Speaker
Matti Laan
(Institute of Physics)
Description
Laser induced breakdown spectroscopy (LIBS) is a promising tool for remote monitoring of erosion/deposition processes at the first wall of ITER. Proper application of LIBS requires knowing the ablation rates of co-deposited layers on plasma-facing components accurately to obtain elemental depth profiles of different elements on the layers from the recorded LIBS spectra. This goal is, however, complicated by the fact that the ablation rate depends on the composition of the layer as well as on its density, morphology, and the phase structure. To clarify the role of each of these parameters, samples with ITER-relevant 2 mm W or W/Al coatings of on Mo and without deuterium content, were prepared by three different procedures and tested by LIBS; here Al was used as a proxy for Be.
In the LIBS measurements, the fluence of » 7 J cm-2-2 at the sample surface was produced by a Nd:YAG laser (l = 532 nm). Time-gated spectra were recorded in the 387-410 nm wavelength interval. The LIBS results were compared with those obtained by scanning electron microscopy (SEM), secondary ion mass spectrometry and X-ray diffraction techniques.
The total intensity of the LIBS spectrum recorded for the coating differed from that recorded for the substrate. In addition, SEM pictures showed that the difference became even larger as the porosity of the sample increased. This finding indicates a more efficient absorption of the laser radiation. Samples of a fixed composition but prepared by different procedures had remarkably different porosity-caused ablation rates: for W/10% Al coating the ablation rate determined from the LIBS depth profiles changed from 50 to 500 nm per laser shot. Effect of other factors like the phase structure of the samples, was negligible.
Co-authors
Antti Hakola
(VTT Technical Research Centre of Finland, 02044 VTT, Finland)
Corneliu Porosnicu
(3National Institute for Lasers, Plasma and Radiation Physics, Bucharest 077125, Romania)
Cristian Lungu
(3National Institute for Lasers, Plasma and Radiation Physics, Bucharest 077125, Romania)
Cristian Ruset
(3National Institute for Lasers, Plasma and Radiation Physics, Bucharest 077125, Romania)
Eduard Grigore
(3National Institute for Lasers, Plasma and Radiation Physics, Bucharest 077125, Romania)
Indrek Jogi
(Institute of Physics, University of Tartu, 50411Tartu, Estonia)
Jelena Kozlova
(Institute of Physics, University of Tartu, 50411Tartu, Estonia)
Jukka Kolehmainen
(DIARC-Technology Inc, DIARC Finland, Finland)
Kaarel Piip
(Institute of Physics, University of Tartu, 50411Tartu, Estonia)
Mart Aints
(Institute of Physics, University of Tartu, 50411Tartu, Estonia)
Matti Laan
(Institute of Physics, University of Tartu, 50411Tartu, Estonia)
Peeter Paris
(Institute of Physics, University of Tartu, 50411Tartu, Estonia)
Sanna Tervakangas
(DIARC-Technology Inc, DIARC Finland, Finland)
