Implementation of 3D blob tracking algorithm inside tokamak scrape-off layer*

One of the burning open problems of achieving fusion within a magnetically confined device is mitigating the megawatt scale plasma outflux on the divertor plates of a tokamak. A quite promising approach is to spread the extreme steady-state power/heat load on the divertor plates via plasma turbulence. Such turbulence in the scrape-off layer (SOL) is primarily mediated via toroidally elongated coherent density structures, called `plasma blobs'. These plasma blobs drift radially outward due to the magnetic field curvature effects. Efficient tracking of such blobs are necessary to understand and control the turbulence in the open-field-line region. However tracking becomes challenging as the shape and size of these blobs change as they propagate in the SOL [1]. We have developed a numerical tool for tracking such arbitrary shape-changing features/structures in 3D as they move. We `triangulate' the closed density isosurfaces and employ a 3D ray-tracing algorithm to discriminate between blobs and density holes. We use Gkeyll simulation data for tracking such blobs as test cases for simplified magnetic field geometry with realistic mass ratio. 

1. R Mukherjee, et. al. Bulletin of the American Physical Society, 2020.