Turbulence and transport physics of the optimized Wendelstein 7-X stellarator

Olaf Grulke

MPI for Plasma Physics, Technical University of Denmark

Tuesday, May 28, 2024

12:00pm

NW17-218 Hybrid

PSFC Seminars

Abstract: Wendelstein 7-X (W7-X) is at the forefront of stellarator fusion research, aiming to establish the physics basis for a HELIAS-type reactor. One key aspect W7-X lies in its optimized magnetic geometry, a crucial element in achieving enhanced plasma confinement by the reduction of neoclassical transport channels, which is a notorious issue of classical stellarator designs. This is achieved by designing the magnetic field with a small effective magnetic ripple. Although this optimization does not explicitly consider turbulent transport channels, the W7-X magnetic field displays interesting stability characteristics. A so-called max-J feature, i.e. peaking of the second adiabatic invariant in the plasma center, causes a suppression of the trapped-electron instability, since no resonance of trapped electron precession and drift velocity exists.

W7-X has recently finished its third scientific operation campaign, where a strong focus of the experimental program has been the assessment of turbulent and neoclassical transport in its magnetic field configuration space and the performance of the newly installed high heat flux divertor units. This presentation will summarize the main experimental findings.