*This work was supported by the United States Department of Energy DEUTERIUM RETENTION IN TUNGSTEN EXPOSED TO CARBON-SEEDED DEUTERIUM PLASMA * Igor I. Arkhipov, Vladimir Kh. Alimov, Dmitrii A. Komarov Rion A. Causey*, Robert D. Kolasinski* A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, RAS, Moscow, Russia *Sandia National Laboratories, Livermore, USA Outline Introduction Experimental Results & Discussion Conclusions *This work was supported by the United States Department of Energy under Contract 512244 with Sandia National Laboratories

Irradiation conditions Introduction Irradiation conditions Pdiv, Pa Flux, D/m2s Ei, eV* C, at.% Tsur, K ITER divertor [1] 4 ~1×1023-24 ≤100 ? 520 & 850 JET [2] ≤20 380-520 PISCES-B [3] ~1×1022 100 0.5; 1; 1.4 350-1200 Ion source [4] ~4×10-5 ~6×1019 500 1 300, 500 Magnetron [5] ~1×1021 400 ≤1 390-1000 [1] G.Federici et al., J. Nucl. Mater. 313-316 (2003) 11-22 [2] J.P. Coad, et.al., J. Nucl. Mater. 313-316 (2003) 419-423 [3] F.C. Sze et.al., J. Nucl. Mater. 266-269 (1999) 1212-1218 [4] M.Poon, et al., J. Nucl. Mater. 337-339 (2005) 629-633 [5] This work

Irradiation conditions Introduction Irradiation conditions Pdiv, Pa Flux, D/m2s Ei, eV* C, at.% Tsur, K ITER divertor [1] 4 ~1×1023-24 ≤100 ? 520 & 850 JET [2] ≤20 380-520 PISCES-B [3] ~1×1022 100 0.5; 1; 1.4 350-1200 Ion source [4] ~4×10-5 ~6×1019 500 1 300, 500 Magnetron [5] ~1×1021 400 ≤1 390-1000 [1] G.Federici et al., J. Nucl. Mater. 313-316 (2003) 11-22 [2] J.P. Coad, et.al., J. Nucl. Mater. 313-316 (2003) 419-423 [3] F.C. Sze et.al., J. Nucl. Mater. 266-269 (1999) 1212-1218 [4] M. Poon, et al., J. Nucl. Mater. 337-339 (2005) 629-633 [5] This work

Material migration in divertor tokamaks Introduction Material migration in divertor tokamaks Distribution of erosion/deposition areas in the JET divertor (1999-2001)* *P.Coad, et al., J. Nucl. Mater. 313-316 (2003) 419

Erosion of carbon by deuterium Introduction Erosion of carbon by deuterium Sputtering yields curves for fusion relevant materials for irradiation by deuterium* (Physical sputtering yields for some ion mass are plotted in the case of W) 100 *G.F. Matthews, J. Nucl. Mater. 337-339 (2005) 1-9

Scheme of erosion/re-deposition processes within the divertor* Introduction Material migration in divertor tokamaks Scheme of erosion/re-deposition processes within the divertor* *G.F. Matthews, J. Nucl. Mater. 337-339 (2005) 1-9

Erosion of tungsten by tritium Introduction Erosion of tungsten by tritium Ion impact energy at the outer divertor target for a completely detached N2 seeded shorts in JET. The effect of ELMs of different sizes is shown* *G.F. Matthews, J. Nucl. Mater. 337-339 (2005) 1-9

D retention in C seeded D-plasma exposed W Experimental results Introduction D retention in C seeded D-plasma exposed W Experimental results Dominant factors: 1. substrate temperature 2. whether carbon is deposited on the W surface There is a carbon-impurity concentration of beginning of C-deposition: 0.75% at 850 K 1% at 750 K Uncontaminated surface: 1. Blisters, bubbles and/or pits are formed 2. D retention decreases with temperature increase C-contaminated surface: 1. a-C:D film or/and W2C layer are formed 2. D retention in C-contaminated W larger than in uncontaminated one The most of deuterium are residing in the carbon films Thin a-C:D film or W2C layer can significantly decrease D-retention in W

