During the course of the step-by-step upgrading of Wendelstein 7-X, the plasma vessel was fitted with inner cladding beginning in September of last year. Graphite tiles are now protecting the vessel walls. In addition, the divertor is used to regulate the purity and density of the plasma. In ten broad strips on the wall of the plasma vessel, the divertor tiles follow the contour of the plasma edge. Specifically, they cover the wall areas on which the particles from the edge of the plasma are diverted in a targeted way. After three months of experiments with the new equipment, the next round of upgrades began at the end of 2017; among other things, new measuring devices and heating systems were installed. The experiments were resumed from July 2018 onwards.
Whilethedivertor had already demonstrated its good impact in the past, the plasma values with help of the extended plasma heating in combination with purified vessel walls could now be significantly increased. The newly installed neutral particle heating injects fast hydrogen atoms into the plasma, which transfer their energy to the plasma particles via collisions. The result was high plasma densities of up to 2 x 1020 particles per cubic meter—values that are sufficient for a future power station. At the same time, the ions and electrons of the hydrogen plasma reached an impressive temperature of 20 million degrees Celsius.
Record stellarator values achieved Wendelstein 7-X for the energy stored in the plasma. By strong microwave heating, the energy content of the plasma exceeded one megajoule for the first time, without the vessel wall becoming too hot. With good plasma values, long lasting plasmas over durations of 100 seconds have been obtained—also one of the best stellarator values to date.