Effect of magnetic drift on the stability structure of the ambipolar condition

TL;DR

This paper investigates how magnetic drift influences the stability and root selection of the ambipolar electric field in non-axisymmetric plasmas, highlighting its impact on potential landscape and susceptibility to fluctuations.

Contribution

It demonstrates that magnetic drift significantly alters the potential landscape, affecting root selection and explaining discrepancies in simulation and experimental results.

Findings

Magnetic drift modifies the potential landscape in ambipolar conditions.

The ambipolar electric field may be more sensitive to fluctuations than previously thought.

Magnetic drift inclusion can reconcile differences between simulation models and experiments.

Abstract

In non-axisymmetric plasmas, the ambipolar condition may have multiple roots. In such cases, the evolution of the ambipolar electric field can be described by the dynamics in a bistable potential, where the relative depth of the potential wells primarily determines the realized root. In this study, we show that the inclusion of the magnetic drift in the orbit model can significantly modify the potential landscape and affect root selection. This effect provides a possible explanation for discrepancies between simulation results obtained using different orbit models, as well as between simulations and experimental observations of ambipolar radial electric field profiles. Further, the analysis suggests that the ambipolar electric field may be more susceptible to fluctuations than previously expected, indicating the potential relevance of noise-induced state transitions.