Abstract
A complete characterization of the time-resolved longitudinal beam phase space is important to optimize the final performances of an accelerator, and in particular this is crucial for Free Electron Laser (FEL) facilities. In this paper we propose a novel method to characterize the profile of a relativistic electron bunch by passively streaking the beam using its self-interaction with the transverse wakefield excited by the bunch itself passing off-axis through a dielectric-lined or a corrugated waveguide. Results of a proof-of-principle experiment at the SwissFEL Injector Test Facility are discussed.
Highlights
Several Free Electron Laser (FEL) facilities are in operation and other are being built to produce high power X-ray coherent radiation, which is used for applications in physics, biology and material science
Shot-to-shot rf phase and electron bunch arrival time jitter translate to an orbit and a transverse position jitter downstream of the transverse deflecting structures (TDS) and on the profile monitor
Several possibilities have been considered to manipulate a relativistic beam using its interaction with the longitudinal wakefield excited by it passing in a dielectric-lined or a corrugated waveguide. They include the possibility to compensate for the energy chirp [10,11,12], and in general to linearize the longitudinal phase space beam distribution resulting from the bunch compression process [13,14], and to drive coherent terahertz radiation inducing an energy modulation [15]
Summary
Cylindrical symmetric dielectric-lined waveguide have been investigated in [17,18,19,20,21,22,23], respectively. For an unambiguous reconstruction of the current profile, the wake potential along the electron bunch must be a strictly monotonic function of the beam longitudinal coordinate. The inputs for the algorithm were the simulated transverse profiles of the beam at the screen when passing on-axis and off-axis in the passive streaker This proves the validity of the reconstruction algorithm when the wake function is known and the wake potential is a monotonic function along the full electron bunch length. Instead, considering both dipole and quadrupole wakes (solid line), there is excellent agreement between the measurement and the model expectation. The linear and the cubic kick factors calculated from the model are 0.62 MV=ðnC m mmÞ and 0.52 MV=ðnC m mm3Þ, respectively, whereas by fitting the experimental data with a cubic polynomial, the corresponding linear and cubic kick factors are 0.63 MV=ðnC m mmÞ and 0.43 MV=ðnC m mm3Þ
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