Hydrogen Plasma Achieved in German Stellarator

One of the world’s largest stellarators generated its first hydrogen plasma on Feb. 3, 2016, marking progress toward development of a power plant favorable to the environment that derives energy from the fusion of atomic nuclei.

Since December 2015, Wendelstein 7-X fusion device at Max Planck Institute for Plasma Physics (IPP) in Greifswald produced more than 300 discharges with the rare gas helium. These discharges served primarily to clean the plasma vessel. The cleaner the vessel wall, the more the plasma temperature increased, finally attaining six million degrees. In addition, plasma heating and data recording were tested, and the first measuring facilities for investigating the plasma were put into operation, including X-ray spectrometers, interferometers, laser scattering and video diagnostics.

“This makes everything ready for the next step,” says Project Head Professor Dr. Thomas Klinger. “We are changing from helium to hydrogen plasmas, our proper subject of investigation.”

At the start of scientific operation of Wendelstein 7-X, a 2-megawatt pulse of microwave heating transformed hydrogen gas into low-density hydrogen plasma. This entails separating the electrons from the nuclei of the hydrogen atoms. Confined in the magnetic cage generated by Wendelstein 7-X, the charged particles levitate without making contact with the walls of the plasma chamber.

“With a temperature of 80 million degrees and a lifetime of a quarter of a second, the device’s first hydrogen plasma has completely lived up to our expectations,” says Dr. Hans-Stephan Bosch, whose division is responsible for operation of Wendelstein 7-X.

The initial experimentation phase will last till mid-March. The plasma vessel will then be opened in order to install carbon tiles to protect the vessel walls, and a so-called “divertor” for removing impurities.

“These facilities will enable us to attain higher heating powers, higher temperatures, and longer discharges lasting up to ten seconds,” says Klinger. Successive extensions are planned until, in about four years, discharges lasting 30 minutes can be produced and it can be checked at the full heating power of 20 megawatts.