Numerical and experimental investigation of ELM filaments on NSTX*

Edge localized modes (ELMs) are routinely observed in H-mode plasma regimes of the National Spherical Torus Experiment (NSTX). During the ELM’s explosive outburst significant amount of heat and particles are ejected from the plasma in the form of filaments. They carry enough energy to the plasma facing components to be able to permanently damage them, hence, it is important to mitigate these events. Studying the fast dynamics of the ELM filaments could lead to development of novel ELM mitigation techniques. Gas-puff imaging was utilized on NSTX to study the dynamics of the ELM filaments. To estimate their frame-by-frame velocity and structure evolution novel analysis techniques were developed.

 

Our initial analysis focused on a single ELM event which featured a distinct ELM filament with clear radial and poloidal velocity peaks. Investigation of the experimental data revealed that the structural parameters of the ELM filament are not significantly different from the intermittent blobs in the scrape-off layer. However, their non-linear triggering phase and propagation dynamics differ greatly. To find the underlying triggering and propelling mechanism, non-linear numerical simulations were performed with M3D-C1 and NIMROD, and they were compared to the experimental findings.