Turbulent transport mechanisms in Wendelstein 7-X plasmas

摘要

Introduction. Radial transport in non-optimized stellarators is dominated by a high neoclassical (NC) contribution. In tokamaks, as this contribution is inherently minimal due to the symmetry of the device, the radial losses are essentially attributed to turbulence [1]. The optimized Wendelstein 7-X (W7-X) stellarator is designed to reduce the NC transport down to tokamak levels. Results from the first and the second experimental campaigns in W7-X suggest that NC transport is not sufficient to explain the radial losses in several scenarios (especially at the edge r_eff> 0.6), opening the door to the turbulent transport contribution as a plausible candidate to explain these discrepancies.