1. Cleaning of co-deposited layers by movable devices based on radiofrequency discharges C. Stancu 1, E.R. Rosini 1, V. Satulu 1, T. Acsente 1, B. Mitu 1, G. Dinescu 1, C. Grisolia 2 1 National Institute for Laser, Plasma and Radiation Physics, Atomistilor 409, PO-Box MG-16, 077125, Magurele, Bucharest, Romania 2 Association Euratom-CEA, CEA Cadarache, DSM/DRFC/SIPP, Saint Paul lez Durance, 13108, France NILPRP

2. 2 Prototype of a castellated tile (W. Daenner et al., Fus. Eng. Des. 61-62 (2002) 61) Castellations: Lxl =20mm x 20mm w =0.7 mm (width) h= 5 mm (height) THE PROBLEM Co-deposition of Tritium with Carbon in gaps

3. 3 Prototype of a beryllium castellated tile (W. Daenner et al., Fus. Eng. Des. 61-62 (2002) 61) Castellations: Lxl =20mm x 20mm w =0.7 mm (width) h= 5 mm (height) -identify a removal process: ablation, sputtering, desorption, chemical etching, oxidation. -elaborate a technique to remove: laser, lashlamp, discharge THE PROBLEM SOLUTIONS Co-deposition of Tritium with Carbon in gaps Our novel approaches: Removal by discharge based devices - Plasma-torch discharge - Inside-Gap Plasma Generator IGPG Removal of the codeposited layer

4. 4 OUTLINE Discharge devices for cleaning: designs and experimental models; Operation details; Removal from bulk carbon materials; A model for the codeposited material; Cleaning of carbon layers from flat surfaces; A model for castellated surface (uncoated and carbon coated); Cleaning of carbon layers from inside gaps of castellated surfaces; Cleaning of other materials (diamond like carbon and JET mirrors); Conclusions. Further work.

5. 5 DESIGNS PLASMA TORCH Designed for scanning: ATMOSPHERIC PRESSURE Principle: expanding radiofrequency plasmas Torch head diameter: 20 mm Couplings room diameter: 38 mm

6. 6 DESIGNS PLASMA TORCH Designed for scanning: ATMOSPHERIC PRESSURE Principle: expanding radiofrequency plasmas Torch head diameter: 20 mm Couplings room diameter: 38 mm INSIDE-GAP PLASMA GENERATOR (IGPG) Grounded castellated surface Movable RF powered electrode Designed for scanning: LOW PRESSURE (1-100mbar) Principle: - control of sheath thickness, so plasma enters in gaps; -a plasma column is formed, with defined diameter. -scanning allowed: plasma column moves while the discharge remains in gaps

7. 7 EXPERIMENTAL MODELS PLASMA TORCH - stainless steel body; - hand held, flexibility for mounting on robotic arm; - couplings realized to the back end: RF power, gas feeding, active water cooling (2 circuits, inside the RF electrode and external jacket)

8. 8 EXPERIMENTAL MODELS PLASMA TORCH - stainless steel body; - hand held, flexibility for mounting on robotic arm; - couplings realized to the back end: RF power, gas feeding, active water cooling (2 circuits, inside the RF electrode and external jacket) INSIDE-GAP PLASMA GENERATOR (IGPG) - RF Electrode (upper) : -copper body, -back insulated with TEFLON; -water cooled -Grounded electrode: castellated Al surface -gaps width: 0.6 -2 mm

9. 9 OPERATION PLASMA TORCH Atmospheric pressure Gas: Argon, Nitrogen Working procedure: scanning in open or controlled atmosphere

10. 10 OPERATION PLASMA TORCH Atmospheric pressure Gas: Argon, Nitrogen Working procedure: scanning in open or controlled atmosphere IGPG Low pressure: 1-100 mbar Gas: Argon with a small air percentage Working procedure: translation along a castellated surface in a vacuum chamber

