【作者】 徐翔；

【导师】 王友年；

【作者基本信息】 大连理工大学 ， 等离子体物理， 2007， 博士

【摘要】 等离子体断路开关(Plasma Opening Switch，简称POS)是脉冲功率驱动器中的关键器件之一。基于等离子体断路开关的电感储能装置较电容储能装置而言具有体积小、成本低、结构简单等优点，在Z箍缩、高功率微波、X射线源、可重复脉冲功率源等装置的设计中有广泛的应用前景。实验已经发现：在POS的导通过程中存在许多复杂的物理现象，如磁场的快速穿透、等离子体密度出现薄化和形成密度激波、多离子体系中轻重离子分离等。这些现象对POS的导通和断开有重要的影响，特别是能量输运将直接影响脉冲功率驱动器的能量转换效率。因此，非常有必要对POS的导通过程及相关物理现象产生的机理进行深入细致地研究。在第二章，基于包含能量输运过程的二维磁流体动力学(Magnetohydrodynamics，简称MHD)理论，我们对柱状长导通POS中导通阶段进行了模拟。结果发现：高密度POS的导通机制是MHD机制，主要是磁压作用决定磁场的穿透过程。在磁场的穿透过程中，磁压使得等离子体在磁场穿透的区域出现密度薄化现象，在磁场激波前沿形成密度激波。同时，由磁压导致的压缩效应使得激波区域的等离子体温度迅速升高。而对于低密度的POS，其导通机制是Hall MHD机制，主要由Hall效应来决定磁场的穿透过程。由于磁压的作用很小，在磁场的穿透过程中并没有出现密度薄化现象，形成的密度激波也不明显，等离子体的温度也没有显著升高。对于低密度长导通的POS，主要是焦耳热的作用使得等离子体的温度上升。考虑能量输运后产生的温度梯度力，对高密度POS中的磁场穿透过程有显著的加速作用，而对于低密度POS中的磁场穿透过程影响不大。在第三章，基于MHD理论，我们推导出高密度长导通POS中能量分配关系的一般表示式，并研究了不同的输入电流波形对能量分配关系的影响。模拟结果表明，当发生器中的电流波形是常电流时，有一半的电磁场能耗散为等离子体的内能和动能；当发生器中的电流波形是线性上升电流时，进来的电磁场能有三分之二转化为磁场能；当发生器中的电流波形是正弦电流波形时，有大半的能量转化为磁场能，扩散到等离子体中的能量只为总能量的36.4％。由于等离子体温度显著升高，有相当多的电磁场能转化为等离子体的内能。在第四章，为了检验程序的可靠性，对长导通POS中的定标关系进行了模拟。首先将模拟结果与理论得到的定标关系进行比较，发现两者是一致的。接着又进一步对HAWK装置中的定标关系进行了模拟，发现模拟结果和实验结果也是吻合的，从而验证了模拟程序的可靠性。本文还在模拟中，把POS右边的真空区包含进来，对在最近的纯氢实验中观察到与传统的定标关系不符的现象给出了的解释。在模拟中发现，漂移到POS下游区的等离子体可显著延长POS的导通时间。考虑下游区等离子体的影响后得到的定标关系，和实验比较相符。在第五章，基于双流体理论，假设电子和离子的温度在导通过程中是恒定的，建立了二维双流体程序，对短导通POS的导通阶段进行了模拟。模拟结果表明：随着POS的导通，出现明显的电荷分离现象，电子从阴极向阳极运动的轨迹象一个S型，在阳极表面形成堆积。在模拟中还观察到明显的轻重离子分离现象。由于轻离子的质量远小于重离子，轻离子的运动的远比重离子快，最终轻离子在磁场前面被反射，而重离子被磁场所穿透。更多还原

【Abstract】 The plasma opening switch (POS) is one of the crucial components for inductive-energy storage pulsed-power accelerators, which have many advantages over the conventional capacitive-energy storage accelerators regard to cost and size, and have wide applications including fast Z pinches, high-power microwaves, X-ray lasers, generation of particle beams, and development of repetitive puled-power sources. Moreover, many complex phenomena such as the fast penetration of magnetic field, the rarefaction of plasma density, the formation of density shock, the ion-species separation in a multi-species POS plasma, and so on, have been found in the conduction phase of a POS. These phenomena play an important role on the conducting and opening of a POS. Especially, the energy transport between plasma and magnetic field is important, and correlates directly with the working efficiency of generator. Therefore, it is very necessary to investigate these phenomena to find the mechanism of a POS conducting and opening.In Chapter 2, based on the single-fluid MHD equations conjunction with the generalized Ohm’s law, a two-dimensional (2D) MHD code has been developed to study the conduction phase of a coaxial long-conduction POS. For the high-density POS, it is found that the magnetic pressure mainly determines the plasma behavior, and the convection effect dominates the penetration of magnetic field. With the penetration of magnetic field, the plasma near the cathode is rarefied, and is compressed by magnetic pressure in the shock region. The temperature of plasma increases noticeably due to the compression effect. But for the low-density POS, it is shown that the Hall effect determines the penetration of magnetic field, and the role of magnetic pressure is little. Therefore, the density rarefaction and the density shock are not noticeable, and the plasma temperature only increases moderately because of the Joule heating. Besides, the influence of the temperature gradient force on the penetration of magnetic field is also investigated. The force of temperature gradient enhances the magnetic penetration significantly in a high-density POS due to the noticeable increase of temperature, but in a low-density POS, it plays little role.In Chapter 3, the energy balance is studied in a coaxial high-density long-conduction POS. The energy transfers between the plasma and the magnetic field are considered in the conduction phase. The focus is on the energy partition between magnetic-field energy and dissipated magnetic-field energy with different rise-in-time electric currents at the generator boundary. It is shown that in the constant-in-time current case, half of the incoming electromagnetic energy goes into the plasma thermal energy and kinetic energy. In the linear rise-in-time current case, about one-third of the total energy dissipates into plasma. In the sinusoidally rise-in-time case, the dissipated energy is 36.4％of the input energy. It is also found that a considerable amount of the input energy goes into plasma thermal energy due to the compression effect and Joule heating effect.In Chapter 4, the scaling relations in a high-density long-conduction POS are investigated to test the code. The simulation results are compared with theoretical data and experimental data. It is shown that all the three groups data match well, which demonstrates that simulations in the paper are reliable. Moreover, an explanation for the recent experiment results using pure hydrogen plasma is given by simulations including the vacuum region on the POS right. It is shown that the downstream plasma plays an important role on the POS conducting. The scaling relation gained by taking into account the influence of downstream plasma approaches the experimental data.Finally, in Chapter 5, a 2D code has been developed to study the conduction phase of a short-conduction POS based on the two-fluid MHD equations conjunction with Maxwell equations, with the assumption that the temperatures of electrons and ions are constant. With the penetration of magnetic field, the charge separation is found. Electrons move from cathode to anode rapidly, and its orbit is like the character S. Meanwhile, ions move slowly. For the multi-species plasma, the ion-species separation is observed. The heavy ions are penetrated by the magnetic field, but the light ions are reflected by the magnetic field.更多还原