This title appears in the Scientific Report :
2021
Measure and properties of heat load profiles on the lower tungsten divertor of WEST in L-mode experiments
Measure and properties of heat load profiles on the lower tungsten divertor of WEST in L-mode experiments
Measure and properties of heat load profiles on the lower tungsten divertor of WEST in L-mode experimentsN. Fedorczaka,*, J. Gasparb, J.P. Gunna, Y. Correa, A. Grosjeana, R. Mitteaua, C. Desgrangesa, R. Dejarnacc, M. Dimitrovac,e, Tsv. K. Popovd,e, J. Bucalossia, E. Tsitronea, T. Loarera, S. Brezi...
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Personal Name(s): | Fedorczak, N. |
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Gaspar, J. / Gunn, J. P. / Corre, Y. / Grosjean, A. / Mitteau, R. / Desgranges, C. / Dejarnac, R. / Dimitrova, M. / Popov, Tsv. K. / Bucalossi, J. / Tsitrone, E. / Loarer, T. / Brezinsek, S. (Corresponding author) | |
Contributing Institute: |
Helmholtz-Institut Erlangen-Nürnberg Erneuerbare Energien; IEK-11 Plasmaphysik; IEK-4 |
Imprint: |
2021
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Conference: | 24th International Conference on Plasma Surface Interactions in Controlled Fusion Devices (PSI 2020), virtuell (virtuell), 2021-01-25 - 2021-01-29 |
Document Type: |
Abstract |
Research Program: |
Plasma-Wand-Wechselwirkung |
Publikationsportal JuSER |
Measure and properties of heat load profiles on the lower tungsten divertor of WEST in L-mode experimentsN. Fedorczaka,*, J. Gasparb, J.P. Gunna, Y. Correa, A. Grosjeana, R. Mitteaua, C. Desgrangesa, R. Dejarnacc, M. Dimitrovac,e, Tsv. K. Popovd,e, J. Bucalossia, E. Tsitronea, T. Loarera, S. Brezinsekf and the WEST team* a CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, Franceb Aix Marseille Univ, CNRS, IUSTI, Marseille, Francec Institute of Plasma Physics, The Czech Academy of Sciences, 182 00 Prague 8, Czech Republicd NIS-Faculty of Physics, St Kliment Ohridski University of Sofia, 1164 Sofia, Bulgariae Emil Djakov Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgariaf Forschungszentrum Jülich, Institut für Energie- und Klimaforschung Plasmaphysik, 52425 Jülich, Germany* See http://west.cea.fr/WESTteamDuring the first phase of WEST tokamak operation, the main lower divertor was composed of a mix of actively cooled tungsten monoblocs and uncooled tungsten-coated graphite plasma-facing components. It exhausted approximately 7.5GJ of conducted energy over 2400 pulses. A set of complementary diagnostics allowed characterizing properties of divertor heat & particle loads on the inertial components: arrays of embedded thermocouples and fiber Bragg gratings, infra-red thermography on both strike point areas within the same field-of-view, and arrays of flush-mounted Langmuir probes. Heat load properties are investigated across a wide range of L-mode conditions: Deuterium and Helium plasmas, from 1 to 9 MW of additional power (LHCD+ICRH), plasma currents from 300 kA to 800 kA at nominal magnetic field BT=3.6T, and various X-point height with respect to the flat divertor (impacting both strike point position & target magnetic flux expansion). We report on the continuous effort made to benchmark the diagnostics and improve the accuracy of heat load analyses. Flushed Langmuir probes were cross calibrated during slow strike point sweepings over the probe arrays, confirming the accurate alignment of the flushed collectors with respect to tile surface. In addition, comparisons with a protruding probe proved the accuracy of a simple model for effective collection area of flushed probes, validating the concept of flushed probes for measuring particle fluxes and electron temperature. Surface heat loads were conjointly estimated from embedded thermal sensors and infra-red thermography at . Arrays of fiber Bragg gratings were installed a few millimetres below the surface of uncooled tiles, providing local bulk temperature dynamics with a spatial resolution of 10mm. This resolution is sufficient to invert temperatures into surface heat load, assuming some geometrical properties of heat load pattern. In particular it was assumed that heat load patterns follow a common gaussian-exponential shape, with unknown widths and amplitude. This shape was confirmed by infra-red thermography. On the other hand, thermography was proven to suffer from ambience reflections and change of surface emissivity during the campaigns, which add difficulties in estimating absolute heat load values from thermography inversion. This critical issue in metallic devices with low surface emissivity is addressed by combining thermography and embedded thermal measurements [1]. Resulting reflection and emissivity maps are shown to vary strongly in space, possibly due to evolving surfaces under erosion and redeposition. Finally, global properties of the lower divertor heat flux pattern in WEST large aspect ratio tokamak will be discussed and confronted to current knowledge of L-mode diverted regimes. [1] J. Gaspar, this conference. *Corresponding author: tel.: +33442253712 e-mail: Nicolas.fedorczak@cea.fr |