Pre-conceptual design of compact-fusion prototypical neutron source target for optimized fusion materials testing

Abstract This work describes a design study of a cyclotron-driven Fusion Prototypic Neutron Source (FPNS) target optimized to meet US specifications for a fusion materials irradiation target. The analysis supports the use of multiple compact deuterium cyclotrons beams at a total current under 40 mA in the range of 35 MeV to 60 MeV converging on flowing annulus of lithium surrounding the sample target. The sample target region is modeled as miniaturized tensile and Charpy bend-bar specimens located within the central region of the annulus. A specific focus of this work is to provide a highly uniform flux trap of fusion-relevant neutrons maximizing the average neutron damage per unit of beam current. This design achieves the desired sample volume (>50 cm3) and damage (>10 dpa/yr) metrics with damage gradient (<40%) within the sample target region. The proposed design is modeled using the neutronic and transmutation analysis codes, PHITS [1] and FISPACT [2], with the assistance of a customized coupling computation platform. Sensitivity analyses are presented investigating the impact of the deuteron beam (height and energy), dimension of the various system elements , and the chosen nuclear data library (deuteron library, neutron library, Damage library) on the ultimate figure of merits including damage dose rate (DPA), gas production. Additionally, a complete transmutation calculation has been carried out on relevant fusion materials: Eurofer97, Silicon Carbide, Alloy 316, V-4Cr-4Ti, and pure tungsten, to ensure relevance of this C-FPNS elemental transmutation spectrum to that of a fusion reactor, especially for high deuterium energies. Implications to materials response of using deuterium energies in the 35-60 MeV range as compared to self-same materials exposed to a true fusion reactor neutron spectrum are presented.