Abstract
The interaction of micro-scale turbulence with zonal flows is one of the key topics in magnetically confined plasma research. We study the stability of drift waves in the presence of large scale flows in the Hasegawa-Wakatani system using spatial averaging. The dispersion relation obtained by this treatment is independent of the radial coordinate and includes resonant terms, which become dominant when the phase speed of the drift wave is comparable to the local advection speed of zonal flow. This dispersion relation is then solved numerically to yield linear growth rates for a small drift wave perturbation against a zonal flow background. The growth rates are similar to those found without zonal flows, when far from the resonant conditions. Close to resonance, both the real frequency and the growth rates differ significantly from the usual case. The stability of zonal flows is also examined.
Highlights
The detrimental impact of micro-scale turbulence on the magnetic confinement of plasma is well established
The dispersion relation obtained by this treatment is independent of the radial coordinate and includes resonant terms, which become dominant when the phase speed of the drift wave is comparable to the local advection speed of zonal flow
We focus on the case of near resonant conditions and quantify the departure of the drift wave frequencies and growth rates from those found for a standard case
Summary
The detrimental impact of micro-scale turbulence on the magnetic confinement of plasma is well established. Turbulent fluctuations in electrostatic plasma potential, plasma density, and temperature lead to increased radial heat and density transport, when compared with classical diffusion-based results. Drift-wave instability is a generic paradigm for generating turbulent fluctuations in magnetised plasmas with a spatial density gradient, perpendicular to the magnetic field vector. With the magnetic field in the z direction and the density gradient in the Àx direction, the infinitesimal perturbation generates a drift wave propagating in the þy direction. In the presence of a non-adiabatic electron response, the mode becomes unpstffiffiaffiffibffiffiffilffieffiffiffi on the scale comparable to the hybrid gyroradius qs 1⁄4 miTe=eB. The nonlinear interaction of large amplitude waves leads to the so-called drift wave turbulence
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