1. SEWG MEETING, Cadarache, June 16th 2009 1/18 Experimental studies on laser induced removal and collection for absorbing particles A.Vatry 1,2, A. Marchand 1, Ph. Delaporte 1, C. Grisolia 2, M. Sentis 1, C. Hernandez 2, H. Roche 2 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

2. SEWG MEETING, Cadarache, June 16th 2009 2/18 MOTIVATIONS The dust have high adhesion force the laser is a good solution for the removal This is the first step for the cleaning Decontamination of fuel tubes (AREVA, ONET, CEA) Microelectronics Particles : Mox substrate : zircalloy Optics Particles : polymer substrate : silicon Particles : organic, metallic substrate : silica Removal technique based on laser cleaning are developed in various field Advantages : handle remote, free contact

3. SEWG MEETING, Cadarache, June 16th 2009 3/18 Experimental set-up aperture Attenuating plate lens laser Examples of optical microscope images of C particles on Si substrate: N 0 particles Substrate with particles d Vacuum chamber N particles PRE set-up Before the irradiationAfter 5 shots at 200mJ/cm² aperture Attenuating plate lens Laser Collector substrate Collection set-up Collector substrates have been observed with an optical and scanning electron microscopes 4 ns – 1064 nm

4. SEWG MEETING, Cadarache, June 16th 2009 4/18 lens XeCl laser target substrate KrF laser 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. Tokamak and Argon discharge Laser at LP3 200nm Experimental set-up Textor ASDEX Upgrade (PSI poster Balden) DC Argon discharge C produced under vacuum (10 -2 mbar) W produced under air C produced under air Dusts production sample

5. SEWG MEETING, Cadarache, June 16th 2009 5/18 Carbon particles produced by laser 200nm 1µm Produced under air: Produced under low pressure: C on Si produced under 10 mbar dHe Layer and particles sizes ~ < 1 µm Very porous Amorphous structure Bande D Bande G I (u.a) Raman shift (cm -1 ) Raman spectrum achieved in PIIM laboratory (Cédric Pardanau) 1µm Separated particles Various shapes sizes ~ < 1 µm Very porous

6. SEWG MEETING, Cadarache, June 16th 2009 6/18 PRE for carbon particles 4 ns – Si substrate Wavelength influence: 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 has low influence, except for a long pulse duration as 200 ns Influence of laser parameters : Pulse duration influence: At 200 ns - 1064 nm PRE = 0 for fluences up to 1.16 J/cm² 1025 nm-1064 nm

7. SEWG MEETING, Cadarache, June 16th 2009 7/18 PRE for carbon particles Si and SiO 2 have very different thermal and optical properties However the curves are quite similar PRE and then removal mechanism do not depend on the substrate properties 50 ns – 308 nm Substrate influence: 4 ns – 1064 nm

8. SEWG MEETING, Cadarache, June 16th 2009 8/18 Collection of carbon particles Almost no intact particles are collected The carbon particles are ablated during the irradiation Collector substrate for d = 5 mm, under 10 -3 mbar, for 1 shot F = 380 mJ/cm² The ejected carbon particles are in the form of very thin nanoparticles or/and atoms KrF laser: 248 nm – 27 ns Carbon particles produced by laser ablation

9. SEWG MEETING, Cadarache, June 16th 2009 9/18 Removal mechanism of carbon particles The removal mechanism is the particle ablation, due to the direct absorption of the laser energy by the particle If the particle is too big, the removal is achieved in several steps

10. SEWG MEETING, Cadarache, June 16th 2009 10/18 Comparison with dust from Tore Supra Carbon particles produced by laser ablation Dust collected in Tore Supra Laser is also efficient for the particle collected in Tore Supra The difference of efficiency is explained by the difference of size 4 ns – Si substrate 248 nm– 27 ns – Si substrate

11. SEWG MEETING, Cadarache, June 16th 2009 11/18 Carbon dust on CFC tile 248 nm - 27 ns - 300 mJ/cm² Before irradiation 5 shots Sample achievement: Result: A laser is focused on a CFC tile Particles are deposited around the crater We irradiate the tile with a laser at 300 mJ/cm² CFC tile

12. SEWG MEETING, Cadarache, June 16th 2009 12/18 Particles produced by PLD with tungsten target 2 kinds of particles Very thin aggregates (foam) Droplets of 1 to 5 µm with very smooth surface Tungsten particles produced by laser W droplets are also produced in plasma device or by arcing in Tokamak Produced by plasma gun Collected in ASDEX Upgrade Produced by laser

