VDU/LEI project in FUSION: background, goals, methods and expected results (PhD student Birutė Bobrovaitė, D r. Liudas Pranevičius)

Project title: Characterisation of W-Coatings for Fusion Applications Project duration 30 months originated from The project is coordinated by  the Materials Research and Testing Laboratory, Lithuanian Energy Institute, Kaunas. The project partner is  the Physics Department of the Vytautas Magnus University, Kaunas.

Outline of the presentation oGoals of the work; oWork package; oExpected results.

Main problem  Mechanism of restructuring and surface relocations under high-flux irradiation at elevated temperatures.  Material erosion by continuous or transient plasma ion and neutral impact, the subsequent transport of the released impurities through and by the plasma and their deposition and/or eventual re-erosion constitute the process of migration.  Due to erosion mechanism and re- deposition materials will interact on plasma facing surfaces.....is to understand physical phenomena of mechanical properties of W and to reduce the impurities in the main chamber

The goal of the research is  the fabrication of W films to be used in plasma-facing components in fusion devices, and the understanding of the mechanism of physical phenomena initiating modifications of mechanical properties of W-based thin films on carbon based substrates under high-flux, low-energy H + ions irradiation in the range of temperatures up to 1000°C.

Descriptions of work  Fabrication of W coatings by magnetron sputter deposition;  Structural and compositional investigation of W coatings;  Plasma/ion beam H exposure of W coatings ;  Studies of W coatings properties after hydrogen ion irradiation ;  Modelling of the surface restructuring and re-deposition effects in W film under high-flux, high-fluence, low-energy hydrogen ion irradiation;

Fabrication of W films Magnetron sputter deposition of W films on carbon based substrates.  Thickness – 3-10  m.  The film surface area – 17  20 cm.  Thickness homogeneity – better than 20%.

Irradiation experiment  Extraction of ions from thermionic arc plasma generated in hydrogen working gas.  Pulsed plasma immersion hydrogen ion implantation using acceleration voltage up to 500 V.  Hydrogen beam implantation using Kauffman ion source (2-5 mA  cm- 2, 300 eV) using facilities of the Poitiers University (France).

Characterization  Microstructure and grain size of films by XRD analysis;  Surface morphology analysis using SEM and AFM analysis;  Film and interface compositional analysis using glow discharge optical emission spectrometry (GDOES) analysis;  Film resistivity measurements using four probe method;  Film thickness homogeneity analysis using large area laser interferometry views;  Studies of film nano-hardness and film erosion properties in collaboration with the Laboratory of Metallurgic Physics of the Poitiers University (France).

Modelling It is planned to consider surface redeposition and reconstruction effects on composition and structure of W films initiated H+ irradiation. The modelling includes three processes:  surface diffusion (thermally activated process),  ballistic surface atom relocation (ion irradiation activated process)  and redeposition of sputtered atoms (W atoms, oxygen, etc.) arriving from plasma.

Expected results  To form dense nanocrystallline thin W films (optimization of film deposition parameters for thickness and homogenity of W films);  To investigate structure and composition of W cotings;  To commit iradiation experiments;  To model surface redoposition and reconstruction effects on composition and structure of W films initiated initiated H irradiation.

Work package list

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