Effects of tungsten surface conditions on carbon deposition

New results are shown on carbon deposition and mixed layer formation on tungsten surfaces in TEXTOR test limiter experiments by varying surface conditions such as surface roughness (Ra: 10 nm–1 μm), temperature (300–900 °C), and initial surface carbon concentration (0–60%). It is found that surface roughness significantly affected C deposition for both W and graphite substrates such as increase in the C deposition and extension of the C deposition area. Not only the surface roughness parameter Ra but also detailed surface morphology closely relate to C deposition on tungsten. Carbon deposition hardly occurred at least above ∼520 °C on tungsten under TEXTOR edge plasma conditions. Carbon behavior on tungsten at 770–930 °C depends on the incident carbon ion energy. Although tungsten and carbon mixing layers affected C deposition, their effect is less than the roughness effect.