French Research Activities on Dust in Fusion + Pr Winter team activities Presented by C Grisolia
Creation processes Diagnostics Removal (most of theses activities under the EFDA umbrella)
Study of creation processes
Study of creation processes in DC discharge
Modelling of dust formation in a DC discharge Investigation method : Separation of the problem into 3 modules: 1. A dust-free DC discharge model 2. Particle nucleation by cluster growth 3. A growth and transport module for dust particles Demonstrated the importance of an activation energy term in the molecular aggregation reaction rate for cluster growth k ij = V σ th ij i + i E exp. b.exp γ i. j RT ( G' + G' ) Negative clusters are trapped in the reversed field region where dust growth can occur i kt j 2 V 0 /d c E eφ Sheath Energetic electrons (γ) Trapped electrons (n e ) and negative ions d c x 0 R x 1 Passing electrons (j) ~ < 1 V NG FDS PC x E 0 n e (cm -3 ) 1E11 1E10 1E9 e=0.1ev E -500000 0 2 4 6 8 10 12 14 x (cm) Electric field and dust number density profiles in a DC glow discharge 10 5 0-5 -10 E (V/cm) -100000-200000 -300000-400000 Dust diameter (nm) 22 20 18 16 14 12 10 8 6 4 2 0 1 2 3 12 14 x (cm) E b = 0.200 ev E b = 0.225 ev E b = 0.230 ev (A Michaud, K Hassoun I, X Bonnin) Dust number density (cm -3 ) 10 10 10 9 10 8 10 7 10 6 10 5 10 4 10 3 10 2 0 2 4 6 8 10 12 14 x (cm) E b = 0.200 ev E b = 0.225 ev E b = 0.230 ev
Study of creation processes in RF argon/acetylene discharge
Laser Induced Fluorescence Laser Absorption spectroscopy
Study of creation processes during laser ablation
Laser Dust production Tokamak and Argon discharge Laser at LP3 lens target XeCl KrF laser Experimental set-up substrate sample Textor C produced under vacuum (10-2 mbar) Dusts are produced by laser ablation of graphite or W target and are collected on substrate The laser-produced dusts have similar morphologies and nature than Tokamak ones. ASDEX Upgrade W produced under air Delaporte, Vatry, LP3/CEA EFDA task postponed in 2011 DC Argon discharge C produced under air 200nm
Study of particle diagnostic
Particle Diagnostic By speckle interferometry
Will give the maximum value of the dust quantity considering All the erosion produced turn to be dust
Speckle Interferometry Principle
Ongoing studies to integrated this technique in ITER possible viewing configurations + optical design sensibility to: vibrations, of normal plane measurements
Particle Diagnostic By laser extinction
Highlights-2010 LES basic setups: Characterization with Light Extinction Spectrometry of Particle Aggregates in Plasma Systems F. Onofri 1, S. Barbosa 1, M. Wozniak 1,2 1 IUSTI, UMR n 6595 CNRS /Université de Provence (France) 2 CEPM, Wroclaw University of Technology (Poland)
Light scattering calculations and experiments with LES on particle fractal aggregates Highlights-2010 Diffusion Limited Aggregation model Scattering and inversion models Electromag. scatt. & inversion models Experiments with LES Experimental test: Flowing SiO 2 aggregates Experimental test (with GREMI) : Aggregate growth in a low pressure Argon-Silane transient discharge
Particle Diagnostic automatic images analysis
i r f m c a d a r a c h e Dust Detection & Tracking V Martin et al, IRFM and INRIA Collaboration with Institut Jean Lamour, Nancy (FR-FCM) Goal : study of interactions between RF sheath behaviour and particle trajectories by Cathode means of fast imaging Studied area Dust cloud Courtesy of IJL Towards Intelligent Video Understanding Applied to Real Time PFC Monitoring monitore
i r f m c a d a r a c h e Association EURATOM-CEA TORE SUPRA Video Tracking of Dust Particles in Tokamaks (AUG, TS ) Automatic routine for robust dust detection and tracking Statistical post-mortem analysis of dust particles trajectories Dust Detection & Tracking Stereoscopy for 3D trajectory reconstruction References: V. Martin et al., monitore project S. Bardin et al., Investigating transport of dust particles in plasmas, RSI 2010 N. Endstrasser et al., Video Tracking and Post-mortem Analysis of Dust Particles from All Tungsten ASDEX Upgrade, PSI 2010
Particle Diagnostic By electrostatic detection
Laboratory tests
First trials on Tore Supra: signal on blind detector but Kapton protection unstuck (?) need calibration not done due to lack of budget purchase of calibration system (hammer type)
Particle Diagnostic By impactors
