Finite Ion Temperature Effects on the Merging of Current-Carrying ELM Filaments in the edge region of a tokamak

TL;DR

This paper investigates how finite ion temperature influences ELM filament dynamics in tokamaks, revealing significant effects on filament merging delay and asymmetric potential structures, which are crucial for understanding edge plasma transport.

Contribution

It introduces a three-dimensional fluid model that incorporates finite ion temperature effects, providing new insights into filament behavior and plasma transport in tokamak edges.

Findings

Increasing ion temperature delays filament merging.

Finite ion temperature causes asymmetric potential and strong poloidal flows.

Transition from radial to rotational dominance occurs with higher ion temperature.

Abstract

Edge-localized-mode (ELM) filaments are crucial for cross-field transport at the tokamak edge; yet, their dynamics are often analyzed using the cold-ion approximation, despite experimental data indicating that Ti~Te . This study employs a normalized three-dimensional fluid model to investigate the influence of finite ion temperature on the dynamics of unidirectional current-carrying ELM-like filaments. We demonstrate that increasing ion temperature substantially alters filament propagation and interaction, resulting in a delay of filament merging despite an increase in total kinetic energy due to a stronger pressure-gradient drive. The examination of single-filament dynamics indicates that finite ion temperature generates asymmetric potential structures, strong poloidal flows, and persistent rotational motion, which channel kinetic energy from radial propagation into vortical dynamics. A comprehensive examination of the ion-to-electron temperature ratio reveals a distinct transition from radially dominated to rotation-dominated behavior as ion temperature increases. These results provide a unified physical explanation for reduced radial transport and delayed merging in the warm-ion domain, emphasizing the necessity of incorporating ion temperature effects in the modeling of ELM filament dynamics and edge plasma transport.