A novel mechanism for spontaneous ExB shear layer formation in scrape-off-layer plasmas

Abstract

We present a novel mechanism for spontaneous shear-flow generation in the scrape-off layer (SOL) of magnetically confined plasmas, arising at abrupt changes in the sheath connection length $L_{\parallel }$. Such transitions occur naturally in the Wendelstein 7-X stellarator. Applying a critical balance treatment for interchange turbulence, we find that $L_{\parallel }$ sets the equilibrium pressure gradient and hence the radial electric field away from the transition, producing an $E\times B$ shear around the transition comparable to the turbulence growth rate. High-fidelity simulations are shown to be consistent with the theoretical prediction.

arXiv comment4 pages, 3 figures