Plasma diagnostic of a low-pressure - high density etching reactor used for the synthesis of composite dusts* G. Lombardi, L. Colina Delacqua, M. Rédolfi, D. Vrel, A. Michau, X. Bonnin and K. Hassouni LSPM, Université Paris 13, CNRS; Institut Galilée, 99 avenue J.-B. Clément, 93430 Villetaneuse, FRANCE *Work supported in part by ANR Contracts JC05_42075, ANR-09-BLAN-0070-01 and EU PWI TF actions WP10-PWI02-02 and 06-01
Abstract and Motivation: A low-temperature high-density plasma reactor has been developed at LIMHP, whose objective is to reproduce some of the plasma/surface processes which can occur in the divertor and far scrape-off layer regions of tokamaks. This CASIMIR II (Chemical Ablation, Sputtering, Ionization, Multi-wall Interaction and Redeposition) device is envisioned as an ITER divertor dome simulator and is able to generate plasma flow in accordance with plasma characteristics simulated for parasitic discharges [1] and expected under the ITER divertor dome [2]. The objective is to explore and understand effects due to preferential sputtering and material migration of first carbon materials targets then mixed material (carbon/tungsten) exposed to an hydrogen/deuterium plasma, as well as characterization of the deposits and dust that such exposure may create. In parallel a Multi-Pin-to-Plane pulsed corona discharge reactor has been designed for the removal and /or dehydrogenation of codeposited hydrogen-containing carbon films and dust. [1] V. Rohde, M. Mayer, ASDEX Upgrade Team, J. Nucl. Mater. 313-316, 337 (2003). [2] K. Matyash, R. Schneider, X. Bonnin, D. Coster, V. Rohde, H. Kersten, J. Nucl. Mater. 337-339, 237 (2005).
Phenomenological description
Mechanism of dust formation
What happens at the divertor surface?
Chemical erosion and physical sputtering of carbon surfaces Transport and kinetics (homogeneous and/or heterogeneous) of hydrocarbons Energy loss/transfer between out-of-equilibrium edge fusion plasma / carbon walls
Physical and/or chemical etching Coagulation Chemistry
Some features of edge fusion plasmas are similar to out-of-equilibrium molecular plasmas (i.e. “cold plasmas”) made of H (or D) / C and containing up to 10 % of carbon
Core plasma
Volume recombination e- or H+ => energy losses
d
H+ and e- fluxes H-atom fluxes
ne ~ 1013 cm-3, Te = few eV and Tg < 1 eV
Sputtering Chemical erosion (H) Recombination H2(v) production CxHy production
Agglomeration Growth
Nucleation
C, H
Soot synthesis (ionic schemes, clusters)
Transport, chemistry, energy transfer in H2/H/CxHy plasmas
Carbon re-deposition Divertor surface
Tore Supra (CEA-Cadarache)
How can we simulate some of these plasma/surface processes?
SEM images from PIIM-CP2M, Marseille (P. Roubin & C. Martin)
CASIMIR II : Chemical Ablation, Sputtering, Ionization, Multi-wall Interaction and Re-deposition ECR source
Microwaves inlet
target
CASIMIR II: diagnostics
Permanent magnet
Spectroscopic diagnostics (densities and temperatures) - Optical Emission Spectroscopy (H/D and carboncontaining species) - UV and visible Broadband Absorption Spectroscopy (carbon-containing species) - FTIR
Aluminium body
stubs
Electrical diagnostics (Langmuir probe)
W C (Be)
Configuration of the magnetic field produced by a cylindrical magnet with axial magnetization [3] [3] T. V. Tran, PhD. Thesis, Université de Grenoble (2006)
Etching chamber : - 16 dipolar plasmas sources close enough together to ensure large enough plasma density (from 1011 cm-3 to 1012 cm-3 depending on the position)
The plasma is localized around each elementary plasma source with perfect azimuthal symmetry
- Pure Carbon, binary C-W and/or ternary C-W-X (X: Be-like element such as lithium, boron, magnesium or calcium) targets located at the top and the bottom of the plasma chamber. The targets will be biased and controlled in temperature.
