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Published by Oak Ridge National Laboratory
Building CR 5600 P.O. Box 2008 Oak Ridge, TN 37831-6169, USA
Editor: James A. Rome Issue 152 April 2016
E-Mail: jamesrome@gmail.com Phone (865) 482-5643
On the Web at http://www.ornl.gov/sci/fed/stelnews
First Wendelstein 7-X experimental
campaign successfully
completed
The first experimental campaign of Wendelstein 7-X (W7-
X), which began on 10 December 2015, was successfully
concluded after 10 weeks of intense and dedicated plasma
operation on 10 March 2016.
The day after the operational permit was granted by the
responsible authority, the “Landesamt für Gesundheit und
Soziales” (LAGuS), the first W7-X plasma was achieved.
The event was followed by numerous guests from the
world-wide science community —most of them by video
broadcast—and the national and international press.
During the first week of plasma operation, using helium
for the first part of the campaign, electron temperatures of
1 keV were achieved, corresponding to about 10 million
°C. The duration of the early plasma discharges was limited
to approximately 50 milliseconds by plasma radiation
from impurities that cool down the hot plasma core. After
the application of short consecutive pulses of electroncyclotron-
resonance heating (ECRH) and, once fully functional,
glow discharge cleaning, the conditioning of the
plasma vessel significantly improved and the plasma discharge
lengths could be extended to about 500 milliseconds.
The first hydrogen plasma (Fig. 1) was produced on 3 February
2016 during an inauguration ceremony in the presence
of the German Federal Chancellor Dr. Angela
Merkel. About 400 guests from science and politics
accepted an invitation and attended the event at IPP Greifswald.
Many fusion researchers and the interested public
around the world could participate by following the live
video stream.
Since these first discharges (see Fig. 2 for helium results),
an intense experimental program was conducted until 10
March 10. There was steady progress and finally plasmas
lasting up to 6 seconds could
Fig. 1. Video image of the first hydrogen plasma. The
image shows a tangential view into the plasma vessel with
wall structures and port openings (providing diagnostics
access). The visible light emission from the plasma forms
a three-dimensional torus, emitting at the edge (the hot
plasma core does not emit large amounts of visible light).
The interface between the confined plasma and the
boundary plasma is visible by the transition from low light
levels to the strongly light emitting regions (courtesy of IPP
in collaboration with Wigner RCP, Hungary).
In this issue . . .
First Wendelstein 7-X experimental campaign
successfully completed
The first experiments began on 10 December 2015,
and were more successful than expected. W7-X
exhibited extremely reliable operation and proper
interplay between the various technical systems, in
particular the cryoplant, the superconducting magnet
system, the device control, and the microwave tubes
of the ECRH system. .............................................. 1
US STELLCON Community Workshop
A workshop was held at MIT on February 16–17 to
discuss and define the stellarator design, physics,
and research needs of the US program. ................ 3
In memoriam: Julian Dunlap
Julian was head of the ATF stellarator in the 1980s–
early 1990s. ............................................................ 4
Stellarator News -2- April 2016
be achieved using 0.5 MW of ECRH power. The initial
limit for the energy injected into the plasma was doubled
from 2 MJ to 4 MJ, after it became evident that the plasma
limiters, which define the plasma boundary, were far from
reaching critical temperatures. Plasmas with the highest
densities and temperatures were achieved using 4 MW of
heating power applied for up to 1 second. At line-averaged
electron densities of about 2 1019 m3 the central temperatures
reached 10 keV (~100 million °C) for the electrons
and 1 keV (~10 million °C) for the ions. At slightly
higher densities close to 3  1019 m3, electron and ion
temperatures of about 7 keV and 2 keV, respectively, were
achieved.
The success of the first experimental campaign exceeded
our initial expectations. Originally, the aim was to perform
an integral commissioning of the W7-X plasma operation,
including ECRH and the first set of plasma diagnostics
(more than 20). However, swift progress enabled many indepth
physics studies. Not least, this was made possible by
the extremely reliable operation and proper interplay
between the various technical systems of W7-X, in particular
the cryoplant, the superconducting magnet system, the
device control, and the microwave tubes of the ECRH system.
Overall 940 discharge programs were performed; 92
of them were technical tests, 446 were dedicated to the
development of the basic plasma performance (e.g.,
plasma-vessel conditioning), and 402 were dedicated to
physics studies. This allowed for a first assessment of:
 the confinement properties of the W7-X magnetic
field configuration,
 transport at the plasma boundary,
 the influence of external error fields (produced by the
so-called trim coils) on the heat load distribution on
the plasma limiters,
 first electron-cyclotron current drive experiments,
 and second harmonic O-mode heating, which is
important for heating the plasma at high densities.
There was strong participation by our international partners,
and more than half of the physics program involved
collaborations: In about 40% of the physics experiments,
proposals were conducted in the frame of European collaborations
and in 24% with partners from the United
States. The largest part of the experiments, however,
involved all parties, which can be seen as a successful
implementation of the one-team approach.
After the completion of the first experimental phase, the
focus is now on careful analysis of the data. The measured
data have to be validated, which often means that diagnostic
calibrations have to be repeated. Numerical codes not
only support the evaluation of the experimental results but
also allow for a first comparison with theoretical predictions.
