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Unipolar arcs in fusion reactors - problem or not?

Hi again! Here is a new blog, now as an actual PhD student. Since my last blog a lot has happened. First of all, my PhD supervisor decided to switch jobs and is going to work for ITER. While the institute searches for a new supervisor, I am mainly publishing/presenting my old work of my Master’s thesis project. This research was about discharges (currents) that flow between the plasma and the divertor (exhaust) wall  of a tokamak.

These arcs or so-called ‘unipolar arcs’ can be triggered on the divertor wall of fusion devices by wall heat loads due to plasma instabilities (e.g. Edge –Localized Modes). Recent work has shown that helium plasma exposure on the divertor wall-material – tungsten - leads to nanostructures or so-called ‘fuzz’, and that these structures increases arc occurrence. Unipolar arcs are non-stationary, which in this case means that the electrons flow from the wall to the plasma in flashes/micro-explosions. This damages the wall and tungsten is migrated into the plasma, leading to plasma cooling.

The question is if/when these arcs occur in fusion devices, and how much is their damage. My research investigated these questions, and, additionally, provided a method for plasma spectroscopy of the induced arc-plasma. The experiments were performed on a linear plasma device that simulates the plasma environment near the divertor wall. The heat load was simulated using laser heating.

Two weeks ago I had an opportunity to show this work on the 26th edition of the Symposium series on Plasma Physics and Radiation Technology in Lunteren, the Netherlands. It was my first conference, and despite its relative small size, it was really interesting! Not only did the conference cover fusion research, it also presented work about plasma applications in the realm of physics, chemistry, biomedicine and technology.

The next coming weeks I hope to do some validation experiments. The linear plasma device I will use for my experiments - MAGNUM-PSI - is a ‘busy’ device however, so it’s hard to get reactor time. It also means that when I’m running the experiments I need a tight schedule in order to do everything in the time I have, probably only 1-2 days. Let’s hope that works out!

Tomorrow I will give a presentation at the PhD Day, a day set up for PhD students from Forschungscentrum Julich and DIFFER to get to know each other.