# Effect of Scrape-Off-Layer Current on Reconstructed Tokamak Equilibrium

## TL;DR

This paper develops methods to incorporate scrape-off-layer current into reconstructed tokamak equilibria, assessing its impact on flux surface positions and edge stability, with minimal changes observed.

## Contribution

It introduces extrapolation techniques to include scrape-off-layer current effects in equilibrium reconstructions, enhancing the accuracy of tokamak modeling.

## Key findings

- Flux surface shifts up to 3 cm due to scrape-off-layer current
- Minimal change in goodness-of-fit when including scrape-off-layer current
- Small impact on edge mode stability from scrape-off-layer modifications

## Abstract

Methods are described that extend fields from reconstructed equilibria to include scrape-off-layer current through extrapolated parametrized and experimental fits. The extrapolation includes both the effects of the toroidal-field and pressure gradients which produce scrape-off-layer current after recomputation of the Grad-Shafranov solution. To quantify the degree that inclusion of scrape-off-layer current modifies the equilibrium, the $\chi$-squared goodness-of-fit parameter is calculated for cases with and without scrape-off-layer current. The change in $\chi$-squared is found to be minor when scrape-off-layer current is included however flux surfaces are shifted by up to 3 cm. The impact on edge modes of these scrape-off-layer modifications is also found to be small and the importance of these methods to nonlinear computation is discussed.