Numerical simulations of high-power diodes

The numerical simulation of intense electron and ion beam diodes is an important tool in the understanding of these devices. Many different computer codes have been written to investigate various aspects of diode design, performance, and scaling. Several engineering codes will be described. Two types of two-dimensional particle-in-cell (PIC) diode simulation codes have been used at Sandia National Laboratories in high-power diode research; an electrostatic-magnetostatic code and a fully electromagnetic code. In a steady-state simulation, the voltage across the diode anode and cathode electrodes is held fixed at some value (peak voltage for example) and the simulation is continued until the gross diode features such as total current or potential distribution undergo acceptably small fluctuations about a steady-state. These codes have been very useful in understanding the effect of various parameter variations on diode performance. As the general understanding of these diodes has improved, more detailed time-dependent information has been required. Fully electromagnetic codes have been developed and applied to diode simulations to investigate inductive effects and to answer questions concerning electromagnetic stability. For example, MAGIC[1] (an electromagnetic code written by B. Goplen of Mission Research Corporation) has been used to address issues such as stability and efficiency in pinched electron beam and applied-B field ion diodes. Some examples of steady-state and electromagnetic simulations will be presented. The particular example of the Hybrid ion diode will be discussed.