Speaker
Thomas Klinger
(Enterprise Wendelstein 7-X)
Description
The optimized stellarator Wendelstein 7-X (W7-X) has started with the goal to demonstrate steady-state plasma operation at fusion relevant plasma parameters. This is to establish the optimized stellarator as a viable fusion power plant concept. The design of W7-X is based on the optimization of the geometric properties of the magnetic field with the aim to minimize neoclassical transport losses in the collisionless regime, to provide good fast ion confinement in the centre of the plasma, to achieve satisfactory equilibrium and stability properties at high β, and to demonstrate viable divertor operation.
The construction of W7-X took 15 years and was completed in mid 2014. After about one year of commissioning (pump-down, cool-down, magnet ramp-up), the device was ready for operation. The commissioning was successfully concluded by the measurement of the magnetic flux surfaces, which has fully confirmend the basic magnetic field topology. In the end of 2015 the first Helium plasmas were created and soon after, Hydrogen plasma operation was started.
A brief overview of the construction and commissioning history of W7-X is given. Initial experiences and first results of Helium and Hydrogen plasma operation are summarized. After only a few weeks of operation, Hydrogen plasmas with 2-3 x 10E19 m-3 line integrated plasma density, 7.5 keV central electron temperature, 1 keV line-averaged ion temperature could be achieved with only 2.5 MW 140 GHz ECR heating power. The pulse duration of 200 ms is determined by impurities but steadily increases with glow discharge wall conditioning. The main observations on transport (energy, particles, impurities), cyclotron wave heating, density control and plasma-wall interaction are reviewed in this paper.
W7-X follows a staged approach to steady-state plasmas. After installation of a water-cooled high heat flux divertor, high power (10 MW) steady-state plasma operation up to pulse lengths of 30 minutes becomes possible.
Co-author
Thomas Klinger
(Enterprise Wendelstein 7-X, Max-Planck Institute for Plasma Physics, Greifswald, Germany)
