What Limits Zonal Flow Saturation in (Nearly) Collisionless Drift-Wave Turbulence?
ORAL
Abstract
Drift wave - zonal flow turbulence has long been known as a self-regulating system. A key question that remains is how are zonal shears regulated with weak frictional damping.
For realistic values of electron adiabaticity in the Hasegawa-Wakatani model, Rayleigh-Kuo can be used as a stability criterion. Rayleigh-Kuo states that for zonal flow stability to occur, it is necessary for the total mean potential vorticity gradient to vanish, i.e. ∇(PV) = ∇( - ∇2<??>) = 0. We explore the relation between this criterion and saturated turbulence levels through the quantity R = Zonal Flow Energy / Drift Wave Energy with varying levels of frictional damping (??) and frozen ∇(). Here, “zonal” means k?? and kz = 0 and “drift wave” means k?? and kz ≠ 0.
Current results show that lower damping scenarios are consistent with Rayleigh-Kuo with R < 1 regions centralized around ∇(PV) = 0. Larger damping appears to break the link between ∇(PV) = 0 and R < 1, suggesting Rayleigh-Kuo isn’t the dominant physics.
Ongoing work is concerned with exploring the relation between Rayleigh-Kuo and R with varying ∇. With these results, we want to quantify the effect of potential vorticity transport on zonal flow saturation and extend this to predator-prey models.
For realistic values of electron adiabaticity in the Hasegawa-Wakatani model, Rayleigh-Kuo can be used as a stability criterion. Rayleigh-Kuo states that for zonal flow stability to occur, it is necessary for the total mean potential vorticity gradient to vanish, i.e. ∇(PV) = ∇( - ∇2<??>) = 0. We explore the relation between this criterion and saturated turbulence levels through the quantity R = Zonal Flow Energy / Drift Wave Energy with varying levels of frictional damping (??) and frozen ∇(). Here, “zonal” means k?? and kz = 0 and “drift wave” means k?? and kz ≠ 0.
Current results show that lower damping scenarios are consistent with Rayleigh-Kuo with R < 1 regions centralized around ∇(PV) = 0. Larger damping appears to break the link between ∇(PV) = 0 and R < 1, suggesting Rayleigh-Kuo isn’t the dominant physics.
Ongoing work is concerned with exploring the relation between Rayleigh-Kuo and R with varying ∇. With these results, we want to quantify the effect of potential vorticity transport on zonal flow saturation and extend this to predator-prey models.
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Presenters
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Taurean Zhang
University of California, San Diego
Authors
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Taurean Zhang
University of California, San Diego
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Patrick H Diamond
University of California, San Diego, UCSD
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Robin Heinonen
University of Rome, Italy