Speaker
Description
The SACLA linear accelerator employs a DC gun with a thermionic cathode, valued for high beam quality, excellent operational stability, and minimal maintenance. We present a comprehensive beam-dynamics analysis of this source and outline a path toward sub-micrometer (0.1 um) normalized emittance. We provide analytical estimates and particle tracking results for four dominant emittance-growth mechanisms: (1) image-charge forces at the cathode, (2) nonlinear space-charge forces arising from imperfect beam-edge geometry, (3) aberrations of the accelerating field, and (4) solenoid-field aberrations caused by longitudinal–transverse momentum exchange. From these contributions we derive a closed-form expression for correlated emittance growth and identify an ''interference'' term that amplifies the net emittance when space-charge and solenoid effects act together.
To mitigate this growth, we propose a compact hybrid magnet that tightly confines the axial field, enabling placement immediately downstream of the gun while keeping the field on the cathode negligible. The device uses permanent ring magnets positioned symmetrically around a central solenoid, allowing precise shaping and longitudinal ''squeezing'' of the field profile. The results offer a practical roadmap for SACLA and transferable insights for low-voltage continuous-wave very-high-frequency injectors and superconducting RF electron guns.
Funding Agency
AO acknowledges funding through the MSCA4Ukraine project 1232628 funded by the European Union. VG acknowledges funding from Swedish Research Council (VR, 2022-03983).
Footnotes
Published in Phys. Rev. Accel. Beams 28, 110101, 2025.
DOI: https://doi.org/10.1103/srht-5hmq
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