The Magnetohydrodynamic Simulation Of A Coaxial Plasma Opening Switch

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 36.4ï¼…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.