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Abstract

An analysis of helium exhaust experiments on JET in the MkII-GB divertor configuration is presented. Helium is pumped by applying an argon frost layer on the divertor cryo pump. Measurement of the helium retention time, tau{*}(He), is performed in two ways: by the introduction of helium in gas puffs and measurement of the subsequent decay time constant of the helium content, tau{d*}(He); and by helium beam injection and measurement of the helium replacement time, tau{r*}(He). In ELMy H-mode, with plasma configuration optimized for pumping, tau{d*}(He) roughly 7.2 × tau{th}(E) is achieved, where tau{th}(E) is the thermal energy replacement time. For quasi-steady internal transport barrier (ITB) discharges, the achieved tau{r*}(He) roughly 4.1 × tau{th}(E) is significantly lower. The achieved helium recycling coefficient, confirmed by an independent measurement to be R(eff) roughly 0.91, is the same in both scenarios. None of the discharges are dominated by core confinement. The difference in tau{*}(He)/ tau{th}(E) is instead due to the confinement properties of the edge plasma, which is characterized by Type I ELMs for the H-mode discharges studied, and Type III ELMs for the quasi-steady ITB discharges. This difference is quantified by an independent measurement of the ratio of the helium replacement time with a helium edge source to the energy confinement time.

Additional information

Authors: ZASTROW K-D, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);COX S J, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);STORK D, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);CHALLIS C D, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);GIROUD C, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);LAWSON K D, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);MEIGS A G, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);MORGAN P D, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);STAMP M F, EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon (GB);VON HELLERMANN M G, FOM Instituut voor Plasmafyisica Rijnhuizen, Euratom-FOM Association, Trilateral Euregio Cluster, Nieuwegein (NL);WHITEFORD A D, Department of Physics, University of Strathclyde, Glasgow (UK);O�MULLANE M G, Department of Physics, University of Strathclyde, Glasgow (UK);BRIX M, Forschungszentrum Jülich GmbH, Jülich (DE);FINKEN K H, Forschungszentrum Jülich GmbH, Jülich (DE);DUX R, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);LOARER T, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR);COFFEY I H, Department of Physics, Queens University, Belfast (UK);HILLIS D, Oak Ridge National Laboratory, Oak Ridge (US);HOGAN J T, Oak Ridge National Laboratory, Oak Ridge (US)
Bibliographic Reference: An article published in: Nuclear Fusion 45 (2005) 163�175
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: stacks.iop.org/NF/45/163
Record Number: 200518050 / Last updated on: 2005-04-06
Category: PUBLICATION
Original language: en
Available languages: en
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