Deuterium retention mechanisms in beryllium

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Deuterium retention mechanisms in beryllium. M. Reinelt, Ch. Linsmeier Max-Planck-Institut für Plasmaphysik EURATOM Association, Garching b. München, Germany. PSI-1828 May 2008. Outline. Motivation Results of thermal release experiments Variation of ... - PowerPoint PPT Presentation

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  • Deuterium retention mechanisms in berylliumM. Reinelt, Ch. Linsmeier Max-Planck-Institut fr PlasmaphysikEURATOM Association, Garching b. Mnchen, GermanyPSI-1828 May 2008

  • Outline

    Motivation Results of thermal release experiments Variation of ...* Irradiation fluence* Implantation temperature * BeO coverage

    Modeling Energy diagram of D / Be

    ConclusionITER cross section

  • MotivationD implantation into beryllium

    Deuterium retention / thermal recycling of ITER main wall

    Be: Fast reaction with O2 / H2O

    Previous experiments: BeO contaminated surfaces Investigation of System Be (+BeO) / D

    Clean Be / D: NO DATA !Be: ~700 m2D,T

  • MotivationD,TVariation by 1 ORDER OF MAGNITUDE !Be: ~700 m2[Anderl et al. 1999]

  • ConceptIssues to be solved:

    Retention in pure Be ? Crystallinity Influence of BeO ? Retention mechanisms ?

    Possible reasons:

    Undefined BeO coverage Undefined crystallinity Unclear retention mechanisms (Needed for quantification)

  • Experimental conceptThermal releaseNRATPDTemperatureProgrammedDesorption Sequential release of D Limited by combination of bulk + surface processes Energy barriers for ... Diffusion Detrapping Recombination

    Single crystalline Be Retention mechanisms1 keV D implantation Hydrogen retentionin situ... (10-11 mbar)Ar sputter cleaning+ annealingXPS / LEIS:Control ofsurface

  • TPD: SpectrumSequential release: Energetically different rate limiting steps 1 keV D+ Implantation (300 K) 21017 D cm-2 m/q= 4 (D2)

  • TPD: Increasing fluenceTPD Spectra recorded in random order ! Fluence dependent behaviour

  • TPD: Increasing fluenceTrapping in ion induced defects

  • TPD: Increasing fluenceStructural modificationsLocal saturation of available binding sitesTrapping in ion induced defects

  • TPD: Increasing fluenceStructural modificationsSample saturationThreshold

  • Retention: Simulation by SDTrim.SPSupersaturationzone

    D accumulation in a depth of 40 nm Bulk saturation concentration: 26 at% D(D/Be = 0.35)

    * Supersaturation * Structural modifications: Surface process?(cut off)SDTrim.SP CalculationTPD Experiments

  • Structural modifications / Surface desorption1st order release 1 DTrapped DMobile2nd order release 2 D D2 (Surface desorption)

  • Structural modifications / Surface desorption

    * Peak shape

    Desorption peak is 1st order

    * Surface area (AFM)

    Release of 60 x (saturation coverage ~ 0.5) AFM: max. 1.2

    Surface recom-bination is not the rate-limiting step

  • TPD: Influence of BeO-coverage

    No change of EA of release from binding states

    No recombination limit Trapping in the bulk

    Formation of BeO-D at the surface

    BeO:D(surface)

  • TPD: Elevated implantation temperatures300K530 K

  • TPD: Elevated implantation temperatures300K530 K

    Different retention mechanism !

    Change of the binding states in the supersaturated areas

    Ion-induced trap sitesunaffected

  • TPD: Elevated implantation temperatures300K530 K

    Different retention mechanism !

