Studies of Reynolds Stress and the Turbulent Generation of Edge Poloidal Flows on the HL-@A Tokamak

TL;DR

This paper reports experimental findings on edge poloidal flows, turbulent stresses, and momentum transport in the HL-2A tokamak, revealing deviations from classical predictions and insights into turbulence-driven flow generation.

Contribution

It presents the first deduction of intrinsic poloidal torque from turbulence data and compares turbulent viscosity with particle diffusivity in tokamak edge plasmas.

Findings

Significant deviation from neoclassical predictions for poloidal flow.

Turbulent poloidal viscosity is comparable to particle diffusivity.

PDFs of flux and Reynolds stress show fat tails and high kurtosis.

Abstract

Several new results in the physics of edge poloidal flows, turbulent stresses and momentum transport are reported. These are based on experiments on the HL-2A tokamak. Significant deviation from neoclassical prediction for mean poloidal flow in Ohmic and L mode discharges is deduced from direct measurements of the turbulent Reynolds stress. The deviation increases with heating power. The turbulent poloidal viscosity is synthesized from fluctuation data, and is found to be comparable to the turbulent particle diffusivity. The intrinsic poloidal torque is deduced from synthesis, for the first time. PDFs of particle flux and Reynolds stress are obtained. Both exhibit fat tails and large kurtosis, suggesting that the momentum transport process represented by the Reynolds stress is not well described by quasilinear calculations.