Linking SPARC power exhaust constraints with the Separatrix Operating Space through SOLPS-ITER modelling and experiments

Recent progress in describing the H-mode operational space and access to small-ELM regimes via the separatrix operating space (SepOS) framework highlights potential pathways towards viable integrated scenarios in SPARC. In this work we connect the main SepOS parameters (upstream T_e,sep, n_e,sep, α_t) to power exhaust (PE) constraints (target parameters T_e,t ,n_e,t, Ne concentration c_Ne) by developing a reduced dimensionality framework (i.e., the PE-constrained SepOS) through the interpretation of SPARC SOLPS-ITER simulation datasets. We frame the dissipative divertor properties in terms of the strong dependence of volumetric divertor momentum and power losses and the ion-electron temperature ratios on T_e,t, while capturing empirically informed estimates of the power width λ_q. Through the T_e,t mappings we identify self-similar ‘dissipation pathways’ in density and Ne seeding parameter space and describe normalizations over input power and cross-field transport that quantitatively link divertor dissipation to upstream SepOS trends. The significant reduction in n_e,sep along strongly Ne seeded dissipation pathways is in good agreement with observations from JET-ILW. The rise in Z_eff largely balances the n_e,sep reduction with moderate overall impact on α_t ∝ n_e,sepZ_eff/T_e,sep². The PE-constrained SepOS framework offers valuable insights for informing SPARC operations and motivates further validation studies on existing machines in high f_rad, partially detached conditions.