Material mixing on plasma-facing components: Compound formation

Abstract

a r t i c l e i n f o a b s t r a c tTwo different tungsten limiters (castellated bulk metal block and W-coated graphite), subjected to high power loads in the TEXTOR tokamak, were examined in order to determine chemical composition of deposits inside the castellated grooves and on side surfaces of the coated limiter. Comprehensive analyses carried out by X-ray diffraction, ion beam analysis and other methods revealed: (i) the formation of tungsten oxide (WO 2 ) inside the castellated grooves; (ii) the formation of tungsten carbides (WC main phase and traces of W 2 C) on side surfaces of the coated limiter. Elemental tungsten was found in deposits on side surfaces only in trace quantities thus indicating that tungsten eroded from the limiter top and transported to the scrape-off layer reacted with carbon. Based on thermodynamic data, the pathways leading to the formation of compounds are discussed.

Nitrogen and neon retention in plasma-facing materials

“…The other important point is the identification of WO 3 on the surface. This is a confirmation of analyses by X-ray diffraction [22,23] done for a castellated tungsten limiter heated to the melting temperature (above 3500°C). Desorption of water from the tungsten bulk was identified as a possible source of oxygen as the increased O(II) signal was detected by spectroscopy.…”

“…The deconvolution of the W4f shows one component at binding energy of 32.4 eV corresponding to the nitride. The other compounds detected on the plate and deconvoluted from W4f, C1s and O1s are carbide (WC) and some traces of tri-oxide (WO 3 ) thus confirming previous studies of material mixing on PFC from TEXTOR [21][22][23]. In the analysis of a not exposed W plate only adsorbed nitrogen was found and it was fully removed by sputtering.…”

An in situ accelerator-based diagnostic for plasma-material interactions science on magnetic fusion devices

“…A second consequence of material mixing is an alteration to the macroscropic thermuomeclianical properties of the PFCs themselves due to changes in surface morphology and composition. Issues such as reduced melting temperature, reduced power handling, and increased brittleness in alloyed mixed material metals fundamentally alter the intended engineering function of the materials [24].…”

“…Data was collected long enough to obtain a smooth experimental detector response function with excellent statistics. For the Geant4 simulation, the complex 24 AmBe neutron emission spectrum was taken from the recommended ISO standard [75], and gammas, produced by inelastic neutron collisions with the detector, were filtered out of the final detector response function in the simulation.…”

Characterization of nano-structured W-, Ti-, V-, and Zr-doped carbon films

“…In the field of nuclear fusion, such metal-containing films appear as by-product due to the used mixture of plasma-facing materials (PFM) in existing and future fusion plasma devices [22][23][24][25][26][27]. The PFMs are eroded by intensive energetic particle and high power loads.…”