On the use of LIBS to determine the fractionalOn the use of LIBS to determine the fractional abundances of carbon ions in the laser plasma plumeabundances of carbon ions in the laser plasma plume

M. Naiim Habib1, Y. Marandet2, L. Mercadier3, Ph. Delaporte3, C. Hernandez1, N. Gierse4, M. Zlobinski4, P. Monier-Garbet1, C. Grisolia1, B. Schweer4, A. Huber4, V. Philipps4

1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 2 PIIM, CNRS – Université de Provence, Marseille, France.

Association EURATOM-CEACEA / DSM / Institut de Recherche sur la Fusion par confinement Magnétique

CEA-Cadarache, 13108 ST-PAUL-LEZ-DURANCE (France)TORE SUPRA

Association EURATOM-CEACEA / DSM / Institut de Recherche sur la Fusion par confinement Magnétique

CEA-Cadarache, 13108 ST-PAUL-LEZ-DURANCE (France)TORE SUPRA

Association EURATOM-CEACEA / DSM / Institut de Recherche sur la Fusion par confinement Magnétique

CEA-Cadarache, 13108 ST-PAUL-LEZ-DURANCE (France)

Association EURATOM-CEACEA / DSM / Institut de Recherche sur la Fusion par confinement Magnétique

CEA-Cadarache, 13108 ST-PAUL-LEZ-DURANCE (France)TORE SUPRA 3 Laboratoire Lasers, Plasmas et Procédés Photoniques, Marseille, France.

4IEK-4, Association EURATOM-FZJ, TEC, Jülich, Germany.

1. Context & Objectives1. Context & Objectives

2. Lab LIBS experimental setup2. Lab LIBS experimental setup

5. Conclusions and outlook 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 fibreSpectrometerLaser

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, Øspot ~ 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 spectra3. 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

(χ2)

Creation of N free parameter sets (T1, T2, fC, fC+, fC2+)

eezijze

zij TnPECnn ,

Local Thermodynamic Equilibrium not satisfied in our ablation conditions. Electron density (ne) determined from Stark broadening of Hα line. Use of a collisionnal-radiative model to calculate the emissivity of the C lines.

ne ≈ 2.6 × 1015 cm-3

T1 ≈ 1.3 eV

T2 ≈ 6 eV

nC/ntot ≈ 0.18

nC2+/ntot ≈ 0.82

nC+/ntot ≈ 0

Nd:YAG laser beam(1064 nm, 1.5 J, 7 ns, Øspot ~ 4.8 mm, 7.2 J/cm²)

Test limiter(polycrystalline graphite)

Side view

4. First 4. First in situin situ experiments in the TEXTOR tokamak experiments in the TEXTOR tokamak Injection of Ninj = 2.9 ± 0.4 × 1014 carbon particles during a plasma discharge

(necentral

= 1.5 × 1019 m-3, Bt = 2.25 T, Ip = 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

2.5x105

2.0

1.5

1.0

0.5

Inte

nsi

ty (

a.u

.)

516514512

Wavelength (nm)

426.8 465.0 658656 679678

Iplasma

Iplasma+laser

CII

426.

7

CIII

464

.7

CIII

465

.0

C2 Swan

D 6

56.1

H 6

56.3

CII

657.

8C

II 65

8.3

CII

678.

4

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 C2 emission intensity increases in the presence of laser-injected carbon particles.

In the lab ablation conditions, plasma plume mainly composed of C2+ ions. C+ lines probably mostly due to recombination of C2+ 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, nabl ≈ 2.5 × 1014 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.