Manipulations of Double Electron Beams within one RF-Period for Seeded SM-LWFA Experiment

Schemes of double electron beams (e-beams) have wide applications in laser wakefield and plasma accelerations. At the ATF the seeded self-modulated laser wakefield acceleration (seeded SM-LWFA) is being conducted, which requires the first e-beam to initiate small plasma wakefield, whose amplitude is significantly amplified by the CO2 laser, and a second e-beam traveling after the first one to probe the accelerated electrons. To create and preserve the significant amount of wakefield in the seeded SM-LWFA experiment, the first e-beam must be ultra-small in spot size and ultra-short in bunch length within the interaction region. To probe the wakefield the separation between both e-beams is required ∼ 10-ps and the second beam must have a smaller intrinsic energy spread and ultra-small beam spot size. Design of the double beams within one RF-period (2856 MHz) to meet these strict requirements at the ATF is presented. Generation and delivery of the double beams through the ATF transport including a bunch compressor are experimentally investigated.