Development of a CR-39 Detection Algorithm and Thomson Parabola Spectrometer for Laser-Driven Proton-Boron Fusion

Accurate diagnostics of sub-to-multi-MeV ion beams are essential for laser-driven ion acceleration and proton–boron (p–B) fusion. CR-39 detectors provide absolute ion number measurements with high sensitivity. Ion tracks are registered when CR-39 is irradiated by energetic ion beams and are revealed through alkali etching, forming pits with geometries that can be described by the Somogyi–Szalay model. On the other hand, the Thomson Parabola Spectrometer serves as an in-situ ion energy spectrometer by deflecting ions through an electric field and a magnetic field onto scintillating screens, with the resulting phosphor emission that can be described by Birk’s model. In this work, an algorithm was developed to extract pit geometry from etched CR-39, optimized for overlapping pits. The algorithm supports customizable parameters to accommodate various etching conditions and detector configurations. Together with restricted energy loss datasets simulated using GEANT4, the energy and angular distributions of the ion beams, generated by a 100-TW ultrafast laser at National Central University in Taiwan, were reconstructed from the pit opening geometries. Furthermore, the response of the P43 scintillator to protons in the 0.2–1.4 MeV range was measured using a fence-structured CR-39 detector placed in front of the screen, showing good agreement with theoretical predictions. These diagnostics will be applied to future experiments on laser–ion acceleration and laser-assisted p–B fusion.