The Wendelstein 7-X (W7-X) reactor is an experimental nuclear fusion reactor called a stellarator. The W7-X is located in Greifswald, Germany at the Max Planck Institute of Plasma Physics(IPP). It was completed in October 2015.
The first stellerator was built at what is now the Princeton Plasma Physics Laboratory in 1958 to explore nuclear fusion as a possible power source. Stellerators use powerful magnetic fields to compress hot plasma in a circular tube to create a fusion reaction. In order to deal with unequal magnetic force on the plasma caused by the circular shape, complex geometries were evolved as well as complex arrangements of magnetic coils. They were popular in the 1950s and 1960s but the tokamak fusion reactor design then became more popular. In a tokamak, just magnetic fields and a current running through the plasma is used for confinement. Eventually, problems with the tokamak design led researchers to return to the stellerator design.
The W7-X is the biggest stellerator in the world. It was designed to run for thirty minutes to test continuous operation. It is donut shaped with ten feet high magnetic coils around the circular tube. The main components of the W7-X are magnetic coils, a cryostat (which cools the magnets), a plasma vessel, a divertor (which removes heavier ions created by the fusion reaction) and heating system (to heat the plasma.) It will reach a particle density of 3 X 1020 particles per cubic meter and a temperature of 130 million Kelvins. ( the Kelvin scale uses the same units as the Celsius scale - one unit of the Celsius scale is equal to 9/5 of one unit on the Fahrenheit scale. 0 on the Celsius scale is 293 on the Kelvin scale.) The size of the donut or torus is about sixteen feet in diameter. The cryostat surrounds the torus and keeps the magnets cooled to a superconducting temperature of 4 degrees Kelvin.
Last year, the W7-X was turned on for the first time and was able to contain a helium plasma. This year, it has demonstrated that it is able to contain a hydrogen plasma. Tests show that the accuracy of the geometry of the complex 3-D magnetic field configuration has an error of less than one part in one hundred thousand. The field configuration is critical to the operation of the W7-X and this level of accuracy is an excellent demonstration of the engineering on the W7-X.
Work will continue on the W7-X until 2019 when it is expected to demonstrate the ability to contain a deuterium plasma and actually produce fusion reactions. It will still not be able to produce more power than it consumes but it will bring fusion research one step closer to the goal of a commercial fusion power reactor.
The W7-X is in direct competition with the giant ITER fusion research project being conducted by an international consortium in France. The ITER is based on a tokamak design. Meantime, there are at least half a dozen fusion research projects in the U.S. where teams of engineers and scientists are exploring alternative designs and fuels for fusion reactors. If any of them are successful, they will be able to create commercial fusion at a size and cost that is a fraction of the resources being expended on the W7-X and ITER reactors.
Wendelstein 7-X under construction:
