Assessing the Numerical Stability of Physics Models to Equilibrium Variation through Database Comparisons

TL;DR

This study compares manual and automated methods for reconstructing tokamak equilibria, analyzing their impact on stability calculations and identifying areas of agreement and discrepancy in key parameters.

Contribution

It provides a comprehensive comparison of manual and automated equilibrium reconstruction tools, highlighting their effects on stability assessments and parameter accuracy.

Findings

Good agreement in scalar parameters between methods

Substantial disagreement in profile quantities like bootstrap current

90% of stability classifications remain consistent across methods

Abstract

High fidelity kinetic equilibria are crucial for tokamak modeling and analysis. Manual workflows for constructing kinetic equilibria are time consuming and subject to user error, motivating development of several automated equilibrium reconstruction tools to provide accurate and consistent reconstructions for downstream physics analysis. These automated tools also provide access to kinetic equilibria at large database scales, which enables the quantification of general uncertainties with sufficient statistics arising from equilibrium reconstruction techniques. In this paper, we compare a large database of DIII-D kinetic equilibria generated manually by physics experts to equilibria from the CAKE and JAKE automated kinetic reconstruction tools, assessing the impact of reconstruction method on equilibrium parameters and resulting magnetohydrodynamic (MHD) stability calculations. We find good agreement among scalar parameters, whereas profile quantities, such as the bootstrap current, show substantial disagreement. We analyze ideal kink and classical tearing stability with DCON and STRIDE respectively, finding that the $\delta W$ calculation is generally more robust than $\Delta^\prime$. We find that in $90\%$ of cases, both $\delta W$ stability classifications are unchanged between the manual expert and CAKE equilibria.