D retention in C seeded D-plasma exposed W Experimental results Introduction D retention in C seeded D-plasma exposed W Experimental results Dominant factors: 1. substrate temperature 2. whether carbon is deposited on the W surface There is a carbon-impurity concentration of beginning of C-deposition: 0.75% at 850 K 1% at 750 K Uncontaminated surface: 1. Blisters, bubbles and/or pits are formed 2. D retention decreases with temperature increase C-contaminated surface: 1. a-C:D film or/and W2C layer are formed 2. D retention in C-contaminated W larger than in uncontaminated one The most of deuterium are residing in the carbon films Thin a-C:D film or W2C layer can significantly decrease D-retention in W

D retention in C seeded D-plasma exposed W Experimental results Introduction D retention in C seeded D-plasma exposed W Experimental results Dominant factors: 1. substrate temperature 2. whether carbon is deposited on the W surface There is a carbon-impurity concentration of beginning of C-deposition: 0.75% at 850 K 1% at 750 K Uncontaminated surface: 1. Blisters, bubbles and/or pits are formed 2. D retention decreases with temperature increase C-contaminated surface: 1. a-C:D film or/and W2C layer are formed 2. D retention in C-contaminated W larger than in uncontaminated one The most of deuterium are residing in the carbon films Thin a-C:D film or W2C layer can significantly decrease D-retention in W

D retention in C seeded D-plasma exposed W Experimental results Introduction D retention in C seeded D-plasma exposed W Experimental results Dominant factors: 1. substrate temperature 2. whether carbon is deposited on the W surface There is a carbon-impurity concentration of beginning of C-deposition: 0.75% at 850 K 1% at 750 K Uncontaminated surface: 1. Blisters, bubbles and/or pits are formed 2. D retention decreases with temperature increase C-contaminated surface: 1. a-C:D film or/and W2C layer are formed 2. D retention in C-contaminated W larger than in uncontaminated one The most of deuterium are residing in the carbon films Thin a-C:D film or W2C layer can significantly decrease D-retention in W

Erosion of tungsten by carbon Introduction Erosion of tungsten by carbon Sputtering yields curves for fusion relevant materials for irradiation by deuterium* (Physical sputtering yields for some ion mass are plotted in the case of W) 100 *G.F. Matthews, J. Nucl. Mater. 337-339 (2005) 1-9

W erosion as function of Te and C impurity concentration* Introduction Erosion of tungsten by carbon W erosion as function of Te and C impurity concentration* *K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

Partially contaminated surface in C-seeded D-plasma Introduction In this work: Partially contaminated surface in C-seeded D-plasma

Top view of magnetron cathode surface Experimental Top view of magnetron cathode surface (6×8×0.5 mm3) Ta mask

Irradiation conditions Experimental Irradiation conditions Pdiv, Pa Flux, D/m2s Ei, eV* C, at.% Tsur, K ITER divertor [1] 4 ~1×1023-24 ≤100 ? 520 & 850 JET [2] ≤20 380-520 PISCES-B [3] ~1×1022 100 0.5; 1; 1.4 350-1200 Ion source [4] ~4×10-5 ~6×1019 500 1 300, 500 Magnetron [5] ~1×1021 400 ≤4 363-773 [1] G.Federici et al., J. Nucl. Mater. 313-316 (2003) 11-22 [2] J.P. Coad, et.al., J. Nucl. Mater. 313-316 (2003) 419-423 [3] F.C. Sze et.al., J. Nucl. Mater. 266-269 (1999) 1212-1218 [4] M.Poon, et al., J. Nucl. Mater. 337-339 (2005) 629-633 [5] This work

