Progress in Developing Spin-Polarized Fusion Fuels for Enhanced Reactor Performance

Spin-polarized fusion can increase the fusion cross section by 50% and significantly enhance fusion power output through increased alpha heating. Experiments with polarized D and ³He in magnetic confinement devices can assess fusion reaction spin-physics, avoid hazardous tritium handling and reduce tritium consumption. Polarized ³He (65% polarization) can be prepared by permeating optically-pumped ³He into shell pellets, while deuterium can be polarized using dynamically polarized ⁷Li-D pellets (70% vector polarization) or frozen-spin H-D pellets (40% vector polarization). Prior work explored the feasibility of diagnosing polarization lifetimes in thermonuclear and beam-plasma scenarios at DIII-D by analyzing the energy, pitch, and poloidal distributions of fusion products, since spin polarization affects these signals. Recent simulations of D-D fusion reactions with ideal polarization show significant variations in the pitch and energy distributions of the fusion products, and a practical assessment of these results is presented. Despite the complex electromagnetic fields in fusion plasmas, this work suggests that polarization can survive, and the most important depolarization mechanisms can be experimentally tested. Potential issues with reactor implementation are discussed, and dedicated injectors and experimental scenarios for DIII-D and other facilities are proposed to study polarization lifetimes and reactor-relevant depolarization mechanisms.