Phase errors and predicted spectral performance of a prototype undulator

A prototype undulator (3.3 cm period, permanent‐magnet hybrid device) has been used to study different magnetic end configurations and shimming techniques for straightening the beam trajectory. Field distributions obtained by Hall‐probe measurements were analyzed in terms of trajectory, phase errors, and on‐axis brightness for the purpose of correlating predicted spectral intensity with the calculated phase errors. An rms phase error of less than 3° is found and 87% of the ideal value of the on‐axis brightness for the third harmonic (nominal gap is 11.5 mm and derived effective K is 2.25) is predicted. The gap dependence of the phase errors and spectral brightness was also analyzed and it was found that the rms phase error remains small at all gap settings.