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| Home > Publications database > The isotope effect on the detachment density in JET-ILW Ohmically confined plasmas |
| Abstract | FZJ-2021-01648 |
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2021
Abstract: The isotope effect on the detachment density in JET-ILW Ohmically confinedplasmasV Solokha1, M Groth1, S Brezinsek2, M Brix3, G Corrigan3, C Guillemaut4, D Harting3,S Jachmich5, U Kruezi6, S Marsen7, S Wiesen2 and JET contributors∗1 Aalto University, P.O. Box 14100, FI-00076, Aalto, Espoo, Finland2 Forschungszentrum Julich GmbH, Institut fur Energie- und Klimaforschung, IEK-4 - Plasmaphysik, 52425 Julich, Germany3 EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK4 Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Lisbon, Portugal5 Ecole Royale Militaire School, Av de la Renaissance 30, Brussels, Belgium6 ITER Organization Route de Vinon sur Verdon, Saint Paul-lez-Durance, France7 Max-Planck-Institute for Plasma Physics, Greifswald, Germany∗ See the author list of E. Joffrin et al. accepted for publication in Nuclear Fusion Special Issue 2019,https://doi.org/10.1088/1741-4326/ab2276Studies in JET with the ITER-like wall (JET-ILW) Ohmic plasmas show that the density range, in which thepartial detachment at both divertor targets is accessible, is affected by the hydrogen isotope species as well asby the divertor geometry. These studies are consistent with previous research showing that the detachmentonset density for different hydrogen species in JET with the carbon wall (JET-C) scales inversely with the ionmass for vertical target (VT) configuration L-mode discharges [1].The isotope effect on the detachment density was reassessed for hydrogen and deuterium plasmas in thevertical and horizontal target (HT) configurations. The density of the detachment onset in the HT configurationfor the deuterium discharges is 10% lower than for the hydrogen at the outer target (OT), while in the VTconfiguration the isotope effect is stronger (30%) and affects detachment onset density at both targets.Simulations with the EDGE2D-EIRENE code [2,3] showed that the deuterium cases have a 50% higher neutraldensity than the hydrogen cases due to the subdivertor entrance conductance dependence on the thermalvelocity of the molecules. The increased neutral densities in the deuterium cases cause two times higherradiation losses in the simulations, while in the experiments bolometry measurements showed only 30% higherradiation losses. On the other hand, the Balmer-alpha emission profiles across the outer divertor plate aremeasured similar in shape and magnitude. Due to the pumping plenum, which reflects 80% of the incidentparticles, and subdivertor geometry of JET, the probability of the recycled particles from the inner target (IT) toreach the cryopump via the IT subdivertor entrance is close to zero. The poloidal ExB drift direction affects themagnitude of the isotope effect by moving particles from the OT to the IT in the normal BT direction (weakerisotope effect) or towards the OT and the cryopump in the reversed BT configuration (stronger isotope effect). Inthe HT configuration, the molecules at the IT can not be pumped, whereas in the VT configuration moleculesfrom both targets could be pumped due to connection to the OT subdivertor entrance by the private flux region.The higher detachment onset densities for heavier isotope species caused by the higher molecular densities.The dependence of molecular transport on the strike-point (SP) position due to the curvature of the target platesis predicted to cause the higher detachment onset densities in cases with higher strike-point positions. Theusage of the low SP position decreases the detachment onset density and increases pumping efficiency, whichleads to better particle control as well as to a bigger influence of the subdivertor entrance conductance andisotope species on the divertor plasma.[1] C.F. Maggi et al, Nucl. Fusion 39 979 (1999).[2] R. Simonini et al, Contrib. Plasma Physics, 34 (1994), 368-373.[3] S. Wiesen, JET ITC-Report, (2006), http://www.eirene.de/e2deir report 30jun06.pdfCorresponding author: tel.: +358(40)257-44-98, e-mail: vladimir.solokha@aalto.fi (V. Solokah)
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