Effects of 3D printed capsule material on activation thin foil irradiation and counting for fusion neutron yield measurements

TL;DR

This study evaluates how 3D-printed capsule materials affect activation foil irradiation and neutron yield measurements in fusion experiments, providing insights for optimizing capsule design and detection methods.

Contribution

It characterizes the impact of different capsule materials, including 3D-printed thermoplastics, on activation foil performance and gamma-ray detection in fusion neutron diagnostics.

Findings

Aluminum and copper foils are suitable for multi-foil irradiation.

3D-printed capsules slightly reduce decay-photon counts, within measurement uncertainty.

Lanthanum-based detectors are viable alternatives to germanium spectrometers.

Abstract

Activation foils are used to independently measure the time integrated neutron yield and total fusion energy produced in both inertial and magnetic confinement fusion, making them crucial in the neutron diagnostic suite. The activated foils must be remotely transported from the neutron source to the detector inside of a small capsule, which can impact both the foil irradiation and the associated activation measurement. The aim of this paper is to evaluate the performance of various activation foils and to characterize the effects of different capsule materials to inform the design choices for future systems, such as the SPARC tokamak. Through a combination of FISPACT simulations and irradiation experiments with a deuterium-tritium neutron generator, we tested several different material choices for foils, capsules, and gamma-ray spectrometers. Aluminum and copper foils are found to be suitable for a multi-foil irradiation configuration. The use of 3D-printed thermoplastic capsules reduces the number of measured decay-photon counts, yet the reduction is smaller than the associated measurement uncertainty. Finally, lanthanum-based detectors are shown to be viable alternatives to the standard high-purity germanium spectrometer, although with poorer energy resolution.