NILPRP

1. NILPRP Cleaning of co-deposited layers by movable devices based on radiofrequency dischargesC. Stancu1,E.R. Rosini1, V. Satulu 1, T. Acsente1, B. Mitu1, G. Dinescu1, C. Grisolia21National Institute for Laser, Plasma and Radiation Physics, Atomistilor 409, PO-Box MG-16, 077125, Magurele, Bucharest, Romania2 Association Euratom-CEA, CEA Cadarache, DSM/DRFC/SIPP, Saint Paul lez Durance, 13108, France

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

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

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

6. INSIDE-GAP PLASMA GENERATOR (IGPG) PLASMA TORCH Movable RF powered electrode Grounded castellated surface 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 Designed for scanning: ATMOSPHERIC PRESSURE Principle: expanding radiofrequency plasmas Torch head diameter: 20 mm Couplings room diameter: 38 mm DESIGNS

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. EXPERIMENTAL MODELS INSIDE-GAP PLASMA GENERATOR (IGPG) PLASMA TORCH - RF Electrode (upper) : -copper body, -back insulated with TEFLON; -water cooled -Grounded electrode: castellated Al surface -gaps width: 0.6 -2 mm - 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)

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

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

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. EROSION RATE (bulk MATERIAL) PLASMA TORCH IGPG • 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 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. RF discharge: 50-150 W -Parallel plate electrodes -Shower type RF electrode -Substrate on the grounded electrode -Carrier gas: argon (Ar) -Precursor: acetylene (C2H2) Vacuum: 10-2-1 mbar Ar C2H2 Flow meter Mass Flow Controllers Gauge Upper electrode Data Acquisition device RF (13.56 MHz) Substrate support Lower electrode Airing Gas cooling trap Vacuum pump P.C. PREPARATION OF A MODEL FOR THE CODEPOSITED LAYER Amorphous Hydrogenated Carbon ( a-C:H ) deposited by Plasma Assisted Chemical Vapor Deposition (PACVD)

14. RF discharge: 50-150 W -Parallel plate electrodes -Shower type RF electrode -Substrate on the grounded electrode -Carrier gas: argon (Ar) -Precursor: acetylene (C2H2) Vacuum: 10-2-1 mbar Ar C2H2 Flow meter Mass Flow Controllers Gauge Upper electrode Data Acquisition device RF (13.56 MHz) Substrate support Lower electrode Airing Gas cooling trap Vacuum pump Carbon films, thickness: 1-10 mm Substrate: silicon, 2mm P.C. PREPARATION OF A MODEL FOR THE CARBON LAYER Amorphous Hydrogenated Carbon ( a-C:H ) deposited by Plasma Assisted Chemical Vapor Deposition (PACVD)

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

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

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

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

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) 19

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 20

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 21

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

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. 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. Exemple: gap width 500 microns Stainless steel cubes a-C:H layers 1 scan (4 sec) 46 scans (184 sec) 101 scan (404 s) Cubes coated with carbon inside gaps (20mm x23mmx20mm) Profile of the remained layer at various scan numbers for gap width 500 microns CLEANING BY A PLASMA TORCH FROM INSIDE GAPS (influence of the geometric aspect ratio of castellated surfaces) Samples preparation Scanning procedure Results: from profilometry A stripe of un-deposited layer is defined from top to bottom 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 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) Profilometry: film thickness: 2.2 microns

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. 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 mm Partial cleaned castellated surface (5 min) Cube extraction for examination on the lateral sides 27

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

29. Ellipsometric measurement of the remaining layer thickness upon depth after various cleaning times d Y,D Linear polarized incident laser beam Linear polarized reflected laser beam Cube face front face 1 (layer thickness) face 2 depth (z) R2 Decrease of the thickness on the front side upon time: R1=0.010 mm/min, R2=0.037 mm/min (Rave=0.033 mm/min) Layer thickness along depth at various cleaning times (data averaged on the four cube sides) Rc=0.24 mm/min (higher rate at upper gap margins) REMOVAL OF CARBONIC LAYERS BY IGPG Cleaning inside gaps: 8 times faster than on the front side

30. REMOVAL BY PLASMA TORCH of OTHER MATERIALS - DLC films Diamond - like carbon film (DLC) Film thickness ~ 510 nm Si substrate <100>, 400 mm thickness, deposited on silicon wafers) 10 cm diameter, resistivity 2-10 Wcm Max-Planck-Institute for Plasma Physics Reactive Plasma ProcessesMaterial Science Garching, Germany Dr. Thomas Schwarz-Selinger Prof. Wolfgang Jacob Supplier:

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

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

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

34. 1 scan 5 scans 20 scans 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 Backside of the mirror Removal after various number of scans Masking the deposited surface

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 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) • 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. NILPRP PROSPECTIVE FURTHER WORK • 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 • Plasma torch cleaning in gaps coated with mixed layers • purpose - study of the cleaning processes (active species), optimization (gas composition, power conditions) • Assessment of cleaning in large systems / real surfaces • purpose - check the validity of obtained results; • THANK YOU FOR YOUR ATENTION !

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

39. Gas Power supply Flow and pressure control (PID) Motion control Pressure monitoring unit Vacuum chamber Cooling IGPG RF Generator Vacuum pump Block diagram and parameters range 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