Predictions of stiff core transport in inductive, burning-plasma devices utilizing the PORTALS core transport solver

High-temperature, high-density plasmas as those expected in burning-plasma devices and fusion power plants are anticipated to exhibit stiff core transport conditions. The combination of high gyro-Bohm transport and dominance of ion temperature gradient driven turbulence forces the core profiles to be pinned to critical gradients. Utilizing the PORTALS framework [P. Rodriguez-Fernandez et al 2024 Nucl. Fusion 64 076034] (with development as part of the SMARTS SciDAC-5 partnership) nonlinear CGYRO [J. Candy et al 2016 J. Comput. Phys. 324 73–93] ] simulations are used to project core profiles and fusion performance in upcoming devices. High-fidelity predictions of performance in SPARC L-mode-like conditions [P. Rodriguez-Fernandez et al 2024 Phys. Plasmas 31 062501] highlight the need of having non-negligible edge pressure gradients to attain energy confinement levels consistent with empirical scaling laws. This paper will present the latest developments and high-fidelity simulations with PORTALS, and will discuss consequences of stiff core transport, the potential breakdown of L-mode scalings when projecting to burning plasmas and the effect of stiff transport on the density peaking in inductive, reactor-like conditions. The potential benefit of increasing impurity content to attain higher core temperature gradients via turbulence stabilization in SPARC will also be discussed, which can mitigate the requirement of high edge gradients for fusion breakeven operation.