Generation of 400 pC electron bunches in laser wakefield acceleration utilizing a structured plasma density profile

We proposed and examined experimentally that the charge of the 100 MeV-class electron bunches from laser wakefield accelerators (LWFAs) can be improved to similar to 400 pC with the aid of a structured nozzle system. A 43 TW laser pulse driver with 30 fs duration is incident on a density structured gas target, which is created by a 4 mm long gas jet and a moveable slender needle nozzle with 0.8 mm diameter. The charge of produced beam increases compared with that from merely a gas jet (similar to 100 pC) and reaches its maximum (similar to 400 pC) at an optimal relative position. Particle-in-cell simulations show that the self-focused spot size and intensity of the laser pulse can be tuned continuously and reveal how the detailed dynamics of the laser pulse evolution, the electron injection, and acceleration in this structured gas target affects the beam charge. This work demonstrates the feasibility of adjusting the laser pulse distribution through its evolution in a plasma to significantly improve the injected charge in LWFAs, which is beneficial for many applications.