Overview of first Wendelstein 7-X high-performance operation

Media type: E-Article
Title: Overview of first Wendelstein 7-X high-performance operation
Contributor: Klinger, T.; Andreeva, T.; Bozhenkov, S.; Brandt, C.; Burhenn, R.; Buttenschön, B.; Fuchert, G.; Geiger, B.; Grulke, O.; Laqua, H.P.; Pablant, N.; Rahbarnia, K.; Stange, T.; von Stechow, A.; Tamura, N.; Thomsen, H.; Turkin, Y.; Wegner, T.; Abramovic, I.; Äkäslompolo, S.; Alcuson, J.; Aleynikov, P.; Aleynikova, K.; Ali, A.; [...]
imprint: IOP Publishing, 2019
Published in: Nuclear Fusion
Language: Not determined
DOI: 10.1088/1741-4326/ab03a7
ISSN: 0029-5515; 1741-4326
Keywords: Condensed Matter Physics ; Nuclear and High Energy Physics
Origination:
Footnote:
Description: <jats:title>Abstract</jats:title> <jats:p>The optimized superconducting stellarator device Wendelstein 7-X (with major radius <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn001.gif" xlink:type="simple" /> </jats:inline-formula>, minor radius <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn002.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn003.gif" xlink:type="simple" /> </jats:inline-formula> plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn004.gif" xlink:type="simple" /> </jats:inline-formula> with central electron temperatures <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn005.gif" xlink:type="simple" /> </jats:inline-formula> were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn006.gif" xlink:type="simple" /> </jats:inline-formula> were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn007.gif" xlink:type="simple" /> </jats:inline-formula> a temperature of <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn008.gif" xlink:type="simple" /> </jats:inline-formula> with <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn009.gif" xlink:type="simple" /> </jats:inline-formula> was transiently accomplished, which corresponds to <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn010.gif" xlink:type="simple" /> </jats:inline-formula> with a peak diamagnetic energy of <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn011.gif" xlink:type="simple" /> </jats:inline-formula> and volume-averaged normalized plasma pressure <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn012.gif" xlink:type="simple" /> </jats:inline-formula>. The routine access to high plasma densities was opened with boronization of the first wall. After boronization, the oxygen impurity content was reduced by a factor of 10, the carbon impurity content by a factor of 5. The reduced (edge) plasma radiation level gives routinely access to higher densities without radiation collapse, e.g. well above <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn013.gif" xlink:type="simple" /> </jats:inline-formula> line integrated density and <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nfab03a7ieqn014.gif" xlink:type="simple" /> </jats:inline-formula> central temperatures at moderate ECRH power. Both X2 and O2 mode ECRH schemes were successfully applied. Core turbulence was measured with a phase contrast imaging diagnostic and suppression of turbulence during pellet injection was observed.</jats:p>

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