O. Grulke1,2 and the Wendelstein 7-X Team1
1. Max-Planck Institute for Plasma Physics, Greifswald, Germany
2. Technical University of Denmark, Kongens Lyngby, Denmark
“The stellarator Wendelstein 7-X: Towards long pulse, high performance operation”
A major goal of the superconducting stellarator Wendelstein 7-X is the exploitation of the reactor potential of the HELIAS concept. Its modular magnetic field configuration is optimized to provide improved neoclassical and fast ion confinement, enhanced MHD stability, and the feasibility of a divertor concept. During the last maintenance phase, Wendelstein 7-X has undergone major modifications with the realization of a fully water-cooled graphite divertor and plasma facing components, which represent the technical completion for long-pulse operation with the goal to increase the energy turnaround to 18GJ over the next operation campaigns. The newly installed high heat flux divertor is capable to withstand steady-state heat flux densities of up to 10 MW/m2. In total, 600 in vessel cooling circuits were installed and successfully commissioned. The heating power of the neutral beam injection system was doubled with the commissioning of two additional injectors, providing in total up to ~8MW of heating power. A new pellet injector system was installed to allow for steady-state core fueling. Additionally, a lot of new or strongly enhanced diagnostics system were installed. With these enhancements, plasma operation restarted in September 2022 for a period of 6 months. Key objectives for the campaign were the demonstration of long-pulse operation with an energy turnaround exceeding 1GJ and studies of enhanced plasma confinement and its relation to neoclassical and turbulent transport phenomena. Long pulseoperation was achieved with discharge lengths of 8min with attached divertor and over 100s in full divertor detachment. Using NBI injection and the associated central peaking of the plasma density profiles, core turbulence could be widely suppressed and the transport of energy and particles reduced to neoclassical levels. This presentation gives an overview of the conduction and key achievements of the last operation campaign.