Harmonic generation FEL magnets: measured b-fields compared to 3D simulations

The Harmonic Generation Free Electron Laser is a short period, high-gain amplifier FEL configured as an optical klystron. It is designed to lase at 3.47 /spl mu/m using a 30 MeV electron beam at the Accelerator Test Facility at BNL. Each of the three superconducting wiggler magnet sections (modulator, dispersion, radiator) has been built and the magnetic fields have been measured. This paper compares the measurement results with three-dimensional nonlinear computer models created with the TOSCA code.