Two-dimensional simulation of dense plasma focus
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摘要: 为了探究稠密等离子体焦点装置内等离子体层的运动规律以及相关设计参数的影响，利用自主开发的FOI程序对Mather型放电室结构下的等离子体层加速过程、焦点形成过程进行二维磁流体力学仿真，得到了与美国劳伦斯利弗莫尔国家实验室可见光实验图像相似的结果。同时，研究了装置的不同充气气压、电流幅值、阳极半径和阴阳极间隙对等离子体层轴向加速过程和箍缩效果的影响。计算结果表明，等离子体层会以一定的弧度沿径向压缩气体，这是引起腊肠不稳定现象的原因之一；等离子体层的轴向运动速度与装置充气压力的平方根成反比，与施加的电流成正比，与装置的阳极半径成反比；增大电流的同时需要延长装置阳极的长度，使箍缩发生在电流达到峰值的时刻；阴阳极间隙的大小对阳极附近等离子体层的轴向运动过程影响不大。Abstract: To investigate the motion law of the plasma sheath in a dense plasma focus (DPF) device and the influence of related design parameters, this paper uses a self-developed FOI program to conduct two-dimensional magnetohydrodynamic simulation of the plasma sheath motion process and focus formation process in the Mather type discharge chamber structure, and obtains results similar to the visible light experimental images of the Lawrence Livermore National Laboratory in the United States. At the same time, the influence of different pressure, current, anode radius and cathode-anode gap on the motion law of the plasma sheath is explored. The calculation results show that the plasma sheath will compress the gas radially with a certain degree of curvature, which is one of the reasons for the instability phenomenon; the axial velocity of plasma sheath is inversely proportional to the square root of pressure, and is proportional to the current. The larger the anode size of the device, the smaller the axial velocity of sheath. To increase the current, it is necessary to extend the anode length to match the focusing time with the current peak. The gap between cathode and anode has little effect on the axial motion process of plasma sheath near the anode.
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Key words:
- dense plasma focus /
- magnetohydrodynamics /
- plasma sheath /
- pinch
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图 1 计算域边界条件示意图
Figure 1. Schematic diagram of boundary conditions in computational domain
图 5 不同电流幅值对等离子体层轴向运动速度、箍缩时刻和压缩比的影响
Figure 5. Influence of different current amplitudes on axial velocity of sheath, pinch time and compression ratio
图 7 阳极半径对箍缩时刻和压缩比的影响
Figure 7. Effect of anode radius on pinch time and compression ratio
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