Scaling of total fusion power with spin polarization and tritium fraction

Determine the dependence of total fusion power in deuterium–tritium tokamak plasmas on spin polarization and tritium fraction across a broad range of operating conditions. Specifically, derive how the total fusion power P_f scales as a function of the spin-polarization cross-section multiplier A_J (and associated nonlinear alpha-heating enhancement) and the core tritium fraction f_T^{co}, including the effects of alpha heating and related nonlinear feedbacks, so that predictive models can accurately quantify power output for various polarization levels and D–T mixtures.

Background

The paper models spin-polarized D–T fuel using an effective multiplier N A_J applied to the standard reactivity to approximate nonlinear alpha-heating effects reported in prior studies. While power-density scaling is analyzed in detail, the authors note that total fusion power depends on global alpha heating and plasma response, which can exceed the simple cross-section enhancement and vary with polarization and fuel mix.

Prior results suggest total power can increase by 80–90% for A_J = 1.5 due to alpha heating, but the authors highlight that they primarily studied fusion power density rather than total power in this work. Establishing a comprehensive scaling law for total fusion power versus polarization fraction and tritium fraction is needed to guide operating strategies that aim to simultaneously improve tritium burn efficiency and plant output.