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SUMMARY:Overview of first Wendelstein 7-X high-performance operation with
island divertor
DTSTART;VALUE=DATE-TIME:20181023T083000Z
DTEND;VALUE=DATE-TIME:20181023T085500Z
DTSTAMP;VALUE=DATE-TIME:20210306T235356Z
UID:indico-contribution-5949@conferences.iaea.org
DESCRIPTION:Speakers: Thomas Klinger (Max-Planck Institute for Plasma Phys
ics)\nThe optimized superconducting stellarator device Wendelstein 7-X res
tarted operation after the assembly of a graphite heat shield and an inert
ially cooled island divertor. This paper reports on results from the first
high-performance plasma operation. Plasma densities of $1-4\\cdot 10^{19}
\\\,\\mathrm{m}^{-3}$ with electron temperature $5-10\\\,\\mathrm{keV}$ we
re routinely achieved with hydrogen gas fuelling\, eventually terminated b
y a radiative collapse. Up to $1.4\\cdot 10^{20}\\\,\\mathrm{m}^{-3}$ plas
ma density was reached with repetitive hydrogen pellet injection. Here\, t
he\nions are indirectly heated\, and at a density of $8\\cdot 10^{19}\\\,\
\mathrm{m}^{-3}$ temperatures $T_e\\simeq T_i = 3.4\\\,\\mathrm{keV}$ were
accomplished\, which corresponds to $nT\\tau_E = 6.4\\cdot 10^{19}\\\,\\m
athrm{keVs/m}$ with peak diamagnetic energy $1.1\\\,\\mathrm{MJ}$. Stable
$25\\\,\\mathrm{s}$ long-pulse helium discharges with $2-3\\\,\\mathrm{M}$
W ECRH power and up to $75\\\,\\mathrm{MJ}$ injected energy were created r
outinely for equilibrium and divertor load studies\, with plasma densities
around $5\\cdot 10^{19}\\\,\\mathrm{m}^{-3}$ and $5\\\,\\mathrm{keV}$ ele
ctron temperature. The divertor heat loads remained far below the limits.
The O/C impurity concentration ratio has decreased in comparison to the pr
evious limiter operation and no intrinsic impurity accumulation along with
high edge radiation were observed in stationary plasmas. During pellet-fu
elled hydrogen discharges\, full detachment was observed with divertor tar
get heat flux reduction by more than $\\times 10$. Both X2 and O2 mode ECR
H schemes were applied and electron cyclotron current drive (ECCD) experim
ents were conducted. During co-ECCD injection experiments with axial curre
nts up to $13\\\,\\mathrm{kA}$\, frequent fast crashes were observed mainl
y in the core electron temperature\, suggesting a fast magnetic reconnecti
on mechanism. The radial electric field measured with (Doppler) and correl
ation reflectometry changes sign at the plasma edge from\n$+10\\ldots+20\\
\,\\mathrm{kV/m}$ to $-10\\ldots-5\\\,\\mathrm{kV/m}$\, fairly independent
of discharge parameters and heating power. Edge and scrape-off layer turb
ulence was measured with both Langmuir probes and reflectometer diagnostic
s. Core turbulence was measured with a phase contrast imaging diagnostic a
nd different levels of broad band turbulence as well as coherent Alfvén m
ode activity were observed.\n\nhttps://conferences.iaea.org/event/151/cont
ributions/5949/
LOCATION:Mahatma Mandir Conference Centre
URL:https://conferences.iaea.org/event/151/contributions/5949/
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