US Department of Energy’s Dual Approach Facilitates Greater Plasma Control During Fusion Reactions

(Photo : Wikimedia Commons/ Oak Ridge National Laboratory)

All nuclear power plants apply the principles of fission, a process where the nucleus of a heavy atom splits into smaller nuclei. As our modern society urgently needs to transition to sustainable energy systems, nuclear fusion is considered a potential option. It can generate four times more energy per kilogram of fuel than fission with near-zero carbon emissions.

How Does Fusion Work?

Nuclear fusion is a reaction where two or more atomic nuclei combine to form one or more different atomic nuclei and subatomic particles. It produces energy by replicating the natural processes that occur on the surface of the Sun. This is achieved by merging two light nuclei to create a single heavier nucleus. The process releases energy because while the resulting nuclei are heavier, their total mass is still less than the mass of the two merged original nuclei.

This method of producing energy is difficult to replicate on Earth. It also requires the generation and control of extremely hot gases called plasmas. These gases can be controlled using electric and magnetic fields since the electrons and ions they possess have electrical charges.

Taming Volatile Plasmas

Researchers at the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) have developed a new method of harnessing fusion to produce electricity. They combined two existing strategies for managing plasma to enable greater overall flexibility.

The new dual approach combines resonant magnetic perturbations (RMP) with an electron cyclotron current drive (ECCD). This combination marks the first time a simulation can facilitate more significant control of volatile plasma during fusion reactions.

According to PPPL staff research physicist Qiming Hu, the dual approach is novel. While the details of the experiment are still being worked out, he and his colleagues are very close to making the new approach a reality. Hu also noted that the process they outlined in their research paper has been demonstrated experimentally. The full capabilities are still being figured out, but it does a great job of advancing their understanding of the potential benefits.

Before fusion can be harnessed to reliably produce electricity, experts are working to discover ways to reduce the occurrence of particle bursts produced from plasma, known as edge-localized modes (ELMs). These bursts periodically release a bit of pressure because it is too much, and they can be dangerous.

The device the team is working with at PPPL's DIII-D National Fusion Facility is a tokamak. It relies on magnetic fields to confine fusion plasma into the shape of a donut. Scientists find ways to prevent ELM bursts from happening since they can interrupt a fusion reaction that causes it to end prematurely and damage the tokamak.

The best method the team has found yet is using resonant magnetic perturbations (RMPs), which help generate additional magnetic fields to control the volatile plasmas. Previous experiments have already shown that the creation of oval or circle-shaped magnetic islands can be helpful, although it requires the generation of RMPs powerful enough to produce them.

Enter the role of electron cyclotron current drive (ECCD). It works by assisting by injecting a microwave beam at the plasma's edge, which altogether lessens the current required to generate RPMs that are strong enough to produce magnetic islands.

Reducing the current needed to produce RMPs can pave the way toward more efficient fusion energy production. It also has the potential to help create commercial-scale fusion devices.