Turbulence Spreading into an Edge Stochastic Magnetic Layer Induced by Magnetic Fluctuation and Its Impact on Divertor Heat Load

Turbulence spreading into the edge stochastic magnetic layer induced by magnetic fluctuation is observed at the sharp boundary region in the large helical device. The density fluctuation excited at the sharp boundary region with a large pressure gradient does not propagate into the boundary region due to the blocking of turbulence spreading by the large second derivative of the pressure gradient. Once the magnetic fluctuation appears at the boundary, the density fluctuation begins to penetrate the edge stochastic layer and the second derivative of the pressure gradient also decreases. The increase of density fluctuation in this layer results in the broadening and reduction of the peak divertor heat load. It is demonstrated that magnetic fluctuation plays a key role in controlling the turbulence spreading at the boundary of plasma which contributes to the reduction of divertor heat load.

Automated summary

Turbulence spreading induced by magnetic fluctuation is observed at the boundary region of the large helical device. Density fluctuation excited at the sharp boundary cannot propagate into the boundary due to the blocking effect of pressure gradient. However, when magnetic fluctuation appears at the boundary, density fluctuation starts to penetrate the edge layer and the pressure gradient decreases. This increase in density fluctuation leads to the reduction of divertor heat load.