The modified Hasegawa-Wakatani (HW) model describes electrostatic resistive drift wave turbulence in a s tokamak edge plasma, which is written in the form of time evolution of fluctuations of the electrostatic potential (φ) and the density (n) in a strong equilibrium magnetic field and nonuniform density. The HW model is a generalization of the Hasegawa-Mima (HM) equation including election resistivity parallel to the magnetic field. This parallel electron motion brings about coupling between the vorticity (ζ = Δφ) and the density through the Ohm's law. [In the HM model, the electron resistivity is negligibly small, and electrons obey the Boltzmann relation (n = φ).]
"Modification" from the original HW model is attributed to treatment of zonal (poloidally symmetric) components of fluctuations. In a two-dimensional version of the HW model, the resistive coupling between the vorticity and the density does not act on the zonal components. It is therefore necessary to subtract the zonal components from the resistive coupling term.
Above animation shows time evolution of φ, n and ζ in a poloidal plane obtained by solving the MHW model numerically. Since the electrostatic potential is nothing but the plasma flow streamfunction, contour plot of φ shows flow structure. We can observe that zonally elongated (in y direction) couter-streaming flows are self-organized by turbulent interaction.
[The term "zonal flow" originally comes from planetary (Earth, Jupiter, etc.) atmospheric flow research.]
