Description
The scrape-off-layer (SOL) of Wendelstein 7-X provides a novel environment for turbulence and other plasma phenomena. The divertor intersects the plasma at toroidally-discrete locations. As a result, the W7-X SOL is unique as it includes patches of constant parallel connection length to the sheath, separated by abrupt transitions. The free energy transfer in the SOL is a combination of parallel dynamics (drift-wave) and diamagnetic (interchange) effects [1], and therefore the unique parallel structure of the W7-X SOL can produce novel dynamics.
Here we present a study of nonlinear turbulent dynamics in environments which mimic the W7-X SOL. We utilize the Hermes-3 multifluid model [2] in curved-slab geometries with varying degrees of fidelity to the W7-X SOL. We show how electric field shearing can manifest due to the abrupt changes in parallel connection length, affecting the nature of transport on both sides of the transition. We also provide descriptions of the turbulent mode behavior with analogies to insular biogeography. A nonlinear mode analysis determines that regions with long connection length exhibit a greater diversity of turbulent modes, as the adiabatic electron response is reduced. The implications for future devices, and how ExB shear layers could appear, will be discussed.
[1] B Scott, Physics of Plasmas 12 062314 (2005)
[2] B Dudson et al., Comp. Phys. Comm. 296 108991 (2024)