DOI: 10.1016/j.sab.2017.09.006

Authors
Ding, H. B. ; Hai, R. ; Liu, P. ; Sun L. Y. ; Zhang, L.

Keywords

Time-of-flight mass spectroscopy; Laser induced breakdown spectroscopy; Tungsten plasma; Multi-charged ions; Dynamic plasma sheath;INDUCED-BREAKDOWN-SPECTROSCOPY; ABLATION; SPECTROMETRY; LIBS

Abstract

In this work, the plasma was produced by irradiating a tungsten target with an 8 ns pulsed Nd:YAG (lambda = 1064 nm) laser in a vacuum chamber under the pressure of 4 x 10(-4) Pa. The optical and particle emissions were systematically investigated using laser induced breakdown spectroscopy and time-of-flight mass spectroscopy respectively. The results showed that not only there were neutral and single ionized atoms in the laser induced plasma, but also quite a number of multi-charged ions were observed. The ion charge state was even up to 6 at the laser power density of similar to 11 GW/cm(2). Time and space resolved optical spectroscopy was investigated by using a bundle of lined fibers. Meanwhile, the time-resolved mass spectrometric study of laser produced tungsten plasma was carried out. The variation in intensities of the different species with time showed that higher charged ions reached their peak intensities earlier. This demonstrated that the higher charged ions had higher velocities and the different charged ions were separated during the expansion process. The kinetic energy corresponding to the velocity of the ions was found to increase exponentially with ionic charge state which was related to the acceleration of the dynamic plasma sheath. (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.

DOI: 10.1063/1.4975735

Authors
Annaloro, J. ; Druguet, M. C. ; Morel, V.

Keywords

CROSS-SECTIONS; IONIZATION; EXCITATION; COLLISIONS; ELECTRONS

Abstract

The most relevant approach leading to a thorough understanding of the behavior of non equilibrium atomic plasmas is to elaborate state-to-state models in which the mass conservation equation is applied directly to atoms or ions on their excited states. The present communication reports the elaboration of such models and the results obtained. Two situations close to each other are considered. First, the plasmas produced behind shock fronts obtained in ground test facilities (shock tubes) or during planetary atmospheric entries of spacecrafts are discussed. We focused our attention on the nitrogen case for which a complete implementation of the CoRaM-N2 collisional-radiative model has been performed in a steady one-dimensional computation code based on the Rankinc-Hugoniot assumptions. Second, the plasmas produced by the interaction between an ultra short laser pulse and a tungsten sample are discussed in the framework of the elaboration of the Laser-Induced Breakdown Spectroscopy (LIBS) technique. In the present case, tungsten has been chosen in the purpose of validating an in situ experimental method able to provide the elemental composition of the divertor wall of a tokamak like WEST or ITER undergoing high energetic deuterium and tritium nuclei fluxes.

DOI: 10.1016/j.sab.2016.11.002

Authors
Bultel, A. ; Grisolia, C. ; Schneider, I.

Keywords

Aluminum; Tungsten; Collisional-radiative model; Laser-induced plasma; Non-equilibrium plasma; Ultrashort pulse;INDUCED BREAKDOWN SPECTROSCOPY; THERMODYNAMIC-EQUILIBRIUM; FACING COMPONENTS; FEMTOSECOND; ARGON; NANOSECOND; PICOSECOND; NITROGEN; LIBS; EXPANSION

Abstract

The question of the Local Thermodynamic Equilibrium (LTE) of laser-induced plasmas is crucial regarding the Laser-Induced Breakdown Spectroscopy (LIBS) technique. The most relevant way to assess theoretically the possible departure from LTE is to develop state-to-state models of the chemical species involved. The present paper illustrates such an elaboration in the case of aluminum and tungsten. Based on this state-to-state approach, the two collisional-radiative models CoRaM-Al and CoRaM-W are elaborated. They include elementary processes under electron and heavy particle impact in thermal non-equilibrium, spontaneous emission, radiative recombination and thermal Bremsstrahlung. These models are applied to the case of ultrashort laser-induced plasmas expanding in an argon gas at different pressure, for which a relevant collisional-radiative model is also elaborated to predict the propagation of the shock wave. The laser conditions are close to those used for a typical LIBS analysis under ultrashort regime. At high argon pressure (10(5) Pa), the relaxation of the plasma takes place according to a rather low departure from LTE, as revealed by the thorough examination of the Boltzmann plots derived from the state-to-state models. This relaxation occurs at temperature higher for aluminum than for tungsten, but close to 10,000 IC from 200 ns. Conversely, at low pressure (10 Pa), the extinction of the plasma is observed at similar to 500 ns, just after a phase corresponding to significant departure from equilibrium. These results support the idea of the choice of short gate delays close to the laser pulse for the LIBS characterization of tungsten matrices in tokamak-like conditions. (C) 2016 Elsevier B.V. All rights reserved.