11. 11 EROSION RATE (bulk MATERIAL) PLASMA TORCH Material: CFC (Tore Supra wall : volume cut samples) -Nitrogen plasma jet -distance tip-surface: 8 mm -RF power: 300 W -gas flow: 2300 sccm -Scan speed: 5 mm/sec

12. 12 EROSION RATE (bulk MATERIAL) PLASMA TORCH Material: CFC (Tore Supra wall : volume cut samples) -Nitrogen plasma jet -distance tip-surface: 8 mm -RF power: 300 W -gas flow: 2300 sccm -Scan speed: 5 mm/sec IGPG Material: Graphite ( static conditions ) - Argon RF discharge - pressure: 37 mbar - RF power: 30 W - gas flow: 600 sccm - distance:50 mm COMPARABLE EROSION RATES FOR CARBON ~ 10 -5 g/sec

13. 13 PREPARATION OF A MODEL FOR THE CODEPOSITED LAYER RF discharge: 50-150 W -Parallel plate electrodes -Shower type RF electrode -Substrate on the grounded electrode -Carrier gas: argon (Ar) -Precursor: acetylene (C 2 H 2 ) Vacuum: 10 -2 -1 mbar RF (13.56 MHz) Flow meter Gauge Mass Flow Controllers P.C. Data Acquisition device Airing Upper electrode Substrate support Lower electrode Ar Vacuum pump Gas cooling trap C2H2C2H2 Amorphous Hydrogenated Carbon ( a-C:H ) deposited by Plasma Assisted Chemical Vapor Deposition (PACVD)

14. 14 PREPARATION OF A MODEL FOR THE CARBON LAYER RF discharge: 50-150 W -Parallel plate electrodes -Shower type RF electrode -Substrate on the grounded electrode -Carrier gas: argon (Ar) -Precursor: acetylene (C 2 H 2 ) Vacuum: 10 -2 -1 mbar RF (13.56 MHz) Flow meter Gauge Mass Flow Controllers P.C. Data Acquisition device Airing Upper electrode Substrate support Lower electrode Ar Vacuum pump Gas cooling trap C2H2C2H2 Amorphous Hydrogenated Carbon ( a-C:H ) deposited by Plasma Assisted Chemical Vapor Deposition (PACVD) Carbon films, thickness: 1-10  m Substrate: silicon, 2  m

15. 15 PREPARATION OF A MODEL FOR THE CARBON LAYER Thickness measurement by Atomic Force Microscopy (AFM) step profile Thickness : 1  m Measurement of the height of the step at the uncoated-coated border

16. 16 Layer thickness: 2  m PLASMA TORCH REMOVAL OF a-C:H LAYERS (FLAT)

17. 17 Layer thickness: 1  m Number of scans: 1 Power: 350 W Nitrogen, mass flow rate: 7500 sccm Layer thickness: 2  m PLASMA TORCH REMOVAL OF a-C:H LAYERS (FLAT) Video speed = 4 x real speed

18. 18 PLASMA TORCH REMOVAL OF a-C:H LAYERS (FLAT) Layer thickness: 1  m Number of scans: 1 Power: 350 W Nitrogen, mass flow rate: 7500 sccm Layer thickness: 2  m 1.66 mm/sec 5 mm/sec

19. 19 PREPARATION OF A MODEL FOR THE CARBON COATED CASTELLATED SURFACE 1.5 mm Step 1: Elaboration of a castellated surface from separate parts (polished Aluminum cubes)

20. 20 PREPARATION OF A MODEL FOR THE CARBON COATED CASTELLATED SURFACE 1.5 mm Step 1: Elaboration of a castellated surface from separate parts (polished Aluminum cubes) Step 2: deposition of a hydrogenated carbon layer on all cube sides castellated piece

21. 21 PREPARATION OF A MODEL FOR THE CARBON COATED CASTELLATED SURFACE 1.5 mm Step 1: Elaboration of a castellated surface from separate parts (polished Aluminum cubes) Step 2: deposition of a hydrogenated carbon layer on all cube sides castellated piece Step 3: Re-assemblage of a castellated surface with the deposited cubes