13. SEWG MEETING, Cadarache, June 16th 2009 13/18 1064 nm - 4 ns - ~700 mJ/cm²248 nm - 27 ns - ~800 mJ/cm² UV range is very efficient to remove the very thin aggregates 0 shot 1 shot Removal efficiency for W thin aggregates Infrared range do not remove efficiently thin aggregates

14. SEWG MEETING, Cadarache, June 16th 2009 14/18 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 PRE of W droplets The pulse duration has an influence too But the damage threshold of the substrate is very low we cannot use picosecond and femtosecond pulse duration for our application 4 ns – Si substrate Wavelength influence: Influence of laser parameters : Pulse duration influence: At 200 ns - 1064 nm PRE = 0 for fluence up to 1,25 J/cm²

15. SEWG MEETING, Cadarache, June 16th 2009 15/18 Collection of tungsten particles Collection: Collector substrate for d = 5 mm, under 2.10 -2 mbar, 1 shot, F = 700 mJ/cm² Collector substrate for d = 3 mm, under air, 5 shots, F = 700 mJ/cm² A lot of intact particles have been collected under air and primary vacuum KrF laser 248 nm – 27 ns

16. SEWG MEETING, Cadarache, June 16th 2009 16/18 Temperature (K) Time (ns) FORTRAN 1D simulation : Temperature below the fusion threshold Studies on tungsten particles removal 30 shots 5 shots 4 ns – 1064 nm – ~700 mJ/cm² No particle damage Collection results are in accordance to FORTRAN simulation Particles could not be ablated Depth (µm) 5 shots 1 shots No particle damage 27 ns – 248 nm – ~800 mJ/cm² Depth (µm) Temperature (K) Time (ns) Particles not removed Temperature below the fusion threshold

17. SEWG MEETING, Cadarache, June 16th 2009 17/18 248 nm - 27 ns - 500 mJ/cm² Before irradiation 5 shots 5 µm Tungsten dust on CFC tile Sample achievement: Result: lens XeCl laser Tungsten target KrF laser CFC tile A laser is focused on a W target Particles are deposited on the CFC tile

18. SEWG MEETING, Cadarache, June 16th 2009 18/18 Summary The laser is efficient to remove dust For tungsten dust specific parameters are required The carbon dust are ablated collection of atom and/or very thin nanoparticles The tungsten droplets are ejected intact collection of micrometer particles

19. SEWG MEETING, Cadarache, June 16th 2009 19/18 Thank you for your attention

20. SEWG MEETING, Cadarache, June 16th 2009 20/18 PRE for W droplet Substrate influence: 50 ns – 308 nm The substrate can has an influence However, in both case, for absorbent and transparent substrate the laser can remove carbon particle 50 ps – 355 nm

21. SEWG MEETING, Cadarache, June 16th 2009 21/18 Temperature (K) Time (ns) FORTRAN 1D simulation: Temperature below the fusion threshold Studies on tungsten particles removal Temperature (K) Time (ns) Depth (µm) Temperature above the fusion and vaporization threshold Vaporization (5828 K) Fusion (3695 K) 30 shots 5 shots 4 ns – 1064 nm – ~700 mJ/cm² No particle damage 5 shots 1 µm Particle damage Collection results are in accordance to FORTRAN simulation Particles could not be ablated Depth (µm) 50 ps – 1064 nm – 540 mJ/cm² Particles not removed

22. SEWG MEETING, Cadarache, June 16th 2009 22/18 Studies on tungsten particles removal 248 nm – 27 ns – 800 mJ/cm² 1025 nm – 450 fs – 300 mJ/cm²355nm – 50 ps 290 mJ/cm² 5 shots4 shots 0 shot1 shot Under the removed particle the substrate is not affected by the laser SEM observations:

23. SEWG MEETING, Cadarache, June 16th 2009 23/18 Field modification around the W particles : 7 ns – 1064 nm – ~ 800 mJ/cm²450 fs – 1025 ns – ~300 mJ/cm²355nm – 50 ps 290 mJ/cm² 15 shots5 shots15 shots Simulation made by Nicolas Bonod (Fresnel Institute) The Si texturization allows the materialization of the field around the particle The interface is in the particles shadow No interface mechanism could be at the origin of the removal Studies on tungsten particles removal 5µm Possible removal mechanism : Particle ablation Explosive evaporation of humidity Thermally induced expansion Local substrate ablation Electrostatic force

