Computer model of crossed-field devices using moving wavelength codes

Abstract

Summary form only given, as follows. DECFA and DEMAG are moving wavelength, particle in cell codes for modeling crossed-field amplifiers (CFAs) and magnetrons. These codes are based on prior efforts of Yu, Koogers and Buneman in 1965. The codes model the interaction between a single traveling wave on a smooth anode surface and the space charge in crossed electric and magnetic fields. The detailed anode vane tip geometry is not included in the model. Periodic boundary conditions are imposed on the sides of the moving interaction wavelength thereby imposing the wave periodicity on the solution. The effect of disturbances in the space charge at other wavelengths is not considered. In spite of the assumptions involved, the codes successfully model the performance of many existing CFAs and magnetrons. Correlation of computer model and experimental results will be presented for typical devices. The only failures of the codes to correlate with device performance have occurred for small gap anode vane tip geometries which degrade the efficiency of electron collection. To avoid such possibilities, the simulation codes need to be supplemented with trajectory tracing studies of electrons between anode vanes. Results of such studies will be presented. Through their diagnostics, the codes provide a means of studying the details of the crossed-field interaction. Of particular current interest are time fluctuations of some of these diagnostics. These fluctuations appear to be chaotic in nature. They develop in the absence of any random inputs but remain bounded in magnitude. The amount of thermionic and secondary emission, are found to have a major effect on these fluctuations. These results are expected to contribute to the understanding of noise mechanisms in crossed-field devices.