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Tungsten-steel and tungsten-chromium composites prepared by RF plasma spraying
Matějíček, Jiří ; Klečka, Jakub ; Čížek, Jan ; Veverka, Jakub ; Vilémová, Monika ; Chráska, Tomáš ; Ganesh, V.
For future fusion reactors, materials able to withstand harsh environments are needed. In particular, this concerns the plasma-facing components which are foreseen to consist of tungsten based plasma-facing armor and structural and cooling part made of steel. Currently, joining of these materials presents a significant challenge. The stress concentration at their interface, which arises due to thermal exposure and the difference in thermal and mechanical properties, can be reduced by composite/graded interlayers. Plasma spraying is among the prospective technologies for their preparation. In this work, tungsten-steel and tungsten-chromium composites were prepared by radio-frequency inductively coupled plasma (RF-ICP) spraying. Initial optimization of the spraying process for pure materials as well as their mixtures was carried out. Basic characterization of the layers for their structure, porosity and composition is presented.
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Thin nitride layers as permeation barriers
Veverka, Jakub ; Matějíček, Jiří ; Lukáč, František ; Pospíšil, D. ; Cvrček, L. ; Nemanič, V.
Permeation barriers represent one of the crucial fields in materials development for thermonuclear fusion. Primary objective of the barriers is to suppress the permeation of hydrogen isotopes (mainly tritium) from future thermonuclear fusion facilities. Secondary objective is to reduce their retention in structural materials. Expected reactor conditions put high demands on the material, as well as on the final barrier quality. Key properties are tritium permeation reduction, absence of defects (especially cracks), high-temperature stability and corrossion resistance, and compatibility with structural materials (mostly ferritic-martensitic steels). Thin nitride layers, identified as promising permeation barriers, were prepared by diffusion-based nitridation and physical vapour deposition (PVD), and characterized.
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Alternative Methods of Permeation Barriers Preparation
Veverka, Jakub ; Matějíček, Jiří
Permeation barriers represent one of the crucial fields in materials development for thermonuclear fusion. Primary objective of the barriers is to suppress the permeation of hydrogen isotopes (mainly tritium) from future thermonuclear fusion facilities. Secondary objective is to reduce their retention in structural materials. Expected reactor conditions put high demands on the material, as well as on the final barrier quality. Key properties are tritium permeation reduction, absence of defects (especially cracks), high-temperature stability and corrossion resistance, and compatibility with structural materials (mostly ferritic-martensitic steels). Thin nitride layers, identified as promising permeation barriers, were prepared by diffusion-based nitridation and physical vapour deposition (PVD), and characterized.
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RE beam generation in MGI disruptions on COMPASS.
Ficker, Ondřej ; Mlynář, Jan ; Macúšová, Eva ; Vlainić, M. ; Weinzettl, Vladimír ; Urban, Jakub ; Čeřovský, Jaroslav ; Farník, Michal ; Markovič, Tomáš ; Papřok, Richard ; Vondráček, Petr ; Imríšek, Martin ; Tomeš, Matěj ; Havlíček, Josef ; Varju, Jozef ; Varavin, Mykyta ; Bogár, Ondrej ; Havránek, Aleš ; Gospodarczyk, M. ; Rabinski, M. ; Jakubowski, M. ; Malinovski, K. ; Zebrowski, J. ; Plyusnin, V. ; Papp, G. ; Pánek, Radomír ; Hron, Martin
In the experiments with the massive gas injection (MGI) triggered disruptions in the COMPASS tokamak, post-disruptive runaway electron (RE) beams are generated occasionally. In this contribution, a relatively large set of discharges from the recent years is analysed in order to improve our understanding of the processes behind the beam generation. It seems that despite the low toroidal field applied in the discharges (typically 1.15 T) the magnetic perturbations may be small enough to allow the acceleration and confinement of the electrons. The influence of the different components and different sections of the frequency spectrum of the magnetic perturbations on the beam generation and RE beam current is examined. Fast visible camera images are also analysed. The relevance of COMPASS runaway electron experiments for large machines is discussed. Moreover, the potential of less common diagnostic tools (Cherenkov detector, vertical ECE, ...) to clarify the role of the pre-disruption fast electron population and the influence of prompt runaway electron losses in the current quench is discussed using the recent test measurements.
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