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 degree 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