Magnetic fusion research aims at energy production on Earth using nuclear fusion reactions. This method would be a greenhouse gas free, sustainable source of baseload electricity without generating long-lived nuclear waste. The problem is that a fusion reactor needs to confine 100 million C temperature Hydrogen plasma which is only possible by strong magnetic fields. The two basic categories of magnetic confinement fusion devices are tokamaks and stellarators. The former has simple axisymmetric geometry while the latter has complicated 3D form. Plasma confinement is studied in both device types on large, industrial-scale experiments. Wigner RCP is participating in most large international experiments by designing, building and operating specialised plasma diagnostic devices (Beam Emission Spectroscopy, BES) and by comparing experimental findings with theory. These diagnostics an reveal both plasma density distribution and fast modulation.

In both devices the edge plasma is prone to instabilities which cause random ejection of plasma filaments. These filaments deteriorate the device performance and threaten the solid state environment. The physics of filaments has been studied in the 2D geometry on tokamaks, but on the Wendelstein 7-X stellarator they were only found recently by researchers from Wigner RCP. The alkali BES diagnostic, installed by Wigner RCP in 2017 reveals details of both local filament activity and density profile in the whole edge region. In this complicated 3D device filaments appear to enter the edge “island divertor” and move energy and particles from the edge plasma to the island core. Also the filament activity is dependent on plasma conditions, in some parameter regimes quasi-coherent coupled oscillations are observed in edge parameters and the strength of filament activity.

The aim of the Ph.D. research topic is the analysis of experimental data obtained mostly from alkali BES diagnostic to reveal the origin, 3D structure and motion of filaments, their interaction with the edge plasma parameters, most notably with the local plasma density modulations measured with the same diagnostic. Also comparison with our own measurements on tokamak devices (EAST, COMPASS, KSTAR, ASDEX Upgrade, JET) and with modeling by other groups are planned. The Wendelstein 7-X experiment is ondergoing upgrade until 2021. After the restart new experiments are planned with upgraded diagnostics where the analysis techniques and findings of the student would play an important role. The student is also expected to take part in these experiments by upgrading and/or operating the alkali BES diagnostic.