Mixed diffusive-convective relaxation of a broad beam of energetic particles in cold plasma

Abstract

We revisit the applications of quasi-linear theory as a paradigmatic model for weak plasma turbulence and the associated bump-on-tail problem. The work, presented here, is built around the idea that large-amplitude or strongly shaped beams do not relax through diffusion only and that there exists an intermediate time scale where the relaxations are convective (ballistic-like). We cast this novel idea in the rigorous form of a self-consistent nonlinear dynamical model, which generalizes the classic equations of the quasi-linear theory to "broad" beams with internal structure. We also present numerical simulation results of the relaxation of a broad beam of energetic particles in cold plasma. These generally demonstrate the mixed diffusive-convective features of supra-thermal particle transport; and essentially depend on nonlinear wave-particle interactions and phase-space structures. Taking into account modes of the stable linear spectrum is crucial for the self-consistent evolution of the distribution function and the fluctuation intensity spectrum.

25 pages, 15 figures

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Cited by in corpus (9)

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• Contributions to the linear and non-linear theory of the beam-plasma interaction
• Quasi-linear model for the beam-plasma instability: analysis of the self-consistent evolution
• One dimensional reduced model for ITER relevant energetic particle transport
• On the viability of the single wave model for the beam plasma instability
• Reanalysis of the beam-plasma instability using the Dyson-like equation formalism
• Analysis of non-diffusive avalanche transport of energetic particles