DEVELOPMENT OF AN ADVANCED COMPUTATIONAL TOOL FOR START-TO-END MODELING OF NEXT GENERATION LIGHT SOURCES

Start-to-end simulation plays an important role in designing next generation light sources. In this paper, we present recent progress in a parallel beam dynamics code, IMPACT, towards the fully start-to-end, multi-physicssimulation of a next generation X-ray FEL light source. We will discuss numerical methods and physical models used in the simulation. We will also present some preliminary simulation results of a beam transporting through photoinjector, beam delivery system, and FEL radiation. COMPUTATIONAL FRAMEWORK The computational framework used for the start-to-end simulation of next generation light sources is the IMPACT code suite. The IMPACT code is a parallel particle-incell code suite for modeling high intensity, high brightness beams in rf proton linacs, electron linacs and photoinjectors. It consists of two parallel particle-in-cell tracking codes IMPACT-Z [1, 2] and IMPACT-T [3] (the former uses longitudinal position as the independent variable and allows for efficient particle advance over large distances as in an RF linac, the latter uses time as the independent variable and is needed to accurately model systems with strong space charge as in photoinjectors), an rf linac lattice design code, an envelope matching and analysis code, and a number of pre- and post-processing codes. Both parallel particle tracking codes assume a quasi-electrostatic model of the beam (i.e. electrostatic self-fields in the beam frame, possibly with energy binning for a beam with large energy spread) and compute space-charge effects self-consistently at each time step together with the external acceleration and focusing fields. The 3D Poisson equation is solved in the beam frame at each step of the calculation. The resulting electrostatic fields are Lorentz transformed back to the laboratory frame to obtain the electric and magnetic self-forces acting on the beam. There are six Poisson solvers in the IMPACT suite, corresponding to transverse open or closed boundary conditions with round or rectangular shape, and longitudinal open or periodic boundary conditions. These solvers use either a spectral method for closed transverse boundary conditions, or a convolutionbased Green function method for open transverse boundary conditions. The convolution for the most widely used open boundarycondition Poisson solver is calculated using an FFT with a doubled computational domain. The computing time of this solver scales like Nlo g(N ) ,w here N