Researchers use Microwaves to Stabilize Fusion Reactor Plasma

With the plasma temperature challenge now nearly in the can, MIT engineers tackle the next big challenge to nuclear fusion: steady reaction.

For the world’s increasing energy needs, neither fossil fuels or renewables, or even nuclear fission, pack the virtually endless “power punch” of nuclear fusion.

Nuclear fission is a process that’s been mastered on Earth for decades, and it’s now powering innumerable nuclear plants around the world.

Unlike fission, nuclear fusion has no radioactive waste and holds no threat to the environment. If anything happens to the reactor, plasma gets released into the atmosphere where nuclei and electrons recombine into hydrogen atoms.

A couple of projects are trying to replicate the fusion process that powers the Sun and sustain life here on Earth, and some are making concrete steps toward that goal.

Read More: ITER Project Brings us Closer to Viable, Large-scale Fusion Power

Temperatures inside fusion reactors get so high, up to millions of degrees, that electrons and nuclei of hydrogen atoms separate, forming a plasma.

Then, light nuclei can fuse together to create heavier nuclei, releasing huge amounts of energy in the process.

That’s the theoretical gist of nuclear fusion, and it’s the same process that takes places inside stars, albeit on an incredibly large scale.

MIT has a research center dedicated to fusion power, the Plasma Science and Fusion Center (PSFC), and has built its own experimental tokamak reactors.

Microwaves for Steady-State Plasma

For nuclear fusion to work in confined places, engineers have to control two things, plasma’s high temperature, and high density.

Tokamak Energy Ltd promises to start producing fusion power on an industrial scale by 2025. The company has recently achieved a major temperature milestone of 15 million degrees inside its ST40 reactor, and the next goal is 100 million degrees.

Current tokamak reactors allow for such temperatures that generate plasma, but only in very short pulses, as they can’t maintain the reaction for long.

MIT’s PSFC engineers have now made another significant improvement to the tokamak technology through an old-new technique that “generates plasma current by launching microwaves into the tokamak, pushing the electrons in one direction — a prerequisite for steady-state operation.”

To test their microwave-based technique, called the Lower Hybrid Current Drive (LHCD), researchers used MIT’s prototype tokamak device, Alcator C-Mod, which was shut down in 2016 after being in operation since 1993.

The LHCD technique isn’t new as it’s been worked on by MIT scientists since the 70s.

Praul Bonoli, a senior research scientist at PSFC, gives a surfing metaphor to explain LHCD technique:

“You are on a surfboard and you have a wave come by. If you just sit there the wave will kind of go by you. But if you start paddling, and you get near the same speed as the wave, the wave picks you up and starts transferring energy to the surfboard. Well, if you inject radio waves, like LH waves, that are moving at velocities near the speed of the particles in the plasma, the waves start to give up their energy to these particles.”

If they don’t incorporate MIT’s LHCD technique, what do ongoing fusion projects have planned for steady operation once they produced plasma?