Beam dynamics study of the photoinjector at Wuhan advanced light source

A full-energy LINAC is under development at Wuhan Advanced Light Source (WALS) to provide beams for the 1.5 GeV storage ring proposed as a fourth-generation synchrotron radiation light source and a future free electron laser (FEL) facility. The LINAC starts from a photoinjector that is able to produce electron beams with low emittance (< 1 mm·mrad), small relative energy spread (< 0.5%), and high bunch charge (~ 1 nC).

To minimize the output emittance and RMS bunch length for the purpose of improving the photoinjector brightness, the influence of different laser pulse profiles on the slice emittance is investigated, and the beam dynamics simulation is performed with non-dominated sorting genetic algorithm-II (NSGA-II) combining with ASTRA code to find the optimal solution at a bunch charge of 1 nC.

In this paper, the beam dynamics optimization of the photoinjector is presented in detail; the simulation results imply that the laser pulse profile with 1σ truncated Gaussian distribution in transverse and flat-top-like temporal distribution is beneficial to the improvement of beam brightness of the photoinjector, which shows an output emittance of 0.63 mm·mrad in the case of intrinsic thermal emittance of 0.43 mm·mrad.