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Multi-scale interaction of driftWave turbulence with large scale shear flows

  • Author(s): McDevitt, Christopher J.
  • et al.
Abstract

Multi-scale methods are utilized within the context of strongly magnetized plasmas to describe the interaction of drift wave turbulence with large scale flow structures. The specific contexts treated correspond to transport barrier formation, magnetic island evolution in the presence of drift wave turbulence, and plasma rotation. Emphasis is placed on identifying critical feedback mechanisms via the study of simple, reduced models, rather than the detailed description of isolated components of the system. In Chapter 2 a two component self-consistent model is derived to investigate a novel mechanism of transport barrier formation. It is found that intense cellular flow, driven by modulational instability of the background turbulence provides a viable candidate mechanism for triggering transport barrier formation in regimes of weak magnetic shear. Similarly, the nonlinear modification of the drift wave phase space topology by the cellular flow is investigated. The presence of a weak non- integrable perturbation in the effective Hamiltonian of the drift wave turbulence, induced by the non-axisymmetric component of the cellular flow, is found to circumvent nonlinear wave trapping as a means of quenching the secondary instability drive of the large scale flow. In Chapter 3, the interaction of a tearing mode with drift wave turbulence is discussed. Wave kinetics and adiabatic theory are utilized to treat the feedback of tearing mode flows on the drift wave turbulence. The stresses exerted by the self-consistently evolved drift wave population density on the tearing mode are calculated by mean field methods. The principal effect of the drift waves is to pump the resonant low-m mode via a negative viscosity, consistent with the classical notion of an inverse cascade in quasi 2-D turbulence. In Chapter 4, the multi-scale methods utilized above are extended to describe the transport of parallel momentum. The primarily fluid description employed above is extended to include momentum exchange between waves and resonant particles. A quasi- linear momentum conservation theorem is proven, demonstrating that the total momentum flux can be decomposed into wave and resonant particle fluxes. Quasi- linear expressions for the radial transport of parallel momentum induced both by waves and resonant particles are derived, providing a comprehensive quasi-linear description of parallel momentum transport induced by electrostatic drift wave turbulence

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