Insights into Density Peaking in Next Generation Fusion Devices: Analysis of Projected SPARC and ARC Plasma Conditions*

Density peaking in tokamaks has been extensively studied in current devices as it provides a lever to increase fusion gain in DT fusion devices.   Despite empirical evidence indicating a link between density peaking and effective collisionality, recent work indicates DT devices  may deviate from observed trends. Surrogate-based approaches using PORTALS [Rodriguez-Fernandez NF 24] enabled profile predictions of SPARC and ARC-like fusion devices utilizing high fidelity, nonlinear gyrokinetic (CGYRO) predictions.  Over 15 sets of profiles have been predicted (ne, Te, Ti simultaneously) for SPARC and ARC plasma conditions that provide insight into the physics of density peaking and projections to fusion pilot plants (FPP).  Analysis of turbulent fluctuations suggest correlation of density peaking with two quantities: density and potential cross phases and temperature to density fluctuation ratios; pointing to the potential origin of density peaking.  In SPARC plasmas, modeling reproduces empirical trends over 30x in effective collisionality while simulations of FPP class devices deviate from empirical scalings.   Details of the nonlinear gyrokinetic modeling, comparisons of results with empirical databases, analysis of turbulent fluctuations, and implications for FPP class devices will be presented.