Recent research published in ‘Nuclear Fusion’ has unveiled promising developments in managing high-Z impurities, specifically tungsten, in fusion-grade H-mode plasmas at the JET-ILW tokamak. The study, led by A.R. Field from the United Kingdom Atomic Energy Authority, highlights a novel mechanism for expelling these impurities from the confined plasma, which is crucial for the efficiency and performance of fusion reactors.
In fusion reactors, high-Z impurities like tungsten can significantly hinder plasma performance, leading to increased radiation losses and reduced energy output. The research demonstrates that by optimizing the temperature gradient at the plasma’s periphery, it is possible to create conditions where these impurities are directed outwards, effectively screening them from the plasma core. This is achieved by maintaining sufficient heating power—greater than 32 MW—resulting in high ion temperature gradients at the H-mode pedestal top.
Field’s team observed that during edge-localized modes (ELMs), while some tungsten impurities may re-enter the plasma, a net efflux occurs between these modes, allowing for a sustained high-performance state. The experiments showed an average D-D neutron rate of approximately 3.2 x 10^16 s^-1 over a period of about three seconds, indicating a robust fusion reaction without an uncontrolled rise in tungsten radiation.
The implications of this research extend beyond the laboratory. By improving impurity management, fusion reactors can achieve higher efficiency and stability, which is vital for commercial viability. The ability to maintain high performance without excessive radiation losses could accelerate the development of fusion energy as a practical and sustainable power source. This research provides critical insights that could inform the design and operation of future fusion reactors, including ITER, the international fusion research facility currently under construction in France.
Field emphasizes the significance of these findings, stating, “Provided steady, high-power heating is maintained, this mechanism allows such plasmas to sustain high performance,” suggesting a pathway for enhancing fusion energy’s role in the global energy mix. As the world seeks cleaner and more sustainable energy solutions, advancements in managing plasma impurities could play a pivotal role in the transition to fusion power.
