Micron-sized dust and nanoparticles produced in the WEST tokamak
Résumé
Highlights : Tungsten nanoparticles produced in a tokamak of tungsten divertor • Micron-sized tungsten dust particles emitted during off normal events • Helium nanobubbles produced at the surface of tungsten dust particles of a tokamak
Abstract: Two populations of dust particles were found during the first phase of operation of WEST. The
one that dominates by size and weight comes from the delamination of tungsten coatings
covering graphite tiles and the emission of droplets of molten materials during off-normal
events. Sizes vary from several microns to tens of microns. More generally, micron-sized dust
particles due to the erosion of all materials present in the vacuum vessel were collected. In
addition, nanocavities were found at the surface of tungsten dust sampled after He plasmas and
were attributed to He trapping in the form of nanobubbles. Tungsten nanoparticles constitute
the second unexpected dust population. They are dominant by their number and were essentially
found at the surface of micron-sized particles. They may result either from the condensation of
an oversaturated vapor above molten tungsten or come from ion-neutral clusters growing in
plasma regions of low temperature until the appearance of solid particles.
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