Computational Techniques for Pulsed Power Design

As modern pulsed-power drivers increase in size and complexity, traditional experimentally based design techniques become impractical. A combination of computational capabilities is necessary for the timely and cost effective design of multi-MJ, 100-ns pulsed power generators operating above 6 MV and 20 MA. We describe the use of several codes needed to optimize the performance of the various pulsed power components in such a generator. The basic elements of machine design require: detailed circuit design codes, and 3-D electrostatic codes, in a 3-D electromagnetic codes/particle-in-cell codes. Circuit codes such as Screamer, Bertha, and PSpice are critically needed to optimize the overall performance of the generator by determining the circuit values of the individual generator components. Very fast codes are needed to complete this iterative solution. The 3-D electrostatic codes such as Coulomb, HiPhi, and Emphasis/Eiger are the workhorses of electrical design and provide the initial mechanical design of most of the high voltage components. Issues such as electric field grading, triple point shielding, electrical field shaping, and field enhancements are only a few of the design elements that must be considered. Electrostatic modeling is inadequate in situations where time- and space-dependent fields exist. In such cases, time-dependent electromagnetic calculations in three spatial dimensions are critical. Maxwell 3-D and Emphasis/Nevada can be used to model the time-dependent electromagnetic effects on critical accelerator elements such as gas switches and complex conducting structures. Using E&M PIC codes such as Quicksilver in 3-D, we can model the performance of vacuum insulator stacks, magnetically insulated vacuum transmission lines (MITLs), and vacuum convolutes. Critical issues include vacuum electron flow, electron losses, and convolute magnetic field nulls. We present examples of real world calculations using these tools on state-of-the-art pulsed power designs