ATRAP: A 2D1/2 beam dynamics code using the Lienard-Wiechert's equations

This paper describes ATRAP (Acceleration and TRAnsport of Particles), a numerical code simulating the beam dynamics. The first objective of this code is the beam quality optimization, in the first meters of an accelerator line, like a photo-injector, for an axi-symmetrical problem and for a negligible weakfield. If the weakfield can be neglected, we do not need to develop a self-consistent code. The Maxwell's equation solution can be obtained with the Lienard-Wiechert' equations for the field created by the charges, and with a spatial harmonic expansion for the external fields. Another major problem in a beam dynamic code is the beam charge modelization. It has been shown [1] that the Gaussian assignment algorithm is superior to the other techniques used. In ATRAP, different algorithms and analytical developments are used, which permit us to keep the same accuracy as that of a self consistent code, reducing the computation time.