1. Dynamic fuel retention and release under ITER like wall conditions in JET V. Philipps 1, T. Loarer 2, M. Freisinger 1, H.G.Esser 1, S. Vartanian 2, U. Kruezi 3, S. Brezinsek 1, G. Matthews 3 and JET EFDA contributors JET-EFDA, Culham Science Centre, OX14 3DB, Abingdon, UK 1 Forschungszentrum Jülich, Association EURATOM – FZJ, Jülich, Germany 2 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 3 EURATOM/UKAEA Fusion Association, Culham Science Centre, UK. * See the Appendix to paper by F. Romanelli et al., Fusion Energy 2010 (Proc. 23st Int. Conf. Daejon, Republic of Korea, 2010) IAEA, Vienna 2010. Background and Motivation JET with ITER-Like Wall  Analysis of T retention under ITER like wall conditions is main objective of the JET ILW project.  Long term fuel (tritium) retention studied by gas balances using cryopump regeneration. Reduction of a factor >10 compared with C walls  This study: dynamic fuel retention (hydrogen retained during plasma operation and released in between discharges and over longer times (night etc.) Diagnostic  calibrated gas injection (JET GIMS)  Neutral pressure measurements in main chamber ( pennings) and subdivertor (baratrons)  Support form mass spectrometer data  Cross calibration of pennings versus baratrons  Consistency check: matching of particle balance in gas injection only ( no plasma) Be coating on Inconel Bulk Be Bulk W W coating on CFC Diverted plasma conditions Dynamic retention in Be walls ( limiter discharges) Wall retention ( D/sec) Gradient of retention (D/sec) Initial wall retention rate (flat top density) Gradient of retention (avarage over 5 sec) Retention rate Gradient Example of a long term limiter shot no sign of saturation 3x10 22 D shot-end retention Plasma content Wall retention Cumulative injection Subdivertor pressure D x 10 23 D x 10 21 X 10 -3 mbar Injection (circles) release until 770 sec (triangles),Extrapolated until next shot (squares) Regeneration Good agreement→ all dynamic retention released injection Release Cryopump regeneration Integral deuterium injection (dynamic wall retention in absence of pumping) and particle release for all limiter shots (limiterdatabase) Retention at shot end up to 3x 10 22 Strong wall retention in start of divertor phase Fast decay within few sec ≈100% of retained deuterium released in between shots (within data accuracy ) Dverted plasmas: plasma interaction largely with W surfaces (+Be-deposits) reduced contact with Be walls Stronger initial retention in divertor phase Decay phase (1.4→ 0.4 x 10 21 /sec) Flat phase : 4x 10 20 D/sec No saturation L-mode diverted, no cryopump active Retention rate Plasma content Cumulative retention Limiter phase Divertor phase L-mode with cryopump Injection cryyopumping Release after shot≈ dynamic retention regeneration With cryopump active, most injected D is pumped by cryopumps Evaluation of dynamic wall retention has larger uncertainty ( mismatch of regegeneration and integrated pressure data Transient dynamic retention (> 10 23 D-atoms, partly released during shot Particle ( D) release after shots follows a power law t – 0.7 ±0.1 Transient wall retention in density ramps with fast release during shot Particle release after shot with power law t – 0.7 ±0.1 for long times Reproducible retention of Be-walls ≈1.5 -0.4 x10 21 D/sec (flat top, no memory effect of previous shots) Retention rate decreases only slightly with time ( 0-8 % /sec), no saturation in JET time scales D-release behavior after discharge ≈ t – 0.7 ±0.1 (very similar to C wall conditions) Nearly all dynamically retained D is released in between shots (within data accuracy) Be retention will provide sufficient wall pumping for start up phase in ITER Wall retention during limiter and divertor phase Injection Release 740 sec and til next shot Limiter Divertor Injection and release (740 sec and extrapolated to next shot ) + cryopump regeneration X 10 21 D-atoms x 10 22 D-atoms x 10 23 pressure (mbar) 82305 a b c d Time ( sec ) Plasma content Div pressure Retention rate Total retention (x 10 22 ) (x 10 21 /sec ) (x 10 -3 mbar ) Div pressure Retention rate Cumulative retention Plasma content 30 consecutive repredocucible limiter shots Time ( sec) Typical shot Acknowledgements This work was supported by EURATOM and carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission.