The shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens’ principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. This novel method, which we refer to as Ion-Bunch Energy Acoustic Tracing (I-BEAT), is a refinement of the ionoacoustic approach. With its capability of completely monitoring a single, focused proton bunch with prompt readout and high repetition rate, I-BEAT is a promising approach to meet future requirements of experiments and applications in the field of laser-based ion acceleration. We demonstrate its functionality at two laser-driven ion sources for quantitative online determination of the kinetic energy distribution in the focus of single proton bunches.
This study showed a pronounced increase of secondary neutron H*(10) values inside the proton treatment room with increasing proton energy without beam modifiers. For example, in beam direction this increase was about a factor of 50 when protons of 75 MeV and 200 MeV were compared. The existence of a peak of secondary neutrons in the MeV region was demonstrated in beam direction (0°). This peak is due to evaporation neutrons produced in the existing surrounding materials such as those used for the gantry. Therefore, any simulation of the secondary neutrons within a proton treatment room must take these materials into account. In addition, the results obtained here show that the use of a range-shifter increases the production of secondary neutrons inside the treatment room. Using a range-shifter, the higher neutron doses observed mainly result from the higher incident proton energy (118 MeV instead of 75 MeV when no range-shifter was used), due to higher neutron production cross-sections.
We report on a target system supporting automated positioning of nano-targets with a precision resolution of 4 µm in three dimensions. It relies on a confocal distance sensor and a microscope. The system has been commissioned to position nanometer targets with 1 Hz repetition rate. Integrating our prototype into the table-top ATLAS 300 TW-laser system at the Laboratory for Extreme Photonics in Garching, we demonstrate the operation of a 0.5 Hz laser-driven proton source with a shot-to-shot variation of the maximum energy about 27% for a level of confidence of 0.95. The reason of laser shooting experiments operated at 0.5 Hz rather than 1 Hz is because the synchronization between the nano-foil target positioning system and the laser trigger needs to improve.
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