On the thermodynamics of SPARC plasma and its role in reducing uncertainties on the way to large fusion gain

Abstract

Independent assessment of the feasibility of controlled nuclear fusion in the proposed SPARC tokamak (Creely et al., J. Plasma Phys., vol. 86, 2020, 865860502; Rodriguez-Fernandez et al., J. Plasma Phys., vol. 86, 2020, 865860503) is difficult because of the uncertainties concerning energy transport in the plasma. We discuss a SPARC scenario – where a burning plasma is obtained – with the help of a well-known general constraint on transport in weakly collisional, axisymmetric, toroidal, low- $\beta$ turbulent plasma (Rogister et al., Phys. Fluids B, vol. 4, 1992, p. 804). This constraint is useful in reducing uncertainties on auxiliary heating as the fusion gain begins to be large. No particular ad hoc model for transport coefficients is invoked. The crucial roles of both suitable tuning of ion cyclotron radiofrequency power and high-temperature pedestal are highlighted.