Experimental demonstration of the correction of coupled-transverse-dynamics aberration in an rf photoinjector

The production of electron bunches with low transverse emittance approaches the thermal emittance of the photocathode as various aberrations are corrected. Recently, the coupled-transverse-dynamics aberration was theoretically identified as a significant source of emittance growth, and a corrector m...

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Published in:Physical review. Accelerators and beams 2019-07, Vol.22 (7), p.072805, Article 072805
Main Authors: Zheng, Lianmin, Shao, Jiahang, Du, Yingchao, Power, John G., Wisniewski, Eric E., Liu, Wanming, Whiteford, Charles E., Conde, Manoel, Doran, Scott, Jing, Chunguang, Tang, Chuanxiang, Gai, Wei
Format: Article
Language:English
Subjects:
Aberration
Emittance
Numerical prediction
Photocathodes
Quadrupoles
Skewed distributions
Solenoids
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Summary:The production of electron bunches with low transverse emittance approaches the thermal emittance of the photocathode as various aberrations are corrected. Recently, the coupled-transverse-dynamics aberration was theoretically identified as a significant source of emittance growth, and a corrector magnet was proposed for its elimination [Phys. Rev. Accel. Beams 21, 010101 (2018)]. This aberration arises when the beam acquires an asymmetric distribution that is then rotated with respect to the transverse reference axis, thus introducing a correlation in the vertical and horizontal planes. The asymmetry is introduced by a weak quadrupole field in the rf gun or emittance compensation solenoid and the rotation is caused by the solenoid. This manuscript presents an experimental study of the coupled-transverse-dynamics aberration in an rf photoinjector and demonstrates its elimination by a quadrupole corrector consisting of a normal and a skew quadrupole. The experimental results agree well with theoretical predictions and numerical simulations, showing that the corrected emittance could reach the thermal value for an electron bunch with a low charge and a short length.
ISSN:2469-9888
2469-9888
DOI:10.1103/PhysRevAccelBeams.22.072805