Search for a command to run...
Old laser system for the laser-ion acceleration are limited to a few or less shots per hour, through the thermal stress induced into the main amplifiers. These low repetition-rate laser systems allowed the manual alignment of the targets for the acceleration without restricting the system performance. With the development of laser systems allowing potentially a laser-ion acceleration with a Hz to kHz repetition-rate, new target systems are necessary to fully utilize these laser-ion and laser-neutron sources. A debris free alternative is the liquid sheet target system during this project developed, which allows the continuous, reproducible supply of a thin water sheet as ion-acceleration target for high repetition-rate applications. With the liquid sheet renewing itself as new liquid flows through the laser-focus point replacing the hole from the last laser shot, the need to realign the target after every shot can be avoided, while also ensuring the same target parameters for every shot. The liquid sheet was created using the impinging of two single liquid jets, resulting through the momentum and mass conservation in the liquid spreading radially outwards from the impinging point. This allows to supply different target thicknesses with one sheet, as the target thickness decreases inversely with the distance from the impinging point. The target liquid will evaporate during operation, as the laser-ion acceleration has to occur in vacuum. Without the vacuum the plasma would be ignited before the target can be reached through the increasing intensity from the focusing laser beam ionizing air molecules, preventing the ion acceleration. The evaporating liquid leads to an increased gas load in the target chamber as well as ultimately to a freezing of the liquid, with ice growing towards the sheet and the nozzles. To prevent this is a heated catcher together with a temperature controlled storage reservoir used, to safely remove the liquid after usage. This dissertation discusses the liquid sheet target system in detail, with all its components from the liquid supply until the used liquid is recycled back in the storage reservoir to be used again. In addition alternatives to the used components, their upgrade options as well as the nozzle production process are explained. The liquid sheet is characterized for H₂O, D₂O as well as their mixture in both the resulting thickness distributions as well as the sheet length. The usable thickness range is limited through the sheet length, the used parabola, which defines the cone angle of the focusing laser beam, as well as the geometrical restrictions of the target system, to prevent the laser from hitting the system components. Furthermore the sheet vacuum operation is discussed in regard to the achievable pressure levels during acceleration, the evacuation process as well as an estimation of laser contrast needed to prevent the target from evaporating before the ions can be accelerated. Lastly the experimental validation of the sheet target system as part of a laser-ion and neutron source is discussed, for which both H₂O and D₂O were tested as target liquids. A Thomson parabola (TP) was used for the on shot analysis of the ion spectra, while radiochromic films (RCFs) measured the angular distribution of the ion beams accelerated. Apart from the influence of ions with different charge-to-mass rations on the measured ion spectra also the scaling of the ion cut-off energies both in dependence of the laser pulse energy and intensity is discussed. The optimized proton and deuteron beams were used to generate neutrons, utilizing a lithium-fluoride neutron converter (with the "pitcher-catcher" schema). The generated neutron doses were detected through various bubble detectors, placed under different angles and distances towards the neutron source, as well as elements of a Bonner sphere spectrometer. The generated normalized neutron yield is then discussed in regard to the angular emission and compared to the neutron yields reported by other authors using both comparably low pulse energy systems as well as systems in the 100 J range. The steps to achieve a continuous, high-repetition rate laser-ion and -neutron acceleration are then discussed together with the accumulated neutron yields achievable for a currently available 5 J, 10 Hz laser system. It is shown, that an optimized high-repetition rate laser-neutron source using only current laser systems could theoretically already surpass the neutron yields generated with high pulse energy, low repetition rate laser systems. This is achieved utilizing the huge difference in the number of shots achievable in a given timeframe.