Paper  Title  Page 

TPAT023  Tests of a 3D Self Magnetic Field Solver in the Finite Element Gun Code MICHELLE  1814 


Funding: Work supported by ONR. We have recently implemented a prototype 3d self magnetic field solver in the finiteelement gun code MICHELLE. The new solver computes the magnetic vector potential on unstructured grids. The solver employs edge basis functions in the curlcurl formulation of the finiteelement method. A novel current accumulation algorithm takes advantage of the unstructured grid particle tracker to produce a compatible source vector, for which the singular matrix equation is easily solved by the conjugate gradient method. We will present some test cases demonstrating the capabilities of the prototype 3d self magnetic field solver. One test case is self magnetic field in a square drift tube. Another is a relativistic axisymmetric beam freely expanding in a round pipe. 

TPAT043  The MICHELLE 2D/3D ES PIC Code: Advances and Applications  


Funding: Office of Naval Research, Naval Research Laboratory.
MICHELLE is a new 2D/3D steadystate and timedomain particleincell (PIC) code* that employs electrostatic and now magnetostatic finiteelement field solvers. The code has been used to design and analyze a wide variety of devices that includes multistage depressed collectors, gridded guns, multibeam guns, annularbeam guns, sheetbeam guns, beamtransport sections, and ion thrusters. Latest additions to the MICHELLE/Voyager tool are as follows: 1) a prototype 3D self magnetic field solver using the curlcurl finiteelement formulation for the magnetic vector potential, employing edge basis functions and accumulating current with MICHELLE's new unstructured grid particle tracker, 2) the electrostatic field solver now accommodates dielectric media, 3) periodic boundary conditions are now functional on all grids, not just structured grids, 4) the addition of a global optimization module to the user interface where both electrical parameters (such as electrode voltages)can be optimized, and 5) adaptive mesh refinement improvements. Applications illustrating these latest additions will be presented, including a relativistic sheet beam gun, a relativistic MIG gun, and a depressed collector optimization example.
*John Petillo, et al., IEEE Trans. Plasma Sci., vol. 30, no. 3, June 2002, pp. 12381264. 

WPAT077  FiniteElement 2D & 3D PIC Modeling of RF Devices with Applications to Multipacting  


Multipacting currently limits the performance of many high power radiofrequency (RF) devices, particularly couplers and windows. Models have helped researchers understand and mitigate this problem in 2D structures, but useful multipacting models for complicated 3D structures are still a challenge. A combination of three recent technologies that have been developed in the Analyst and MICHELLE codes begin to address this challenge: highorder adaptive finiteelement RF field calculations, advanced particle tracking on unstructured grids, and comprehensive secondary emission models. Analyst employs highorder adaptive finiteelement methods to accurately compute driven RF fields and eigenmodes in complex geometries, particularly near edges, corners, and curved surfaces. To perform a multipacting analysis, we use the mesh and fields from Analyst in a modified version of the selfconsistent, finiteelement gun code MICHELLE. MICHELLE has both a fast, accurate, and reliable particle tracker for unstructured grids and a comprehensive secondary emission model. We will demonstrate this capability on an RF coupler. 