Irradiation conditions Experimental Irradiation conditions Pdiv, Pa Flux, D/m2s Ei*, eV At.% C Tsurface, K ITER [1] 4 ~1×1023-24 ≤100 ? 520 & 850 JET [2] ≤20 380-520 PISCES-B [3] ~2×1022 100 0.5; 1; 1.4 350-1200 Ion source [4] ~4×10-5 ~6×1019 500 1 300, 500 Magnetron [5] ~1×1021 400 ≤4 363-773 *Ei≈ZUsheath + 2Ti ≈ Te(3Z+1), Usheath≈3Te/e0 Ti≈Te/2 Ei- ion impact energy Z- charge state of the impacting ion Usheath- sheath potential Te& Ti – temperatures of electrons and ions [1] G.Federici et al., J. Nucl. Mater. 313-316 (2003) 11-22 [2] J.P. Coad, et.al., J. Nucl. Mater. 313-316 (2003) 419-423 [3] F.C. Sze et.al., J. Nucl. Mater. 266-269 (1999) 1212-1218 [4] M.Poon, et al., J. Nucl. Mater. 337-339 (2005) 629-633 [5] This work

Irradiation conditions Experimental Irradiation conditions Pdiv, Pa Flux, D/m2s Ei, eV At.% C Tsurface, K ITER [1] 4 ~1×1023-24 ≤100 ? 520 & 850 JET [2] ≤20 380-520 PISCES-B [3] ~1×1022 100 0.5; 1; 1.4 350-1200 Ion source [4] ~4×10-5 ~6×1019 500 1 300, 500 Magnetron [5] ~1×1021 400 ≤4 363-773 [1] G.Federici et al., J. Nucl. Mater. 313-316 (2003) 11-22 [2] J.P. Coad, et.al., J. Nucl. Mater. 313-316 (2003) 419-423 [3] F.C. Sze et.al., J. Nucl. Mater. 266-269 (1999) 1212-1218 [4] M.Poon, et al., J. Nucl. Mater. 337-339 (2005) 629-633 [5] This work

W erosion as function of Te and C impurity concentration* Introduction Erosion of tungsten by carbon W erosion as function of Te and C impurity concentration* *K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

Experimental conditions D ion energy, eV Time, sec Flux, (m-2s-1) Fluence, Erosion, nm/sec 200 1800 1× 1019 2× 1024 ≤1 nm/sec Ei=400 eV Rp, nm (SRIM 2003) Kerosion Kdiffusion (m2s-1) Conclusion R D2+→W 2 - 1× 10-9 * No limits for diffusion 1 C+→W 0.1 1× 10-19 ** Thin C-W mixed layer * T=770 K **T=1030 K [1] R. Fraunfelder, J. Vac. Sci.Technol. 6 (1969) 388 [2] K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

Erosion of tungsten Experimental Estimation: V erosion=1.5-2 μm/30 min ~1 nm/s ~6×1019 at.W/m2s Initial surface Closed area Eroded surface Plasma-impact area Interference fringes (Linnik micro-interferometer)

Erosion of tungsten by carbon Experimental Erosion of tungsten by carbon Sputtering yields curves for fusion relevant materials for irradiation by deuterium* (Physical sputtering yields for some ion mass are plotted in the case of W) *G.F. Matthews, J. Nucl. Mater. 337-339 (2005) 1-9

Experimental conditions D ion energy, eV Time, sec Flux, (m-2s-1) Fluence, Erosion, W at./m2s 200 1800 1× 1019 2× 1024 ≤6×1019 Ei=400 eV Rp, nm (SRIM 2003) Kerosion Kdiffusion (m2s-1) Conclusion R D2+→W 2 - 1× 10-9 * No limits for diffusion 1 C+→W 0.1 1× 10-19 ** Thin C-W mixed layer * T=770 K **T=1030 K 1%C in plasma: 1018 C/m2s→ 1017 W/m2s [1] R. Fraunfelder, J. Vac. Sci.Technol. 6 (1969) 388 [2] K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

