Experimental Investigation of Proton Induced Thermal Shocks and Magnetohydrodynamic Effects in Molten Metal Pion Production Targets for a Neutrino Factory

Neutrinos are one of the basic subatomic particles among electrons, protons and many more, which build all matter. Neutrinos appear in three different types. Sources of neutrinos are the sun and nuclear power plants. But the type of neutrinos created there is not exactly known and the type changes between their creation to their detection, so only assumptions can be made. This change of type is called “neutrino oscillation”. In order to enable the nuclear physisists to find out more about the neutrinos and the neutrino oscillation, a neutrino factory will be built which will produce a high intensity neutrino beam with exactly known parameters like number of particles and type of neutrinos. This neutrino beam can then be used to investigate the properties of the neutrinos at near and far detectors. In cooperation with other laboratories CERN has started a study of some of the many technological challenges of a neutrino factory. A major issue of the facility is the pion production target where pions are produced by shooting a proton beam onto matter (target). These pions then decay into neutrinos. At CERN the choice was made to concentrate on the development and investigation of a liquid metal target, particularly mercury. Experiments were fixed to show the feasibility of a liquid metal target. The experiments should cover ejection and capture of the jet, hydrodynamics, distortion of the jet by proton beam interaction, behaviour of the mercury jet in high magnetic fields and handling liquid metals. In this dissertation theoretical studies have been collected and analysed as well as experimental studies have been performed. The main part consists of the preperation and performance of the experimental studies. To use a liquid metal target is a completely new technology and there exists no experience in this field. The experiments are an important part of the whole project as they should verify the validity of the theoretical studies and consequently confirm the definitive feasibility of a liquid metal target station. The first part of this dissertation explains the motivation for and the goal of the project, an overview of the theoretical background of nuclear physics and a description of the future neutrino factory. The next part describes some theoretical studies concerning the evaluation of models for the target and their behaviour at intense proton beam impact, located in high magnetic fields. Theoretical models should show the understanding of the liquid metal target, especially concerning the hydrodynamics including cavitation on proton impact. After that the main part describes the experiments which will provide benchmarks for theoretical models of the behaviour of liquid metal under the given circumstances and gives details about their realization. The experiments consist of setups which are used to place mercury inside very strong magnetic fields and in the line of proton beams. The reaction of the mercury to these inducements is observed optically by recording high speed videos of the events. These videos are used to evaluate some key parameters like the velocity and direction of escaping droplets when the mercury is disrupted due to the impacts. The concluding parts eventually include the results of the experiments and the extrapolated consequences for the final neutrino factory target design. The experiments show that the simulations are not very far from the reality. The effects on the mercury correspond widely to the simulations and they are considerable. Nevertheless the effects are within a range that a neutrino factory based on a mercury jet target seems to be feasible