Characterization of injection and confinement improvement through impurity induced profile modifications on the Wendelstein 7-X stellarator

Lunsford, R.; Killer, C.; Nagy, A.; Gates, D. A.; Klinger, T.; Dinklage, A.; Satheeswaran, G.; Kocsis, G.; Lazerson, S. A.; Nespoli, F.; Pablant, N. A.; von Stechow, A.; Alonso, A.; Andreeva, T.; Beurskens, M.; Biedermann, C.; Brezinsek, S.; Brunner, K. J.; Buttenschön, B.; Carralero, D.; Cseh, G.; Drewelow, P.; Effenberg, F.; Estrada, T.; Ford, O. P.; Grulke, O.; Hergenhahn, U.; Höefel, U.; Knauer, J.; Krause, M.; Krychowiak, M.; Kwak, S.; Langenberg, A.; Neuner, U.; Nicolai, D.; Pavone, A.; Puig Sitjes, A.; Rahbarnia, K.; Schilling, J.; Svensson, J.; Szepesi, T.; Thomsen, H.; Wauters, T.; Windisch, T.; Winters, V.; Zhang, D.; Zsuga, L.

doi:10.1063/5.0047274

Title: Characterization of injection and confinement improvement through impurity induced profile modifications on the Wendelstein 7-X stellarator

Journal Article · 01 August 2021 · Physics of Plasmas

DOI: https://doi.org/10.1063/5.0047274 · OSTI ID:1812532

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Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Max Planck Institute for Plasma Physics, Greifswald (Germany)
Forschungszentrum Jülich, IEK-4 Plasmaphysik, Jülich 52428, Germany
Center for Energy Research, Budapest 1121, Hungary
Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540, USA
Max-Planck-Institut für Plasmaphysik, Greifswald 17491, Germany
Fusion National Laboratory, CIEMAT, Madrid 28040, Spain

Pulsed injections of boron carbide granules into Wendelstein 7-X stellarator (W7-X) plasmas transiently increase the plasma stored energy and core ion temperatures above the reference W7-X experimental programs by up to 30%. In a series of 4 MW electron cyclotron resonance heating experiments, the PPPL Probe Mounted Powder Injector provided 50 ms bursts of 100 μm granules every 350 ms at estimated quantities ranging from approximately 1 mg/pulse to over 30 mg/pulse. For each injection, the stored energy was observed to initially drop and the radiated power transiently increased, while the radial electron density profile rose at the edge as material was assimilated. Once the injected boron carbide was fully absorbed, the density rise transitioned to the core while the stored energy increased above the previous baseline level by an amount linearly correlated with the injection quantity. During the injection, the ion temperature gradient steepened with peak core ion temperatures observed to increase from a nominal 1.7 keV to over 2.6 keV for the largest injection amounts. Enhanced performance is accompanied by a reversal of the radial electric field at ρ < 0.3, indicating that the core transport has switched to the ion root. These observations are suggestive of a change in transport and provide further evidence that externally induced profile modifications provide a possible path to enhanced W7-X performance metrics.

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Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE

Contributing Organization:: W7-X Team

Grant/Contract Number:: AC02-09CH11466

OSTI ID:: 1812532

Journal Information:: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 8 Vol. 28; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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