Preparations for the next experimental campaign have
already started. The plasma vessel has been vented and
many peripheral systems have been removed to gain
access to the plasma vessel. During the next 14 months,
the so-called test divertor unit (TDU) will be installed. It is
an inertially cooled island divertor with exactly the shape
of the water-cooled steady-state high heat flux divertor,
which is currently manufactured and is scheduled to be
installed after the next experimental campaign. With the
inertially cooled TDU and the full coverage of heat shields
Fig. 2. Radial profiles of electron densities (left) and plasma temperatures (right) of a helium plasma heated by 4 MW
of ECRH. The electron temperature and density can be obtained from scattering of laser light on the plasma electrons
(Thomson scattering). Electron cyclotron emission (ECE) measures the electron temperature. From imaging X-ray
spectroscopy (XICS), profiles of electron and ion temperatures can be inferred (courtesy of S. Bozhenkov, G. Fuchert,
M. Hirsch, A. Langenberg, N. Pablant and E. Pasch).
Stellarator News -3- April 2016
and baffles with carbon tiles, Wendelstein 7-X will be
ready for high-power plasmas (8 MW) lasting up to 10
seconds. This campaign is scheduled to start in the first
half of 2017.
The Wendelstein 7-X Team
IPP Greifswald, Greifswald Germany
US STELLCON Community
Workshop
A workshop was held at the Massachusetts Institute of
Technology (MIT) on February 16–17 to discuss and
define stellarator design, physics, and research needs for
the US program. Approximately 35 researchers from the
US fusion and plasma physics community attended and
contributed to the presentations and discussions. The
meeting was co-led by David Anderson (U. Wisconsin)
and David Gates (PPPL), and the local organization was
led by Abhay Ram (MIT). The agenda and presentations
are available online at
http://www-internal.psfc.mit.edu/STELLCON/Presentations/
Agenda_v6.html
Discussions on first day covered a range of scientific and
technical issues, organized by the following topics:
 Magnetic configurations (A. Boozer)
 Turbulence and transport optimization (H. Mynick)
 3D divertors (J. Lore)
 Plasma-material interface in 3D systems (D. Andruczyk)
 Fast particle confinement (D. Spong)
 MHD/high  (C. Hegna)
 Impurity confinement and accumulation (M. Landreman)
 Reactor issues (L. El-Guebaly)
 Design improvements and coil simplification
(D. Gates)
For each topic, a designated discussion leader (indicated
above) started by summarizing the key issues, their criticality
to overall progress, possible solutions, available
tools, and a ‘straw-man’ approach. The summaries incorporated
pre-meeting input from the research community.
Each initial summary was followed by an open discussion
of all aspects of the topic.
The second day started with a summary of the key issues
and ideas from the first-day discussions. This was followed
by discussions of the research approaches, tools,
and facilities needed to address the scientific issues from
the first day, organized in the following areas:
 Needs and priorities in analytic theory (J. Friedberg)
 Needs and priorities in code development and computation
(J. Canik)
 Needs and priorities in technology (J. Minervini)
 Issues best addressed experimentally on international
facilities (H. Neilson)
 Needs and priorities in the domestic experimental
program (S. Knowlton)
This was followed by a discussion led by D. Gates and D.
Anderson, of action items and plans for further work . In
general, the attendees reached substantial concensus in the
discussions of the research needs and new developments.
This was summarized to include the following conclusions:
 A computational tool is needed to evaluate and optimize
3D divertor configurations
 Advances and opportunities in turbulence optimization
are exciting, and experimental validation is
important
 New coil simplification approaches offer exciting
opportunities
 Detailed comparisons between experiments and
extended MHD are important and should be very
fruitful.
In addition, participants agreed to launch a comparative
study of optimized configurations with either quasi-helical
symmetry or quasi-axial symmetry. Several volunteers
agreed to take part and contribute to the study.
Finally, it was agreed that the topics, issues, and opportunities
discussed at the workshop will be summarized in a
community report, using the research-needs report format.
Contributing authors were identified and charged to draft
sections of the report, which will be circulated to the
attendees for discussion and completion. An additional
meeting may be held, if needed, to complete the report and
finalize the identified research needs and opportunities for
stellarators and 3D magnetic configurations in the US program.
M. Zarnstorff, PPPL
D. Anderson, University of Wisconsin, Madison
D. Gates, PPPL
Stellarator News -4- April 2016
In memoriam: Julian Dunlap
Julian Dunlap, who led the Experimental Plasma Physics
section of the ORNL Fusion Energy Division during the
operation of the ATF stellarator in the 1980s–early 1990s,
died unexpectedly on April 9 at age 84. Julian came to
ORNL in 1959 after completing his PhD at Vanderbilt
University, and worked on several mirror plasma confinement
experiments before switching to tokamak research
with the ORMAK machine. He led MHD stability studies
on the ORMAK and ISX-B tokamaks before becoming
section head during the ATF era. After ATF shut down in
1991, he worked on stability experiments on the PBX-M
tokamak at Princeton Plasma Physics Laboratory before
retiring in 1994. He was a Fellow of the American Physical
Society.

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