Characterization of Predicted Confinement and Transport in an ARC-class Tokamak Power Plant*

We present the results of an INFUSE-funded project aimed at characterizing the microturbulence dynamics expected in a future ARC-class power plant, and the extent to which these same dynamics will be observed in SPARC. Here, the phrase ARC-class is used to denote a compact, high-field tokamak power plant capable of producing several hundred MW of fusion power at large Q_fus, with minimal extrapolation required from SPARC parameters and operational conditions. We focus on inductive scenarios consistent with the ARC V1C parameters presented at the 2021 APS-DPP meeting (R₀ = 3.65 m, a = 1.02, B_T = 11.6 T, I_p = 10.5 MA, κ =1.7, δ = 0.54, β_N = 1.2, /n_G = 0.6, H_98y,2 = 1.0, P_fus = 500 MW). To do so, we first calculate self-consistent 1.5D transport solutions using the OMFIT STEP workflow, combining pedestal stability predictions made with EPED and core transport solutions made using TGYRO and TGLF-SAT2. This workflow predicts solutions quite similar to what was previously predicted for SPARC, as well as the ITER baseline scenario and other inductive burning plasmas. At the predicted confinement factor H_98,y2 ~ 1 (achieved using only central radio frequency-like heating, without core fueling or torque) the plasma is well-coupled, with significant ion thermal transport driven by ion temperature gradient (ITG) modes. Temperature profile shapes and scale lengths are quite close across all three devices, with the largest uncertainty coming from the amount of density peaking achieved. Furthermore, the first nonlinear gyrokinetic profile predictions of an ARC-class device have been performed using the CGYRO code in combination with a newly-developed surrogate model-based transport code (P. Rodriguez-Fernandez et al, Nuclear Fusion 62 076036 (2022)), and are in excellent agreement with the TGLF predictions. Comparisons to analogous SPARC and ITER profile predictions made with both TGLF and direct gyrokinetic simulations will be discussed.