Here's One Way to Make Fusion Reactors Much Better

Caroline Delbert
·3-min read
Photo credit: TASS - Getty Images
Photo credit: TASS - Getty Images

From Popular Mechanics

  • Scientists from the Department of Energy have nailed down the best shapes of waves to stabilize tokamak reactors.

  • Tokamaks are subject to accumulating magnetic disruptions that scientists are working to control.

  • In a model, these researchers found they can change up the beams that target the disruptions.

Scientists working on behalf of the Department of Energy (DoE) say they’ve taken a step toward a more stable future for experimental nuclear fusion tokamak reactors.

In a new paper in Physical Review Letters, the team explains its new method of identifying and stopping heat disruptions in an ongoing way. By using a model to emulate conditions that stop the disruptions, the scientists realized these conditions are much less limiting than they previously believed.

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Tokamaks are fusion reactors that contain a donut-shaped stream of unfathomably hot matter that’s elevated and kept in the plasma state, mimicking the chemical reaction that “powers” stars. The plasma is shaped and secured by a powerful magnetic field, but tokamaks have been plagued by a phenomenon where even relatively extreme heat accumulates in certain places at the edge of the reaction zone and, if not resolved, knocks the reactor out of temperature.

Researchers have been extremely interested in solving this pervasive problem, and in recent years, they’ve identified ways to find and stop the edge localized modes (ELMs). “Fortunately, scientists have learned to tame these ELMs by applying spiraling rippled magnetic fields to the surface of the plasma that fuels fusion reactions,” the DoE says in a statement. “However, the taming of ELMs requires very specific conditions that limit the operational flexibility of tokamak reactors.”

The “spiraling rippled magnetic fields” are aimed into the tokamak plasma stream in a way that, roughly, scrambles the developing ELMs and prevents them from reaching a point where they disrupt the plasma reaction. In previous work, scientists used narrower spirals. Now, the new model shows that much wider spiral signals can be used instead, which in turn widens the conditions in which the signals effectively stop ELMs.

This idea—that tokamaks can run in a less narrow band of operating parameters in order to keep ELMs at bay—is pretty key. Fusion reactions are well understood in theory, but no tokamak has reached plasma state reaction for more than part of a second. If one way to reach that goal sooner and with more success is to carefully control how the tokamak runs, then that’s information we should have.

A reactor that only works in extreme, near-perfect conditions that we can’t feasibly create ultimately isn’t useful, no matter how cutting-edge it is. Virtually infinite energy from a fusion reactor only matters if the fusion reactor works and is cost effective to run. In their statement, DoE scientists compare this to an airplane that can only fly at one specific, narrow altitude band—even if we could get there, then there’s no margin for error and no flexibility.

The DoE is working on multiple (likely dozens or more!) projects involving tokamaks right now, testing individual ideas in separate studies and using models and simulations to recreate conditions inside these still-enigmatic reactors. In this statement, they say they’re excited to start combining insights and seeing what’s next on the road to self-sustaining plasma fusion.

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