From: Chalmers University of Technology
Published June 21, 2017 09:32 AM

Deceleration of runaway electrons paves the way for fusion power

Fusion power has the potential to provide clean and safe energy that is free from carbon dioxide emissions. However, imitating the solar energy process is a difficult task to achieve. Two young plasma physicists at Chalmers University of Technology have now taken us one step closer to a functional fusion reactor. Their model could lead to better methods for decelerating the runaway electrons, which could destroy a future reactor without warning.

It takes high pressure and temperatures of about 150 million degrees to get atoms to combine. As if that was not enough, runaway electrons are 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.

It is these runaway electrons that doctoral students Linnea Hesslow and Ola Embréus have successfully identified and decelerated. Together 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”.

When 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.

Read more at Chalmers University of Technology

Image: Although the vacuum chamber in the British fusion reactor JET has a wall made of solid metal, it can melt if it gets hit by a beam of runaway electrons. It is these runaway elementary particles that doctoral students Linnea Hesslow and Ola Embréus have successfully identified and decelerated. (Credit: Eurofusion)

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