High Power Proton Beam Shocks and Magnetohydrodynamics in a Mercury Jet Target for a Neutrino Factory

The feasibility of liquid metal jet targets for secondary particle production with high power proton beams has been studied. The main aspects of the thesis were benchmark experiments covering the behaviour of liquid targets under thermal shock waves induced by high power proton beams, and also magnetohydrodynamic effects. Severe challenges were imposed by safety issues and the restricted beam time to the tests in ISOLDE at CERN and at the High Magnetic Field Laboratory at Grenoble. Restricted access times in high radiation level areas were of the order of minutes and in this short time span, the complete experimental setup had to be performed and verified. The involvement of mercury as liquid target material and its activation during beam tests demanded special confinement precautions. The setup for both experiments was based on the use of a high speed camera system for observation of the mercury target. The presence of high radiation or high magnetic field required the installation of the sensitive camera system at distances up to 15 m. The method of shadow photography had to be used because of the highly reflective surface of mercury. During proton beam tests at the CERN ISOLDE facility and at Brookhaven AGS, the behaviour of a mercury target as a function of various proton beam parameters was analysed. The experimental results allow for extrapolation from the present data by one order of magnitude to the final design of a high power jet target foreseen for a neutrino factory. Observed velocities of the mercury splash were up to 45 m/s. The experimental setup used at the High Magnetic Field Laboratory allowed a successful demonstration of injecting a 12 m/s mercury jet with a diameter d=4 mm into a 20 T solenoidal field. The results of this experiment revealed the magnetohydrodynamic effects, which occur in the free jet and in the supplying mercury circuit, and serve as benchmark for numerical codes. The extrapolation to the nominal parameters of a neutrino factory shows that the concept of a jet target is a valid option.