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Materials science challenges in magnetic fusion

par Caroline CHAMPENOIS - publié le

séminaire du laboratoire
mercredi 29 novembre de 11:00 à 12:00

Robert D. Kolasinski

Sandia National Laboratories, Energy Innovation Department, Livermore, CA 94550 USA

abstract :

It is widely recognized that the science of plasma - material interactions (PMI) is central to the realization of magnetic fusion as an energy source. Predicting how materials behave in the extreme environments characteristic of fusion devices remains among the most daunting and complex technical challenge s in materials science. The plasma - facin g surfaces of a fusion reactor will be exposed to a combination of high - flux deuterium - tritium (D - T) plasmas, high - energy fusion products, as well as impurities . These energetic particles will continually reconfigure the exposed surfaces . While this is obv iously one of the main mechanisms leading to material degradation, the implications are far broader than this. Surface structure affects many topics of importance to tokamak operation, including transport of tritium fuel through the plasma - facing material, sputtering (and therefore impurity transport into the core plasma), as well as recycling of hydrogen isotopes back into the plasma.

Our research effort at Sandia/CA focuses on one of the most challenging aspects of the PMI problem : how intense low - energy hydrogen and helium implantation dynamically modifies the structure of plasma - facing materials. The mechanisms that underlie this surface modification include surface - to - bulk transport of implanted species , defect nucleation, nanostructure growth, and stre sses induced in materials during plasma exposure. There are considerable gaps in the understanding of the complex physics governing the material response to plasma, particularly within the implantation zone and first 5 0 nm into the bulk. To decipher these mechanisms, we have developed a RF linear plasma device capable of exposin g materials to the relevant plasma conditions . Using ex - situ optical spectroscopy and helium ion microscopy , we are examining the linkage between nanostructure evolution and near - sur face He bubble growth . The RF plasma source will also serve as a test - bed for in - situ and in - vacuum surface diagnostics. In parallel with testing practical material systems, our research effort aims to break down the complexity of plasma - material interacti ons into basic atomic - scale processes using low energy ion beam experiments performed in a well - controlled high - vacuum environment. As an example of this work, recent low energy ion scattering experiments will be presented that illustrate the ability to de tect the binding configuration of hydr ogen adatoms .

An envisioned outcome of this research is a comprehensive physical picture of hydrogen and helium behavior in the near - surface that will enable accurate predictions of surface composition and structure ev olution during plasma exposure. Going forward, this scientific basis for understanding dynamic effects in the near - surface will have an essential role in guiding the development of new plasma - facing materials for future magnetic fusion experiments.

About Sandia National Lab : Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE - NA0003525.

About the speaker : Robert Kolasinski is a materials scientist in the Energy Innovation Department at Sandia National Laboratories, in Livermore, CA. While at Sandia, Rob’s research efforts have focused on plasma - material interactions for magnetic fusion energy, hydrogen stora ge, and infrastructure for fuel cell electric vehicles. Rob received M.S. (2001) and Ph.D. (2007) degrees from the California Institute of Technology in mechanical engineer ing following undergraduate study at Rutgers University. While at Caltech, he studie d ion - surface interactions in plasma propulsion systems as part of a collaboration with the Advanced Propulsion Group at the NASA Jet Propulsion Laboratory. In 2016, Rob was selected for Department of Energy Office of Science Early Career Award.

contact : Yves Ferro

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