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D retention in O-covered and pure beryllium Motivation Experimental results Interpretation 1.Retention 2.Sample characterisation 3.Mechanisms Outlook Outline:

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Presentation on theme: "D retention in O-covered and pure beryllium Motivation Experimental results Interpretation 1.Retention 2.Sample characterisation 3.Mechanisms Outlook Outline:"— Presentation transcript:

1 D retention in O-covered and pure beryllium Motivation Experimental results Interpretation 1.Retention 2.Sample characterisation 3.Mechanisms Outlook Outline: Matthias Reinelt, Christian Linsmeier Max-Planck-Institut für Plasmaphysik EURATOM Association, Garching b. München, Germany 09 /10 July 2007

2 C W H,D,T ITER cross section Motivation 1: ITER ~ 700 m 2 Be Be: fast reaction with O 2 and H 2 O Previous experiments: Often oxygen contaminated surface Investigation of System Be – O – D System Be – D: no data Be: fast reaction with O 2 and H 2 O Previous experiments: Often oxygen contaminated surface Investigation of System Be – O – D System Be – D: no data Implantation of D into Be first wall Investigation of the D retention in Be System Be – D ( Be – T) Implantation of D into Be first wall Investigation of the D retention in Be System Be – D ( Be – T)

3 Motivation 2: Literature Diffusion: E D 0.04 to 2.5 eV Solubility: E S 0.1 to 1 eV Saturation0.3 to 0.4 D/Be... [Anderl 1999] 0.1 – 60 keV Retention adjusted for 100eV implantation Variation of 1-2 ORDERS OF MAGNITUDE Possible sources of uncertainties Chemical composition Sample structure Mechanisms

4 Issues: 1. Retention in pure Be 2. Surface characterization 3. Retention mechanisms 4. Influence of BeO

5 Experiment: Preparation 1 keV D + Implantation (Mass separated) Retained quantity Cleaning: 3 keV Ar + XPS/LEIS Annealing (1000 K) Cleaning: 3 keV Ar + XPS/LEIS Annealing (1000 K) BeO coverage < 0.2 ML mbar up to 1000 K BeO coverage < 0.2 ML mbar up to 1000 K Polished, single crystalline Be Polished, single crystalline Be

6 Experiment: Retention TPD Temperature Programmed Desorption TPD Temperature Programmed Desorption Electron impact heating / TC QMS Retention = TPD/NRA amount Incident amount (measured current) Retention = TPD/NRA amount Incident amount (measured current) NRA D( 3 He, 4 He)p NRA D( 3 He, 4 He)p Desorption rate

7 Experiment: Desorption TPD Temperature Programmed Desorption TPD Temperature Programmed Desorption Electron impact heating / TC QMS Sequential release of D Energy barriers for... Diffusion Detrapping Recombination Binding states of D Retention mechanisms Sequential release of D Energy barriers for... Diffusion Detrapping Recombination Binding states of D Retention mechanisms Desorption rate

8 Issue 1: Deuterium retention in pure Be

9 Retention at RT-implantation Maximum concentration: D/Be = keV D (exp.: 3 keV D 3 + )

10 Simulation: SDTrim.SP > max. concentration: Supersaturation Be SDTrim.SP not applicable Erosion rate (sputtering) < Concentration build-up (implantation) Supersaturation Structural modifications D/Be = 0.35

11 Retention: Literature

12 Retention: Elevated temperature Review [Anderl 1999] pure Be (1 keV) Be (+ BeO) 1 and 1.5 keV

13 Summary: Retention 1 keV Deuterium clean beryllium ~80% Retention at low fluences Saturation: Retained areal density 2·10 17 D cm -2 (reached at 2·10 17 D cm -2 incident fluence) Maximum local concentration D/Be=0.35 Local supersaturation in the bulk at 1·10 17 D cm -2 Nearly constant retention up to 530 K No significant influence of BeO coverage

14 Issue 2: Surface characterization

15 Substrate properties: REM Single crystalline (11-20) Be disk (after several hours at 1000 K in UHV)

16 Substrate properties 90°, Zoom

17 Substrate properties (1010) (1120) T 1000 K, several hours: Recrystallisation to low-indexed surfaces Formation of facetted crystallites substantial process T 1000 K, several hours: Recrystallisation to low-indexed surfaces Formation of facetted crystallites substantial process (0001)

18 Substrate properties Cleaning: Cycles of 3 keV Ar + / 1000 K Recrystallisation + Erosion Cleaning: Cycles of 3 keV Ar + / 1000 K Recrystallisation + Erosion

19 Substrate properties: Deuterium irradiation Cycles of Cleaning D Implantation Degassing 1000 K Cycles of Cleaning D Implantation Degassing 1000 K

20 Substrate properties: Morphology + Recrystallisation + Erosion + Structural modifications + Recrystallisation + Erosion + Structural modifications 500 nm Cycles of Cleaning D Implantation Degassing 1000 K Cycles of Cleaning D Implantation Degassing 1000 K AFM

