In fusion devices, optimizing neutral beam injection systems requires improving the neutralization efficiency of negative ion beams. However, the dynamic evolution of neutralization efficiency and its dependence on beam-plasma interaction mechanisms are not yet fully understood. To address this issue, this study aims to clarify the transient neutralization dynamics of high-energy negative ion beams in plasma targets and identify the key parameters that govern the efficiency, based on a self-developed two-dimensional, three-velocity particle-in-cell/Monte Carlo collision model. The neutralization process of the negative hydrogen ion beam was systematically simulated, encompassing various operating conditions of ion beam energy (10 keV–1 MeV) and background plasma density (–). The neutralization efficiency exhibits non-monotonic behavior, reaching a peak of 79.9% for 100 keV beams at a 30% ionization degree of the background plasma before declining due to cumulative collisional losses. The maximum neutralization efficiency decreases significantly with higher beam energy but increases at elevated background plasma densities. The key factors influencing neutralization efficiency have been comprehensively identified, and partial results show good agreement with published experimental data. These findings not only enhance the theoretical understanding of neutralization mechanisms for high-energy negative ion beams, but also provide an effective reference for improving neutralization efficiency in practical applications.
This study investigates the dynamic neutralization of high-energy negative ion beams in fusion plasma, using advanced particle-in-cell simulations. It reveals the key factors affecting neutralization efficiency, such as beam energy and plasma density, providing valuable insights for improving neutral beam injection systems in fusion devices.