Neutron-Lean D-3He Fusion by Asymmetric Enhancement of the Primary Reaction: A Spin-Polarized Non-Thermal Hot Tail

Abstract

This paper focuses on a modified fuel that combines the theory of spin-polarized fuel with non-thermal "hot-tail" reactions for D-T, D-3He, and D-D reactions. We find that this combination is particularly advantageous for the D-3He fuel in several respects. First, a large reactivity enhancement: one order of magnitude at 10 keV for a small hot tail (F = 0.1), rising to two orders of magnitude for a larger one (F = 0.6), with polarization adding a further factor of 1.5. Second, an ideal ignition energy far below the thermal value: 9.5 keV at F = 0.3 down to 3.2 keV at F = 0.5, which polarization reduces further to 3.8 keV and 1.3 keV, respectively. Third, the asymmetric enhancement between the primary reaction and the secondary reactions in the fuel opens the possibility of a neutron-lean reaction. Quantifying this with a neutrons-per-watt metric, we find that a thermal D-3He plasma at 10 keV is barely neutron-lean at all (90-95% of the D-T neutron rate per watt), whereas a hot tail of F = 0.1 reduces it by 4.7-7.7x and the polarized non-thermal fuel at its ignition point reaches 3.0-5.4% of the D-T value, with only 0.4-2.4% of the fusion power carried by neutrons. The range spans prompt removal versus complete in-situ burnup of the bred tritium. Applied to a 200 MW worked example anchored on the ARTEMIS D-3He reactor design, this is a first-wall neutron loading of 0.008-0.043 MW/m^2 against 1.45 MW/m^2 for D-T in the same chamber, extending the time to reach 20 dpa from about 1.5 full-power years to 27.