Researchers from the Princeton Plasma Physics Laboratory and collaborators have developed a new numerical model to simulate the acceleration of pellets in thermonuclear fusion devices. This work, led by J. Corbett and R. Samulyak, alongside F. J. Artola, S. Jachmich, M. Kong, and E. Nardon, focuses on understanding and predicting the behavior of shattered pellet injection (SPI) in fusion reactors, with implications for plasma control and mitigation strategies.
The team has created a direct numerical simulation model for the rocket-like acceleration of pellets in fusion devices, integrated into PELOTON, a 3D Lagrangian particle pellet code. This model has been validated using SPI experiments conducted in the Joint European Torus (JET), one of the world’s largest operational tokamaks. The model accounts for the non-uniform charging of the ablation cloud by hot plasma electrons and local plasma gradients, which lead to differential pressure on the high-field-side compared to the low-field-side, driving the pellet rocket acceleration.
The researchers implemented models for both pure deuterium and deuterium-neon mixture pellets. They developed a new plasma cooling model within PELOTON to predict background plasma states, which distributes the ablated material and accounts for various energy losses and heating mechanisms. The plasma profiles predicted by this cooling model were compared with simulations from JOREK and INDEX, other plasma simulation codes, showing good agreement.
The PELOTON simulations of rocket acceleration and the trajectories of deuterium fragments were consistent with experimentally measured trajectories in JET. Notably, the team found that composite deuterium-neon pellets containing 0.5% neon experienced smaller deviations in their trajectories compared to pure deuterium pellets. They also explored various spatial configurations of pellet fragments and demonstrated the impact of cloud overlap on rocket acceleration, as well as the influence of plasma state gradients.
The practical applications of this research for the energy sector, particularly in fusion energy, are significant. Understanding and predicting pellet acceleration can improve plasma control and mitigation strategies, enhancing the efficiency and safety of fusion reactors. This work paves the way for future simulations of SPI in projected ITER plasmas and the development of a scaling law for rocket acceleration, which could be crucial for the design and operation of next-generation fusion devices.
This research was published in the journal Nuclear Fusion, providing a robust foundation for advancing fusion energy technologies.
This article is based on research available at arXiv.