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Abstract
Resistive drift-wave turbulence in a slab geometry, one of the candidates for anomalous transport in magnetized plasmas, is studied by statistical closure methods and direct numerical simulations in the first part of the thesis. The two-field Hasegawa-Wakatani (HW) fluid model, which evolves the electrostatic potential and plasma density self-consistently, is a paradigm for understanding the generic nonlinear behavior of multiple-field plasma turbulence. A realizable Markovian statistical closure is applied to the HW model; detailed spectral properties, nonlinear energy transfers, and turbulent transport calculations are discussed. The closure results are also compared to direct numerical simulation results; excellent agreement is found. A previous suggestion by Koniges et al. (1992) about the role of coherent structures on the large depression of saturated transport from its quasilinear value in a certain regime of the HW model is refuted. Instead, the depression of transport is well explained by the spectral balance equation of the statistical closure. Meanwhile, the transport scaling with the adiabaticity parameter, which measures the strength of the parallel electron resistivity, is analytically derived and understood through weak- and strong-turbulence analysis.
In the second part, some general aspects of turbulent transport, namely the entropy balance equation and Onsager symmetry, are discussed. The entropy balance equation is a universal relation between the turbulent transport and the dissipation in the physical system. Though subtle, the relationship between the transport and dissipation persists in all of the plasma turbulence models--e.g., the Landau-fluid model and the HW model. A physical picture for this important balance equation is developed based on the Casimir property of the entropy functional. Another generic issue in transport theory, the Onsager symmetry, is also critical for understanding multi-field turbulence. Some misconceptions and misuses of the Onsager symmetry are discussed. For far-from-equilibrium physical systems, an analysis similar to Onsager's original one results in a generalized Onsager relation. In systems modeled by realizable Markovian closures, the generalized Onsager relation always holds; in some cases, it may reduce to the original Onsager symmetry of the transport matrix.
