I will present an ongoing research on wakefield and wakepotential calculation for ultra-relativistic electron bunch moving through accelerating cavity structures.

Accurate and efficient numerical tools have become the key demands for the design of accelerator as the bunch length of interest is getting shorter for modern accelerator. To help the study on the effects of very high frequency elecromagnetic fields generated by short bunches within accelerating components, we have developed a high-order spectral element discontinuous Galerkin code, NEKCEM. NEKCEM is designed for high performance on parallel, and provides mesh capability for complex structures.

Maxwell equations are solved to obtain the wake field of a Gaussian bunch moving at the speed of light, and wakepotentials are computed by integrating the wake force over time for various cavity structures. I will demonstrate wake potential calculations for cylindrically symmetric cavity structures with arbitrary transition between circle-cross sections on various bunch sizes. This work shows a first step to simulate ultimately 1-km-long accelerator structure for short bunch, typically 0.1 milimeter.