L Ge, L Lee, A. Candel, C Ng, K Ko, SLAC A Moving Window Algorithm with h and p Refinements on Unstructured Grids for Accelerator Wakefield Computations L Ge, L Lee, A. Candel, C Ng, K Ko, SLAC X Luo, M Shepard, RPI The moving window technique is commonly used in simulating short-range wakefields in particle accelerators to reduce computational requirements and its implementation on the finite-difference grid is straightforward. We present the first parallel algorithm for using moving window on the unstructured finite-element grid to resolve small beam bunches with higher resolution and increased speed. This capability has been developed to allow h or/and p refinement with curvilinear tetrahedral meshes and incorporated into the SLAC 3D parallel time domain field solver T3P. Application to an accelerator cavity coupler shows a tenfold reduction in execution time and memory usage without loss in accuracy . Moving Window using p-refinement Motivation Short-range wakefield simulation High resolution is required in the beam region Only beam region needs to be simulated Moving window techniques commonly used in finite difference grids to reduce computational requirements Inside window: p > 0 Outside window: p = 0 Significantly reduces execution time and memory usage Snapshots of electric fields in wakefield calculation ILC coupler short-range wakefield simulation 800 micron beam size 400 micron edge length 13 million elements 5 windows in the run 1/10th of execution time 1/10th of memory usage Beam size ~ 300 micron Beam pipe radius: 39 mm Estimated > 100 million tetrahedral elements 4 1 Parallel Finite-Element Time-Domain Solver – T3P Moving Window using h-refinement Inhomogeneous vector wave equation: Refine mesh only around moving beam 2 Spatial discretization: Hierarchical edge based finite-elements Transfer solution vectors using a new projection method; significantly reduce computational resources Temporal discretization: implicit Newmark-beta scheme Each time step, solve the following linear system: are previous and current step’s unknown and driven force Electric fields with three refined meshes 5 2 Moving Window technique in T3P Summary and Future Work First moving window algorithm for short-range wakefield computations with unstructured grids h/p refinement with curvilinear tetrahedral meshes to be transferred from current window configuration to the next window configuration when particle beam moves out of the window Both moving window techniques in h- and p- refinements are validated by simulations New projection method is an effective and accurate way for parameter transfers between two meshes. Both h- and p- refinements can drastically reduce execution time and memory usage Future work: Make mesh refinement on-line Combine p- and h- refinements in a single moving window Beam transit through three refined meshes Solution transfer Solution transfer 3 6 This work is supported by U.S. DOE ASCR, BES & HEP Divisions under contract DE-AC02-76SF00515.