Applications and status of the finite-element MICHELLE gun & collector simulation code

The MICHELLE two-dimensional (2D) and three-dimensional (3D) steady-state and time-domain particle-in-cell (PIC) code has been employed successfully by industry, national laboratories, and academia and has been used to design and analyze a wide variety of devices, including multistage depressed collectors, gridded guns, multibeam guns, annular-beam guns, sheet-beam guns, beam-transport sections, and ion thrusters. Recent work has included time dependent application for rf guns and photoemission gun applications. Time domain effects in RF guns and collector modeling has shown to be an important effect to capture. Thermionic emission in IOT guns and guns operating in the transition from space charge limited to temperature limited regimes require special attention to accurately predict the gun performance. Modeling thermal beams through guns and into transport regions multiplies the run time by a factor of about the increase in the number of particles to support a thermal beam distribution. As a result, a parallel version of MICHELLE is being developed to hold run times down. In the typical vacuum tube, the beam entering a collector is often in one of two states; as a DC beam or as a spent beam resulting from an RF interaction. The DC beam entering the collector is easily treated by the steady-state algorithm. This regime of operation often gives the highest peak power loads, which is an important design constraint to manage in the development process. However, MICHELLE can apply its time-domain ES PIC model to the bunched beam as well. In this case, the spent beam from an interaction region (from an interaction code or a PIC code) is brought into the collector as a function of time. One RF period of the beam is required and it is repeated and injected into the collector domain until a time-dependent steady-state has been achieved. Examples of new capabilities and applications will be presented.