A new look at the specification of ITER plasma wall interaction and tritium retention J. Roth a, J. Davis c, R. Doerner d, A. Haasz c, A. Kallenbach a, A. Kirschner e, R. Kolasinski f, B. Lipschultz b, A. Loarte g, O. Ogorodnikova a, V. Philipps e, K. Schmid a, W. Wampler h, G. Wright i, D. Whyte b, a IPP Garching, EURATOM Association, Germany, b MIT PSFC, Cambridge, MA USA, c UTIAS, Toronto, Canada d Fusion Energy Research Program, UCSD, La Jolla, CA , USA, e Institut für Energieforschung 4, FZ Jülich, EURATOM Association, Germany, f Sandia Laboratories, Livermore, CA, USA, g ITER Cadarache, France, h Sandia Laboratories, Albuquerque, NM, USA, i FOM, Rijnhuizen, The Netherlands

Wall and divertor fluxes from B2/EIRENE (Kukushkin) Wall flux multiplied by 4±3 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 Plasma Phys. Control. Fusion 50 (2008) Previous approach

Assess status of laboratory and tokamak data pertaining to hydrogenic retention and underlying processes Particle fluxes to PFCs: Main chamber: Assumed fluxes and surface temperatures for empirical estimates (here example for high flux case) Two cases considered: total wall flux 1x10 24 /s (max. machine scaling) total wall flux 1x10 23 /s (B2/EIRENE Kukushkin) Divertor: Fluxes obtained from B2_EIRENE calculation (equilibrium 1084) total divertor flux 3x10 24 /s Assess status of laboratory and tokamak data pertaining to hydrogenic retention and underlying processes Present approach

Erosion Yields: for wall simplified assumption Y C = Y Be = 0.02 for divertor: full energy, temperature and flux dependence Co-deposition ratio: D/C, D/Be, D/W Dependent on temperature, energy, flux ratio: Carbon: (D+T)/C = (2.0 ·10 -2 ) E ( (D+T) / C ) 0 e (2268/T) Beryllium: (D+T)/Be = (5.82 · ) E 1.17 ( (D+T) / Be ) e (2273 /T) Tungsten (D+T)/W = (5.13 · ) E 1.85 ( (D+T) / W ) 0.4 e (736 /T)

D retention in tungsten: Upper margin: D/m 2 = 1.5 · ( 0.55 /(1 · )) Lower margin: D/m 2 = 8 · ( 0.66 /(1 · )) Temperature dependence: D/m 2 = · e (-T/185) No effects of simultaneous D and He implantation included. Present approach

Projections Explore what the various empirical and numerical models predict for retention in ITER Vessel Walls: Assumptions from tokamak experience: High flux 1x10 24 /s: 50% dep. in main chamber 37.5% dep. in inner divertor 15.5% dep. in outer divertor Low flux (0.1 of high flux): 75% dep. in inner divertor 25% dep. in outer divertor Divertor dep. prop. to plasma flux No divertor erosion, no re-erosion

Projections CFC divertor / Be walls: ERO code with divertor erosion, re-erosion and co-deposition Assumptions: 1% Be in incident flux inner divertor 0.1% Be in incident flux outer divertor 30 g at 10 5 s All-W device: Implantation and retention (without effects of n-damage) - Break-down of retention in W for different areas - Large wall areas most important

Summary Material comparison: no absolute prediction for ITER not including n-damage effects This work is an identification of areas needing additional research, rather than a material selection recommen- dation. Use of this work to select or de-select a material is probably not wise. Issues such as lifetime, dust and plasma contamination should be included. all-C materials initial ITER mix Be wall + W divertor all-W materials C vessel wall Be vessel wall all-W materials 150W/mK 50W/mK high wall flux low wall flux Be wall with CFC divertor

Future work Estimate of the effect of neutron induced damage for trap creation and subsequent T retention Current assessment: Retention by ion beams within m range with the best match to ITER conditions being the ones from Wright and Wampler - Traps for hydrogen appear may reach 0.6% of the W concentration, 15 times the natural trap density - In a W wall, in saturation, 3·10 27 traps available (equivalent to 15 kg of tritium if all filled) - Modelling of trap creation and subsequent filling beyond mm range not yet available Estimate effect of transient heating of surfaces on trapping in all materials Improve treatment of material transport, including re-erosion from divertor plates and main chamber local re-deposition Include effect of material mixing

Underestimation in new evaluation Due to: - neglecting outer divertor erosion - divertor transport and deposition on cooler surfaces Need for coupling of wall erosion (DIVIMP) with divertor erosion and transport (ERO/TRIDYN) Overestimation of retention in previous evaluation due to - neglection of saturation - very conservative treatments of n-damage effects Overall satisfactory agreement, new data more optimistic due to higher temperatures and neglect of outer divertor erosion Comparison of evaluation methods