Physics feasibility study of a collective Thomson scattering diagnostic for SPARC

The SPARC tokamak is a compact high-field device that will operate at high plasma density with the aim to demonstrate net fusion energy. The experimentally unexplored plasma conditions in SPARC will require a carefully selected set of diagnostics for plasma monitoring and control. Here we explore conceptual design options and potential measurement capabilities of a collective Thomson scattering diagnostic at SPARC. We show that a 140 GHz X-mode CTS system is the most attractive option in terms of optimizing the signal-to-noise ratio and limiting sensitivity to refraction, as well as from a technological readiness perspective. Such a setup can provide core-localized measurements of the fusion alpha distribution function, main-ion temperature and toroidal rotation, fuel-ion ratio, and ³He content with relevant spatio-temporal resolution. Our proposed diagnostic layout can in principle be integrated into SPARC and could provide a valuable addition to its diagnostic suite at limited development costs and time.