Blob interaction in 2D scrape off layer simulations

TL;DR

This paper investigates how interactions among plasma blobs in the scrape-off layer affect their dynamics, using a 2D fluid simulation and a novel tracking algorithm to analyze deviations from isolated blob behavior.

Contribution

It introduces a new blob tracking method and extends it to study interacting plasma blobs with varying properties, revealing how interactions influence blob velocities and size-velocity scaling.

Findings

Blob interactions lead to higher average velocities.

Decreasing intermittency increases deviations from isolated blob laws.

The tracking algorithm's accuracy depends on parameter choices.

Abstract

Interaction of coherent structures known as blobs in the scrape-off layer of magnetic confinement fusion devices is investigated. Isolated and interacting seeded blobs as well as full plasma turbulence are studied with a two dimensional fluid code. The features of the blobs (size, amplitude, position) are determined with a blob tracking algorithm, which identifies them as coherent structures above a chosen density threshold and compared to a conventional center of mass approach. The agreement of these two methods is shown to be affected by the parameters of the blob tracking algorithm. The benchmarked approach is then extended to a population of interacting plasma blobs with statistically distributed amplitudes, sizes and initial positions for different levels of intermittency. As expected, for decreasing intermittency, we observe an increasing number of blobs deviating from size-velocity scaling laws of perfectly isolated blobs. This is found to be caused by the interaction of blobs with the electrostatic potential of one another, leading to higher average blob velocities. The degree of variation from the picture of perfectly isolated blobs is quantified as a function of the average waiting time of the seeded blobs.