Magnetic measurements and analysis of trajectory straightness of 20 mm period hybrid undulator

摘要

The U20 is a prototype NdFeB-cobalt steel hybrid device of 20 mm period length with twenty five periods and designed to provide a magnetic flux density from 2400 G (rms) to 500 G (rms) in the 10 mm-20 mm gap range. The electron trajectory and the field harmonics are analyzed on the basis of the Hall probe measurements on U20. The electron trajectory of the U20 undulator lacks straightness. The trajectory straightness is done by locally manipulating the magnetic field strengths at select locations. It is demonstrated that improvement of the phase error and field harmonics are achieved through trajectory straightness.