Drift waves and transport

Abstract

Drift waves occur universally in magnetized plasmas producing the dominant mechanism for the transport of particles, energy and momentum across magnetic field lines. A wealth of information obtained from quasistationary laboratory experiments for plasma confinement is reviewed for drift waves driven unstable by density gradients, temperature gradients and trapped particle effects. The modern understanding of Bohm transport and the role of sheared flows and magnetic shear in reducing the transport to the gyro-Bohm rate are explained and illustrated with large scale computer simulations. The types of mixed wave and vortex turbulence spontaneously generated in nonuniform plasmas are derived with reduced magnetized fluid descriptions. The types of theoretical descriptions reviewed include weak turbulence theory, Kolmogorov anisotropic spectral indices, and the mixing length. A number of standard turbulent diffusivity formulas are given for the various space-time scales of the drift-wave turbulent mixing. [S0034-6861(99)00803-X] CONTENTS

Vacuum Ultraviolet Spectroscopy at TEXTOR

“…from the STRAHL modeling; see The elevated level of diffusivity in the radial range near half minor radius is in rough agreement with theoretical predictions from ion temperature gradient instability 25 and from gyro-Bohm behavior. 26 A Fig. 6.…”

Plasma Turbulence Imaging via Beam Emission Spectroscopy in the Core of the DIII-D Tokamak

“…Pressure gradients inherent to such plasmas are thought to drive drift-wave turbulence [1], which in turn drives cross-field transport at levels far exceeding the irreducible minimum of collisionally-driven "neoclassical" transport. Plasma turbulence is thought to be dominantly electrostatic in nature [2], and so radial transport arises from correlated fluctuations in the density, radial E×B velocity, temperature and parallel and poloidal velocities [3].…”

Study of Turbulent Fluctuations Driven by the Electron Temperature Gradient in the National Spherical Torus Experiment

“…From this, we might conclude that it is difficult to perform localized measurements of plasma turbulence with coherent scattering of electromagnetic waves. Fortunately, this estimate is valid only for an isotropic turbulence, which is not the case of tokamak plasmas where short-scale fluctuations satisfy the relation [1,2] (with B the magnetic field, q the magnetic safety factor and R the plasma major radius). For all practical purposes, then, we can assume…”

“…Indeed, since most explanations of this phenomenon are based on some type of turbulence [1][2][3], understanding plasma transport depends upon understanding turbulence. Unfortunately, since this is a tremendously difficult problem, the cause of anomalous energy losses in tokamaks is still an outstanding issue.…”