Plume segregation observed in hydrogen and deuterium containing plasmas produced by laser ablation of carbon fiber tiles from a fusion reactor ☆ L. Mercadier a,b, ⁎, J. Hermann a , C. Grisolia b , A. Semerok c a LP3 – UMR 6182 CNRS – University of Marseille, 163, Av. De Luminy, 13288 Marseille, France b CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France c CEA Saclay DPC/SCP/LILM, Bât. 467, 911911 Gif sur Yvette, France abstract article info Article history: Received 2 December 2009 Accepted 17 April 2010 Available online 29 April 2010 Keywords: LIBS Deuterium Plume segregation Laser plasma The plasma produced by the irradiation of a hydrogen and deuterium containing carbon fiber composite with infrared laser pulses of 4-ns pulse duration has been investigated. The experiments were carried out under argon at reduced pressure. Microscopic analyses of the irradiated sample surface were performed to measure the ablation depth. Time- and space-resolved optical emission spectroscopy was applied to characterize the evolution of spectral line emission as a function of time and distance from the surface. Particular attention was paid to the time-of-flight characteristics of the hydrogen and deuterium Balmer α spectral lines. According to the different atomic masses of both isotopes, the expansion of hydrogen into the low pressure argon atmosphere was found to be slightly faster than that of deuterium. The effect of plume segregation is pressure dependent and tends to increase the analytical signal of heavy atoms with respect to lighter ones during laser-induced breakdown spectroscopy. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In fusion reactors, plasma — wall interactions due to high particle fluxes result in the erosion of plasma facing components (PFC) leading to the formation of co-deposited layers. This formation is accompa- nied with fuel deposition (deuterium, tritium) [1]. In order to fulfill safety requirements related to the accumulation of hydrogen isotopes in the vacuum vessel [2], the quantities of trapped deuterium and tritium need to be controlled. Laser-induced breakdown spectroscopy (LIBS), based on the analysis of the optical emission of laser-produced plasma, appears to be an adequate technique to measure the concentrations of hydrogen isotopes in the PFC. LIBS allows for almost non-destructive stand-off and in situ multielemental analysis [3]. However, the technique has one main drawback that consists of the difficulty to perform quantitative measurements. In fact, in case of many complex materials, calibration is inefficient. In that case, the only way to perform quantitative measurements consists to deter- mine the elemental composition of the plasma from the spectra analysis. The so-called calibration-free LIBS measurements [4] generally require the fulfillment of the following conditions: (i) the material ablation process is stoechiometric, (ii) the plasma is in local thermal equilibrium, and (iii) the segregation of elements in the ablation plume is negligible. In the present study, we have focused our attention to the role of plume segregation due to the mass-dependent expansion velocities of the plasma species. In fact, lighter particles are characterized by larger velocities and their lifetime in the high temperature plasma core is expected to be shorter [5]. As a consequence, the analytical signal may be altered in the way that the concentrations of elements having large atomic mass would be overestimated with respect to the lighter elements. The effect may have an influence on the concentrations measurements of deuterium and tritium trapped in the co-deposited layers on the PFC. Hydrogen and deuterium have a particular interest to investigate the plume segregation: both isotopes have different atomic masses but almost equal excitation energies. Thus, their relative spectral line intensities are not influenced by the plasma temperature and electron density. The different expansion characteristics of hydrogen and deuterium are therefore easily observable using optical emission spectroscopy [6]. Both isotopes are present in the carbon fiber composite (CFC) tile that was extracted from the fusion reactor Tore Supra for the present study [7]. 2. Experiment Material ablation was produced by an Nd:YAG laser (Quantel, model Brio) delivering pulses of 100-mJ energy and 4-ns duration. The laser was operated at 1064 nm. The laser pulse energy was attenuated to 5 mJ by turning the beam polarization with the aid of a Spectrochimica Acta Part B 65 (2010) 715–720 ☆ This paper was presented at the 5th Euro-Mediterranean Symposium on Laser Induced Breakdown Spectroscopy, held in Tivoli Terme (Rome), Italy, 28 September–1 October 2009, and is published in the Special Issue of Spectrochimica Acta Part B, dedicated to that symposium. ⁎ Corresponding author. LP3 – UMR 6182 CNRS – University of Marseille, 163, Av. De Luminy, 13288 Marseille, France. Tel.: +33 4 91 82 92 90. E-mail address: mercadier@lp3.univ-mrs.fr (L. Mercadier). 0584-8547/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2010.04.011 Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab