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Insight into the co-deposition of deuterium with beryllium: influence of the deposition conditions on the deuterium rete

Insight into the co-deposition of deuterium with beryllium: influence of the deposition conditions on the deuterium retention and release . G . De Temmerman a,b , M.J. Baldwin a , R.P. Doerner a , D. Nishijima a , K. Schmid c.

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Insight into the co-deposition of deuterium with beryllium: influence of the deposition conditions on the deuterium rete

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  1. Insight into the co-deposition of deuterium with beryllium: influence of the deposition conditions on the deuterium retention and release G. De Temmermana,b, M.J. Baldwina, R.P. Doernera, D. Nishijimaa, K. Schmidc a Center for Energy Research, University of California at San Diego, USA bPresent address: EURATOM/UKAEA Fusion Association, Culham Science Centre, UK cMax-Planck Institut fuer Plasmaphysik, Garching, Germany G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  2. Motivation • Hydrogen isotope retention is a challenging problem for ITER • Material migration process will lead to the co-deposition of material eroded from the PFCs with deuterium/tritium  accumulation in the growing layer Almost an order of magnitude variation in measured D/Be levels No systematic influence of the oxygen content in the layer What defines the retention in Be layers ? How to resolve these discrepancies to allow reliable predictions ? Thermal desorption of deuterium in co-deposits ? 1R.A. Causey, D.S. Walsh, J. Nucl. Mater. 254 (1998), 84-86; 2R.A. Causey et al, Proc. of the international workshop on present status and future prospect of tritium material interaction studies, Toyama, Japan, 1996; 3M.J. Baldwin et al, J. Nucl. Mater. 337-339 (2005) 590-594, 4M. Mayer, J. Nucl. Mater. 240 (1997) 164-167 G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  3. Experiments in PISCES-B • PISCES-B is a linear plasma device • Steady state plasma generated by an arc discharge initiated by a heated LaB6 cathode Beryllium (or W) target ion flux: 2.5-3.5·1022 m2s-1 Te~ 6 eV target bias –50/-150 V Ttarget~ 600°C Tungsten substrate B field Be or W target W substrate G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  4. Experiments in PISCES-B • PISCES-B is a linear plasma device • Steady state plasma generated by an arc discharge initiated by a heated LaB6 cathode Beryllium (or W) target ion flux: 2.5-3.5·1022 m2s-1 Te~ 6 eV target bias –50/-150 V Ttarget~ 600°C Tungsten substrate B field Be or W target Retention: NRA, TDS Morphology: SEM W substrate Influence of particle energy, deposition rate, temperature on the retention G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  5. Raw data: range of possible D/Be values • General graph of the generated data Average energy of the particles reflected from target (and impinging on deposition probe) E0: energy of the particles impinging on target • Some trends identified • D/Be when substrate temperature or Be deposition rate • D/Be when energy of the incoming D particles G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  6. Influence of the deposition conditions Average energy of the incident particles • Examine each series of data for which only one parameter is varied Deposition rate Substrate temperature Influence of the individual parameters established G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  7. Parametric dependence of D/Be • An empirical relation is proposed to describe the evolution of D/Be • Regression analysis of all the data to determine the free parameters taking into account the influence of the individual parameters 5G. De Temmerman, et al, Nucl. Fusion, in press G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  8. Parametric dependence of D/Be • Retention mechanism appears to be a mix of co-deposition and implantation • deposition rate: co-deposition • energy: implantation Prediction of D/Be in PISCES-B layers possible Comparison to other data ?? G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain 8

  9. Comparison to literature data • Comparison with previously published papers from different machines (plasma devices not ion beam) • Causey: exp. in TPE • Markin: BeO layer • Good agreement between literature data and model • Apparent discrepancies between the different data can be explained by the different experimental conditions, to which the retention is sensitive Retention in ITER co-deposited layers will depend on layer formation conditions and location Good basis for prediction of retention in ITER G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  10. Layer morphology T=100°C, P=6mtorr T=300°C, P=6mtorr • Evolution of the morphology consistent with Thornton’s structure zone diagram (PVD) [6] P 6J. Thornton, J. Vac. Sci., 11 (1974) 666 P=6mtorr (15% Ar) T=100°C P=6mtorr (15% Ar) T=300°C T=100°C, P=1.5mtorr T=300°C, P=1.5mtorr Layer morphology depends on deposition conditions (pressure, temperature, gas composition) T G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  11. Influence of Ar on the retention/desorption • Be layers created under similar conditions, but with different Ar fractions • Desorption peak shifted towards higher temperatures when Ar is present in the plasma • Amount of retained deuterium decreases with Ar fraction G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  12. Layer morphology and desorption • Layers deposited with different neutral pressures, gas composition, substrate temperature • 2 desorption peaks depending on deposition conditions • 2nd peak may be linked to the formation of BeD2 (see P3-05, R.P. Doerner et al, O-21 M. Reinelt) G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  13. Influence of pressure and gas composition on D/Be • Scaling equation still valid for different pressures/gas compositions • Deposition rate, temperature and energy of incident D particles define the retention Predictions of the retention in co-deposited layers need to take deposition conditions into account G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  14. Illustration of the variation of T/Be in the ITER divertor • Rough estimate of how the T/Be ratio may vary in the divertor • Use particle fluxes from A. Kukushkin [report ITER_D_27TKC6 (2008)] • Be fractions from DIVIMP [K. Schmid, EFDA Task TUNMOD] • No re-erosion, design temperatures used • This does not pretend to be an accurate prediction for ITER !!! Average T/Be in the divertor: -Roth et al [R1]: 0.1 -De Temmerman scaling:0.008 G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain 14

  15. Implications for T removal by bake-out of the ITER vessel • Presence of Ar will affect the amount of T removed during a bake-out 75% remaining 35% remaining Layers formed in pure deuterium release the trapped fuel more easily Presence of Ar in the ITER divertor may limit the amount of tritium recovered by baking-out G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain 15

  16. Conclusions • Both deuterium retention and thermal release are affected by the deposition conditions • An empirical equation has been proposed to account for the effect of Be deposition rate, temperature and energy of incident D particles on the retention • Pressure, temperature and gas composition, affect the layer morphology and thermal release behaviour Retention in ITER co-deposited Be layers will depend on layer formation conditions and thus location inside the vessel Presence of Ar in the ITER divertor will tend to make thermal release of tritium more difficult G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain

  17. Thank you !! G. De Temmerman 18th PSI Conference, May 26-30 2008, Toledo, Spain 17

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