Simulation study of high-quality electron beam injector for external injection of laser plasma wakefield acceleration
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The laser wakefield acceleration (LWFA) with external injection requires high-quality, ultra-short electron bunches, which can be produced by using a photocathode injector based on the room-temperature RF electron gun. In this paper, the physics design of such a photocathode injector system is discussed for two operating modes: low charge (10 pC) and high charge (50 pC). The front end of the injector was optimized by combining the beam dynamics simulation software ASTRA with the multi-objective genetic algorithm NSGA-II. The downstream section was simulated using CSRtrack and ASTRA to optimize the magnetic chicane and match the Twiss parameters. A slit collimator was inserted in the middle of the chicane to filter part of the electrons, and hence shorten the bunch length and reduce the relative energy spread. The obtained beam parameters meet the requirements for an external injection of the LWFA, where the electrons can be further accelerated from 100 MeV to 1.5 GeV. Such a photocathode injector combined with the LWFA has the potential to be applied in the accumulation injection of a 1.5 GeV storage ring at Wuhan Advanced Light Source.
Abstract
The laser wakefield acceleration (LWFA) with external injection requires high-quality, ultra-short electron bunches, which can be produced by using a photocathode injector based on the room-temperature RF electron gun. In this paper, the physics design of such a photocathode injector system is discussed for two operating modes: low charge (10 pC) and high charge (50 pC). The front end of the injector was optimized by combining the beam dynamics simulation software ASTRA with the multi-objective genetic algorithm NSGA-II. The downstream section was simulated using CSRtrack and ASTRA to optimize the magnetic chicane and match the Twiss parameters. A slit collimator was inserted in the middle of the chicane to filter part of the electrons, and hence shorten the bunch length and reduce the relative energy spread. The obtained beam parameters meet the requirements for an external injection of the LWFA, where the electrons can be further accelerated from 100 MeV to 1.5 GeV. Such a photocathode injector combined with the LWFA has the potential to be applied in the accumulation injection of a 1.5 GeV storage ring at Wuhan Advanced Light Source.