Analytic Model and Optimization of Transmission-Line Impedance Transformers for Tens of MA-Class Pulsed Power Accelerator

The monolithic radial transmission line (MRTL) is a key component in tens of MA-class pulsed power accelerators, which connects the multiparallel modules of the prime pulsed power sources to the central vacuum insulator stack and magnetically insulated transmission line (stack-MITL system). The choice of electrical parameters of MRTL is essential for the entire accelerator design, which would bring great influences on the peak output current and the power couple efficiency. In Phys. Rev. Special Topics-Accel. Beams, 2015, 18(10): 110401, some semianalytical formulae have been proposed to optimize the MRTL impedance that maximizes the peak current or peak power on the stack-MITL system. However, the formulae are only valid under several assumptions that are thought to be unpractical. In this article, an analytic model of the accelerator is developed to optimize the electrical parameters of MRTL. Analytical expressions of the output voltage and current at the terminal of MRTL are deduced. By simplifying the analytic model, mathematical expressions of the optimal MRTL output impedance that maximizes the peak current or peak power delivered from the prime power sources to the stack-MITL system are obtained. The factors that contribute to the optimal impedance are analyzed comprehensively with short-circuit load and Z-pinch load. Conclusions are beneficial to design the pulsed power accelerator in the future.