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Entropy 2016, 18(4), 143;

Mixed Diffusive-Convective Relaxation of a Warm Beam of Energetic Particles in Cold Plasma

CREATE Consortium, Via Claudio, 21, Napoli 80125, Italy
ENEA, C. R. Frascati, Via E. Fermi, 45, Frascati (Roma) 00044, Italy
Department of Space Plasma Physics, Space Research Institute, Russian Academy of Sciences, 117997 Moscow, Russia
Department of Physics, Roma Tre University, Via della Vasca Navale, 84, Roma 00146, Italy
Department of Physics, Sapienza University of Rome, P.le Aldo Moro, 5, Roma 00185, Italy
Department of Physics, University of Naples Federico II, Via Cinthia, Napoli I-80126, Italy
Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou 310027, China
Author to whom correspondence should be addressed.
Academic Editor: Giorgio Sonnino
Received: 9 December 2015 / Revised: 29 February 2016 / Accepted: 11 April 2016 / Published: 16 April 2016
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This work addresses the features of fast particle transport in the bump-on-tail problem for varying the width of the fluctuation spectrum, in the view of possible applications to studies of energetic particle transport in fusion plasmas. Our analysis is built around the idea that 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 idea in the form of a self-consistent nonlinear dynamical model, which extends 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 essentially depending on nonlinear wave-particle interactions and phase-space structures. Taking into account the modes of the stable linear spectrum is crucial for the self-consistent evolution of the distribution function and the fluctuation intensity spectrum. View Full-Text
Keywords: plasma kinetic equations; particle beam interactions in plasmas; nonlinear phenomena plasma kinetic equations; particle beam interactions in plasmas; nonlinear phenomena

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Carlevaro, N.; Milovanov, A.V.; Falessi, M.V.; Montani, G.; Terzani, D.; Zonca, F. Mixed Diffusive-Convective Relaxation of a Warm Beam of Energetic Particles in Cold Plasma. Entropy 2016, 18, 143.

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