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- Q.T. Zhao, G. Asova, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, M. Krasilnikov, X. Li, O. Lishilin, G. Loisch, D.M. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, T. Rublack, C. Saisa-ard, F. Stephan
DESY Zeuthen, Zeuthen, Germany
- G. Asova
INRNE, Sofia, Bulgaria
- C. Saisa-ard
Chiang Mai University, Chiang Mai, Thailand
- Q.T. Zhao
IMP/CAS, Lanzhou, People's Republic of China
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The Photo Injector Test Facility at DESY in Zeuthen (PITZ) was built to test and optimize high-brightness electron sources for free electron lasers (FELs) like FLASH and European XFEL. Although the beam emittance has been optimized and experimentally demonstrated to meet the requirements of FLASH and XFEL, transverse beam asymmetries, such as wing structures and beam tilts, were observed during many years of operation with different generations of guns. These cannot be explained by simulations with the rotationally symmetric gun cavities and symmetric solenoid fields. Based on previous RF coupler kick, solenoid field imperfection studies and coupling beam dynamics, the beam asymmetries most probably stem from rotated quadrupole field error in the gun section. A thin-lens static quadrupole model is applied in the RF gun section simulations to fit the position and intensity of quadrupole field errors by comparing the beam asymmetry directions in experiments and ASTRA simulations. Furthermore, by measuring the laser position movement at the photo cathode and the corresponding beam movement at downstream screens, the integrated quadrupole field strength can also be extracted.
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