Wendelstein 7-X
Encyclopedia
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...
(nuclear fusion reactor
Fusion power
Fusion power is the power generated by nuclear fusion processes. In fusion reactions two light atomic nuclei fuse together to form a heavier nucleus . In doing so they release a comparatively large amount of energy arising from the binding energy due to the strong nuclear force which is manifested...
) currently being built in Greifswald
Greifswald
Greifswald , officially, the University and Hanseatic City of Greifswald is a town in northeastern Germany. It is situated in the state of Mecklenburg-Vorpommern, at an equal distance of about from Germany's two largest cities, Berlin and Hamburg. The town borders the Baltic Sea, and is crossed...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
by the Max-Planck-Institut für Plasmaphysik
Max-Planck-Institut für Plasmaphysik
The Max-Planck-Institut für Plasmaphysik is a physics institute for the investigation of plasma physics, with the aim of working towards fusion power...
(IPP), which will be completed by 2015. It is a further development of Wendelstein 7-AS. The purpose of Wendelstein 7-X is to evaluate the main components of a future fusion reactor built using stellarator
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...
technology, even if Wendelstein 7-X itself is not an economical fusion power plant.
The goal of fusion research is to produce energy in a roughly similar fashion as the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. To ignite the fusion in a stellarator, the plasma must be confined by magnetic fields and heated to 100 million kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
; this is not quite the same as what happens inside the Sun, which confines its plasma mainly by gravity and ignites it through extreme pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
rather than extreme temperatures (the Sun is very hot at its core, but is estimated to be at "only" 15 million kelvin rather than 100 million); however, the gravity of the Sun cannot be created artificially on Earth, and very high temperatures are considerably easier to create on Earth than very high pressures.
Wendelstein 7-X, when finished, will be the largest fusion device created using the stellarator
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...
concept. It is planned to operate with up to 30 minutes of continuous plasma discharge, demonstrating an essential feature of a future power plant: continuous operation.
Design and main components
Wendelstein 7-X is mainly a toroidToroid (geometry)
In mathematics, a toroid is a doughnut-shaped object, such as an O-ring. Its annular shape is generated by revolving a plane geometrical figure about an axis external to that figure which is parallel to the plane of the figure and does not intersect the figure...
, consisting of 50 non-planar and 20 planar superconducting magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
ic coils
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
, 3.5 m high, which induce a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
that prevents the plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
from colliding with the reactor walls. The 50 non-planar coils are used for adjusting the magnetic field.
The main components are the magnetic coils, cryostat
Cryostat
A cryostat is a device used to maintain cold cryogenic temperatures. Low temperatures may be maintained within a cryostat by using various refrigeration methods, most commonly using cryogenic fluid bath such as liquid helium. Hence it is usually assembled into a vessel, similar in construction...
, plasma vessel, divertor and heating systems.
The coils are arranged around a heat insulating cladding which is 16 meters in diameter called the cryostat. A cooling device produces enough liquid helium to carry away 5,000 watts of heating power to cool down the magnets and their enclosure (about 425 metric tons) to superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...
temperature. The plasma vessel, built of 20 parts, is on the inside, adjusted to the complex shape of the magnetic field. It has 299 holes for plasma heating and observation diagnostics. The whole plant is built of 5 almost identical modules, which are assembled in the experiment hall.