Written by Tim Lash, Focus Fusion Society Contributor. Edited by Ignas Galvelis, Supervising Director.
At the Max Planck Institute for Plasma Physics (MPIPP) in Greifswald Germany, a team of scientists and engineers continue working to bring the worlds largest stellarator online. A stellarator is a type of toroidal magnetic confinement fusion reactor. The most common form of toroidal fusion reactor is a tokamak. Tokamaks are shaped like ordinary doughnuts. Stellarators retain the basic doughnut shape but twists its way around to make the loop. This design, while far more complex, allows physicists to craft more ideal magnetic confinement fields. The machine under construction in Germany is called the Wendelstein 7-X (W7-X).
The W7-X was first powered up at the end of 2015. However, it did not produce plasma until February of 2016. A series of initial operational tests ran for several months followed by a shut-down period. This current shut-down period enables completion of the reactor’s interior. The interior requires a lining of carbon tiles to act as a thermal barrier as plasma electron temperatures approached 100 million degrees. At higher plasma temperatures the tiles protect the confinement vessel walls from melting. A plasma diverter is also being installed to cull hot plasma that escapes the confinement field. This escaping high energy plasma needs to be removed before it can impact the reactor walls. Such impacts can potentially pierce the reactor vessel, or at the very least introduce impurities into the plasma.
Another round of testing is nearing to evaluate the diverter design. Assuming that design proves functional another shut-down will follow. At that time water cooling will be added to the carbon tiles. Introducing a coolant loop into the device brings another set of engineering challenges. Yet this active cooling component will allow the reactor to run at design power of 10 MW for thirty minutes. That level of operation will allow for a full program of fusion research to begin in this stellarator design. An interesting project, but still far behind many competing fusion projects. The W7-X is scheduled to be brought back online in 2018.
So far it has been smooth sailing for the W7-X. Initial measurements of the magnetic confinement field demonstrated results that exceeded prediction.