Exploring the stability of blanket pebble bed with plasma events

Abstract

Plasma control instability is one of the inherent challenges in fusion reactors. Pebble beds, composed of assembled particles, are employed in blanket models to achieve neutron multiplication and tritium breeding using different materials. However, electromagnetic (EM) forces induced by plasma events can disturb the pebble bed, potentially altering its internal structure and the initial packing characteristics. These structural changes can significantly affect the physical properties and stability of the pebble beds. Despite its importance, studies investigating the structural behavior of pebble beds under the influence of EM force disturbances remain limited. This paper investigates the structural evolution of the Be pebble beds under the EM force perturbations in the fusion reactors. Using a coupled approach of Finite Element Analysis (FEA) and Discrete Element Method (DEM), the multiscale characteristics of the pebble bed are analyzed at mesoscopic and microscopic levels. Key factors, including the local packing factor, particle slip, force transmission, force chains, fabric anisotropy, wall forces, and energy dissipation, are systematically evaluated. The results indicate that EM force generated during plasma instability events significantly influence the pebble bed structure. EM force perturbations notably affect particle slip, fabric anisotropy, wall forces, and local packing factors, while the changes for the force chains are minimal. The force transmission within the pebble bed primarily aligns with the direction of the applied EM force. Additionally, the perturbation energy is mainly dissipated as frictional and strain energy. These findings provide valuable insights into the structural evolution of pebble beds under EM disturbances, offering guidance for improving the design and structural stability of pebble beds in fusion reactors.