22. 22 REMOVAL OF CARBONIC LAYERS FROM INSIDE GAPS: PLASMA TORCH Layer thickness: 1  m

23. 23 REMOVAL OF CARBONIC LAYERS FROM INSIDE GAPS: PLASMA TORCH Scanning speed: 2 mm/s Number of scans: 5 Gap width: ~1.5 mm Nitrogen, 7500 sccm Power: 350 W Distance tip surface: 5mm Plasma diameter: 2 mm

24. 24 REMOVAL OF CARBONIC LAYERS FROM INSIDE GAPS: PLASMA TORCH Scanning speed: 2 mm/s Number of scans: 5 Gap width: ~1.5 mm Nitrogen, 7500 sccm Power: 350 W Distance tip surface: 5mm Plasma diameter: 2 mm

25. 25 CLEANING BY A PLASMA TORCH FROM INSIDE GAPS CLEANING BY A PLASMA TORCH FROM INSIDE GAPS (influence of the geometric aspect ratio of castellated surfaces) Samples preparationScanning procedure Removal conditions Nitrogen flow = 8200 sccm RF power = 350 W Distance from top face of the built castellation = 2mm Scanning speed = 5mm/s Gap width = 0.5 – 1.5 mm Results: from profilometry Stainless steel cubes a-C:H layers Cubes coated with carbon inside gaps (20mm x23mmx20mm) A stripe of un-deposited layer is defined from top to bottom Conclusions: Removal of a-C:H layers from inside gaps demonstrated for gap widths 0.5-1.5 mm - Narrower the gap, higher the removal rate - Higher removal rate at the gap entrance - Carbon removal is efficient even on the bottom of the gap (down to 23 mm) Profile of the remained layer at various scan numbers for gap width 500 microns Profilometry: film thickness: 2.2 microns 1 scan (4 sec)46 scans (184 sec)101 scan (404 s) Exemple: gap width 500 microns

26. 26 MEASUREMENTS ON CARBON REMOVAL FROM INSIDE GAPS -experimental Investigation of the bottom part of the castellation (a-C:H deposited Si ) Removal from the bottom demonstrated

27. 27 REMOVAL OF CARBONIC LAYERS FROM INSIDE GAPS: IGPG Cleaning by IGPG (Ar:94%, air 6%, 50 W, 27 mbar) Carbon coated castellated surface (thickness: 1.2  m Partial cleaned castellated surface (5 min) Cube extraction for examination on the lateral sides

28. 28 REMOVAL OF CARBONIC LAYERS BY IGPG front face 1 face 2 depth (z) Ellipsometric measurement of the remaining layer thickness upon depth after various cleaning times Linear polarized incident laser beam Linear polarized reflected laser beam Cube face  d (layer thickness)

29. 29 REMOVAL OF CARBONIC LAYERS BY IGPG R2R2 Layer thickness along depth at various cleaning times (data averaged on the four cube sides) R c =0.24  m/min (higher rate at upper gap margins) Decrease of the thickness on the front side upon time: R 1 =0.010  m/min, R 2 =0.037  m/min (R ave =0.033  m/min) front face 1 face 2 depth (z) Ellipsometric measurement of the remaining layer thickness upon depth after various cleaning times Linear polarized incident laser beam Linear polarized reflected laser beam Cube face  d (layer thickness) Cleaning inside gaps: 8 times faster than on the front side

30. 30 REMOVAL BY PLASMA TORCH of OTHER MATERIALS - DLC films Diamond - like carbon film (DLC) Film thickness ~ 510 nm Si substrate, 400  m thickness, deposited on silicon wafers) 10 cm diameter, resistivity 2-10  cm Max-Planck-Institute for Plasma Physics Reactive Plasma Processes Material Science Garching, Germany Dr. Thomas Schwarz-Selinger Prof. Wolfgang Jacob Supplier:

