Statistical characterization of turbulence in the boundary plasma of EAST

In Ohmic heated low confinement mode (L-mode) discharges, the intermittent statistical characteristics of turbulent fluctuations have been investigated in the edge and the scrape-off layer (SOL) plasma on EAST (the experimental advanced superconducting tokamak) by fast reciprocating Langmuir probe measurements.

Plasma structures (blobs and holes) are observed and found to originate together inside the edge shear layer where the skewness (S) of the ion-saturation current fluctuations is close to zero. The probability density functions of the density fluctuations in edge and SOL plasma show a well-defined parabolic relation between the S and the kurtosis (K).

In edge plasma with holes, the geodesic acoustic mode (GAM) is identified with a dominant frequency fpeak ∼ 5–7 kHz both in floating potential fluctuations and ion-saturation current fluctuations. However, the GAM can only be detected in the floating potential fluctuations rather than the ion-saturation current fluctuations in the edge plasma with blobs.

The ESEL (edge-SOL electrostatic) code based on interchange dynamics is used to simulate the experimental results on EAST. Reasonable agreement between the ESEL simulation and the EAST experiment is reached. Experimentally, the parallel SOL flow shows a remarkable dependence on the plasma density, which resembles the theoretical predicted Pfirsch–Schlüter flow but with a much higher magnitude at the outboard mid-plane of EAST.