Program UR: General purpose code for synchrotron radiation calculations

Abstract

A computer code for calculating synchrotron radiation emitted by a relativistic particle moving in an arbitrary three-dimensional magnetic field is described. The electric and magnetic fields (Liénard-Wiechert fields) are calculated in the time domain, and a Fourier transform of the radiation field yields the radiation spectrum over a large range of harmonic frequencies. The code is completely general accepting either a measured magnetic field map or a simulated field representing, for example, a tapered undulator. Simple expressions are derived for the fields and the equations of motion using the transverse beam angles as variables. The horizontal and vertical polarized components are expanded to second order in the beam angles, the observation angles, and the opening angle of radiation (1/γ), and the three-dimensional equations of motion are solved numerically at each time step, making the code fast and reliable. The beam emittance and the beam energy spread are simulated by either Monte Carlo sampling or deterministic sampling. Comparison with two other codes will be presented. Good agreement was found in both cases. As a practical example, we examined the effect of random magnetic field errors on the on-axis angular flux density for Undulator A at the Advanced Photon Source. It was confirmed that random magnetic field errors play an important role when predicting the spectral performance of real-life insertion devices.