Engineers have gained fresh insight into so-call ‘Alfvén eigenmodes’ which could bring cheap fusion power one step closer to a reality.
This unstable, wave-like disturbance are produced by fusion reactions and can cause the loss of alpha particles and endanger reactor walls causing a reaction to become unstable and fail. The new findings will advance our understanding of the fusion process.
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‘Alfvén eigenmodes’ have always been a significant challenge for Engineers working with the doughnut-shaped “tokamaks”, the next-generation of fusion reactors.
The problem is that once heated up to temperatures ~100 million degrees Celsius, the reactors tritium and deuterium fuels react and emit high-energy helium ions called alpha particles. These particles can overheat the plasma and instead of sustaining fusion reactions cause them to become unstable.
We show that the degradation of fast-ion confinement in steady-state DIII-D discharges is quantitatively consistent with predictions based on the effects of multiple unstable Alfvén eigenmodes on beam-ion transport. Simulation and experiment show that increasing the radius where the magnetic safety factor has its minimum is effective in minimizing beam-ion transport. This is favourable for achieving high-performance steady-state operation in DIII-D and future reactors. A comparison between the experiments and a critical gradient model, in which only equilibrium profiles were used to predict the most unstable modes, show that in a number of cases this model reproduces the measured neutron rate well.Abstract from the paper published today
The engineering team behind the research used deuterium beam ions to simulate the alpha particles which would normally occur in fusion reactors. They were able to observe how Alfvén waves caused a 40% loss of high-energy particles.
This modelling demonstrates for the first time that is possible to accurately predict the effects of multiple Alfvén waves on energetic particles in the real-world tokamak reactor.
The results are a major step forward in understanding the fusion process and could allow engineers to plan for specific plasma conditions that would lower the rate of particle loss by controlling the number of Alfvén waves.