The threshold energies of sputtering Experimental The threshold energies of sputtering Irradiation T, K Eth, eV Kerosion at Ei= 400 eV C+, N+, O+ →W 293 ~35 ~ 0.1 Ta+ →W ~2 D2+→W 160-200 ≤0.0001 D2+→WO 65 D2+→WC 150 ≤ 0.0001

DEUTERIUM RETENTION IN TUNGSTEN AT HIGH LEVEL OF SURFACE EROSION Experimental DEUTERIUM RETENTION IN TUNGSTEN AT HIGH LEVEL OF SURFACE EROSION

Experimental conditions D ion energy, eV Time, sec Flux, (m-2s-1) Fluence, Erosion, W at./m2sec Temperature, K 200 1800 1× 1019 2× 1024 ~6×1019 363-773 Ei=400 eV Rp, nm (SRIM 2003) Kerosion Kdiffusion (m2s-1) Conclusion R D2+→W 2 - ~ 1× 10-9 * No limits for diffusion 1 C+→W 0.1 ~ 1× 10-19 ** Thin C-W mixed layer * T= 773 K **T=1030 K [1] R. Fraunfelder, J. Vac. Sci.Technol. 6 (1969) 388 [2] K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

Diffusion coefficient for C in a wide concentration range for C in W* Introduction Diffusion coefficient for C in a wide concentration range for C in W* *K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

Experimental conditions D ion energy, eV Time, sec Flux, (m-2s-1) Fluence, Erosion, W at./m2sec Temperature, K 200 1800 1× 1019 2× 1024 ~6×1019 363-773 Ei=400 eV Rp, nm (SRIM 2003) Kerosion Kdiffusion (m2s-1) Conclusion R D2+→W 2 - ~ 1× 10-9 * No limits for diffusion 1 C+→W 0.1 ~ 1× 10-19 ** Thin C-W mixed layer * T= 773 K **T=1030 K [1] R. Fraunfelder, J. Vac. Sci.Technol. 6 (1969) 388 [2] K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

Experimental conditions D ion energy, eV Time, sec Flux, (m-2s-1) Fluence, Erosion, W at./m2sec Temperature, K 200 1800 1× 1019 2× 1024 ~6×1019 363-773 Ei=400 eV Rp, nm (SRIM 2003) Kerosion Kdiffusion (m2s-1) Conclusion R D2+→W 2 - ~ 1× 10-9 * No limits for diffusion 1 C+→W 0.1 ~ 1× 10-19 ** Thin C-W mixed layer * T= 773 K **T=1030 K [1] R. Fraunfelder, J. Vac. Sci.Technol. 6 (1969) 388 [2] K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

H diffusivity vs temperature for W Experimental H diffusivity vs temperature for W 773 K E. Serra, G. Benamati, O.V. Ogorodnikova, J. Nucl. Mater. 255 (1998) 105-115

H diffusivity vs temperature for W Experimental H diffusivity vs temperature for W 773 K R. Fraunfelder, J. Vac. Sci.Technol. 6 (1969) 388

H diffusivity vs temperature for W Experimental H diffusivity vs temperature for W 773 K A.P. Zakharov, V.M. Sharapov, E.I. Evko, Soviet Mater. Sci. 9 (1973) 149

Experimental conditions D ion energy, eV Time, sec Flux, (m-2s-1) Fluence, Erosion, W at./m2sec Temperature, K 200 1800 1× 1019 2× 1024 ~6×1019 363-773 Ei=400 eV Rp, nm (SRIM 2003) Kerosion Kdiffusion (m2s-1) Conclusion R D2+→W 2 - ~ 1× 10-9 * No limits for diffusion 1 C+→W 0.1 ~ 1× 10-19 ** Thin C-W mixed layer * T= 773 K **T=1030 K Kdiffusion ~ 1× 10-9 m2s-1 →h=(Dt)1/2~ 1mm [1] R. Fraunfelder, J. Vac. Sci.Technol. 6 (1969) 388 [2] K. Schmid, J. Roth, J. Nucl. Mater. 313-316 (2003) 302-310

