Magnetic configuration effects on the Wendelstein 7-X stellarator

the W7-X Team

Research output: Contribution to journalArticlepeer-review

128 Scopus citations

Abstract

The two leading concepts for confining high-temperature fusion plasmas are the tokamak and the stellarator. Tokamaks are rotationally symmetric and use a large plasma current to achieve confinement, whereas stellarators are non-axisymmetric and employ three-dimensionally shaped magnetic field coils to twist the field and confine the plasma. As a result, the magnetic field of a stellarator needs to be carefully designed to minimize the collisional transport arising from poorly confined particle orbits, which would otherwise cause excessive power losses at high plasma temperatures. In addition, this type of transport leads to the appearance of a net toroidal plasma current, the so-called bootstrap current. Here, we analyse results from the first experimental campaign of the Wendelstein 7-X stellarator, showing that its magnetic-field design allows good control of bootstrap currents and collisional transport. The energy confinement time is among the best ever achieved in stellarators, both in absolute figures (τE > 100 ms) and relative to the stellarator confinement scaling. The bootstrap current responds as predicted to changes in the magnetic mirror ratio. These initial experiments confirm several theoretically predicted properties of Wendelstein 7-X plasmas, and already indicate consistency with optimization measures.

Original languageEnglish
Pages (from-to)855-860
Number of pages6
JournalNature Physics
Volume14
Issue number8
DOIs
StatePublished - Aug 1 2018

Funding

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014– 2018 under grant agreement 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. This work is partially supported by the US Department of Energy under a project agreement with the Max Planck Institute for Plasma Physics.

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