Applications of the michelle 2d/3d electron gun and collector code

Abstract

Summary form only given. Three-dimensional (3D) electron guns, focusing channels, and collectors are the trend to improved device performance, and accurate modeling of these devices leads to reductions in development time and costs. This includes gridded guns, multibeam guns, sheet beam guns, quadrupole focusing, multibeam collectors, and asymmetrical collectors. The new MICHELLE1 2D/3D steady-state and time-domain particle-in-cell (PIC) code that employs electrostatic and now magnetostatic finite-element field solvers. In recent years the code has been employed successfully to design and analyze a wide variety of devices that include the above and also ion thrusters. In this presentation we will present how MICHELLE has been used to model a variety of devices. Two designs in particular are a MM/SMM wave sheet beam gun and a Ka band gun with quadrupole (strong) focusing. The design of a sheet beam electron gun is underway at NRL for application to a MM/SMM wave orotron. The gun design parameters are for a beam of 3 mm by 40 mum (aspect ratio of 75:1), and a total current of 50-100 mA. The smaller of these dimensions is set by the requirement that the beam thickness be smaller than the transverse scale length of Lperp = gammabetalambda/2pi. The preliminary gun design utilizes an immersed flow design with a flat rectangular cathode. Further results from this design effort will be presented. At mm-wavelengths, a key limitation to the peak and average power of vacuum electronics devices stems from the difficulty of control and confinement of high-current density beams. In this paper we summarize an ongoing design study of a strong-focusing lattice employing permanent magnet quadrupoles (PMQs) capable of transporting a sub-mm radius electron beam for vacuum electronics applications