Speaker
Thomas Windisch
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1098.pdf
Reflectometry at Wendelstein 7-X:
Initial results from the first island divertor campaign
T Windisch1 , D Carralero2 , T Estrada2 , A Krämer-Flecken3 , GM Weir1
1 Max-Planck-Institute for Plasma Physics, Greifswald, Germany
2 Centro de Investigationes, Medioambientales y Technologicas (CIEMAT), Madrid, Spain
3 Institut für Energie- und Klimaforschung, Forschungszentrum Jülich, Germany
The different reflectometry diagnostic systems at W7-X are versatile tools for investigating
the coherence and poloidal propagation of density fluctuations. Doppler reflectometry systems
with fixed tilt angles θ = 18 ◦ in V-band (o−mode) and W-band (x−mode) are used to derive
radial electric field Er in a broad density range ne = 0.75 . . . 14 · 1019 m−3 . A poloidal correlation
reflectometry (PCR) system in K/Ka -band (o−mode) operates in an radially overlapping region
with the W -band Doppler system and allows for cross-calibration of the necessary assumptions
in the derivation of Er . With a novel Doppler phased array antenna (W-band) the tilt angle can
be modified without movable parts. This allows to measure the fluctuation spectrum in a broad
wavenumber range k⊥ ≤ 15 cm−1 . The radial accessible range extends across the separatrix to
the scrape-off layer (SOL) region. In contrast to the first operation phase with a limiter con-
figuration [1, 2], the SOL is dominated by a m/n = 5/5 island chain which intersects with the
divertor tiles. The paper introduces the capabilities of the individual reflectometry systems and
presents initial results from the first W7-X island divertor campaign. Special attention is paid to
the 5/5 island in the SOL where strong modifications of fluctuations characteristics and Er are
typically observed.
References
[1] T Windisch et al. Plasma Phys. Control. Fusion 59 105002 (2017)
[2] A Krämer-Flecken et al. Nucl. Fusion 57 066023 (2017)
