Major breakthrough could help fix one of nuclear fusion’s greatest dangers

11 Jan 2019

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Keeping a lid on nuclear fusion’s enormous power may be one step closer following the discovery of a new radio frequency process.

For decades now, scientists have attempted to prove nuclear fusion as a feasible form of energy production. However, trying to bring the fusion reaction that powers the sun into the confines of a small chamber is, understandably, a difficult and dangerous task.

This means maintaining a stable plasma and preventing any disruptions in the process for prolonged periods of time. Now, researchers at the US Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) may have found a way to do just that, significantly reducing much of the danger in the equation.

Publishing its findings in Physical Review Letters, the researchers focused on so-called tearing modes, where instabilities in the plasma create ‘magnetic islands’ that lead to major disruptions.

These bubble-like structures can grow and trigger disruptive events, thereby halting fusion reactions and damaging the tokamak reactor chamber used to contain the plasma. Back in the 1980s, attempts to prevent tearing modes involved radio frequencies (RF) to drive current in the plasma.

However, what the researchers of that time failed to realise was that small changes to the temperature of the plasma could make it more stable once a key threshold in power is exceeded.

Bigger than previously thought possible

Using the latest method developed at PPPL, researchers are able to perform ‘RF current condensation’, where a concentration of RF within the magnetic islands prevents the power within them from growing out of control.

“The power deposition is greatly increased,” said Allan Reiman, a theoretical physicist at PPPL and lead author of the paper. “When the power deposition in the island exceeds a threshold level, there is a jump in the temperature that greatly strengthens the stabilising effect. This allows the stabilisation of larger islands than previously thought possible.”

Looking to the future, the researchers believe the newly discovered process could be very beneficial to the nuclear fusion mega-project known as the International Thermonuclear Experimental Reactor (ITER) in France.

“There is worry about islands getting large and causing disruptions in ITER,” Reiman said. “Taken together, these new effects should make it easier to stabilise ITER plasmas.”

Colm Gorey was a senior journalist with Silicon Republic