Taking one step closer to a functional fusion reactor

The model takes high pressure and temperatures of about 150,000,000°C to get atoms to combine. Runaway electrons are also wreaking havoc in the fusion reactors that are currently being developed.

In the promising reactor type tokamak, unwanted electric fields could jeopardise the entire process. Electrons with extremely high energy can suddenly accelerate to speeds so high that they destroy the reactor wall.

These runaway electrons are the ones that have been successfully identified and decelerated by doctoral students Linnea Hesslow and Ola Embréus. With their advisor, Professor Tünde Fülöp at the Chalmers Department of Physics, they have been able to show that it is possible to effectively decelerate runaway electrons by injecting so-called heavy ions in the form of gas or pellets. For example, neon or argon can be used as ‘brakes’.

As the electrons collide with the high charge in the nuclei of the ions, they encounter resistance and lose speed. The many collisions make the speed controllable and enable the fusion process to continue. Using mathematical descriptions and plasma simulations, it is possible to predict the electrons’ energy – and how it changes under different conditions.

Linnea Hesslow, one of the students said: “When we can effectively decelerate runaway electrons, we are one step closer to a functional fusion reactor. Considering there are so few options for solving the world’s growing energy needs in a sustainable way, fusion energy is incredibly exciting since it takes its fuel from ordinary seawater.”

Professor Tünde Fülöp also added: “The interest in this work is enormous. The knowledge is needed for future, large-scale experiments and provides hope when it comes to solving difficult problems. We expect the work to make a big impact going forward.”

Even though over the past 50 years there has been great progress made on fusion energy research, there is still no commercial fusion power plant in existence yet. It’s currently all eyes are on the international research collaboration related to the ITER reactor in southern France.

Fusion energy occurs when light atomic nuclei are combined using high pressure and extremely high temperatures of about 150,000,000°C. The energy is created the same way as in the sun, and the process can also be called hydrogen power. Fusion power is a much safer alternative than nuclear power, which is based on the splitting (fission) of heavy atoms.

However, if something does go wrong in a fusion reactor, the entire process stops and it grows cold. Unlike with a nuclear accident, there is no risk of the surrounding environment being affected.

Hesslow continued: “Many believe it will work, but it’s easier to travel to Mars than it is to achieve fusion. You could say that we are trying to harvest stars here on earth, and that can take time. It takes incredibly high temperatures, hotter than the centre of the sun, for us to successfully achieve fusion here on earth. That’s why I hope research is given the resources needed to solve the energy issue in time.”

The fuel in a fusion reactor weighs no more than a stamp, and the raw materials come from ordinary seawater.