Prototyping activities supporting the design of the SPARC neutron camera

The SPARC tokamak, now under construction in Devens, MA by Commonwealth Fusion Systems (CFS), will include a poloidal neutron camera to measure the radial profiles of both neutron emissivity and ion temperature. SPARC is predicted to achieve burning plasma conditions (Q_p > 5) and a peak DT fusion power of 140 MW, corresponding to 5 X 10¹⁹ neutrons per second [1]. The SPARC neutron camera plans to make use of single crystal chemical vapor deposition (sCVD) diamonds and deuterated liquid organic scintillators to cover SPARC's large dynamic range and provide spectrometric measurements of both 2.45 and 14.1 MeV neutrons from DD and DT reactions respectively. In this work we present the results of recent prototyping activities supporting the design of the SPARC neutron camera. This includes results from a custom prototype deuterated-xylene scintillator as well as sCVD diamonds. Using a prototype collimator assembly built by CFS, we share results from a complete prototype neutron camera channel under irradiation with 14.1 MeV neutrons. We assess the impact of gammas from inelastic scattering as well as neutron down-scatter and in-scatter on the spectrometric performance of both detectors. We also share synthetic tomography results from the ToFu code [2], including propagation of geometric and counting uncertainties through the reconstruction of emissivity and ion temperature profiles.

[1] A. Creely et al. 2020 JPP

[2] D. Vezinet et al. 2016 Nucl. Fusion 56 086001