All opinions expressed herein are those of the authors and should not be reproduced, quoted in publications,
or used as a reference without the author’s consent.
Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy.
Published by Oak Ridge National Laboratory
Building CR 5600 P.O. Box 2008 Oak Ridge, TN 37831-6169, USA
Editor: James A. Rome Issue 149 August 2015
E-Mail: jamesrome@gmail.com Phone (865) 482-5643
On the Web at http://www.ornl.gov/sci/fed/stelnews
Recent Milestones in the Wendelstein
7-X Commissioning
Since the last status report in Stellarator News 147, April
2015, the commissioning of Wendelstein 7-X (W7-X) has
continued very successfully! Although the evacuation of
the plasma vacuum revealed rather quickly that the seals
on all turbomolecular pumps had to be replaced, the next
evacuation was able to start in the middle of June after a
large effort of the assembly group. Further leak checks
indicated a few smaller leaks, which were immediately
repaired.
In April, the magnet system and the support structure had
been cooled down to 4 K, and tests of the two operation
modes began. The test of the short-standby mode (SSM)
and the standard mode (SM) were successfully finished by
the end of April.
Therefore, testing of the superconducting coils started on
April 27, 2015. After adjusting all the quench detection
(QD) systems, each of the 7 magnetic coils circuits (5 for
the nonplanar and 2 for the planar coils), with 10 identical
coils each, has been tested at currents up to 5–10 kA.
These tests of the single circuits were concluded by mid-
June with successful results: no quench, no insulation
fault, low resistance at all connections between coils and
bus system, and deformations and mechanical strains in
the expected range, as calculated from finite element
model (FEM) calculations. At the beginning of July the
magnetic coil system as a whole was made operational
within 7 working days. After a recheck of the quench
detection balancing, the limiter configuration was operated
at steps of 2, 6, and 10 kA, and with the full current
for 2.5 T, i.e., 12.8 kA. Later the standard configuration
was commissioned, too. Again, the mechanical movements
of all coils were measured and confirmed the FEM
simulations. In these phases, the He mass flow in all coils
and current leads had to be adjusted to get even cooling,
and the energy balance of the insulation and of the current
leads had to be reconfirmed. All the systems worked fine
and according to predictions.
In this final stage of the magnetic field testing, the first
magnetic flux surface measurements were performed and
revealed right from the start good magnetic surfaces, as
indicated in Fig. 1. With an electron gun, electrons were
created that move along the magnetic field and depict the
magnetic surfaces. With a fluorescent stick, which is mapping
the cross-section, a Poincaré plot is created that demonstrates
the flux surface. With this the most important
result of the W7-X assembly and commissioning has been
achieved: Wendelstein 7-X has been built with high precision
and has a magnetic field structure that will allow it to
successfully confine a plasma.
In the coming weeks, the plasma vessel is being baked to
150 °C to clean the inner surfaces, and when all cables,
peripheral components, and diagnostics and control sys-
Fig. 1. Well-formed flux surfaces were measured.
In this issue . . .
Recent Milestones in the Wendelstein 7-X Commissioning
Vacuum leaks were repaired and the W7-X coils were
tested individually and together, and everything was
in accord with specifications. The flux surfaces were
measured and were well formed. ........................... 1
Stellarator News -2- August 2015
tems are ready, the device will be ready for operation. First
plasmas are expected for later this fall.
PD Dr. Hans-Stephan Bosch
Director of Operations Wendelstein 7-X
Max-Planck-Institut für Plasmaphysik
Wendelsteinstr. 1
17491 Greifswald Germany
Tel. (03834) 88 - 2212/2000, Fax: -2709
E-mail: Hans-Stephan.Bosch@ipp.mpg.de