Description
ST40 is a high-field, compact spherical tokamak, with a mission to expand the physics and technology basis for this route to fusion energy. ST40 operates with deuterium neutral beam injection into deuterium plasmas, thus the occurrence of the following nuclear reactions is likely D + D → T + H, D + D → He + n (2.45 MeV), D + T → He + n (14 MeV). Two neutral beams are injected in ST40 plasma tangentially in the co-current direction delivering around 1.0 MW at 55 kV and approximately 0.8 MW at 24 kV, respectively [1]. Neutron measurements play a key role in the evaluation of fusion power reached in a plasma shot by providing neutron yield measurements as well as it helps with plasma control and optimization of auxiliary plasma heating.
The results of neutron measurements from recent ST40 experimental campaign are presented in this work. The data was obtained using n eutron diagnostic systems on ST40, which were designed to provide measurements of 2.45-MeV neutrons. The systems implement various instruments , including neutron organic scintillators based on stilbene crystal and EJ309 liquid scintillator, 50-µm thickness diamond detector together with In-ion activation foils. The detectors were previously characterised with Co-60 and Cf-252 radiation sources with implementation of Monte-Carlo simulations [2].
Prior to the next ST40 campaign, absolute neutron calibration of ST40 is planned to be performed using a DD fast neutron generator. The preparation steps and actions on the calibration are discussed in this work.
[1] S. A. M. McNamara, et al, “Achievement of ion temperatures in excess of 100 million degrees Kelvin in the compact high-field spherical tokamak ST40,” Nuclear Fusion, vol. 63, 054002, 2023.
[2] M. V. Iliasova, et al, “Characterisation of Diamond and Organic Scintillation Detectors Utilising Radiation Sources for Continuous Plasma Operation”, Review of Scientific Instruments, 95, 083556, 2024.