21 Substrate properties: Elemental composition Be + 3 ML BeO (surface layer) Segregation of Be at the surface Annealing (Recrystallisation) of the surface above 1000 K Segregation of Be at the surface Annealing (Recrystallisation) of the surface above 1000 K (45°, 500 eV He + ) clean Be surface + 3 ML BeO (buried)

22 Summary: Surface characterisation Annealing T 1000 K Diffusion of Be Recrystallisation Segregation of Be to the surface Coverage of thin BeO surface layers by Be T 1000 K + ion bombardment Erosion processes + recrystallization to single crystallinity + structural modifications

23 Issue 3: Retention mechanisms

24 Temperature Programmed Desorption pure, annealed Be at RT 1 keV D + implantation saturation NRA: retained amount

25 Increasing fluence Low-temp. release: Structural modifications High-temp. release: Trapping in defects (intrinsic or ion-induced) local saturation of binding states local saturation of binding states

26 Increasing fluence SDTrim.SP: Supersaturation D/Be = 0.35 SDTrim.SP: Supersaturation D/Be = 0.35

27 Implantation at elevated temperature Population / creation of different binding states 300 K 530 K Expectation: * no occupation of low temperature states *retention loss of 30 % measured: only 14% retention at elevated temperature is higher than expected D from low temperature stage is trapped differently Phase transformation ?

28 Issue 4: Influence of BeO coverage

29 * Closed BeO coverage (3 ML) has no (measurable) effect on retention * No shift of desorption states no recombination-limited desorption mechanisms * Additional state at 750 K: BeO – D ? * Closed BeO coverage (3 ML) has no (measurable) effect on retention * No shift of desorption states no recombination-limited desorption mechanisms * Additional state at 750 K: BeO – D ?

30 Modelling Low temperature stage Polanyi-Wigner-Equation (Arrhenius expression) High temperature stage Rate-limiting step is detrapping from bulk sites TMAP7 Desorption spectrum Desorption of surface adsorbed gases Diffusion, trapping and surface recombination...

31 High temperature stage: TMAP7 Vacuum const mbar surface flux rate dependent rate dependent, heating Be bulk with 2 traps D Parameters: Diffusivity, Solubility, Trapping / Detrapping rates, Trap concentrations,...

32 High temperature stage: TMAP7 Model is reasonably accurate Does NOT reproduce all details ! diffusivity, solubility, traps, profile broaden peaks Microstructure ?

33 Low temperature stage: PW Input of measured temperature ramps into simulation !

34 Low temperature stage: PW

35 Energies: System Be – D E (D-Atom) Surface Ion induced defects Structural modifications Be bulkVacuum E atomic D = 0 eV

36 Energies: System Be – D E S = eV D atomic E 0 0 E Ad = eV [Küppers] D 2 molecular E BE (1/2 D 2 ) = eV Surface -2.1 eV -2.2 eV E D = 0.29 eV [Abramov] -1.5 eV +0.2 eV E (D-Atom)

37 Summary: Retention mechanisms Retained amount < 1·10 17 D cm -2 Trapping in intrinsic / ion induced defects Supersaturation > 1·10 17 D cm -2 Creation of structural modifications Binding of D to these modifications Elevated temperature Change of the structural modifications Thin BeO surface layers Surface has no recombination-limiting influence Binding as BeO-D

38 Summary Projection for ITER Projection for ITER Retention of the pure Be wall: 700 m 2 net erosion areas No isotope effects Maximum retention for 1 keV / 0° incidence < 7g T Retention of the pure Be wall: 700 m 2 net erosion areas No isotope effects Maximum retention for 1 keV / 0° incidence < 7g T Retention of Be wall Retention of Be wall Be X W pure Be Be 2 C BeO Retention in Be with mixed material surface layers Retention in Be with mixed material surface layers Mixed materials WXCWXC WXCWXC WO X

39 Summary Projection for ITER Projection for ITER Be – O – C – W pure Beryllium Be 2 C BeO Be X W Be 2 C BeO Be X W Mixed material surface layers Mixed material surface layers Mixed materials Mixed materials Implantation / Retention in... pure Substrate

40 Road map Substrate evolution with implantation / temperature ramping: Ternary systems, Ultrathin carbon layers Experimental data: TPD+NRA+XPS+ISS / REM+AFM Experimental data: TPD+NRA+XPS+ISS / REM+AFM Inventory and desorption from mixed materials: THICK layers of BeO / Be 2 C / Be X W Inventory and desorption from mixed materials: THICK layers of BeO / Be 2 C / Be X W Expermental data for Be – D Expermental data for Be – D Modelling: TMAP7 Modelling: TMAP7 Mixed Materials Mixed material surface layers Mixed material surface layers MD / DFT – Calculations MD / DFT – Calculations THIN surface layers of BeO / Be 2 C / Be X W Retention + Mixing / Diffusion / Phases,... THIN surface layers of BeO / Be 2 C / Be X W Retention + Mixing / Diffusion / Phases,...


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