Gamma-ray Measurements for Burning Plasma Scenario Developments

Gamma-rays generated in nuclear reactions have been used on the Joint European Torus (JET) for many decades to study the main mechanisms of fast-ions slowing down, redistribution and losses, as well as for the development optimal plasma scenarios with auxiliary plasma heating. The recent JET deuterium-tritium experiments verified the feasibility of using confined αparticles for diagnosing and monitoring the D-T fusion rate [Kiptily V.G. et al 2024 Nucl. Fusion 64 086059]. In addition, a novel technique for the determination of the plasma core temperature was tested by means of the Tp fusion reaction γ-ray measurements. Several fusion plasma devices utilising magnetic confinement aimed at achieving burning deuterium-tritium plasmas, are under construction or at an early design stage. The Diagnostics for these machines will be a critical factor to their success and is an area of active research in the fusion community. Gamma-ray measurements, as well as neutron diagnostics are amongst a very restricted set of plasma diagnostics that will be practical in these future D-T fusion machines by virtue of their tolerance to the harsh radiation environments they will be required to work within. In this paper, we propose several applications using γ-ray diagnostics during all reactor exploitation phases, from the no-/low-activation to the burning D-T plasmas, for setup of plasma discharges, characterisation of the auxiliary plasma heating, development of optimised plasma scenarios and α-particle studies. Nuclear reactions generating γ-rays, which are suitable for measurements in fusion devices, have been selected. Recommendations for their usage based on the previous experience of the γ-ray diagnostic operation on JET are provided. This paper provides insights for design and modelling of γ-ray diagnostic systems as well as testing them in currently working fusion devises before their use in the burning plasma machines.