    Change of the binding states in the supersaturated areas

    BeD2 formation (Decomposition ~ 570 K)

    Ion-induced trap sitesunaffectedBeD2BeO:D(surface)

  • Implanted / Co-deposited1 keV Ion implanted(this work)D/Be plasma co-deposited(de Temmerman)300 K

  • Implanted / Co-deposited300 KSupersaturated material1 keV Ion implanted(this work)D/Be plasma co-deposited(de Temmerman)

  • Implanted / Co-deposited300 KIon-induced traps in the bulk1 keV Ion implanted(this work)D/Be plasma co-deposited(de Temmerman)

  • Implanted / Co-deposited300 K600 K530 KFormation of BeD2see also posterP3-05 by R. Doerner

  • Qualitative interpretation of data[Anderl et al. 1999]clean Be (1 keV)Be (+ BeO)1 and 1.5 keVStructural modificationsBeD2Ion-induced traps in the bulk lattice~ Constant retention300 400 500 600 700 800 900 1000 Specimen exposure temperature [K]

  • Identification of retention mechanisms

    Quantification: TMAP7 / Rate equations

  • TMAP7: D transport bulk / surfaceInput parameters

    Trap concentration profile by SDTrim.SP Saturated trap sites (TPD) Temperature ramp (TPD)

    Literature: Diffusion barrier 0.29 eV Dissolution energy 0.1 eV

    Free parameters

    Detrapping energies ET1 = 1.88 eV ET2 = 2.05 eV

  • Schematic energy diagramE (D-Atom)TPD Spectrum Activation energiesAtomic D E0 0Position / State0Temperature [K]Desorption rate [a.u.]

  • Schematic energy diagram[ES = -0.10 eV]Atomic D E0 0E (D-Atom)Positions in the undisturbed bulk latticeMobile state[ED = 0.29 eV]Temperature [K]Desorption rate [a.u.]

  • Schematic energy diagram[ES = -0.10 eV]Atomic D E0 0SurfaceE (D-Atom)Surface processesMobile state[ED = 0.29 eV][EAd = 0.87 eV]Molecular D2 [EBE (1/2 D2) = -2.278 eV]Temperature [K]Desorption rate [a.u.]

  • Schematic energy diagram[ES = -0.10 eV]Atomic D E0 0[EAd = 0.87 eV]Molecular D2 [EBE (1/2 D2) = -2.278 eV]SurfaceMobile state[ED = 0.29 eV]E (D-Atom)Activation energies obtained from modeling of TPD spectraTemperature [K]Desorption rate [a.u.]

  • Schematic energy diagramm[ES = -0.10 eV]Atomic D E0 0[EAd = 0.87 eV]Molecular D2 [EBE (1/2 D2) = -2.278 eV]SurfaceMobile state[ED = 0.29 eV]E = 1.25 eV 1.33 eVE (D-Atom)E = 1.88 eV 2.05 eVIon-induced defectsSupersaturatedstatesActivation energies obtained from modelling of TPD spectraBeD2Temperature [K]Desorption rate [a.u.]

  • ConclusionDeuterium retention in beryllium

    Binding states / retention mechanisms identified and quantified

    Hydrogen retention in ITER: negligible contribution of "pure" Be wall (< 7 g T by implantation) Thin BeO surface layers are not rate-limiting for thermal recycling Formation of BeD2 at elevated temperatures

    Currently: DFT calculations

    Detailed understanding of D / Be

  • Appendix

  • Literature data[Lossev,Kppers 1993]Surface desorption ?

  • Substrate characterization: SEMCleaning:Cycles of 3 keV Ar+ / 1000 K Recrystallization + erosion

  • Substrate characterization: SEM(1010)(1120)T 1000 K, several hours:Recrystallization to low indexed facets SEM

  • Substrate characterization: AFM500 nmRecrystallizationErosion D Induced structural modificationsAFMCycles of Cleaning D Implantation Degassing 1000 K

  • SEM: bubble & channel formation ?This work:Anderl et al. [1992]:Higher fluences Const. retention Aggregation ! Bubbles, pores, OPEN channels Fluence 41017 D cm-2

    CLOSED nanosized structural modifications !

  • Chemical surface compositionBeO coverage < 0.2 ML < 1day (10-11 mbar) > 1000 K

    Cleaning by Ar+ bombardmentAnnealing 1000 K

    XPScleaned &annealed