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Recent activities related to laser‐plasma acceleration at Advanced Photon Research Center, Japan Atomic Energy Research Institute are presented. Gas density measurements of a pulsed gas valve and wakefield measurements have been performed with two types of interferometers. A wakefield of 20 GV/m excited in the gas‐jet plasma has been obtained at a plasma density of 7×1017 cm−3. We have shown by 1D‐3V particle‐in‐cell simulation that a high quality electron beam with a transverse emittance of 0.3 π mm‐mrad and with an energy of 7.0±0.5 MeV can be produced using a colliding optical injection. Our proposed experiments using a 100 TW laser beam and a 150 MeV electron beam are also presented.

We investigate a laser wakefield excited by intense laser pulses, and the possibility of generating an intense bright electron source by an intense laser pulse. The coherent wakefield excited by 2 TW, 50 fs laser pulses in a gas‐jet plasma around 1018 cm−3 is measured with a time‐resolved frequency domain interferometer (FDI). The results show an accelerating wakefield excitation of 20 GeV/m with good coherency. This is the first time‐resolved measurement of laser wakefield excitation in a gas‐jet plasma. The experimental results agree with the simulation results and linear theory. The pump‐probe interferometer system of FDI will be modified to the optical injection system as a relativistic electron beam injector. In 1D particle in cell simulation we obtain results of high quality intense electron beam generation.

A plasma lens experiment is planned at SLAC with high energy electron beams and high plasma density. We have developed a PIC code, SPLASH (Simulation of Plasma Lens and Synchrotron-radiation in Hybrid), for computer simulations of this experiment. The plasma lens focusing effects are simulated for the beam energy at 30 and 50 GeV and the plasma density between np/nb=0.1 and 100. The original bunch size is 3 and 5 μm in radius. Due to plasma focusing, the beam size is reduced, which is progressively more effective when the relative plasma density increases from the “underdense” regime to the “overdense” one. However, field compensation due to the plasma return current renders the plasma focusing effect suppressed when the plasma density further increases to the “superdense” regime. The beam waist is located between ±20 mm around the original focal point. In the most effective case, the beam is focused from 5 μm to 2 μm and from 3 μm to 1 μm.