稠密等离子体焦点粒子-流体混合模拟

The Dense Plasma Focus (DPF) is a high-energy-density plasma device capable of producing extreme plasma conditions, which makes it promising for applications in fusion energy, radiation sources, and materials science. However, the dynamical process of DPF involve multi-scale processes, ranging from macroscopic magnetohydrodynamic (MHD) instabilities to microscopic kinetic ion behavior, which are not fully captured by traditional single-approach simulations. In this study, a self-consistent electromagnetic hybrid simulation framework is developed to investigate the complete physical process of DPF, including the run-down, run-in, pinch formation, and generation of high-energy ion beams. In the proposed model, ions are treated kinetically using the particle-in-cell (PIC) method, while electrons are described as a quasi-neutral massless fluid. The full set of Maxwell’s equations is solved by the finite-difference time-domain (FDTD) method without invoking the Darwin approximation, allowing electromagnetic waves to propagate self-consistently in both plasma and vacuum regions. A predictor-corrector iteration scheme is implemented to ensure stable and accurate time advancement in the hybrid algorithm. The model is first validated against simulation results from the LLNL laboratory obtained with the LSP code, showing good agreement in pinch timing despite slight differences in plasma geometry. Further validation with the UNU device confirms the accuracy of the hybrid model in simulating axial acceleration and circuit coupling. Using the verified model, the full DPF process is simulated. It is revealed that during the pinch phase, m = 0 magnetohydrodynamic instabilities lead to the formation of localized plasma necks, where magnetic fields exceed 200 T and axial electric fields reach ~10¹¹ V/m. These extreme fields accelerate ions to energies up to 1.5 MeV, and a broad spectrum of ~100 keV ion beams is also observed. The results indicate that beam-target interactions driven by these accelerated ions constitute the primary mechanism for neutron production in DPF. This work demonstrates that the hybrid PIC-fluid-FDTD approach provides an efficient and physically comprehensive tool for modeling multi-scale plasma dynamics in DPF and similar high-energy-density devices.