High energy proton detection in Draco PW experiments

Exploiting the strong electromagnetic fields that can be supported by a plasma, high-power laser driven compact plasma accelerators can generate short, high-intensity pulses of high energy ions with special beam properties interesting for many application areas. The transition of laser driven ion accelerators from physics experiments to turn-key sources for these applications relies on improvement of generated beam parameters (kinetic energy, flux), as well as increased reproducibility, robustness and scalability to high repetition rate. Recent developments at the high-power laser facility DRACO-PW enabled the production of polychromatic proton beams with unprecedented stability [1] which enabled the first in vivo radiobiological study to be conducted using a laser-driven proton source [2]. Yet, the ability to achieve highest energies around or even beyond the 100 MeV frontier is matter of ongoing research, mainly addressed by exploring advanced acceleration schemes. In parallel to the testing of these schemes an important challenge is to provide convincing evidence that these very high energies could be reached at all for a significant number of particles. Occurring complications are due to the nature of the multi-species beams with typically exponentially decaying spectra and low shot statistics of laser-plasma experiments at the necessary laser pulse energy levels. The latter is in particular complicated for highly non-linear acceleration regimes with intrinsically low reproducibility. In this talk we summarize our approaches for the spatial and spectral characterization of our proton beam parameters with cut-off energies larger than 80 MeV. Key is the combination of a multitude of different methods based on different detection principles established for single shot measurements. Time-of-flight methods are discussed for energy cross-calibration of our Thomson parabola spectrometers and the use of different screen types for on-shot particle number calibration is presented.