Magnet and Tracking Analysis of Quadrupole Scanning Method for Emittance Measurement

Since transverse emittance serves as a critical parameter for evaluating the performance of an electron-beam injector, accurate emittance measurement directly affects the engineering realization of not only the injector but also the entire accelerator-based facility involved. Based on the typical beam injector developed at Huazhong University of Science and Technology (HUST injector), the quadrupole magnet scanning (Q-scanning) method is employed for emittance measurement. Suitable selections are made for the existing devices within the beamline, which reduce the measurement errors associated with emittance. An analysis is conducted on the selected quadrupole magnets (Q-magnets), along with an examination of the impact of fringe fields on emittance measurements, including the effects of different edge field conditions and the direct representation of fringe fields in the transfer matrix. The analysis results clearly demonstrate the importance of device selection in the Q-scanning method and the direct effects of fringe fields on various aspects.