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

Investigation of the D retention in Be Motivation 1: ITER C W H,D,T ITER cross section ~ 700 m2 Be Implantation of D into Be first wall Investigation of the D retention in Be System Be – D (  Be – T) Be : fast reaction with O2 and H2O Previous experiments : Often oxygen contaminated surface Investigation of System Be – O – D System Be – D : no data

Motivation 2: Literature Diffusion: ED 0.04 to 2.5 eV Solubility: ES 0.1 to 1 eV Saturation 0.3 to 0.4 D/Be ... [Anderl 1999] 0.1 – 60 keV Retention adjusted for 100eV implantation Possible sources of uncertainties Chemical composition Sample structure Mechanisms Variation of 1-2 ORDERS OF MAGNITUDE

Surface characterization Retention mechanisms Influence of BeO Issues: Retention in pure Be Surface characterization Retention mechanisms Influence of BeO

Experiment: Preparation 1 keV D+ Implantation (Mass separated) Retained quantity Polished, single crystalline Be Cleaning: 3 keV Ar+ XPS/LEIS Annealing (1000 K) BeO coverage < 0.2 ML 1 day @ 10-11 mbar up to 1000 K

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

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

Issue 1: Deuterium retention in pure Be

Retention at RT-implantation 1 keV D (exp.: 3 keV D3+) Maximum concentration: D/Be = 0.35

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

Retention: Literature

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

Summary: Retention 1 keV Deuterium  clean beryllium ~80% Retention at low fluences Saturation: Retained areal density 2·1017 D cm-2 (reached at 2·1017 D cm-2 incident fluence) Maximum local concentration D/Be=0.35 Local supersaturation in the bulk at 1·1017 D cm-2 Nearly constant retention up to 530 K No significant influence of BeO coverage

Issue 2: Surface characterization

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

Substrate properties 90°, Zoom

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

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

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

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

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

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

Issue 3: Retention mechanisms

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

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

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

Implantation at elevated temperature 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 ? Population / creation of different binding states 300 K 530 K

Issue 4: Influence of BeO coverage

Influence of BeO coverage * 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 ?

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

High temperature stage: TMAP7 Parameters: Diffusivity, Solubility, Trapping / Detrapping rates, Trap concentrations,... Vacuum const. 10-10 mbar surface flux rate dependent D Be bulk with 2 traps rate dependent, heating surface flux

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

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

Low temperature stage: PW

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

Energies: System Be – D E (D-Atom) Surface ED = 0.29 eV [Abramov] D atomic E0≡ 0 +0.2 eV ES = -0.10 eV EAd = -0.85 eV [Küppers] -1.5 eV -2.1 eV -2.2 eV D2 molecular EBE (1/2 D2) = -2.278 eV Surface

Summary: Retention mechanisms Retained amount < 1·1017 D cm-2  Trapping in intrinsic / ion induced defects Supersaturation > 1·1017 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

✔ Summary Projection for ITER ✔ Retention of the pure Be wall: net erosion areas No isotope effects Maximum retention for 1 keV / 0° incidence < 7g T Projection for ITER Retention of Be wall Mixed materials pure Be ✔ ✔ BeXW Be2C BeO WXC WOX Retention in Be with mixed material surface layers

Summary Projection for ITER Implantation / Retention in ... Mixed material surface layers Mixed materials Be – O – C – W Be2C BeO BeXW pure Beryllium pure Substrate

Road map Expermental data for Be – D Experimental data: TPD+NRA+XPS+ISS / REM+AFM Modelling: TMAP7 MD / DFT – Calculations Mixed Materials Inventory and desorption from mixed materials: THICK layers of BeO / Be2C / BeXW Substrate evolution with implantation / temperature ramping: Ternary systems, Ultrathin carbon layers Mixed material surface layers THIN surface layers of BeO / Be2C / BeXW Retention + Mixing / Diffusion / Phases, ...