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Patrick Diamond - One of the best experts on this subject based on the ideXlab platform.

  • Frictionless Zonal Flow Saturation by Vorticity Mixing
    arXiv: Plasma Physics, 2018
    Co-Authors: Patrick Diamond
    Abstract:

    Consideration of wave--Flow resonance addresses the long-standing problem of how zonal Flows (ZF) saturate in the limit of weak or zero frictional drag, and also determines the ZF scale. For relevant magnetic geometries, the frequently quoted tertiary instability requires unphysical enhancement of ZF shear and thus is irrelevant to the near-marginal, frictionless regime. We show that resonant vorticity mixing, which conserves potential enstrophy, enables ZF Saturation in the absence of drag, and so is effective in the Dimits up-shift regime. Vorticity mixing is incorporated as a nonlinear, self-regulation effect in an extended 0D predator--prey model of drift--ZF turbulence. This analysis determines the saturated ZF shear and shows that the mesoscopic ZF width scales as $L_{ZF}\sim f^{3/16} (1-f)^{1/8} \rho_s^{5/8} l_0^{3/8}$ in the relevant adiabatic limit (i.e., $\tau_{ck} k_\|^2 D_\| \gg 1$). $f$ is the fraction of turbulence energy coupled to ZF and $l_0$ is the mixing length absent ZF shears. We calculate and compare the stationary Flow and turbulence level in frictionless, weakly frictional, and strongly frictional regimes. In the frictionless limit, the results differ significantly from conventionally quoted scalings derived for frictional regimes. The Flow is independent of turbulence intensity. The turbulence level scales as $E \sim (\gamma_L/\varepsilon_c)^2$, which defines the extent of the "near-marginal" regime to be $\gamma_L < \varepsilon_c$, for the case of avalanche-induced profile variability. Here, $\varepsilon_c$ is the rate of dissipation of potential enstrophy and $\gamma_L$ is the characteristic linear growth rate of fluctuations. The implications for dynamics near marginality of the strong scaling of saturated $E$ with $\gamma_L$ are discussed.

  • Nonlinear excitation and damping of Zonal Flows using a renormalized polarization response
    Bulletin of the American Physical Society, 2007
    Co-Authors: Fred Hinton, Patrick Diamond
    Abstract:

    The nonlinear interaction of drift-wave turbulence and zonal Flows is considered using an analogy with dressed test-particles in a stable plasma. The incoherent mode coupling potentials from the drift waves are treated as a source of noise driving the zonal Flows. The coherent mode coupling potentials are included in a renormalized nonlinear polarization response to this noise source, analogous to the shielding of test-particles. The nonlinear damping of zonal Flows and the conditions for a steady turbulent state are determined from the nonlinear polarizability. This calculation attempts to systematically address the effects of fluctuations and turbulence on the otherwise ’neoclassical’ zonal Flow polarization response. Thus it offers the possibility of identifying new nonlinear, kinetic ’channels’ for the coupling of zonal Flow energy to dissipation. The implications for zonal Flow Saturation will be discussed. This work was supported by DoE Grant No. DE-FG02-04ER54738.

  • Response to “Comment on ‘Dynamics of zonal Flow Saturation in strong collisionless drift wave turbulence’ ” [Phys. Plasmas 11, 1744 (2004)]
    Physics of Plasmas, 2004
    Co-Authors: Eun Jin Kim, Patrick Diamond
    Abstract:

    The Comment of Krommes is addressed. It is shown that all of the substantive claims therein are incorrect.

Eun Jin Kim - One of the best experts on this subject based on the ideXlab platform.

P H Diamond - One of the best experts on this subject based on the ideXlab platform.

  • dynamics of zonal Flow Saturation in strong collisionless drift wave turbulence
    Physics of Plasmas, 2002
    Co-Authors: Eun Jin Kim, P H Diamond
    Abstract:

    Generalized Kelvin–Helmholtz (GKH) instability is examined as a mechanism for the Saturation of zonal Flows in the collisionless regime. By focusing on strong turbulence regimes, GKH instability is analyzed in the presence of a background of finite-amplitude drift waves. A detailed study of a simple model with cold ions shows that nonlinear excitation of GKH modes via modulational instability can be comparable to their linear generation. Furthermore, it is demonstrated that zonal Flows are likely to grow faster than GKH mode near marginality, with insignificant turbulent viscous damping by linear GKH. The effect of finite ion temperature fluctuations is incorporated in a simple toroidal ion temperature gradient model, within which both zonal Flow and temperature are generated by modulational instability. The phase between the two is calculated self-consistently and shown to be positive. Furthermore, the correction to nonlinear generation of GKH modes appears to be small, being of order O(ρi2k2). Thus, the...

J. A. Krommes - One of the best experts on this subject based on the ideXlab platform.

Miklos Gyulassy - One of the best experts on this subject based on the ideXlab platform.

  • Saturation of elliptic Flow and the transport opacity of the gluon plasma at RHIC
    Nuclear Physics A, 2002
    Co-Authors: Dénes Molnár, Miklos Gyulassy
    Abstract:

    Abstract Differential elliptic Flow and particle spectra are calculated taking into account the finite transport opacity of the gluon plasma produced in Au+Au at E cm ∼130 A GeV at RHIC. Covariant numerical solutions of the ultrarelativistic Boltzmann equation are obtained using the MPC parton cascade technique. For typical pQCD (∼3 mb) elastic cross sections, extreme initial gluon densities, d N g / d η∼15 000 , are required to reproduce the elliptic Flow Saturation pattern reported by STAR. However, we show that the solutions depend mainly on the transport opacity, χ=∫ d z σ t ρ g , and thus the data can also be reproduced with d N g /d η ∼1000, but with extreme elastic parton cross sections, ∼45 mb. We demonstrate that the spectra and elliptic Flow are dominated by numerical artifacts unless parton subdivisions ∼100–1000 are applied to retain Lorentz covariance for RHIC initial conditions.

  • Saturation of elliptic Flow and the transport opacity of the gluon plasma at rhic
    arXiv: Nuclear Theory, 2001
    Co-Authors: Dénes Molnár, Miklos Gyulassy
    Abstract:

    Differential elliptic Flow and particle spectra are calculated taking into account the finite transport opacity of the gluon plasma produced in Au+Au at Ecm ~ 130 A GeV at RHIC. Covariant numerical solutions of the ultrarelativistic Boltzmann equation are obtained using the MPC parton cascade technique. For typical pQCD (~3 mb) elastic cross sections, extreme initial gluon densities, dN/deta ~ 15000, are required to reproduce the elliptic Flow Saturation pattern reported by STAR. However, we show that the solutions depend mainly on the transport opacity, $\chi=\int dz \sigma_t\rho_g$, and thus the data can also be reproduced with dN/deta ~ 1000, but with extreme elastic parton cross sections, \~45 mb. We demonstrate that the spectra and elliptic Flow are dominated by numerical artifacts unless parton subdivisions ~100-1000 are applied to retain Lorentz covariance for RHIC initial conditions.