Suppression of turbulence in the drift-resistive plasma where zonal flow changes direction

Abstract

The edge region of quasi-adiabatic plasma is pedagogically simulated by the dynamics between the electric potential phi and the electron density n whose equilibrium density gradient is negative and held fixed. The zonal flow (ZF) V is either enforced sinusoidally or generated self-consistently from the turbulence. Cross-phase delta between phi and n, which is important in the determination of the turbulence level and the transport, is strongly influenced by the ZF. In the region near V = 0, delta becomes negative due to the large gradient of the ZF. It is found that the instabilities are quenched there, and the fluctuations decay. The ZF thus works as a transport barrier in the region where the ZF changes direction with large gradient.