Numerical Study of Injection Mechanisms for Generation of Mono-Energetic Femtosecond Electron Bunch From the Plasma Cathode

Acceleration gradients of up to the order of 100GV/m and mono-energetic electron bunch up to 200MeV have recently been observed in several plasma cathode experiments. However, mechanisms of self-injection in plasma are not sufficiently clarified, presently. In this study, we carried out 2D PIC simulation to reveal the mechanisms of Laser Wake Field Acceleration (LWFA). Electron density gradient at vacuum-plasma interface is important condition for electron’s self-injection owing to plasma wave breaking. Steep electron density gradient (∼ plasma wave length) causes rapid injection and produces an electron bunch with rather high charge and less than 100fs duration. By this calculation, we obtained the electron bunch width of about 40fs and the maximum energy achieved more than 20MeV. The charge amount of > 3MeV electrons in one bunch was estimated as 50pC with the steep density gradient, while it was 10pC with the gentle one.