Dynamic fuel retention and release under ITER like wall conditions in JET

1. D x 10 21 Plasma content Dynamic fuel retention and release under ITER like wall conditions in JET V. Philipps1, T. Loarer2, M. Freisinger1, H.G.Esser1, S. Vartanian2, U. Kruezi3, S. Brezinsek1, G. Matthews3 and JET EFDA contributors JET-EFDA, Culham Science Centre, OX14 3DB, Abingdon, UK 1Forschungszentrum Jülich, Association EURATOM – FZJ, Jülich, Germany2CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 3EURATOM/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. Plasma content (x 1022 ) Wall retention D x 10 21 Cumulativeinjection Cumulativeretention (x 1021 /sec) D x 10 23 Retention rate Subdivertorpressure (x 10-3mbar) X 10-3mbar Divpressure JET with ITER-Like Wall Background and Motivation 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) • 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.) Bulk Be Be coating on Inconel W coating on CFC Bulk W Dynamic retention in Bewalls ( limiterdischarges) Divertedplasmaconditions L-mode with cryopump • Dverted plasmas: plasma interaction largely with W surfaces (+Be-deposits) • reduced contact with Be walls regeneration Release after shot≈ dynamic retention Injection L-mode diverted, no cryopump active • Example of a long term limiter shot • no sign of saturation • 3x1022 D shot-end retention cryyopumping Plasma content Time ( sec) Stronger initial retention in divertor phase Decay phase (1.4→ 0.4 x 1021/sec) Flat phase : 4x 1020 D/sec No saturation 30 consecutive repredocucible limiter shots Retention rate Typical shot 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 Limiter phase 82305 Initial wall retention rate (flat top density) Gradient of retention (avarage over 5 sec) b Retention rate a Cumulative retention Plasma content X 1021 D-atoms x 1022 Divertor phase Gradient Wall retention ( D/sec) Retention rate Gradient ofretention (D/sec) Time ( sec) c d Div pressure Total retention pressure (mbar) Wall retention during limiter and divertor phase Divertor D-atoms x 1023 Injection (circles) release until 770 sec (triangles) ,Extrapolated until next shot (squares) Regeneration Good agreement→ all dynamic retention released Cryopump regeneration Limiter injection Time ( sec) Release Transient dynamic retention (> 1023 D-atoms, partly released during shot Injection and release (740 sec and extrapolated to next shot ) + cryopump regeneration Injection Release 740 sec and til next shot Particle ( D) release after shots follows a power law t– 0.7 ±0.1 t – 0.7 ±0.1 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 ) • 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 x1021 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 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.