| Transmission and convergence of high power current pulses are the most important research issues for large scale pulsed power devices. Because of low inductance, high holding off electric field and high transmission energy density, magnetically insulated transmission line (MITL) has been applied widely in pulse power facilities. With the increasing of driver scale and vacuum transmission distance, positioning and support for the MITL electrodes becomes the most challenging technical problems that have to face. According to former investigations, both gravely deviation from ideal position and improper support design may result in serious energy loss even lead to transmission failure. So MITL design and fabrication are core questions which dominate final realization for pulsed power drives.In this dissertation, electrodes positioning and its influence to power flow and transmission efficiency were investigated according to coax MITL, which is the most used structures in pulsed power drivers. Research work mainly focuses on two aspects theoretically and experimentally, i.e. influence of electrode deviation to ideal position and influence of support to power flow. Work of this dissertation is aimed to explore the most possible way to introduce support structure in MITL.Theoretically, electron movement in eccentric MITL gap was analyzed with single particle model. Power flow process under condition of coax eccentricity was simulated with three dimensional particle-in-cell (PIC) codes. Circuit simulation and PIC simulation were carried out with respect to MITL performance with high inductive support. These works constitute the base for experiment design of the following work. Theoretical results indicate that eccentricity of the coax will cause MITL energy loss, which highly depends on the eccentricity degree. If with support, a10μH helical or500Ω resistor could restrict energy loss as4%, or1%, respectively.Experimentally, eccentric coax and with support were carried out to understand the influence to MITL power flow on the first fast linear transformer driver (LTD) in China, which is a10-stage driver and could generates1MV pulse on10Ω match load. In eccentricity experiment, different eccentricities were introduced artificially and tested. In support experiment, high inductive helical and high resistive insulators were used to help center the inner electrode of coax, and their influence to power flow were compared. In these experiments, a set electrical parameter diagnostic system, including D-dot, B-dot, Rogowski coil and resistor voltage divider, was build up. All of these diagnostic were optimized due to the special vacuum electronic environment in MITL gap. Eccentric experiments show that eccentric coax brings about mild current loss and serious current nonuniformity. Moreover greater eccentricity leads to more loss. A10μH helical support results in almost no loss in anode current but a little loss in cathode current (～3%). While in the resistive insulator supported MITL, anode and cathode current transmission efficiency are99.32%and99.08%, respectively. As validation for measurements, MITL voltage was calculated with flow impedance theory and compared with experiment result. The consistency indicates experimental results are believable.Works of this dissertation confirms the importance of centering MITL, and verifies the feasibilities of using high inductive helical or high resistive insulator as a support in present LTD system. In order to apply such support in higher voltage and higher power MITLs, inductive support needs to consider multi-point supporting and the inductance reduction induced. Resistor support needs to consider the problems of high voltage insulation and voltage grading. Work of this dissertation is an exploration to long MITL designs in the next generation.of pulsed power drivers, and is helpful to deepen our understanding to vacuum power flow under the actual engineering status. |
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