A functional fusion reactor may still be a dream, but it's a dream that is slowly becoming a reality with numerous research efforts and experiments aiming to unlock the near unlimited supply of clean energy that such a reactor would provide. The challenges scientists face in getting nuclear fusion to work are undeniably difficult, but not insurmountable, and two young physicists have recently solved one of the major problems engineers have been grappling with for almost half a century.

Nuclear fusion is the process that powers our sun. Deep inside our home star, hydrogen atoms are squashed together to form helium. This fusion process releases huge amounts of energy, but requires extremely high pressures and temperatures and has been challenging to recreate in a controlled way here on Earth.

Last year, researchers at MIT brought us closer to a fusion future by placing plasma under what they say is the most pressure ever created in a fusion device. Now, two researchers from the Chalmers University of Technology have unlocked another piece of the puzzle.

One of the problems engineers have faced as they develop modern experimental tokamak type fusion reactors is that of runaway electrons. These are electrons with extremely high energy that can suddenly, and unexpectedly, accelerate to incredibly high speeds that can destroy the reactor wall without warning.

Doctoral students Linnea Hesslow and Ola Embréus have devised a new technique to effectively decelerate these runaway electrons by injecting "heavy ions", such as neon or argon, into the reactor. As the electrons collide with the high charge in the nuclei of these ions, they slow down and become much more controllable.

"When we can effectively decelerate runaway electrons, we are one step closer to a functional fusion reactor," says Linnea Hesslow.

Hesslow and Embréus have created a model that can effectively predict the electrons' energy and behavior. Using mathmatical descriptions and plasma simulations the physicists are now able to effectively control the speed of the runaway electrons without interrupting the fusion process.

The nuclear fusion challenge is not a simple or easy task to overcome, but each little development such as this one brings us closer to the clean energy through fusion dream. The Chalmers team is incredibly optimistic that a fusion-powered future is possible.

"Many believe it will work, but it's easier to travel to Mars than it is to achieve fusion," says Linnea Hesslow. "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 center 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 discovery was recently published in the journal Physical Review Letters.

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