The Wendelstein 7-X (W7-X) stellarator at the Max Planck Institute for Plasma Physics (IPP) in Greifswald, Germany, produced its first hydrogen plasma on February 3, 2016. The milestone discharge was initiated with a 2-megawatt microwave pulse, heating a small quantity of hydrogen gas and confining the resulting plasma for approximately one-quarter of a second. Diagnostic measurements confirmed the successful formation of a plasma with an electron temperature of 80 million Kelvin and an ion temperature of 10 million Kelvin, marking the start of the device's operational phase. This follows the successful creation of the first helium plasma in December 2015, which served as a commissioning step to clean the plasma vessel's interior surfaces. Source: IEEE Spectrum
W7-X is the world's largest and most advanced stellarator, a magnetic confinement concept that uses a complex, three-dimensional array of external coils to shape the plasma. Unlike tokamaks, stellarators do not require a large, inductively driven plasma current to maintain confinement, making them immune to current-driven disruptions and inherently suited for steady-state operation. The primary objective of W7-X is not to achieve net energy gain but to demonstrate that its highly optimized, quasi-isodynamic magnetic field can effectively confine a high-temperature, high-density plasma with minimal neoclassical transport, a key challenge for previous stellarator designs. This validation is critical for assessing the stellarator's viability as a future power plant concept. Source: IEEE Spectrum
W7-X is the world's largest and most advanced stellarator, a magnetic confinement concept that uses a complex, three-dimensional array of external coils to shape the plasma.
The device's magnetic cage is generated by 50 non-planar and 20 planar superconducting coils made from niobium-titanium, cooled to cryogenic temperatures. This system is engineered to produce a magnetic field strength of up to 3 Tesla on the plasma axis. The precision required for the coil geometry and assembly was a significant engineering feat, with tolerances on the order of millimeters over the machine's 16-meter diameter. The initial plasma heating for this first operational phase (OP1.1) relies on electron cyclotron resonance heating (ECRH). Future operational phases will incorporate additional heating systems, including neutral beam injection and ion cyclotron resonance heating, to access higher performance regimes. Source: IEEE Spectrum
The successful first hydrogen plasma initiates a multi-year research program designed to systematically increase the device's capabilities. The initial experimental campaigns will focus on characterizing plasma behavior and benchmarking it against sophisticated physics models that guided the machine's design. Subsequent phases will involve installing a water-cooled divertor, which is essential for handling high heat fluxes and enabling long-pulse operations. The ultimate goal for W7-X is to sustain high-performance plasmas for up to 30 minutes, which would be a major step forward for the stellarator concept and provide crucial data for the design of a future fusion power plant. The results will offer a direct comparison to leading tokamak programs like ITER. Source: IEEE Spectrum