” he says. With the pilot plant, the company is focusing more on practicality and economics. Current knowledge, “shifts the challenges to engineering.”

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