The dynamics of edge-core coupling is critically important to the optimization of magnetically confined fusion plasmas. Since early proposals, there has been persistent speculation that inward propagation of turbulence from the boundary is a possible means to energize the edge-core coupling region. However, the detailed mechanism of this process has remained a mystery until recent experiments observed that regular, intense gradient relaxation events generated blob-void pairs very close to the last closed flux surface. Blobs ($\tilde{n}>0$) propagate outward and detach from the bulk plasma, while voids ($\tilde{n}<0$) propagate inward, and so stir the core plasma. Here, we demonstrate that this heretofore ignored process of void emission can drive a broad turbulent layer of width $\sim 100{\rho }_s$, for typical parameters. The mechanism is the Cherenkov emission of drift waves from inward-propagating voids. The model shows promise to resolve several questions surrounding the shortfall problem and the strong turbulence in the edge-core coupling region.

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• Drift waves
• Magnetic confinement fusion
• Plasma turbulence
• Magnetically confined plasmas
• Tokamaks