Radial structure of vorticity in the plasma boundary of ISTTOK tokamak

TL;DR

This paper reports the first experimental measurements of vorticity and vorticity flux in the plasma boundary of the ISTTOK tokamak, revealing their role in shear flow and non-equilibrium statistical properties.

Contribution

It provides the first direct measurements of vorticity in a tokamak plasma boundary and compares these with theoretical models, highlighting universal fluctuation behaviors.

Findings

Vorticity flux feeds into shear flow in plasma edge

Vorticity probability distribution exhibits fat tails with q-Gaussian shape

Fluctuations follow a universal shape indicating self-similarity

Abstract

The first experimental measurements of vorticity and vorticity flux in a fusion device were performed in tokamak ISTTOK. This is an important achievement since vorticity plays a key role in the transport of energy and particles in plasmas and fluids. The measurements were performed with a specifically designed array of Langmuir probes in the plasma edge of the small tokamak ISTTOK. The experimental results presented in this paper, allowing for the first time a direct comparison with theoretical models, show that the vorticity flux feeds into the shear flow in the tokamak plasma edge region. The Probability Distribution Function of the vorticity exhibit fat tails with a q-Gaussian shape typical of a non-equilibrium process. Self-similarity in the probability distribution function of several parameters, including vorticity and vorticity flux, is observed indicating that there is no morphological change in the coherent structures in the plasma boundary region and that the fluctuations in the Reynolds stress, vorticity and vorticity flux follow a universal shape.