24. SEWG MEETING, Cadarache, June 16th 2009 24/18 Studies on tungsten particles removal First calculations about electrostatic force (266 nm- 4ns- 800 mJ/cm²): Comparison between Van der Waals force and Electric force : Force between positive charge of 5 µm particles and photo-electrons at 4ns : F = ~ 2x10 -7 N The adhesion force between a metal particle (with deformation) and the silicon subtrate is ~10 -6 or 10 -7 N This is the same order of magnitude Pulse duration influence : For picosecond and femtosecond regime multiphotonic effect More photoelectrons Higher removal efficiency Pulse duration influence: Si substrate

25. SEWG MEETING, Cadarache, June 16th 2009 25/18 Particle removal mechanism Thermally induced expansion Local substrate ablation Explosive evaporation Destruction of substrate Mechanical process temporal parameters Adsorbed humidity Particle ablation depends on materials Electrostatic force Different physical mechanisms could lead to the particle removal Several mechanisms could be involved simultaneously in the removal

26. SEWG MEETING, Cadarache, June 16th 2009 26/18 Influence des paramètres laser (sur Si): Durée dimpulsion : À 200 ns - 1064 nm PRE = 0 pour F = 1,16 J/cm² 1025 nm-1064 nm Influence des paramètres laser (sur Si): Durée dimpulsion : À 200 ns - 1064 nm PRE = 0 À 200 ns - 1064 nm PRE = 0, jusquà F = 1,25 J/cm²

27. SEWG MEETING, Cadarache, June 16th 2009 27/18 Temperature (K) Time (ns) FORTRAN 1D simulation: Temperature below the fusion threshold Studies on tungsten particles removal Temperature (K) Time (ns) Depth (µm) 30 shots 5 shots 4 ns – 1064 nm – ~700 mJ/cm² No particle damage 5 shots 1 µm Particle damage Collection results are in accordance to FORTRAN simulation Particles could not be ablated Depth (µm) 50 ps – 1064 nm – 540 mJ/cm² Particles not removed 2 Fusion (3695 K) Vaporisation (5828 K) Temperature above the fusion and vaporization threshold Possible removal mechanism : Particle ablation Explosive evaporation of humidity Thermally induced expansion Local substrate ablation Electrostatic force

28. SEWG MEETING, Cadarache, June 16th 2009 28/18 Temperature (K) Time (ns) FORTRAN 1D simulation : Temperature below the fusion threshold Studies on tungsten particles removal 30 shots 5 shots 4 ns – 1064 nm – ~700 mJ/cm² No particle damage Collection results are in accordance to FORTRAN simulation Particles could not be ablated Depth (µm) 5 shots 1 shots No particle damage 27 ns – 248 nm – ~800 mJ/cm² Depth (µm) Temperature (K) Time (ns) Particles not removed

29. SEWG MEETING, Cadarache, June 16th 2009 29/18 C particles at 0.1 Pa, F = 1.6J/cm² v = 3800 m.s -1 v = 4240 m.s -1 C particles on Si substrate at 0.1 Pa (velocity slope of the linear regression curve for 1 µs ) v = 3150 m.s -1 v = 3920 m.s -1 v = 4390 m.s -1 mJ/cm² J/cm² time (ns) Dynamic of ejection for carbon particle Substrate influence:Fluence influence: These graphs are performed with pictures of the light emitted by the ejected particle or ablated species take with a CCD intensified

30. SEWG MEETING, Cadarache, June 16th 2009 30/18 Efficacité denlèvement – particules de tungstène Influence des paramètres laser (sur Si): Durée dimpulsion : À 200 ns - 1064 nm PRE = 0, jusquà F = 1,25 J/cm² 0 tir5 tirs 1064 nm – 200 ns - 625 mJ/cm² 1064 nm - 4 ns - ~700 mJ/cm² 1025 nm - 450 fs - ~300 mJ/cm² 0 tir 5 tirs

31. SEWG MEETING, Cadarache, June 16th 2009 31/18 Outlook LASK V1 P=10 -6 Pa T= 200°C max Environment : Dust collection : adhesion LASK V2 P=Atm T= 50°C Environment : Dust collection : aspiration These studies help to the elaboration of a removal device based on laser cleaning for Tore Supra. This is a first step for the ITER removal device