Computer simulations of the wiggler spectrum

Abstract

The amount of structure seen in the wiggler spectrum, particularly at energies below the critical energy, depends on several parameters such as the beam emittance, magnetic field errors and the amount of tapering of the device. Simulations will be presented using the proposed Wiggler A at the Advanced Photon Source, which may be operated both in the undulator regime and the wiggler regime. A simple description of the wiggler spectrum is presented that emphasizes the importance of the magnitude of the deflection parameter K in practical computer simulations. Results will be given for the on-axis angular flux density for K between 6 and about 8, and comparison will be made with the bending magnet approximation. It is verified that a small beam emittance will not completely smooth fluctuations in the spectrum, even for energies well above the critical energy, for an otherwise ideal insertion device. It is shown that a small gap-taper dramatically smears the harmonics and provides a bending-magnet-type spectrum well below the critical energy. The importance of being able to simulate random magnetic field errors is addressed.