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稠密等离子体焦点（DPF）是一种脉冲强流放电装置，在粒子加速器、受控核聚变、空间推进及脉冲中子源等领域有着广泛应用。本文采用耦合外电路的双温磁流体动力学模型，研究了DPF的轴向加速和径向内爆过程，并探讨了装置参数对等离子体运动的影响规律。首先，通过与实验结果的对比，验证了双温磁流体模型的准确性。然后针对DPF装置开展了物理过程及规律的理论和模拟研究。研究表明在洛伦兹力的作用下，DPF等离子体鞘沿轴向不断加速，到达内电极末端后部分等离子体沿径向向内压缩，最终在对称轴上形成高温高密等离子体。对于大型DPF装置，增加电路电压能显著提升电流水平；同时阴阳极半径之比应尽可能小，这可以在其他参数不变的情况下，有效提高DPF的峰值电流和箍缩电流。Dense plasma focus (DPF) is a pulsed high current discharge device, which is widely used in particle accelerator, controlled nuclear fusion, space propulsion and pulsed neutron source. However, existing models for DPF dynamics, including semi-empirical snowplow approximations and particle-in-cell (PIC) methods, face limitations in balancing computational efficiency with comprehensive physical descriptions. In contrast, magnetohydrodynamic (MHD) models enable comprehensive analysis of macroscopic phenomena (e.g., sheath motion, current distribution, fluid instabilities) and parametric impacts (e.g., electrode geometry, gas pressure, driving current waveforms) on DPF performance. Although MHD cannot self-consistently resolve kinetic behaviors like high-energy particle beams or neutron production during pinch phases, it remains highly valuable for investigating macroscopic DPF physics when quantitative neutron yield analysis is unnecessary. Therefore, a two-temperature MHD model coupled with an external RLC circuit is developed in this paper, incorporating electron-ion thermal nonequilibrium, resistive effects, and plasma transport coefficients derived from Braginskii formulations. The model is rigorously validated against experimental data from two benchmark DPF devices (UNU and UDMPF1), demonstrating excellent agreement in current waveform, voltage profile, and radial implosion trajectory. The research shows that the DPF plasma sheath is continuously accelerated along the axial direction under the action of the Lorentz force. When it moves to the end of the inner electrode, the plasma sheath bends radially inward and is eventually compressed on the symmetry axis to form high-temperature and high-density plasma. For the UNU device, simulations reveal distinct plasma evolution phases: (1) Axial acceleration (0–2.5 μs), where the current sheath attains velocities up to 90 km/s under Lorentz force dominance, with ion temperatures rising from 1 eV to 100 eV. (2) Radial implosion (2.78–2.90 μs), during which plasma density increases by an order of magnitude (to ~10²⁴ m⁻³) and ion temperatures surge to ~1 keV through magnetically driven compression. Further studies also find that for large DPF devices, reducing the inductance and increasing the capacitance, the circuit current is prone to saturation; while increasing the circuit voltage has a more significant effect on the current increase. This paper shows that for large DPF devices, the ratio of the anode radius to cathode radius needs to be as small as possible, which can increase the peak current and pinch current of DPF as much as possible under the condition that other parameters remain unchanged.
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Keywords:
- Dense plasma focus /
- magnetohydrodynamic simulation /
- plasma acceleration /
- pinch
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