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The multipactor (MP) is a well-known phenomenon. The existence of resonant trajectories can lead to electron avalanche under certain field levels and surface conditions, and can limit the performance of high power superconducting (SC) radio-frequency (RF) devices. In this paper we describe features of the ANALYST particle tracking code PT3P developed for MP simulations in real 3D RF structures, such as cavities, couplers, RF windows etc. Also we present the results of MP simulations in HOM couplers of TESLA, SNS and FNAL 3 rd harmonic cavities. We discuss the comparison of simulations with experimental results.

The 3D finite-element gun and collector modeling code, MICHELLE, has been under development at SAIC in collaboration with industrial partners and national laboratories (ref. 1). This development program has been designed to address the shortcomings of current beam optics simulation and modeling tools for vacuum electron devices. The program specifically targets problem classes including gridded-guns, sheet-beam guns, multi-beam devices, and anisotropic collectors, with a focus on improved physics models. The code includes both structured and unstructured grid systems for meshing flexibility. Advances have been made in the areas of accurate particle tracking through the mesh and beam emission methods, including new models for thermionic, temperature-limited, Child's law and secondary emission.

The MICHELLE code is a new Finite-Element (FE) two-dimensional (2D) and threedimensional (3D) electrostatic particle-in-cell (PIC) code that has been designed to address the recent beam optics modeling and simulation requirements for vacuum electron devices, ion sources, and charged-particle transport. Problem classes specifically targeted include depressed collectors, gridded-guns, multi-beam guns and sheet-beam guns. The focus of the development program is to combine modern finite-element techniques with improved physics models. The code employs a conformal mesh, including both structured and unstructured mesh architectures for meshing flexibility, along with a new method for accurate, efficient particle tracking. New particle emission models for thermionic beam representation are included that support primary emission, and secondary emission is handled with an advanced model. This presentation focuses on two significant advances to MICHELLE over the past year; hybrid structuredunstructured mesh support, and a time-domain electrostatic algorithm.With hybrid structuredunstructured mesh support, MICHELLE takes advantage of the best features of both meshes. Smooth, Htructured mesh blocks enable fast accurate particle tracking in simple geometric regions. Unstructured mesh blocks facilitate mesh generation in the vicinity of complicated geometry, where structured blocks are difficult or intractable. Unstructured blocks also accommodate adaptive mesh refinement.The electrostatic time-domain model represents MICHELLE evolving to the next level. Many problems exist where a time-domain electrostatic model is appropriate. The MICHELLE architecture was specifically designed to support both the steady-state "gun" model and the time domain model. *

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