Thermo-oxidation of carbon codeposits and particles release during laser ablation in an oxygen atmosphere and its extrapolation to ITER codeposits

• Published in: Fusion engineering and design 2015-11, Vol.100, p.646-651
• Main Authors: Alegre, D., Gasior, P., Kubkowska, M., Tabares, F.L.
• Format: Article
• Language: English
• Subjects: Annealing; Carbon; Carbon codeposits; Codeposition; Deuterium; Dust; Emission; Laser ablation; Laser ablation in gas; Laser-induced plasma; Lasers; Redeposition; Tritium removal
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2015.09.001

•Suppression of codeposit redeposition around laser crater in oxygen atmosphere.•Deuterium emission during ablation is almost suppressed in oxygen after 5th pulse.•Indication of thermal oxidation of remaining film during each laser pulse.•First laser pulse emit large dust particles with almost initial D concentration.•Probable D content decreases of dust from carbon and W/Be codeposits in oxygen. In this paper the laser ablation of tokamak carbon codeposits in vacuum and different gases will be presented. A strong deuterium emission decrease has been observed from the third laser pulse at the same location, which suggests the annealing of a part of the remaining codeposit (up to 0.5–0.7μm) to temperatures of 400–600°C. In addition, at the third pulse in oxygen deuterium emission is close to the noise level, indicating its earlier elimination by thermo-oxidation from the remaining film on the laser spot. Moreover, the suppression of the redeposited film surrounding the laser impact has also been observed together with CO+ emission. Both observations indicate a fast reaction of the laser-activated oxygen molecules with the released hydrocarbon molecules and probably also with the hot, emitted dust particles. On the other hand, dust particles ejection has been analyzed by fast camera. Large particles with almost the initial deuterium concentration have been observed to be produced in the first laser pulse. Finally a brief future-work study with ITER metallic—W and Be—codeposits with a few % of trapped deuterium has been made. In that case the produced dust particles are expected to have part of the initial deuterium due to the large annealing temperatures required for its elimination. This deuterium concentration will probably be reduced during laser ablation in an oxygen atmosphere.