Optimization of wall conditioning methods in nuclear fusion – Faculty of Engineering and Architecture – Ghent University

Total energy consumption in the world continues to rise. Most of this energy comes from burning fossil fuels, leading to massive greenhouse gas emissions. Alternatively, nuclear fusion can be used to build a clean, stable and sustainable energy source.

Nuclear fusion is the fusion of the nuclei of different atoms to form a new atom. Part of the mass is converted into energy. If this process can be controlled, nuclear fusion can become a sustainable energy source.

One of the most important possibilities for limiting the reactants (the atomic nuclei that react with each other) in a nuclear fusion reaction is magnetic confinement. Because no material can withstand the temperatures required for fusion (up to 150 million degrees!), The plasma in the fusion reactor (formed by the high temperatures) must always be kept at a safe distance from the wall.

To ensure this, the plasma is kept in a magnetic field: Atomic nuclei are positively charged and the Lorentz force on the nuclei causes the plasma in the magnetic field to follow a more or less circular or helical orbit around the field lines. The magnetic field is shaped in such a way that nuclei that want to escape from the circle are pushed back into it by the Lorentz force. Examples of machines that work according to this principle are the tokamak, the stellarator and the poly well.

The performance of fusion plasma is highly dependent on the interaction between the plasma and the reactor wall components. A necessary method to control the consequences of the plasma-wall interaction is to optimize the condition of the surfaces of the reactor walls, namely wall conditioning,

“In my Ph.D. I conducted experimental research into the conditioning methods that can be used in the superconducting stellarator Wendelstein 7-X (W7-X). The first purpose of my research was to compare the conditioning effect of different wall conditioning techniques used in W7-X in terms of the removed gas, the minimization of the impurity content and the subsequent plasma performance. The second goal was to provide a comprehensive description of the various conditioning mechanisms relevant to the W7-X, ”explains Andrei.

“Finally, a conditioning optimization was performed to maximize the efficiency of the techniques. This looked at the modification of the surface of the plasma-oriented components and the plasma performance, while always guaranteeing good and safe conditions for the discharge. The wall conditioning strategies found will be used in the future operating phases of the superconducting stellarator W7-X, ”concludes Andrei.

Read a more comprehensive summary or the full PhD

PhD title: Study and optimization of wall conditioning methods for the superconducting stellarator W7-X

ContactAndrei GoriaevKristel Crombé

Andrei Goriaev received his bachelor’s degree in quantum electronics from Saint Petersburg State University. He then obtained a master’s degree in Coherent Optics from the same university. During his bachelor’s and master’s studies, Andrei researched X – ray generation of femtosecond laser plasma. This work resulted in 1 publication in a peer-reviewed journal and a few conference papers. In parallel with his master’s degree in physics, Andrei also completed a special part-time course in economics and management.

The PhD student earned his second master’s degree in nuclear fusion and engineering physics as part of the Erasmus Mundus Fusion EP program. He has taught in particular at Carlos III University of Madrid, Spain, Complutense University of Madrid, Spain and University of Ghent, Belgium. His graduation thesis, devoted to spectral reflectivity measurements of metal mirrors for diagnosing fusion plasmas, was performed at the Forschungszentrum Jülich, Germany.

In addition, Andrei has completed several internships at various institutes in the EU, such as IRFM-CEA, Cadarache, France, IPP Prague, the Czech Republic and the Max-Born-Institute, Berlin, Germany. Andrei worked on the PhD project “Study and optimization of wall conditioning methods on the superconducting stellarator W7-X”. The PhD candidate’s research results allow him to obtain a joint doctorate between the Laboratory of Plasma Physics, the Royal Military Academy and Ghent University. The PhD candidate is the first author of 3 publications in nuclear fusion related to wall conditioning studies on W7-X and upgrades of the TOMAS unit for wall conditioning, plasma surface interaction and plasma start-up studies. In addition, he co-authored 17 peer-reviewed journal articles presenting research findings in wall conditioning, plasma surface interaction, plasma diagnostic development, and fusion plant operation.

Andrei participated in the following scientific activities in the EUROfusion consortium under the PhD program. “Preparation and operation of W7-X campaigns” included work on the W7-X in IPP Greifswald, Germany and the constellation Uragan-2M in KIPT, Ukraine. Development of the TOMAS project at the Forschungszentrum Jülich, Germany, in the framework of the “Preparing for effective PFC utilization for ITER and DEMO” work package. As a continuation of the current project, Andrei has been awarded the EUROfusion Research Scholarship to expand its work in wall conditioning, plasma production and plasma surface interaction studies relevant to superconducting fusion plants W7-X, JT-60SA and ITER.

Editor: Jeroen Ongenae – Illustrator: Roger Van Hecke

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