Dust collected in MAST and in Tore Supra. Nanoparticle growth in laboratory plasmas

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1 FDR-FM Association EURATOM-EA Dust collected in MAST and in Tore Supra. Pardanaud 1,. Martin 1, P. Roubin 1,. Arnas 1 and G. De Temmerman 2 1 Lab. PIIM, NRS-Université de Provence, UMR 6633, Marseille, France 2 EURATOM/UKAEA Fusion association ulham Science enter, Abingdon, UK Nanoparticle growth in laboratory plasmas A. Mouberi 1,. Arnas 1, F. Bénédic 2, G. Lombardi 2, K. assouni 2, X. Bonnin 2 1 Lab. PIIM, NRS-Université de Provence, UMR 6633, Marseille, France 2 LIMP, UPR 1311 NRS, Université Paris XIII, Villetaneuse, France 1

2 Outline Dust produced in the MAST tokamak quantitative analyses (mass) qualitative analyses (shape, structure, composition) Dust collected in Tore Supra neutralizers qualitative analyses (shape, structure, composition) arbonaceous nanoparticles growth in laboratory plasmas graphite cathode sputtering in D discharges microwave discharges in Ar/ 4 / 2 onclusion (similarities, differences) 2

3 Dust collected in the MAST tokamak M6 campain ( ) = 2 x 2000 shots de 0.3 s PFs: graphite, stainless steel 8 locations of collection by vacuuming below mid-plane. 3 groups of location: x x erosion-dominated locations swept by strike points (foot of the central column, tiles) private flux region (dome) shadowed locations (toroidal gaps, ports, under Langmuir probe, upper surface of magnetic coils) 3

4 Dust collected in the MAST tokamak Quantitative analyses outer toroidal gap of tiles + inner toroidal gap of tiles, m = ( ) mg ports, m = 4.2 mg dome, m = 4.1 mg -> 1.86 mg/m² tiles, m = 3.9 mg -> 0.52 mg/m² Total mass > 46.6 mg ( atomes/s) onsistent with dust transport and formation dust transport towards shadowed areas sweeping of the outer strike point towards the tile outer toroidal gap (dust transport) private flux region = dome eroded-dominated regions = tiles Qualitative analyses: SEM, TEM, RTEM, EDX, IR absorption spectroscopy, Raman microscopy 4

5 SEM, TEM, RTEM show everywhere: 1) metallic particles (nm to µm size) arcing on vessel and magnetic coils (stainless steel) metallic impurities during plasma ignition on inductive coils 2) carbonaceous grains (~ µm), irregular shape heterogeneous structure (amorphous to graphite-like) coming from redeposited layers when they contain metallic impurities otherwise, pulled out from divertors during disruption 3) carbonaceous nanoparticles, different structure (amorphous, onion-like) Evidence of homogeneous growth: consistent with divertor plasma: dense and cold Nanoparticles (5-10nm) 5

6 Raman micro-spectroscopy for a given location, heterogeneous structure: amorphous carbon to disordered graphite the most amorphous grains located on the dome surface (private- flux region) box 31 grain 1 box 31 grain 2 box 31 grain 3 box 31 grain 6 IR absorption spectroscopy Dust in the outer toroidal gap of tiles (shadowed area): D,, aromatic =, Raman shift (cm -1 ) Plan: Raman micro-spectroscopy currently done - correlation between the features deduced from spectra and the corresponding surface area collection 6

7 Dust in the Tore Supra tokamak toroidal limite r ne utralize r Deposits collected on the leading edge of neutralizers (PhD M. Richou) 7

8 200 μm 20 μm self-similar tips parallel tip-axes concentric shells porosity network heterogeneous growth with specific features 1 1 μm

9 20 nm locally graphitic structure onion-like particles similar to carbon black graphite-encapsulated metal nanoparticules evidence of homogeneous growth in the edge plasma 9

10 Nanoparticles produced in tokamak edge plasmas, divertor plasmas (TEXTOR, TS, MAST ) Tokamaks with graphitic PFs: sputtering (physical erosion) 4 release (chemical erosion) 2 stages of growth in cold plasmas: 1) molecular precursors (complex chemical pathway) nucleation 2) growth of nanoparticles 10

11 2 examples of carbon nanoparticle growth in laboratory plasmas: From cathode sputtering in D discharges experimental set up molecular precursors, nanoparticle growth From hydrocarbon species in microwave discharges experimental set up molecular precursors, nanoparticles growth 11

12 Glow discharges Argon = 0.6 mbar V pol ~ V P ~ 100 W J ~ 10 A/m² 5 N e = N i ~ cm -3, T e = 3 ev dans la LN Emission spectroscopy Laser extinction and diffusion 1 : Graphite cathode 4 : Langmuir probe 2 : Anode 5 : Thermocouple 3 : Dust collector 6 : Optical window 200 nm 12

13 athode sputtering EDF Thompson s model (1968): Sputtering from collisional cascade EDF of sputtered carbon atoms at the graphite surface, θ = 0 E i = 100 ev Taking into account collisions -Ar = carbon cooling mechanism <E> ev Decrease of the sputtered atom energy Thermalization with argon (200 ) 3.45 ev ,2 0,4 0,6 Mean energy ~ 11 ev E (ev) cathode distance (cm) cooling mechanism produces supersaturated carbon vapor condensation and carbon cluster formation, n modeling of neutral, negative cluster growth: n, n - K. assouni et al (LIMP) 13

14 Experimental growth law Taille (nm) Growth by cluster deposition Durée de la décharge (s) agglomeration of nanoparticules, 6-15 nm size + deposition agglomeration of nucleus of 2-3 nm size + deposition 8 nm ~ 40 nm 14

15 Microwave discharges Bell jar reactor Ar/ 4 / 2 mixture [ 4 ]: 3%, [ 2 ]: 1% Orange emission in the peripheral plasma by heated dust particles Total pressure: 200 mbar Microwave power: W N e ~ cm -3, T e ~ 1 ev 15

16 A4 model (K. assouni) Radicalar growth of PA and nucleation mechanism Mechanism of Poly-Aromatic ydrocarbons (PAs) formation (1) Linearization 2 === + yclization === + ydrogen Abstraction arbon Addition (AA) ondensation of 2 pyrene (A4) molecules cyclisation. + nanoparticle nucleous 16 (1) Wang et Frenklach., omb.flame (1997)

17 RTEM micrographs 3 nm 0.1µm in-situ IR absorption spectroscopy (diode laser): presence of ex-situ IR absorption spectroscopy: presence of PAs with 3, 4 aromatic rings chromatography in gas phase: presence of PAs with 2, 3, 4 aromatic rings 17

18 onclusion (1/2) Nanoparticles produced in different plasma conditions have similar structure 1) 2) 1) carbon sputtering discharges: low pressure, low input power 2.5 nm 3 nm 2) Ar/ 4 / 2 discharges: higher pressure, higher input power 3) 4) 3)Tore Supra (limiter tokamak) 4)MAST (divertor tokamak) 2 nm 5 nm

19 But, in the considered laboratory plasmas, molecular precursors are different : 1) carbon sputtering discharges: n, n - 2) Ar/ 4 / 2 discharges: complex chemical pathway PAs onfirmation: 1) hromatography 2) IR absorption spectroscopy 3) Mass spectrometer (plan) Molecular precursors in Tore Supra and MAST? 1) IR absorption spectroscopy: - TS neutralizers deposits : flat spectra - MAST: one spectrum (D,, =, ) 2) Mass spectrometer (Tore Supra) 3) hromatography analyses?