Tunable Laser-Plasma Acceleration with Ionization Injection

Abstract

Accelerating electrons to relativistic energies by an intense laser field interacting with a plasma is a widely considered concept to drive future applications such as compact light sources. The strong requirements on the electron beam quality imposed by these applications requires to precisely control the injection and acceleration dynamics and hence the parameters of the laser-plasma accelerated electrons. This thesis studies electron beam generation with ionization injection in a nitrogen doped hydrogen plasma, focused on tunability and improvement of electron beam parameters. A capillary type plasma target was developed and characterized with Computational Fluid Dynamic (CFD) simulations allowing extensive parameter scans. It is demon- strated that electron beam parameters can be tuned in a wide range with peak energies between 200MeV and 350MeV, bunch charges between 100pC and 350pC at percent- level shot-to-shot stability, by varying the laser focus position, laser pulse energy, plasma density and the nitrogen concentration. The accelerator performance could be optimized by controlling beam loading effects with a combination of the nitrogen concentration and the laser pulse energy, resulting in electron beams with reduced energy spread at simultaneously increased peak charge density. The laser pulse energy showed the strongest influence on the transverse beam parameters, allowing to fine-tune beam divergence and beam emittance, a crucial prerequisite to optimize electron beams for the transport with electron beam optics. The broad parameter scans could be reproduced with Particle-In-Cell (PIC) simulations, providing an in-depth understanding of the injection and acceleration dynamics in the ionization injection scheme. The presented results and the identified scalings can give a guideline for the operation regime for future experiments and to develop improved plasma targets to further enhance the electron beam quality.