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Beidler, C. D.; Smith, H. M.; Alonso, A.; Andreeva, T.; Baldzuhn, J.; Beurskens, M. N. A.; Borchardt, M.; Bozhenkov, S. A.; Brunner, K. J.; Damm, H.; Drevlak, M.; Ford, O. P.; Fuchert, G.; Geiger, J.; Helander, P.; Hergenhahn, U.; Hirsch, M.; Höfel, U.; Kazakov, Ye. O.; Kleiber, R.; Krychowiak, M.; Kwak, S.; Langenberg, A.; Laqua, H. P.; [...]

Demonstration of reduced neoclassical energy transport in Wendelstein 7-X

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  • Media type: E-Article
  • Title: Demonstration of reduced neoclassical energy transport in Wendelstein 7-X
  • Contributor: Beidler, C. D.; Smith, H. M.; Alonso, A.; Andreeva, T.; Baldzuhn, J.; Beurskens, M. N. A.; Borchardt, M.; Bozhenkov, S. A.; Brunner, K. J.; Damm, H.; Drevlak, M.; Ford, O. P.; Fuchert, G.; Geiger, J.; Helander, P.; Hergenhahn, U.; Hirsch, M.; Höfel, U.; Kazakov, Ye. O.; Kleiber, R.; Krychowiak, M.; Kwak, S.; Langenberg, A.; Laqua, H. P.; [...]
  • imprint: Springer Science and Business Media LLC, 2021
  • Published in: Nature
  • Language: English
  • DOI: 10.1038/s41586-021-03687-w
  • ISSN: 0028-0836; 1476-4687
  • Keywords: Multidisciplinary
  • Origination:
  • Footnote:
  • Description: <jats:title>Abstract</jats:title><jats:p>Research on magnetic confinement of high-temperature plasmas has the ultimate goal of harnessing nuclear fusion for the production of electricity. Although the tokamak<jats:sup>1</jats:sup> is the leading toroidal magnetic-confinement concept, it is not without shortcomings and the fusion community has therefore also pursued alternative concepts such as the stellarator. Unlike axisymmetric tokamaks, stellarators possess a three-dimensional (3D) magnetic field geometry. The availability of this additional dimension opens up an extensive configuration space for computational optimization of both the field geometry itself and the current-carrying coils that produce it. Such an optimization was undertaken in designing Wendelstein 7-X (W7-X)<jats:sup>2</jats:sup>, a large helical-axis advanced stellarator (HELIAS), which began operation in 2015 at Greifswald, Germany. A major drawback of 3D magnetic field geometry, however, is that it introduces a strong temperature dependence into the stellarator’s non-turbulent ‘neoclassical’ energy transport. Indeed, such energy losses will become prohibitive in high-temperature reactor plasmas unless a strong reduction of the geometrical factor associated with this transport can be achieved; such a reduction was therefore a principal goal of the design of W7-X. In spite of the modest heating power currently available, W7-X has already been able to achieve high-temperature plasma conditions during its 2017 and 2018 experimental campaigns, producing record values of the fusion triple product for such stellarator plasmas<jats:sup>3,4</jats:sup>. The triple product of plasma density, ion temperature and energy confinement time is used in fusion research as a figure of merit, as it must attain a certain threshold value before net-energy-producing operation of a reactor becomes possible<jats:sup>1,5</jats:sup>. Here we demonstrate that such record values provide evidence for reduced neoclassical energy transport in W7-X, as the plasma profiles that produced these results could not have been obtained in stellarators lacking a comparably high level of neoclassical optimization.</jats:p>