Design of a low-temperature plasma reactor used for simulating plasma interactions with mixed materials targets and deposit removal with a multi-pin-plane plasma device* L. Colina Delacqua1, M. Redolfi1 G. Lombardi1, A. Michau1, X. Bonnin1 and K. Hassouni1 1LIMHP,
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).
What happens at the divertor surface?
Phenomenological description
Mechanism of dust formation
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
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
δ
Volume recombination e- or H+ => energy losses 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
Transport, chemistry, energy transfer in H2/H/CxHy plasmas
Agglomeration Coagulation
Chemistry
Growth
Nucleation
C, H
Soot synthesis (ionic schemes, clusters)
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 Chemical Ablation, Sputtering, Ionization, Multiulti-wall Interaction and Re-deposition Microwaves inlet
CASIMIR II: diagnostics
Permanent magnet
target
stubs
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
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)
- 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
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.
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
Morphological characterisation Analysis of the re-deposition by: SEM, AFM, XRD, TEM, Raman diffusion, FTIR
Infrared analysis
Mass spectrometry
Morphological characterization
100 plasma off plasma on
100000
Transmittance (%)
ECR source
C2D2 C2D4
10000 I (c/s)
C3D3 CD C
1000
C2
Csp3-H
The surface had been eroded and fiber shape deposits have been formed
0
5
10 15 20 25 30 35 40 45 50 55 m/z (amu)
Mass spectra obtained in etching chamber of the CASIMIR II reactor
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
FTIR spectrum of brown deposits
Light molecules (CxDy with x≤3) are eroded from the carbon target
Material deposits elimination N2/O2 MultiMulti-PinPin-toto-Plane pulsed corona discharge
The goal of this study consists on removing the deposit produced from the erosion of carbon targets in the CASIMIR II reactor Working conditions : 80%N2 / 20%O2, 0.6 W, atmospheric pressure, 60 min
- The corona discharge is generated with the help of a Marx generator
Infrared analysis
- The discharge system consists of a 300 pins multi-pin anode and a plane electrode - The typical gap distance is around 1 cm and the plane-cathode, on which deposits are placed, may be heated up to 330 K with the help of small cylindrical heating rod
Deposit weight (mg)
4.6
- The feed gas enters the discharge cell from the bottom plane electrode and the flue gas resulting from the interaction between the discharge streamers and the soot/deposits exits from a second exit hole drilled in the cathode. LIMHP-CNRS-UPR 1311 Institut Galilée Université Paris 13, 99 avenue J. B.Clément – F-93430 Villetaneuse, France Fax : +33 1 49 40 34 14
100
Erosion rate : 0,2 mg.h-1
90
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
4.0
- The electrode system is placed in a 56 mm diameter cylindrical Pyrex cell
N2 / O2 (80:20)
Transmission (%)
SEM pictures of carbon target surfaces before and after discharge
No C=C nor Csp2-H characteristics bands CN
96
3500 100
CN
98
0
1 2 Treatment time (h)
3
Erosion rate of the CASIMIR II deposits exposed under the air-MPP corona discharge
40 3500
O3
3000
2500 2000 1500 -1 Wavenumber (cm )
1000
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 : Ligia COLINA DELACQUA –
[email protected] Michaël REDOLFI –
[email protected] +33 1 49 40 34 39 http://www.limhp.fr/
19th International Plasma-Surface Interactions Conference, San Diego, USA, May 24-28, 2010 – Poster P2-17