Morphological characterisation Analysis of the re-deposition by: SEM, AFM, XRD, TEM, Raman diffusion, FTIR
Infrared analysis
Mass spectrometry
Morphological characterization
100 Transmittance (%)
plasma off plasma on
100000 C2D2 C2D4
10000 I (c/s)
C3D3 CD C
1000
C2
100
SEM pictures of carbon target surfaces after discharges after C. Arnas, PIIM)
0
5
No C=C nor Csp2-H characteristics bands
CN
Csp3-H
96
10 15 20 25 30 35 40 45 50 55 m/z (amu)
Mass spectra obtained in etching chamber of the CASIMIR II reactor
The surface had been eroded and fiber shape deposits have been formed
CN
98
3500
Picture of brown deposits on the walls and ECR source magnets
C-C 3000
2500 2000 1500 -1 Wavenumber (cm )
1000
No unsaturated aliphatic molecules nor molecules containing aromatic rings
ATR-FTIR spectrum of brown deposits
Light molecules (CxDy with x ≤3) are eroded from the carbon target
A goal of this study consists on removing the deposit produced from the erosion of carbon targets in the CASIMIR II reactor
Tungsten sputtering using a dipolar plasma source
Working conditions : 80%N2 / 20%O2, 0.6 W, atmospheric pressure, 60 min Pulsed corona discharge
C Ar, Wpolarisé, 1E-2mbar 30000
Intensity (counts)
W (401,535 nm)
20000
10000
W deposit @
10-2
Infrared analysis
mbar 4.6
N2 / O2 (80:20)
100
Erosion rate : 0,2 mg.h-1
90 Transmission (%)
Sans polarisation -10V, 20mA -20V,40mA -30V,50mA -40V,60mA -50V,70mA -60V,70mA -70V,70mA -80V,70mA -90V -100V -110V -120V -130V -140V -200V -300V
Deposit weight (mg)
WC
- Qualitative and quantitative in-situ analysis of soot precursors - Detection of positive and negative ions, as well as neutrals (including radicals) - Energy Distribution Functions for Ions
With this new reactor design, we are able to generate lowpressure high-density hydrogen plasmas able to produce mixed-materials deposits.
Working conditions : D2, 3000W, 1×10-2 mbar, 60 min
First results…
Mass spectrometry (Plasma Monitor Hiden EQP500)
Variations in plasma density as function of the distance from the source and the microwave power [4]. These calculations were done assuming a single source. [4] L. Latrasse et al, Plasma Sources. Sci. Technol. 16 (2007) 7-12
4.4
4.2
CO2
80
Adsorption/desorption processes with O-atom, ozone and nitrogen oxides lead to the deposit oxidation
CO N2 O
70 60 50
0
4.0 401.0
401.2
401.4
401.6
401.8
402.0
0
1 2 Treatment time (h)
3
40 3500
O3
3000
2500 2000 1500 -1 Wavenumber (cm )
1000
Wavelength (nm)
Erosion rate of the CASIMIR II deposits exposed under the air-MPP corona discharge
W
Shape of the targets used in the CASIMIR Reactor
OES spectra of atomic W line for several applied bias
LSPM-CNRS UPR 3407 Institut Galilée Université Paris 13, 99 avenue J. B.Clément – F93430 Villetaneuse, France http://www.lspm.cnrs.fr
W deposit obtained on a Si substrate located nearby the W target
FTIR spectrum of the gas phase leaving the reactor during the treatment of deposit in the air-MPP corona discharge
The deposit oxidation leads to their erosion by producing gaseous hydrocarbons
Possible solution for cleaning walls
Corresponding authors : Guillaume LOMBARDI –
[email protected] +33 1 49 40 34 39
IX Frontiers in Low Temperature Plasma Diagnostics, Zinnowitz, Germany, May 9-12, 2011
