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Rapid thermal emittance and quantum efficiency mapping of a cesium telluride cathode in an rf photoinjector using multiple laser beamlets
oleh: Lianmin Zheng, Jiahang Shao, Eric E. Wisniewski, John G. Power, Yingchao Du, Wanming Liu, Charles E. Whiteford, Manoel Conde, Scott Doran, Chunguang Jing, Chuanxiang Tang
Format: | Article |
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Diterbitkan: | American Physical Society 2020-05-01 |
Deskripsi
Thermal emittance and quantum efficiency (QE) are key figures of merit of photocathodes, and their uniformity is critical to high-performance photoinjectors. Several QE mapping technologies have been successfully developed; however, there is still a dearth of information on thermal emittance maps. This is because of the extremely time-consuming procedure to gather measurements by scanning a small beam across the cathode with fine steps. To simplify the mapping procedure and to reduce the time required to take measurements, we propose a new method that requires only a single scan of the solenoid current to simultaneously obtain thermal emittance and QE distribution by using a pattern beam with multiple beamlets. In this paper, its feasibility has been confirmed by both beam dynamics simulation and theoretical analysis. The method has been successfully demonstrated in a proof-of-principle experiment using an L-band radio-frequency photoinjector with a cesium telluride cathode. In the experiment, seven beamlets were generated from a microlens array system and their corresponding thermal emittance and QE varied from 0.93 to 1.14 μm/mm and from 4.6% to 8.7%, respectively. We also discuss the limitations and future improvements of the method in this paper.