Dust in suspension in Tore Supra, sucked and analysed by several means (IRSN) CPC : Condensation Particle Counter EEPS = Engine Exhaust Particle Sizer Spectrometer Particle size range : 5,6-560 nm Reported diameter : equivalent electrical mobility diameter Electrometer channels : 22 Time resolution : 10 size distributions/sec (1 measure/0,1sec) AEROSIZER : Particle Size Distribution Analyzer Particle size range : 0,5-100 µm Reported diameter : equivalent aerodynamic diameter Resolution : 64 size channels per decade
Study of particle removal by photo cleaning techniques
photo-cleaning methods for removing the dusts deposited on the divertor surfaces Ph. Delaporte 1, A.Vatry 1,2, H. Roche 2 C. Grisolia 2, M. Sentis 1, 1 Lasers, Plasmas and Photonic Processes Laboratory, Marseille, France www.lp3.univ-mrs.fr 2 Association Euratom/CEA, DRFC/SIPP, Saint Paul lez Durance, France EFDA supported activities
Photo cleaning Method Procedure and experimental setup EFDA supported activities
Photo Experimental cleaning set-up Method PRE set-up Collection set-up laser Attenuating plate aperture lens Laser KrF Attenuating plate aperture lens Substrate with particles Vacuum chamber Collector substrate d Examples of optical microscope images of C particles on Si substrate: Before the irradiation N PRE = 1 N After 5 shots at 200mJ/cm² 0 Collector substrates have been observed with an optical and scanning electron microscope 1,0 PRE for 5 shots 0,8 0,6 0,4 0,2 N 0 particles C on Si 4 ns 1064 nm N particles 0,0 0 200 400 600 800 1000 1200 Fluence (mj/cm²) Review meeting DTM, June 2009
Photo cleaning Method: C particles Particles produced by laser ablation Various shapes and sizes ~ < 1 µm Very porous amorphous structure 1µm 200nm Wavelength influence: Pulse duration influence in IR: 1,0 1 PRE for 5 shots 0,8 0,6 0,4 0,2 4 ns Si substrate 1064 nm 532 nm 355 nm 266 nm PRE for 5 shots 0,8 0,6 0,4 0,2 450 fs 50 ps 7 ns 0,0 0 200 400 600 800 1000 1200 Fluence(mJ/cm²) 0 0 200 400 600 800 1000 1200 Fluence (mj/cm²) Laser is very efficient to remove carbon particles For F> 500 mj/cm² More than 80% of particles are removed Wavelength has a low influence on the PRE Pulse duration (few ns to fs) has clearly no influence on the efficiency of laser removal process for carbon dust. Experiments perform with 200ns pulse @ 1064nm show that the threshold removal increase, but the process remain efficient.
Photo cleaning Method: Conclusions for C particles studies - Laser removal of carbon dust is efficient (>90%) even at low fluence - The irradiation parameters have almost no influence on the process efficiency large process window. - The ablation mechanism is the ablation of the material. - The ablation products are ejected as vapour form and can quickly condensate or aggregate in aggregates of few nanometres.
Photo cleaning Method: W particles Particles produced by laser ablation Very fine aggregates Droplet of 1 to 5 µm with very smooth surface 1µm Wavelength influence: Pulse duration influence: 1,0 0,8 PRE for 5 shots 0,8 0,6 0,4 0,2 1064 355 266 4 ns PRE for 5 shots 0,6 0,4 0,2 450 fs-1025 nm 50 ps-1064 nm 4 ns-1064 nm 0,0 0 200 400 600 800 1000 1200 Fluence (mj/cm²) 0 0 200 400 600 800 1000 1200 Fluence (mj/cm²) Laser could be efficient to remove tungsten particles but for specific parameters Wavelength has a great influence on PRE UV beam is more efficient than infrared one The pulse duration has an influence The damage threshold of the Si substrate is very low in ultrashort pulse duration regime limitations of our investigations
Photo cleaning Method: collection of W particles KrF laser 248 nm 27 ns Collector substrate for d = 3 mm, under air, 5 shots, F = 700 mj/cm² Collector substrate for d = 5 mm, under 2.10-2 mbar, 1 shot, F = 700 mj/cm² Metallic particles are ejected and collected in whole part without any damage. Process is efficient under atmospheric pressure of air and primary vacuum
Photo cleaning Method: conclusions for W particles studies - Laser removal of metallic particle is efficient under some conditions. - To remove metallic particles, laser wavelength must be short (UV) or pulse duration must be shorter than hundred of picosecond. - The ablation mechanism is supposed to be the electrostatic forces induced by the photoelectrons extracted from the particle. - The ablation products have the same shape and size than the original dust.
