Three-dimensional, time-dependent simulation of Inductive Output Tubes

We report on a 3-dimensional (3D), time-domain simulation code (NEMESIS [1]) for Inductive Output Tubes (IOTs). NEMESIS integrates the equivalent circuit equations in time coupled with the Lorentz force equations for particle trajectories. The RF fields are found by using the cavity voltage as a scale factor in either an analytic model (Kosmahl and Branch [2]) or by means of a 3D field map generated by electromagnetic structure simulators. The electron trajectories are integrated in these RF fields as well as using magnetostatic focusing fields. Two Poisson solvers had previously been implemented in 2D: (1) using the method of successive over relaxation (SOR), and (2) a multi-grid (MG) algorithm. NEMESIS was successfully benchmarked [1] for an IOT developed at CPI (K5H90W-2) using the SOR solver, and this result was recovered using the MG solver. We report on the implementation of a fully 3D Poisson solver based on the PETSc library [3]. The IOT used to validate NEMESIS is azimuthally symmetric; hence, a 2D solution is/was adequate to simulate the tube. Initial results in 3D, therefore, primarily constitute a test of the 3D algorithm. The initial 3D simulations are in agreement with the former 2D results. The impact of the additional number of macro-particles and grid cells on the run time of the 3D formulation is not excessive compared to the 2D simulation. The technique, results, and run times will be discussed, as will future research plans.