Reduction of edge plasma turbulence via cross-phase decrease by zonal fields

Abstract

Transport of the near-adiabatic plasma is simulated numerically. The zonal flow (ZF) V along the poloidal direction is found to emerge self-consistently from the non-zonal turbulence. Zonal fields are found to feed back to turbulence by reducing the cross phase. As a result the turbulence is localized with depressed peaks. Turbulence is very low and the cross phase delta is negative near V = 0, where the gradient V' (vorticity) of ZF along the radial direction is large. The fluctuations are almost localized where the zonal-density gradient (n) over bar' is a positive peak and V is locally large. Positive ( n) over bar' or positive V '' is shown to reduce the cross phase between the electric potential and the density fluctuation.