Methods of the analysis Experimental Methods of the analysis C/D-plasma irradiation: planar DC magnetron Eions (D2+; C+; N+, O+, Ta+)= 400 eV Flux=1×1019 D/m2s, 30 min Mechanically & electrochemically polished Hot-rolled tungsten foil (99.0 at.%) Size = 6×8×0.5 mm3 Profiles & chemical state of impurities: X-ray Photoelectron Spectroscopy (XPS) Depth profiles of C, O, W 3 kev Ar+, 2×2 mm2, 0.4 μm Deuterium profiles: Nuclear Reaction Analysis (NRA): 0 - 0.5 μm: D(3He,α)H reaction 0.5 - 7 μm: D(3He,p)4He reaction Deuterium retention: Thermal Desorption Spectroscopy (TDS) D2 & HD molecules were detected by QMS Temperature range: 300-1100 K Heating rate = 3.2 K/s

Results & Discussion NRA & TDS data m 6

Results & Discussion NRA data 3

Results & Discussion XPS data (3 keV Ar at fluence=1×1019 Ar/m2 )

Results & Discussion NRA data 3

Blistering in the temperature range 363-653 K Results & Discussion Blistering in the temperature range 363-653 K Pre-TDS; T=563 K at fluence=2× 1024 D/m2

Results & Discussion TDS data

Results & Discussion TDS data T1=650-710 K T2=900-1000 K

Results & Discussion TDS modeling: contributions from 1.4 eV traps and blisters (TMAP7) at 563 K

Three types of traps can explain our TDS data Near-surface layer (≤ 0.5 m): 1.4 eV traps= one D in vacancy 2. Sub-surface layer (≤ 7 m): 1.8-2.1 eV= D chemisorption on blister/bubble wall + D2 molecules inside 3. Bulk (up to 1 mm): 1.8-2.1 eV traps= D chemisorption on inner walls of small cavity and voids

Fitting of TDS data are in progress

Results & Discussion NRA & TDS data m Bulk trapping !

General experimental results Results & Discussion General experimental results Strong W sputtering Blistering Enhanced D retention NRA ≈ TDS from 363 to 563 K NRA<<TDS from 563 to 773 K

Conclusions General conclusions Blistering & enhanced D retention even at strong W surface sputtering are revealed Irradiation temperature of 550-600 K corresponds to transition from a near/sub-surface to a bulk D trapping in polycrystalline W foils Carbon influence: enhanced W erosion; W2C barrier layer formation & increased D retention

Conclusions General conclusions Blistering & enhanced D retention even at strong W surface sputtering are revealed Irradiation temperature of 550-600 K corresponds to transition from a near-surface to a bulk D trapping in polycrystalline W Carbon influence: enhanced W erosion; W2C barrier layer formation & enhanced D retention

Conclusions General conclusions Blistering & enhanced D retention even at strong W surface sputtering are revealed Irradiation temperature of 550-600 K corresponds to transition from a near-surface to a bulk D trapping in polycrystalline W Carbon influence: enhanced W erosion; W2C barrier layer formation & enhanced bulk D retention

Scheme of plasma-surface interaction No erosion D-C plasma D  stop diffusion & retention 4 nm W a-C:H film Carbon-modified layer (W2C, WC)

Scheme of plasma-surface interaction Erosion rate  1 nm/s D-C plasma  no limits for diffusion  high retention level in bulk D 2 m 1 nm W a-C:H film Carbon-modified layer (W2C, WC)

To be or not to be for D retention in W strongly depends on irradiation parameters and surface conditions

Thank you for attention