In the relentless pursuit of clean and sustainable energy, fusion power stands as a beacon of hope, promising an almost inexhaustible source of energy. Central to this endeavor is the ITER tokamak, a massive international project aimed at demonstrating the feasibility of fusion power. However, the path to harnessing this power is fraught with challenges, one of which is the management of tungsten (W) migration on the ITER divertor, a critical component of the tokamak.
A recent study published in the journal “United Nuclear Fusion” sheds light on this complex issue. Led by F. Chang from the Department of Mechanical and Aerospace Engineering at the University of California San Diego, the research investigates the influence of angular distribution of sputtered tungsten atoms on their migration in the ITER divertor region. The study utilizes ERO2.0 simulations to unravel the intricacies of this phenomenon.
The divertor, a part of the tokamak’s inner wall, plays a crucial role in managing the intense heat and particle flux generated during fusion reactions. It is coated with tungsten, a material chosen for its high melting point and low erosion rate. However, the surface of the tungsten divertor might undergo changes in morphology, potentially leading to the formation of microscopic fuzz structures. These changes can influence the angular distribution of sputtered tungsten atoms, thereby altering their migration patterns.
The study demonstrates that while the migration of tungsten ions is restricted by the field lines and thus not sensitive to the angular distribution, the migration of neutral tungsten atoms is heavily influenced by the direction of their initial velocity. This is due to the line-of-sight redeposition mechanism, where neutral atoms travel in straight lines until they encounter a surface or are ionized.
“Neutral atom deposition at a location far from the erosion location is suppressed by ionization of atoms,” explains Chang. This suppression results in neutral atom deposition peaking close to the strike points, regardless of the angular distributions. The strike points are the locations where the magnetic field lines intersect the divertor, marking the primary sites of erosion and deposition.
The study also compares the angular distributions of tungsten sputtered from a flat surface and a fuzzy surface. Using TRI3DYN simulations, the researchers found that a flat surface favors sputtering in the forward direction of the incident neon ions, while a fuzzy surface enhances sputtering in the backward direction. Despite these differences, the deposition profiles from the two surface types were not significantly different.
This finding has profound implications for the energy sector. It suggests that the angular distribution changes caused by the formation of fuzz on the divertor region might not significantly affect tungsten migration in the ITER tokamak. This could simplify the design and maintenance of future fusion reactors, as the formation of fuzz might not necessitate complex adjustments to manage tungsten migration.
Moreover, understanding the behavior of tungsten in the divertor is crucial for developing strategies to mitigate its erosion and manage its migration. This knowledge can contribute to the longevity and efficiency of fusion reactors, bringing us one step closer to realizing the dream of clean, sustainable fusion power.
As Chang puts it, “This research provides a deeper understanding of the physical processes at play in the ITER divertor, which is essential for the development of future fusion reactors.” The study not only advances our knowledge of impurity transport in tokamaks but also paves the way for innovative solutions to the challenges posed by tungsten migration. In the quest for fusion power, every breakthrough brings us closer to a future powered by clean, abundant energy.