Magnetic entrapment fusion without the magnets
Tokamaks that use Magnets to contain the high-temperature plasma, in which atomic nuclei fuse and release energy, have come into the limelight in recent months due to the tremendous advances in superconducting magnets. Despite these advances, however, traditional fusion with magnetic confinement is still years away from fulfilling nuclear fusion’s promise of abundant, carbon-free electricity.
But tokamaks aren’t the only route to fusion energy. The Seattle-based FuZE-Q reactor from Zap Energy, slated for completion in mid-2022, eliminates the need for costly and complex solenoids. Instead, the machine sends pulses of electrical current along a column of highly conductive plasma, creating a magnetic field that simultaneously traps, compresses, and heats the ionized gas. This Z-pinch approach – so called because the current squeezes the plasma along the third, or Z-axis, of a three-dimensional grid – could potentially generate power in a device that is simpler, smaller, and cheaper than the massive tokamaks or laser fusion machines in development today.
Z-squeezed plasmas have been plagued by instabilities in the past. Without a perfectly even pressure, the plasma wrinkles and kinks and falls apart within ten nanoseconds – far too short to generate usable amounts of electricity.
Zap Energy’s approach, known as shear flow stabilization, tames these instabilities by varying the flow of plasma along the column. The design envelops the plasma near the central axis of the column with faster flowing plasma – imagine a steady stream of cars driving in the center lane of a freeway, unable to change lanes because of on Heavy traffic rushing past both sides. This arrangement holds the fusion reactive plasma together and compresses longer than previous Z-pinch configurations could.
“We believe our reactor is the most cost-effective, compact and scalable solution with the shortest path to commercially viable fusion power,” said Ben Levitt, director of research and development at Zap Energy. Levitt predicts that Zap will hit Q = 1, or scientific break-even, by mid-2023 – the point where the energy released by the fusing atoms equals the energy required to create the conditions for fusion – what would make it the first merger project to that.
Given the long history of broken promises in fusion energy research, this type of claim is skeptical. But Zap’s climb up an excruciatingly steep technology curve was quick and impressive. The startup was founded in 2017 as a spin-off of the FuZE (Fusion Z-pinch Experiment) research team at the University of Washington. The company produced its first fusion reactions as early as the next year. Prior to founding the company, the university team worked with researchers from the Lawrence Livermore National Laboratory. They won a number of US Department of Energy grants that enabled them to test the sheared flow approach at increasingly higher energy levels. To date, the company has raised more than $ 40 million.
When deuterium gas is injected into Zap Energy’s FuZE-Q reactor, electrodes initiate synchronous pulses that remove electrons from the deuterium atoms to create a plasma or ionized gas. The plasma accelerates towards the assembly area where the current creates a radial shear or pinch in the plasma stream. This magnetic field maintains stability as it simultaneously traps, compresses, and heats the plasma to fusion conditions – Zap Energy
So far, experiments have confirmed simulations that predict that the plasma will remain stable when Z-pinch currents are amplified. The new machine, estimated to cost around $ 4 million, will increase the strength of the pulses from 500 kiloamps to over 650 kA – the approximate threshold that Levitt and his team believe can break even.
“Will the plasma remain stable if we continue to increase the energy we put into it? That’s the trillion dollar question, ”says Levitt. “We have a lot of high fidelity simulations that show that the physics doesn’t change, that the shear flow mechanism works when we go to a higher inherent energy. But we need evidence and we are not far from it. ”
The real world has often mocked the most reliable simulation-based predictions – especially in plasma physics, where unexpected instabilities arise with the slightest change in conditions. And even if the new FuZE-Q machine reaches the scientific break-even point, it will be left to a future machine to produce the even higher currents that are necessary to exceed the technical break-even point at which the electrical output at the output exceeds that required to generate the fusion reaction. Zap hopes to hit this milestone in 2026.
“Will the plasma remain stable if we continue to increase the energy we put into it? That is the trillion dollar question. ”
—Ben Levitt, Zap Energy
“Many teams have tried for decades to get the z-pinch approach working, and now Zap has figured out a way to stabilize it with the shear flow,” said Matt Moynihan, a former nuclear engineer for the Navy and a fusion company advisor. “It’s exciting that it works in the conditions they tested, but now we need to see if this stability holds up if they scale up the power enough to get net energy from it.”
What no one denies is the critical need for a carbon-free, always-on power source. It could be nuclear fusion, but mainstream approaches are too expensive and too slow to affect the climate crisis. Zap’s reactor could one day also be used for advanced space propulsion. Attached to a spacecraft, the end of a Z-pinch reactor could be left open to allow the fast moving plasma to escape and release a jet of material that could propel a spacecraft forward.
At this point, both fusion-powered space travel and fusion-powered electricity stay in the theoretical realm – but Zap Energy is aiming at the stars.
This article will appear in the January 2022 print edition as “A Pinch of Fusion”.
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