1. On the use of LIBS to determine the fractional abundances of carbon ions in the laser plasma plume M. Naiim Habib 1, Y. Marandet 2, L. Mercadier 3, Ph. Delaporte 3, C. Hernandez 1, N. Gierse 4, M. Zlobinski 4, P. Monier-Garbet 1, C. Grisolia 1, B. Schweer 4, A. Huber 4, V. Philipps 4 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 2 PIIM, CNRS – Université de Provence, Marseille, France. 3 Laboratoire Lasers, Plasmas et Procédés Photoniques, Marseille, France. 4 IEK-4, Association EURATOM-FZJ, TEC, Jülich, Germany. 1. Context & Objectives 2. Lab LIBS experimental setup 5. Conclusions and outlook  In a tokamak, plasma-surface interactions → erosion of the Plasma Facing Components (PFCs) → plasma pollution by impurities, dust, codeposition.  To keep the dust quantity below the safety limit requirements imposed to the ITER project, it is necessary to control the quantity of eroded material.  In tokamaks, spectroscopic measurements routinely used to monitor particle fluxes into the plasma.  Window transmission  with operation time  absolute calibration of spectroscopic measurements regularly required.  Transport + Deposition + Re-erosion  link between the measured carbon particle flux and the quantity of eroded material has to be examined. Optical fibre Spectrometer Laser Line of sight of the spectroscopic diagnostic  Experimental method proposed:  How many laser-injected particles will effectively penetrate into the plasma?  Is it possible to evaluate the fractional abundances of carbon ions in the plasma plume from Laser-Induced Breakdown Spectroscopy (LIBS)? Sample (graphite) Plasma plume Nd:YAG Laser Echelle spectrometer + ICCD Imaging spectrometer + ICCD 1064 nm, 5 ns, 10 Hz, 50 J/cm², Ø spot ~ 100 µm  Ejection velocity (time- and space- resolved analyses)  Identification of the emitted species (LIBS) (spatially integrated measurements) P = 0.5 mbar Ar 3. Modelling of the experimental spectra × N N values of χ 2 Selection of the best solutions Creation of N new free parameter sets Line emissivities calculation × M Comparison with experiment ( χ 2 ) Creation of N free parameter sets (T 1, T 2, f C, f C+, f C2+ )  Local Thermodynamic Equilibrium not satisfied in our ablation conditions.  Electron density (n e ) determined from Stark broadening of H α line.  Use of a collisionnal-radiative model to calculate the emissivity of the C lines. n e ≈ 2.6 × 10 15 cm -3 T 1 ≈ 1.3 eV T 2 ≈ 6 eV n C /n tot ≈ 0.18 n C2+ /n tot ≈ 0.82 n C+ /n tot ≈ 0 Nd:YAG laser beam (1064 nm, 1.5 J, 7 ns, Ø spot ~ 4.8 mm, 7.2 J/cm²) Test limiter (polycrystalline graphite) Side view 4. First in situ experiments in the TEXTOR tokamak  Injection of N inj = 2.9 ± 0.4 × 10 14 carbon particles during a plasma discharge (n e central = 1.5 × 10 19 m- 3, B t = 2.25 T, I p = 350 kA, NBI heating).  Test limiter located at 4 cm outside the last closed flux surface. UV radially resolving spectrometer ICCD camera (view diameter ~ 8 cm; CII 426 nm filter; 5 ms intensification gate) sample surface r λ (nm) Echelle spectrometer CIII 229.7 CI 247.9 CII 250.9 & 251.2 laser-induced plasma  Fractional abundances of carbon ions different from those measured at 50J/cm²  new lab experiments in the TEXTOR ablation conditions are required.  Knowledge of the amount of particles effectively penetrating into the plasma:  in situ absolute calibration of the diagnostic.  determination of the amount of material eroded from the bulk.  CII, CIII and C 2 emission intensity increases in the presence of laser-injected carbon particles.  In the lab ablation conditions, plasma plume mainly composed of C 2+ ions.  C + lines probably mostly due to recombination of C 2+ ions with electrons.  Good agreement between the experimental and simulated spectra, but further investigations on radiation transport and on the temperature spatio- temporal evolution are needed.  Fit of an experimental spectrum (delay = 200 ns, gate = 20 ns, n abl ≈ 2.5 × 10 14 particles):  The model used to simulate the experimental spectra gives encouraging results, but study of radiative transfer along the line of sight and of the evolution of the plasma plume is necessary.  New lab experiments in the TEXTOR ablation conditions required to interpret the data.  New in situ experiments required to better understand the influence of the various parameters, and to study the impact of the laser plasma plume on the local conditions of the tokamak plasma.