Optimizing Laser-Wakefield accelerator performance by varying gas density profiles using PIC codes

Laser-wakefield accelerators, providing high-energy electrons on a small scale, are promising alternatives to conventional particle accelerators. High field gradients in the regime of several GeV/m grant significant energy gain already in the range of millimeters and therefore table-top applications of LWFA are feasible.
Nevertheless, improving the beam quality is essential for future applications. With the development of particle-in-cell (PIC) algorithms, a time resolved analysis of plasma based accelerators became available, providing a steady optimisation potential of the electron beam. Using the PIC code PIConGPU, the influence of a density down-ramp on the characteristic Courant-Snyder parameters and the evolution fundamental beam properties is presented in this work. Through the visualisation of these quantities on the millimeter scale of the plasma, the oscillation of the beam parameters and the expansion of the beam waist in the down-ramp region can be demonstrated and furthermore, the average energy and total amount of charge in the main electron bunch is determined at the end of each plasma stage.
Thus, a detailed discussion of the down-ramp influence on the Courant-Snyder parameters, the bunch-charge and the beam energy, is provided for every simulation. Comparing the results with a reference simulation reveals optimisation possibilities of all mentioned parameters.
It is shown, that a perfectly matched beam is not yet reached for the assumed setup, but still an optimal density profile, combining low beam divergence and high energy and bunch charge, is suggested in the end of this work.