DOI: 10.1088/0031-8949/2017/T170/014003

Authors

Keywords

laser induced breakdown spectroscopy; spatial regularities of the laser-induced plasma plume; detection of hydrogen isotopes;EROSION/DEPOSITION; SPECTROSCOPY

Abstract

ITER plans foresee the quantitative diagnostics of fuel retention in reactor walls at nearatmospheric pressures. Using laser induced breakdown spectroscopy for this purpose assumes a reliable resolving of Balmer a-lines of hydrogen isotopes in spectra of plasma produced by focused laser radiation onto the target surface. To develop LIBS for quantitative diagnostics of fuel retention during the maintenance breaks of ITER, the effect of background gas pressure on the laser-induced plasma characteristics has been studied. The background pressure limits the expansion rate of plasma and as a result it leads to higher plasma concentrations. At the same time the limiting factor of the resolving of hydrogen isotope lines is the lines broadening by Stark effect, which is the function of electron concentration. The resolving of lines become possible recording spectra at longer delay times after the laser pulse. On the other hand, at longer delays the signal-to-noise ratio decreases. As a compromise, we found that at atmospheric pressure and at delay times > 2000 ns, a fitting of H a and D a lines by Voigt contours allows a reliable discrimination of these lines.

DOI: 10.1016/j.fusengdes.2017.03.173

Authors
Aints, M. ; Grigore, E. ; Hakola, A. ; Jogi, I. ; Kolehmainen, J. ; Kozlova, J. ; Lungu, C. ; Mandar, H. ; Paris, P. ; Piip, K. ; Porosnicu, C. ; Ruset, C. ; Tervqakangas, S.

Keywords

ITER relevant coatings; Laser induced breakdown spectroscopy; (LIBS) diagnostics; Ablation rate; Surface morphology;TILES; JET

Abstract

Laser induced breakdown spectroscopy (LIBS) has been applied to study ITER-relevant coatings with different surface morphology and crystallinity. LIBS elemental depth profiles were compared with those obtained by secondary ion mass spectrometry (SIMS). Depending on surface morphology and crystallinity, the laser ablation rate of the coatings changed by an order of magnitude, the highest ablation rate had samples prepared by thermoionic vacuum discharge. The inclusion of aluminum (proxy for beryllium) increased the ablation rate by a factor of >6. In addition, for W-Al coatings the ablation was non-stoichiometric. (C) 2017 Elsevier B.V. All rights reserved.

DOI: 10.1016/j.nimb.2017.01.072

Authors
Hakola, A. ; Karhunen, J. ; Krieger, K. ; Laan, M. ; Lahtinen, A. ; Markelj, S. ; Oberkofler, M. ; Paris, P. ; Pecovnik, M. ; Pelicon, P. ; Piik, K. ; van der Meiden, H. ; Vavpetic, P. ; Zaloznik, A.

Keywords

Focused ion beams; Deuterium; He-3; Nuclear reaction analysis; 3HIXE;DEUTERIUM

Abstract

Micro nuclear reaction analysis (micro-NRA) exploiting the nuclear reaction D(He-3,p)He-4 was used for post-mortem analyses of special marker samples, exposed to deuterium plasma inside ASDEX Upgrade (AUG) tokamak and to the deuterium plasma jet in the Pilot-PSI linear plasma gun. Lateral concentration profiles of deuterium and erosion/deposition profiles of the marker materials were obtained by a combination of micro-NRA and particle inducedX-ray emission by He-3 beam (3HIXE). In the case of AUG samples, where 25 nm thick W marker layers had been deposited on unpolished and polished graphite substrates, the effect of surface roughness on local erosion and deposition was also investigated. The lateral distribution of W concentration showed that erosion is much more distinct in the case of polished samples and the resulting surface shows a ""leopard"" skin pattern of W accumulated on carbon aggregates left on the surface from polishing. The Pilot-PSI samples indicated preferential accumulation of deuterium a few mm off from the centre of the region affected by the plasma beam. This is connected with the largest surface modifications while the thick deposited layers at the centre do not favour deuterium retention per se. The results were cross correlated with those obtained using laser-induced breakdown spectroscopy (LIBS). With its quantitative abilities, micro-NRA provided essential calibration data for in situ LIES operation, as well as for complementary post mortem Secondary Ion Mass Spectroscopy (SIMS). (C) 2017 EURATOM. Published by Elsevier B.V. All rights reserved.