Photo cleaning Method: general conclusions - Laser irradiation can easily induced the mobilization of carbon and metallic dust. - To be efficient for all the kind of dust with a single laser source, the process must use a ns UV laser. - The ultrashort pulse laser can also remove all the dust, but their average power is not compatible with the cleaning of large surface - The ablation products are ejected as atoms and nanoaggregates or are un-modified for the metallic dust. - As the mechanisms do not depend of the surface properties, the laser removal do not modify the substrate.
Photo cleaning Method: shock wave studies 10 mm laser plexiglas 1 (a) (b) (c) UV silica or aluminum (d) (e) (f) Images of the removal of C particles from castellation (1mm width, 10mm deep, 20mm long). The ejection mechanism is due to the shock wave generated during the laser-matter interaction. The shock wave induced by the focalisation of a laser close to the dust lead to the ejection of these dust. This technique appears to be very efficient to move dust from castellation towards cold zones.
Photo cleaning Method: influence of P Laser removal of metallic dust: At atmospheric pressure the photoelectrons create negative ions by collision with oxygen atoms, and these negative charges stay longer above the particle. The reduction of pressure will have two effects: - Increase of the removal threshold - Increase slightly the distance of ejection However, theses modifications are lower than 10% for both parameters when pressure varies from atmospheric pressure to 10-3 mbar. Then, the gas pressure does not affected significantly the process efficiency for metallic particles. 14 Laser removal of carbon dust: 12 A reduction of the gas pressure leads to an 10 increase of the ejection distance of the 8 ablation products (cf curves). The process 6 is still efficient but the collection 4 system must be set closer to the 2 surface when pressure increases. 0 distance (mm) 16 10 Pa 1 10 Pa 2 0,1 Pa 0 5000 10000 15000 20000 temps (ns)
Photo cleaning Method: influence of substrate (shock wave) Laser-induced shock wave cleaning: This process is strongly dependant of the gas pressure for the generation of shock wave. When the pressure reduces, the intensity of the shock wave is strongly reduced too. We succeed in removal dust from castellation for pressure down to 1Pa, but the process velocity was strongly reduced. The laser-induced shock wave process is not efficient when pressure is lower than few Pa.
Study of particle removal by multi point plasma discharges
M de ice for de osit remo al and detritiation Deposit weight (mg) 4.6 4.4 4.2 N 2 / O 2 (80:20) Erosion rate : 0,2 mg.h -1 4.0 0 1 2 3 Treatment time (h) 100 Transmission (%) 90 80 70 60 50 CO CO 2 N 2 O FTIR analysis O 3 40 3500 3000 2500 2000 1500 1000 Wavenumber (cm -1 )
conclusions Creation processes: lot of work on dust creation in SOL plasmas very interesting for operation perturbation but main dust production pathway ELMs, VDEs, Disruption could be approximated and studied by analogy with laser ablation Diagnostics: particle tracking (in video) very interesting but for fundamental physics trajectories, velocities, transport (!) electrostatic detector helpfull but need to work with W particles difficulties to operate close to the plasma (dust transport measurment) dust in suspension (mobilisable one) could measured by laser extinction but be interest to blow in the ashtray? dust in ssupension could be measured by impactors in the gas outflow but. speckle is the most suitable for envelope estimation but only erosion accessible Dust removal: laser well suited to unstick particles especially small one or welded metal dropplet other techniques could be used to destroy small particles
Proposed activities for the coming years Ongoing activities : production of calibrated particles metallic particles studies of physical properties SSA, Size, treatment (destruction?) of these particles with: plasma torch RF plasma Tritium implentation and in vitro/in vivo studies collaboration with Romanian team (Dr Dinescu, Bucaresti)