A new look at the specification of ITER

plasma wall interaction and tritium retention

J. Rotha, J. Davisc, R. Doernerd, A. Haaszc, A. Kallenbacha, A. Kirschnere, R. Kolasinskif, B. Lipschultzb, A. Loarteg, O. Ogorodnikovaa, V. Philippse, K. Schmida, W. Wamplerh, G. Wrighti, D. Whyteb,

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 92093-0417, 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) 03001

Previous approach

• Assess status of laboratory and tokamak data pertaining to hydrogenic retention and underlying processesParticle 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 1x1024/s (max. machine scaling)

total wall flux 1x1023/s (B2/EIRENE Kukushkin)

Divertor: Fluxes obtained from B2_EIRENE calculation (equilibrium 1084)total divertor flux 3x1024/s

• Assess status of laboratory and tokamak data pertaining to hydrogenic retention and underlying processes

Present approach

Present approach

Erosion Yields: for wall simplified assumption YC = YBe = 0.02for divertor: full energy, temperature and flux dependence

Co-deposition ratio: D/C, D/Be, D/WDependent on temperature, energy, flux ratio:Carbon:(D+T)/C = (2.0 ·10-2) E-0.43 ((D+T)/C)0 e(2268/T)

Beryllium:(D+T)/Be = (5.82 ·10-5) E 1.17 ((D+T)/Be)-0.21 e(2273 /T)

Tungsten(D+T)/W = (5.13 ·10-8) E 1.85 ((D+T)/W)0.4 e(736 /T)

D retention in tungsten:Upper margin:

D/m2 = 1.5 ·1022 (0.55/(1 ·1014+0.55))Lower margin:

D/m2 = 8 ·1021 (0.66/(1 ·1018+0.66))Temperature dependence:

D/m2 = 56.88 ·1020 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 1x1024/s:

50% dep. in main chamber37.5% dep. in inner divertor15.5% dep. in outer divertor

Low flux (0.1 of high flux):75% dep. in inner divertor25% dep. in outer divertor

Divertor dep. prop. to plasma fluxNo divertor erosion, no re-erosion

Projections

CFC divertor / Be walls:ERO code with divertor erosion, re-erosion and co-depositionAssumptions: 1% Be in incident flux inner divertor0.1% Be in incident flux outer divertor

30 g at 105 sAll-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 ITERnot 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

mat

erial

s

initi

al IT

ER mix

Be wall +

W

divertor

all-W

materials

C vess

el w

all

Be ve

ssel

wal

l

all-W materials

150W/m

K 150W/m

K

50W/m

K50W

/mK

high wall flux

low wall flux

Be wall

with

CFC

diverto

r

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, 3·1027 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 evaluationDue 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