31. 31 RELATED WORK ON MATERIAL REMOVAL BY PLASMA TORCH - DLC films – surface preparation DLC probe mounted on the holder DLC SAMPLE HOLDER Zone prepared to be exposed to plasma Tilted view 8mm Distance: 6 mm DLC coated Si wafer with a cut away untreated sample (width ~ 8 mm)

32. 32 RELATED WORK ON MATERIAL REMOVAL BY PLASMA TORCH - DLC films – evaluation of removal efficiency 1 scan 2 scans 3 scans 4 scans 5 scans 6 scans 7 scans 8 scans Removal conditions: Nitrogen flow = 5700 sccm RF power = 350W Distance plasma source- sample = 3 mm Scanning speed = 5 mm/s

33. 33 RELATED WORK ON MATERIAL REMOVAL BY PLASMA TORCH - surfaces exposed to JET plasma EFDA-JET, UKAEA Culham, United Kingdom Dr. Alexandru Boboc Preliminary tests on mirrors used in JET Supplier:

34. 34 MATERIAL REMOVAL BY PLASMA TORCH mirrors from JET Removal conditions: PLASMA TORCH Nitrogen flow = 6400 sccm RF power = 350W Distance plasma source – mirror = 7 mm Scanning speed = 5 mm/s 1 scan5 scans20 scans Backside of the mirror Masking the deposited surface Removal after various number of scans

35. 35 CONCLUSIONS Atmospheric pressure plasma torch (small dimensions, flexible); IGPG alternative, a possible approach; Material removal from CFC materials was demonstrated (bulk removal rate ~10 -5 g/sec); Removal of a-C:H layers from inside gaps with the plasma torch was demonstrated for gap widths down to 500  m: Narrower the gap, higher the removal rate Higher removal rate at the gap entrance Carbon removal is efficient even on the bottom of the gap (down to 23 mm) Other materials can also be removed by plasma torch: Dense DLC Co-deposited layers from hidden surfaces previously exposed to tokamak plasma Possible applications in other sectors: cleaning of molds, biofilms in dental applications.

36. 36 PROSPECTIVE FURTHER WORK Plasma torch cleaning in gaps coated with mixed layers –purpose - study of the cleaning processes (active species), optimization (gas composition, power conditions ) NILPRP Selection and elaboration and of an experimental model for the codeposited layer and castellated surfaces –Move to mixed carbon/metal materials (ITER-like: Tungsten/Carbon + Hydrogen, Tungsten/Beryllium (or substitutes)+Hydrogen) –purpose - assessment and comparison of the efficiency of different techniques on the same material and featured surface Assessment of cleaning in large systems / real surfaces –purpose - check the validity of obtained results; THANK YOU FOR YOUR ATENTION !

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38. 38 Computer controlled plasma jet set-up with scanning facility Diagram of the plasma jet surface cleaning set-up PLASMA TORCH M STEPPER MOTOR M STEPPER MOTOR MFC SUPPLY AND CONTROL UNIT COMPUTER -GAS FLOW COTROL -MOTION CONTROL -TEMPERATURE CONTROL -POWER CONTROL -Z MEASUREMENTS RF GENERATOR COOLING UNIT (Pump + Temperature sensors) MATCHING BOX X Y Ar N 2 GAS CYLINDERS Sub-systems: -Plasma torch device -RF power supply system -gas feeding system -cooling system -motion control system

39. Vacuum chamber Vacuum pump RF Generator Cooling Motion control Power supply Flow and pressure control (PID) Pressure monitoring unit Gas IGPG Parameters range RF power: 10 -200 W, 13.56 MHz Gas: Argon Mass flow rate: 1-7000 sccm Pressure range: 1-400 mbar Water flow rate (cooling rate): 0.3 l/min Translation speed: 0- 16 cm/min Distance IGPG-surface: 18-45 mm Block diagram and parameters range