Beam dynamics of the low-energy beamline of MESA considering space charge and higher-order multipole contributions

The research for new physical phenomena in particle physics and an explanation of astrophysical observations calls for experiments with ever-increasing precision and/or energy. In order to measure the observables with high statistics at accelerators as they are planned in Mainz within an appropriate time, a high number of events are needed, requiring higher beam currents than achievable with conventional linear accelerators. In the case of the planned accelerator MESA in Mainz, the goal is a beam current of 10mA. To provide this high beam power on the one hand and to thermally control it on the other hand, the beam will be redirected through the accelerating cavities after passing the experiment. The cavities now decelerate the beam returning the beam energy to the field of the cavity and therefore recovering it. This concept of an energy recovery linear accelerator (ERL) can also be used as a new generation of synchrotron radiation sources for material and fundamental research. The quality of the beam, described by the emittance, is basically determined by the electron source. For this reason, ERLs turn out to be more flexible than storage rings, where the emittance is determined by the dynamical equilibrium between radiation damping and the emittance growth due to various heating effects. A dedicated design of the electron gun and the low-energy beam transport is mandatory for good beam quality. This thesis describes the choice of beamline magnets, their simulation, and their measurements. The same applies to the chopper system, which is important for longitudinal beam preparation. Furthermore, the whole beamline was simulated and constructed collaboratively. To improve the emittance, a new laser system was installed. The goal of providing a normalized emittance ε < 1mmmrad at the experiment of the accelerator in combination with high beam current and therefore high charge density leads to strong space charge forces. These non-linear forces cause unwanted emittance growth. Due to the 1/γ${}^3$ dependency, these effects have a particularly big influence in the low energy beamline. The increase of the emittance was determined by simulations of the whole beamline and compared with the experiment. Additionally, unwanted multipole fields lead to emittance growth. Their contribution can be calculated from simulations of single magnets. Dedicated diagnostic elements measured the transverse properties at several places along the beamline. Subsequently, these properties were compared with the simulation results, demonstrating the strong influence of non-linear magnetic fields.