Improving the quality of enegetic electron beams produced by Laser Wake Field Acceleration

Laser Wake Field Acceleration (LWFA) of relativistic electron bunches is a promising method to produce a large amount of energetic particles with a table-top equipment. To date, the quality of the electron beams produced with the widely used scheme employing a gas-jet system and a single femtoscond laser pulse is very poor, the energy spread being of the order of 100 % and the angular divergence usually exceeding several degrees. The Intense Laser Irradiation Laboratory (ILIL, IPCF-CNR) in Pisa, Italy, is currently deeply involved, both on the experimental and theoretical sides, in studies devoted to increase the beam quality of the LWFA produced electron beams. Here we report on the two parallel activities of ILIL in this field. The first achieved its main results started with an experiment held at the LOA facility, based on LWFA in preformed plasmas obtained with the exploding foils technique and demonstrating the production of a relativistic electron bunch with a record value of angular divergence (less than one degree) but still with a large energy spread. The second activity is presently at the theoretical/numerical stage and is aimed to produce electron bunches with both small transverse and longitudinal emittances by taking advantage of the partial nonlinear, longitudinal wave-breaking of the Langmuir wave behind the pulse crossing a sharp density downramp. In this way a large amount of electrons can be injected in a controlled way in the accelerating region of the wake. PIC simulations (3D in the fields and 2D in the coordinates) demonstrate that, once concurring trappin