Abstract
Emittance is a key figure-of-merit for high brightness electron beams that enable the success of a broad range of modern accelerator-based instruments. With the successful implementation of the emittance compensation scheme and beam-shaping techniques to align each temporal beam slice in phase space, slice emittance starts to play a more dominating role in determining the beam quality. In this paper, we develop an approach, combining simulations and analytical calculations, to systematically study the evolution of the slice emittance in a very high frequency gun photoinjector, which is under intense R worldwide for driving the next generation continuous-wave accelerators. Our approach is capable of tracing various sources that introduce curvature in the transverse phase space, corresponding to the growth of the slice emittance. It is shown that nonlinear transverse space charge forces in the vicinity of cathodes and the spherical aberration of the focusing solenoid are the main sources of nonlinear forces, while in a long drift section space charge forces can actually compensate for nonlinear transverse position-momentum correlations and hence recover the emittance. We further demonstrate that the sources of nonlinearities can be controlled by tailoring the transverse beam density profile and the design of solenoid lenses.
Highlights
Beam transverse emittance is a key figure of merit for photoinjector-driven electron accelerators, such as freeelectron lasers (FELs) [1,2,3,4,5,6], inverse Compton scattering sources [7,8], energy recovery linacs [9,10], and ultrafast electron diffraction [11,12] and microscopy [13,14,15]
The evolution of the slice transverse emittance in a very high frequency (VHF) gun photoinjector has been systematically studied in this paper
We found that the slice emittance accounts for a large proportion of the final projected emittance
Summary
Beam transverse emittance is a key figure of merit for photoinjector-driven electron accelerators, such as freeelectron lasers (FELs) [1,2,3,4,5,6], inverse Compton scattering sources [7,8], energy recovery linacs [9,10], and ultrafast electron diffraction [11,12] and microscopy [13,14,15]. This paper focuses on the beam transverse emittance evolution in a VHF gun photoinjector. Numerous theoretical models have been established and experiments have been performed to best align the transverse phase space of the beam temporal slices, minimizing the projected emittance of the entire beam. The evolution of the slice transverse emittance is analyzed in a VHF gun photoinjector, and the sources of nonlinear transverse forces leading to slice emittance growth are studied with theoretical analysis and beam dynamics simulations. IV, we will demonstrate that the evolution analysis exhibited in the VHF gun photoinjector can be employed in typical S-band photoinjectors
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