Adaptive mesh refinement for particle-tracking calculations

Particle orbit errors in multipacting and dark current computations can arise from inadequate field representation, poor surface modeling, and from the integration algorithm used to advance the particles. Established fields-based adaptive mesh refinement (AMR) methods selectively improve the field and surface representation over several iterations in finite-element codes but they are not optimized for particle tracking. In particular, field emission and secondary emission models require precise surface representations and highly accurate field representations near surfaces, and these requirements are not adequately addressed in standard AMR techniques. In this paper we report on extensions to existing AMR support in the Analyst software package for particle tracking, including adaptive improvement of near-surface and on-surface field representations. We present the application of two mesh refinement metrics to AMR in multipacting and gun code calculations. It is shown that the methods yield a rapidly convergent value for the electron gun current. In the multipacting computation example, additional resonances are uncovered that were not evident in the initial mesh.