Confinement in Wendelstein 7-X limiter plasmas

Hirsch, M.; Dinklage, A.; Alonso, A.; Fuchert, G.; Bozhenkov, S.; Höfel, U.; Andreeva, T.; Baldzuhn, J.; Beurskens, M.; Bosch, H.‐S.; Beidler, C. D.; Biedermann, C.; Blanco, E.; Brakel, R.; Burhenn, R.; Buttenschön, B.; Cappa, Á.; Czarnecka, A.; Endler, M.; Estrada, T.; Fornal, T.; Geiger, J.; Grulke, O.; Harris, J. H.; Hartmann, D.; Jakubowski, M.; Klinger, T.; Knauer, J.; Kocsis, G.; König, R.; Kornejew, P.; Krämer–Flecken, A.; Krawczyk, N.; Krychowiak, M.; Kubkowska, M.; Książek, I.; Langenberg, A.; Laqua, H. P.; Lazerson, S.; Maaßberg, H.; Marushchenko, N. B.; Marsen, S.; Moncada, V.; Moseev, D.; Naujoks, D.; Otte, M.; Pablant, N.; Pasch, E.; Pisano, F.; Schröder, T.; Stange, T.; Stephey, L.; Szepesi, T.; Pedersen, T. S.; Mora, H. Trimiño; Thomsen, H.; Takahashi, Hayato; Turkin, Y.; Wauters, T.; Weir, G.; Wenzel, U.; Werner, A.; Wolf, R. C.; Wurden, G. A.; Zhang, D.

doi:10.1088/1741-4326/aa7372

Cited by 17 publications

(15 citation statements)

References 18 publications

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“…4. Comparing with tokamak data (rephrased to the stellarator scaling ISS04 [26,27]), the energy confinement time of W7-X limiter plasmas [28] is well within the range of tokamak high-confinement (H-mode) plasmas, which is the reference for achieving a burning fusion plasma in ITER (Pfusion/Pheating = 10) [29].…”

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confidence: 99%

Magnetic configuration effects on the Wendelstein 7-X stellarator

et al. 2018

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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 nonaxisymmetric 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 minimise 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 (E > 100ms) 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 W7-X plasmas, and already indicate consistency with optimisation measures.

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confidence: 99%

Magnetic configuration effects on the Wendelstein 7-X stellarator

et al. 2018

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“…Good diagnostic coverage is essential for physics studies at W7-X. In particular, profile information for electron temperature and density is necessary, for example, for confinement and transport studies [12,13], for investigations of profile resilience with ECRH deposition [8], and is also an important input for numerical codes. At W7-X the Thomson scattering system is a standard profile diagnostic for electron temperature and density.…”

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confidence: 99%

The Thomson scattering diagnostic at Wendelstein 7-X and its performance in the first operation phase

et al. 2017

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The optimized stellarator Wendelstein 7-X started operation in December 2015 with a 10 week limiter campaign. Divertor experiments will begin in the second half of 2017. The W7-X Thomson scattering system is an essential diagnostic for electron density and temperature profiles. In this paper the Thomson scattering diagnostic is described in detail, including its design, calibration, data evaluation and first experimental results. Plans for further development are also presented. The W7-X Thomson system is a Nd:YAG setup with up to five lasers, two sets of light collection lenses viewing the entire plasma cross-section, fiber bundles and filter based polychromators. To reduce hardware costs, two or three scattering volumes are measured with a single polychromator. The relative spectral calibration is carried out with the aid of a broadband supercontinuum light source. The absolute calibration is performed by observing Raman scattering in nitrogen. The electron temperatures and densities are recovered by Bayesian modelling. In the first campaign, the diagnostic was equipped for 10 scattering volumes. It provided temperature profiles comparable to those measured using an electron cyclotron emission diagnostic and line integrated densities within 10% of those from a dispersion interferometer.

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“…The experimental programs during OP1.1 were predominantly planned to commission the machine together with operational diagnostic systems [7]. Additionally a number of experiments addressed aspects of the optim ization of W7-X [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%