1. Joachim Roth: SEWG Gas balance, JET, July, 2008 Recent analysis of Tritium retention in ITER Report from the joint EU-US meeting at MIT combining the ITPA SOL/DIV, EFDA PWI TF and ITER PWI Team B. Lipschultz, J. Roth, A.Loarte, V. Philipps, A. Kallenbach, K. Schmid, R. Doerner, D. Whyte, G. Wright, A. Haasz, J. Davis, R. Kolasinski, B. Wampler

2. Joachim Roth: SEWG Gas balance, JET, July, 2008 Meeting held at MIT on June,23-24, 2008 Evaluation of retention in different materials in ITER Monday (start 8:30 AM) Session 0 – 08:30 – 09:00 Introduction and discussion of goals (Roth and Lipschultz) Session 1 (chair, Roth) – Goal: Agree on wall fluxes and temperatures over the entire vessel for use in empirical and code models of erosion, re-deposition and retention (09:00 - 10:30) Kallenbach – Review scaling from ASDEX-Upgrade and application to ITER (10 minutes) Lipschultz – Review multiple machine scaling and application to ITER (10 minutes) Discussion - till 10:10 Break 10:10-10:30 Agenda:

3. Joachim Roth: SEWG Gas balance, JET, July, 2008 Session 2 (chair – Kallenbach) – Goal: Be and C erosion sources and resultant flow paths for C and Be. Schmid – Model calculations of C, Be sources and resultant paths for impurity transport and final deposition - should cover modelling of Be wall flux for Doerner (20 minutes) Philipps – ERO code calculations (Kirschner) for CFC divertor erosion including Be influxes and resultant deposition and retention. (20 minutes) Philipps – empirical scaling of Be and C erosion and co-deposition based on JET (10 minutes) Whyte – empirical scaling of multiple C-wall tokamaks for both Be and C (10 minutes) Discussion till lunch Lunch 12:30-14:00 Discussion continued till 15:00 Agenda:

4. Joachim Roth: SEWG Gas balance, JET, July, 2008 Session 3 (Chair – Doerner) Goal – Review the current lab and tokamak data for D retention in C, Be and W. (15:30-18:00) Doerner – Data on concentration in co-deposited layers vs temperature and flux for Be, C and W (10 minutes) Haasz – Data basis for W from ion beams and linear plasma devices (10 minutes) Kallenbach – Retention measurements in all-W AUG and extrapolation to ITER (10 minutes) Lipschultz/Whyte – Retention measurements in C-mod and extrapolation to ITER (10 minutes) Discussion till end of day Agenda:

5. Joachim Roth: SEWG Gas balance, JET, July, 2008 Tuesday (start 8:30) Session 4 (chair – Philipps) - Goal: Review of assumptions in codes modeling retention in W, on ranges of recombination, neutron damage and its conversion to trap sites (08:30-10:10) Whyte – Parameters for modeling of DIONISOS and C-Mod (15 minutes) Kolasinski – DIFFUSE and TMAP7 modeling of TPE results(15 minutes) Roth/Schmid for Ogorodnikova – Modeling of data from ion beams and linear devices (15 minutes) Wampler – Assessment of n-induced damage and hydrogen trap site characteristics (15 minutes) Whyte – Assessment of n-induced damage and hydrogen trap site characteristics (15 minutes) Break 10:10-10:30 Discussion continued until 12:00 12:00-13:30 – Lunch Session 5 (Chair – Lipschultz) – Goal: Finalize calculations and figures based on earlier sessions (13:30 - end of day) Schmid, Whyte, Kolasinski, empirical estimates – final calculation if different Agenda:

6. Joachim Roth: SEWG Gas balance, JET, July, 2008 Wall and divertor fluxes from B2/EIRENE (Kukushkin) Wall erosion/deposition from DIVIMP Divertor erosion/deposition using ERO Co-depostion from exp. data Retention in W from exp. data extrapolated by diffusion codes Recent EU evaluation: e.g. review PPCF, PSI Toledo

7. Joachim Roth: SEWG Gas balance, JET, July, 2008 High FluxLow Flux Wall Flux1E24 /s1E23 /s Carbon yield0.02 Be yield0.01 Wall deposition50%0 Outer divertor deposition 1/4 Inner divertor deposition 3/4 D/CRegression equation from PISCES D/BeRegression equation from PISCES Retention in WFit to data base at 500 K Temp. dependence for different fluxes Effect of n damageMaximum amount between 370g and 2 kg, to be settled by Bill and Dennis Different approach: An plasma experimentalist view:

