Experimental demonstration of the recoil proton track imaging method for ICF deuterium-tritium neutron spectroscopy on a tandem proton accelerator

The diagnosis of primary deuterium-tritium (DT) neutron spectrum is crucial for inertial confinement fusion (ICF) experiments. To meet the real-time diagnostic requirements for high-yield (up to 2×10¹⁹) ICF primary DT neutrons in the future, we have designed a neutron spectrometer based on the recoil proton track imaging method. Here, we demonstrate this method through proton energy spectrum measurements on an EN-6 tandem accelerator. The detector system comprises a gas-filled chamber, an imaging unit, and a vacuum chamber housing a silicon wafer beam degrader and a Faraday cup detector, which serves as a proton beam intensity monitor. We obtained a series of mono-energetic proton track images and corrected them with the camera's flat-field response. The measured track images are in good agreement with Geant4 simulation results. A proton beam energy spectrum with multi-peak structure is obtained after silicon wafer degradation by using 7.5 MeV mono-energy protons on an EN-6 tandem accelerator, and the proton spectrum is measured by a Si-PIN detector. The peak and relative intensity of the proton beam spectrum unfolded from track images are consistent with the measured Si-PIN result in the high-energy region. The unfolding results show lower degraded beam energy distribution in the lower energy region due to a smaller proton beam spot size and non-uniformity at the degrader effective area. Finally, we discuss the applicability of the neutron spectrometer in ICF experiments. In NIF experiments with neutron yields exceeding 5.28×10¹⁸, the spectrometer can provide measurements with adequate reliability. In summary, this study represents a significant step toward the practical application of the recoil proton track imaging method for ICF primary DT neutron measurements.