Speaker
Description
Handling and mitigating heat fluxes to plasma-facing components remains one of the primary challenges for magnetic fusion devices. In future high-field compact machines relying on high-temperature superconducting coils (e.g., SPARC [J. D. Lore 2024]), the heat-flux decay length $\lambda_q$, which characterizes the width of the Scrape-Off Layer (SOL), is predicted to be critically small according to experimental scaling laws derived from medium-sized tokamaks (Eich Law [T. Eich 2013], Scarabosio Law [A. Scarabosio 2013]). Nevertheless, extrapolation to currently unexplored conditions present large uncertainties and some studies point out a possible change of turbulence regime breaking the validity of the scaling laws in reactor-like conditions (e.g., XGC1 gyrokinetic code [C. S. Chang 2017], BOUT++ two-fluid code [Z. Y. Li 2019]). In this context, our objective is to provide a physically motivated, turbulence-simulation-based estimate of $\lambda_q$ for a high-field compact tokamak. To this end, as a first step, parameter scans based on 3D turbulence simulations in slab geometry — selected for their reduced computational cost — were carried out using the SOLEDGE3X code [H. Bufferand 2024] [R. Düll 2024] [V. Quadri 2024]. In particular, the main $B_{\mathrm{pol}}^{-1}$ dependence in the scaling laws was recovered. At fixed $B_{\mathrm{tor}}$, this behavior can be attributed to the linear increase of $\lambda_q$ with the parallel connection length $L_{\parallel}$ (proportional to the safety factor), as structures can propagate farther in the SOL due to reduced parallel damping. Additionally, the effects of the major radius $R$, toroidal field $B_{\mathrm{tor}}$, magnetic shear $s = r/q \cdot dq/dr$, and collisionality $\nu_{ei}$ were investigated. Finally, preliminary results of similar scans performed in toroidal geometry are presented, highlighting the effect of geometry on $\lambda_q$.