The first plasma:
the Wendelstein 7-X fusion device is now in operation
December
10, 2015
On
10th December 2015 the first helium plasma was produced in the Wendelstein 7-X
fusion device at the Max Planck Institute for Plasma Physics (IPP) in
Greifswald. After more than a year of technical preparations and tests,
experimental operation has now commenced according to plan. Wendelstein 7-X,
the world’s largest stellarator-type fusion device, will investigate the
suitability of this type of device for a power station.
10th December 2015: The first plasma
in Wendelstein 7-X. It consisted of helium and reached a temperature of about
one ... [more]
Foto: IPP
Following nine years of construction work and more than a
million assembly hours, the main assembly of the Wendelstein 7-X was completed
in April 2014. The operational preparations have been under way ever since.
Each technical system was tested in turn, the vacuum in the vessels, the
cooling system, the superconducting coils and the magnetic field they produce,
the control system, as well as the heating devices and measuring instruments.
On 10th December, the day had arrived: the operating team in the control room
started up the magnetic field and initiated the computer-operated experiment
control system. It fed around one milligram of helium gas into the evacuated
plasma vessel, switched on the microwave heating for a short 1,3 megawatt pulse
– and the first plasma could be observed by the installed cameras and measuring
devices. “We’re starting with a plasma produced from the noble gas helium.
We’re not changing over to the actual investigation object, a hydrogen plasma,
until next year,” explains project leader Professor Thomas Klinger: “This is
because it’s easier to achieve the plasma state with helium. In addition, we
can clean the surface of the plasma vessel with helium plasmas.”
The first plasma in the machine had a duration of one tenth of a second and achieved a temperature of around one million degrees. “We’re very satisfied”, concludes Dr. Hans-Stephan Bosch, whose division is responsible for the operation of the Wendelstein 7-X, at the end of the first day of experimentation. “Everything went according to plan.” The next task will be to extend the duration of the plasma discharges and to investigate the best method of producing and heating helium plasmas using microwaves. After a break for New Year, confinement studies will continue in January, which will prepare the way for producing the first plasma from hydrogen.
The first plasma in the machine had a duration of one tenth of a second and achieved a temperature of around one million degrees. “We’re very satisfied”, concludes Dr. Hans-Stephan Bosch, whose division is responsible for the operation of the Wendelstein 7-X, at the end of the first day of experimentation. “Everything went according to plan.” The next task will be to extend the duration of the plasma discharges and to investigate the best method of producing and heating helium plasmas using microwaves. After a break for New Year, confinement studies will continue in January, which will prepare the way for producing the first plasma from hydrogen.
Background
For comparison: View into the empty
plasma vessel, recorded by a black-white-camera installed inside the plasma
vessel ... [more]
Photo: IPP
The
objective of fusion research is to develop a power source that is friendly to
the climate and, similarly to the sun, harvests energy from the fusion of
atomic nuclei. As the fusion fire only ignites at temperatures of more than 100
million degrees, the fuel – a thin hydrogen plasma – must not come into contact
with cold vessel walls. Confined by magnetic fields, it floats virtually free
from contact within the interior of a vacuum chamber. For the magnetic cage,
two different designs have prevailed – the tokamak and the stellarator. Both
types of system are being investigated at the IPP. In Garching, the Tokamak
ASDEX Upgrade is in operation and, as of today, the Wendelstein 7-X stellarator
is operating in Greifswald.
At
present, only a tokamak is thought to be capable of producing an
energy-supplying plasma and this is the international test reactor ITER, which
is currently being constructed in Cadarache in the frame of a worldwide
collaboration. Wendelstein 7-X, the world's largest stellarator-type fusion
device, will not produce energy. Nevertheless, it should demonstrate that
stellarators are also suitable as a power plant. Wendelstein 7-X is to put the
quality of the plasma equilibrium and confinement on a par with that of a
tokamak for the very first time. And with discharges lasting 30 minutes, the
stellarator should demonstrate its fundamental advantage – the ability to
operate continuously. In contrast, tokamaks can only operate in pulses without
auxiliary equipment.
The
assembly of Wendelstein 7-X began in April 2005: a ring of 50 superconducting
coils, some 3.5 metres high, is the key part of the device. Their special
shapes are the result of refined optimisation calculations carried out by the
“Stellarator Theory Department”, which spent more than ten years searching for
a magnetic cage that is particularly heat insulating. The coils are threaded
onto a ring-shaped steel plasma vessel and encased by a steel shell. In the
vacuum created inside the shell, the coils are cooled down to superconduction
temperature close to absolute zero using liquid helium. Once switched on, they
consume hardly any energy. The magnetic cage that they create, keeps the 30
cubic metres of ultra-thin plasma – the object of the investigation – suspended
inside the plasma vessel.
The
Wendelstein 7-X fusion device
Photo:
IPP, Thorsten Bräuer
The
investment costs for Wendelstein 7-X amount to 370 million euros and are being
met by the federal and state governments, and also by the EU. The components
were manufactured by companies throughout Europe. Orders in excess of 70
million euros were placed with companies in the region. Numerous research
facilities at home and abroad were involved in the construction of the device.
Within the framework of the Helmholtz Association of German Research Centres,
the Karlsruhe Institute of Technology was responsible for the microwave plasma
heating; the Jülich Research Centre built measuring instruments and produced
the elaborate connections for the superconducting magnetic coils. Installation
was carried out by specialists from the Polish Academy of Science in Krakow.
The American fusion research institutes at Princeton, Oak Ridge and Los Alamos
contributed equipment for the Wendelstein 7-X that included auxiliary coils and
measuring instruments.
Isabella Milch
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