Filament Shape Characterization on NSTX

Filamentary transport accounts for a significant fraction of the unwanted heat and

particle cross-field losses in a tokamak. It can account for decreased lifetime of plasma facing components (PFCs) and can be detrimental to plasma confinement. Hence, understanding the ELM filaments underlying physics is important for the operation of future fusion reactors. Filamentary structures are observed on NSTX in the background plasma (blobs) and during the edge localized mode eruptions (ELM filaments). Filaments can be measured by several diagnostics. The highest signal-to-noise ratio is generally provided by the gas-puff imaging (GPI) diagnostics. GPI measures plasma fluctuations in the scrape-off layer and outer plasma edge by observing the intensity fluctuations of the line-emission during the gas-neutral plasma interaction.

We investigate filamentary structures in the background SOL plasma as well as during the explosive outbursts during the edge localized mode (ELM) instabilities. The structural dynamics of these filaments could be directly connected to their impact on the PFCs important to investigate them. Filaments are analyzed through the following steps: pre-processing, structure identification/segmentation and tracking, shape quantification with descriptors and curve fitting.

This work was made possible by funding from the Department of Energy for the Summer Undergraduate Laboratory Internship (SULI) program. This work is supported by the US DOE Contract No. DE-AC02-09CH11466.