Figure 2

Results for laser-accelerated proton bunches: (a) Shows the schematic of the experiment setup. A high power laser (ATLAS-300) is focused with an off-axis parabola (OAP) onto a foil target. Two permanent magnetic quadrupoles (PMQ) are used to focus a short ion bunch. A dipole magnet (DM) is used to remove electrons and low energy ions from the swift ion bunch, which is focused within the ionoacoustic detector. (b) Acoustic signals of single proton bunches. The design energies attenuated to 6.2, 6.7, 7.2 and 7.8 MeV on entering the water volume, are set by positioning of the PMQs. The solid line is the measured acoustic signal and the dashed line corresponds to the calculated signal from the retrieved spectrum in (d). (c) Depth dose curves corresponding to the different energy settings. The dose on the central axis is \(\,D(z)=\frac{1}{\rho }\cdot \frac{1}{2\pi {\sigma }_{r}^{2}}\cdot {B}_{s}(z)\). (d) Absolute proton energy distributions of single proton bunches of the different design energy settings in the ion focus. The inset reveals a focal plane image of a single proton bunch at the position of the detector entrance, taken with an image plate. The σ_r marks the lateral extension evaluated with I-BEAT.