Understanding the Role of Equilibrium Uncertainty in Physics Assessments on DIII-D

In this work, we provide a proof-of-concept demonstration for a potential workflow that can help to qualify sensitive analysis routines built upon kinetic tokamak equilibrium reconstructions. The Consistent Automatic Kinetic Equilibrium (CAKE code) [1] provides consistent and automatic kinetic equilibria, but several assumptions are still made in the process of defining these equilibria, such as spline knot locations, smoothing factors, and the separatrix electron temperature. For a selection of DIII-D discharges, select families of kinetic equilibria are created using different sets of profile assumptions for the same time slice. The resulting equilibria families are assessed as functions of Grad-Shafranov error, measurement error, profile structure, transport, and stability to determine how assumptions made early in the equilibrium reconstruction process can impact uncertainties in the final physics results. These assumptions are shown to have a significant impact on the code results, especially in the edge region. This work mitigates the challenges of kinetic tokamak equilibria reconstructions by assessing equilibrium uncertainty using the CAKE code.

[1] Z.A. Xing, “CAKE: Consistent Automatic Kinetic Equilibrium reconstruction”, Fusion Engineering and Design, 163, 112163 (2021)