8. Joachim Roth: SEWG Gas balance, JET, July, 2008 Area (m 2 ) Tsurf (K) Flux atoms (/m 2 s) E atoms (eV) Flux ions (/m 2 s) E ions (eV) Flux ions (1/s) outer divertor 11,213259E221,56E2237,2E22 22,395931,1E244,654E239,89,5E23 37,675203,2E22296,1E221264,7E23 422,13182,2E21333E21946,6E22 Inner divertor 11,153223,3E220,92E221,92,3E22 24,44664,8E233,371,7E237,57,3E23 34,93823,9E2295,6E22202,7E23 46,13243,2E2111,25,8E21253,5E22 dome 1623202,8E221,4 wall high flux 1505007E211003,5E23 ELMs505003E212001,5E23 wall low flux 12004501,75E211003,5E23 wall atoms 12504501,5E2120 upper divertor 1354502E22201,5E221005,2E23 ELMs354509E2010003,15E22 Sum wall450121,4E24 Sum divertor2,6E24 Flux conditions: e.g. High flux limit, 1E24 /s (Bruce)

9. Joachim Roth: SEWG Gas balance, JET, July, 2008 D/Be yield D/C yield Chem yield Eroded C Depos C T in CEroded Be Depos Be T in Be T in WITER Mix T in W/Be outer divertor001E-37,3E195E203,4E2101E211,6E181,8E201,6E181,5E18 000,0021,9E214E217,0E2008E211,0E192,3E201,0E19 0,060,020,011,4E225E205E192,8E221E215,2E194E201,4E215,2E19 0,060,020,011,9E214E216,6E20 Inner divertor001E-32,3E191E201,3E2103E202,7E179,5E192,7E17 001E-47,5E191E215,8E2002E223,3E195,4E203,3E19 0,010 2,7E213E203,2E202,7E216E206,6E185,1E206,6E18 0,0100,027,1E203,5E202,5E20 wall high flux0,050,0207E212E222,8E211,7E228,9E202,6E20 0,070,0203E211,0E225,6E20 wall low flux0,050,0207E211,7E222,2E21 wall atoms0,0100,021,5E227,5E214E222,6E202,5E21 upper divertor0,050,0201,0E222,6E221,2E21 0,050,0206,3E201,6E212,6E20 Sum wall4,3E228,1E227,6E21 Sum divertor2,2E223,5E222,8E21 total6,5E229,2E211,2E233,7E201,0E229,8E218,5E21 Erosion data from literature Co-deposition from Russ D in W from data base Numbers before correcting the temperature by 100 K

10. Joachim Roth: SEWG Gas balance, JET, July, 2008 Erosion yields: Comparison with Y C =0.02, Y Be =0.01 1% Be 2% C

11. Joachim Roth: SEWG Gas balance, JET, July, 2008 For beryllium: From De Temmerman et al., Nucl. Fusion 48 (2008)075008 Co-deposition with Be: Regression formula from PISCES

12. Joachim Roth: SEWG Gas balance, JET, July, 2008 Von Keudell determined retention below 200C behaved differently than above 200C For ITER we can ignore everything below 200C Impact of deposition rate on D/C is still unknown (so I ignore it, which is saying its saturated) Temperature scales as exp(2268/T) similar to metal codeposits (between 473 < T < 973K) D/C scales with incident D energy as E (-0.43) different from metal codeposits (15 < E <100 eV) Co-deposition with C: Regression formula from PISCES (Russ)

13. Joachim Roth: SEWG Gas balance, JET, July, 2008 Data base for retention in W: e.g. fluence dependence at 500 K

14. Joachim Roth: SEWG Gas balance, JET, July, 2008 Assumed temperature dependence is the envelope of the maxima. In most cases it overestimates the inventory. With better knowledge of temperatures and fluxes better estimates can be achieved. Normalised to 2x10 24 /m 2 Data base for retention in W: e.g. temperature dependence at 2x10 24 /m 2 y = 56.88*exp(-x/185)

15. Joachim Roth: SEWG Gas balance, JET, July, 2008 New EU-US evaluation: Retained tritium vs. discharge duration

16. Joachim Roth: SEWG Gas balance, JET, July, 2008 Recent EU evaluation: e.g. review PPCF, PSI Toledo

17. Joachim Roth: SEWG Gas balance, JET, July, 2008 Reasonable agreement, but still open questions: What is the reason for uncertainty of factor of 10 in wall flux? Can this uncertainty be reduced? What is the re-deposition fraction in the main vessel. Is it reducing net erosion? Does it lead to co-deposition at cool vessel walls? Why is divertor erosion not important for erosion and co- deposition? Does the divertor material matter for tritium retention? Deposition and co-deposition is known to occur not only on divertor targets. This is not taken into account. How can we include this effect? ERO and DIVIMP code with grid extended to the walls must support the present rough assumptions.