Optimizing wall conditioning methods in nuclear fusion

(04-07-2022) Andrei Goriaev, in his PhD, investigates how to optimize the interaction between the plasma and the wall in a nuclear fusion reactor, during magnetic confinement.

The total energy consumption in the world continues to increase. Most of the energy comes from burning fossil fuels, leading to huge 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 into a new atom. In the process, some of the mass is converted into energy. If this process can be done in a controlled way, nuclear fusion can become a sustainable energy source.

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

To ensure this, the plasma is held in a magnetic field: atomic nuclei are positively charged and the Lorentz force on the nuclei causes the plasma to describe a more or less circular or spiral path around the field lines in the magnetic field. 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 operate on this principle are the tokamak, the stellarator, and the polywell.

The performance of fusion plasmas is highly dependent on the interaction between the plasma and the reactor wall components. A necessary method to control the effects of the plasma-wall interaction consists of optimizing the state of the reactor wall surfaces, namely wall conditioning,

"In my PhD, I conducted experimental research on the conditioning methods that can be applied in the superconducting stellarator Wendelstein 7-X (W7-X). The first objective of my research was to compare the conditioning effect of different wall conditioning techniques applied in W7-X with respect to the gas removed, the minimization of the impurity content and the subsequent plasma performance. The second goal was to provide a comprehensive description of the different conditioning mechanisms relevant to W7-X," Andrei explains.

"Finally, a conditioning optimization was performed to maximize the effectiveness of the techniques. This involved looking at the modification of the surface of the plasma-oriented components and the plasma performance, while always ensuring good and safe conditions for the discharge. The wall conditioning strategies found will be used during future operating phases of the superconducting stellarator W7-X," Andrei concludes.

Read a more detailed summary or the entire PhD

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PhD Title: Study and Optimisation of Wall Conditioning Methods on the Superconducting Stellarator W7-X

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Contact: Andrei Goriaev, Kristel Crombé

Andrei Goriaev

Andrei Goriaev completed his bachelor’s degree in Quantum Electronics at Saint-Petersburg State University. After, he received the master’s degree in Coherent Optics at the same university. During the bachelor and master studies, Andrei investigated X-ray generation by the femtosecond laser plasma. This work resulted in 1 publication in a peer-review journal and a few conference proceeding contributions. In parallel to his master studies in physics, Andrei also completed part-time specialist education in the field of economics and management.

The PhD candidate received his second master’s degree in Nuclear Fusion and Engineering Physics following the Erasmus Mundus Fusion EP programme. In particular, he attended classes at University Carlos III of Madrid, Spain, Complutense University of Madrid, Spain and Ghent University, Belgium. The master thesis work dedicated to spectral reflectivity measurement of metallic mirrors for fusion plasma diagnostics was done in Forschungszentrum Jülich, Germany.

Besides that, Andrei did numerous internships in different institutes across the European Union such as IRFM-CEA, Cadarache, France, IPP Prague, Czech Republic and Max-Born-Institute, Berlin, Germany. Andrei has been working on the PhD project “Study and optimization of wall conditioning methods on the superconducting stellarator W7-X”. The PhD candidate’s research outcome allows him to obtain a joint doctoral degree between Laboratory for Plasma Physics, Royal Military Academy and Ghent University. The PhD candidate is the first author of 3 publications in nuclear fusion related to the wall conditioning studies on W7-X and upgrades of the TOMAS device for wall conditioning, plasma–surface interaction and plasma start-up studies. Moreover, he is a co-author of 17 peer-review journal articles presenting research results in wall conditioning, plasma-surface interaction, plasma diagnostics development and fusion device exploitation.

Andrei has participated in the following scientific activities within the EUROfusion consortium during the doctoral programme. “Preparation and exploitation of W7-X campaigns” included work on W7-X in IPP Greifswald, Germany and the stellarator Uragan-2M in KIPT, Ukraine. The development of the TOMAS project at Forschungszentrum Jülich, Germany, under the working package “Preparation of efficient PFC operation for ITER and DEMO”. As a continuation of the current project, Andrei has been awarded the EUROfusion researcher grant to extend his work in wall conditioning, plasma production, and plasma-surface interaction studies relevant to superconducting fusion devices W7-X, JT-60SA and ITER.

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Editor: Jeroen Ongenae - Illustrator: Roger Van Hecke