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- Nyqvist, Robert, 1983, et al.
(author)
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Fast Ion Driven Alfvén Eigenmodes within the q=1 Radius
- 2009
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In: 36th European Physical Society Conference on Plasma Physics 2009, EPS 2009; Sofia; Bulgaria; 29 June 2009 through 3 July 2009. - 9781622763368 ; 33 E2, s. 1527-1530
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Conference paper (peer-reviewed)
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- Nyqvist, Robert, 1983, et al.
(author)
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Spreading of collimated particle beams within a generalized Fokker-Planck diffusion equation
- 2009
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In: Nuclear Science and Engineering. - 0029-5639 .- 1943-748X. ; 163:1, s. 85-90
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Journal article (peer-reviewed)abstract
- Recently, an expansion of the Boltzmann scattering operator describing the angular spreading of particle beams was given that included the effects of large angle scattering processes, thus generalizing the classical Fokker-Planck equation, valid in the limit of small angle scattering. The present work aims at making an analytical comparison between predictions based on the classical Fokker-Planck equation and those based on a generalized one, which includes a first-order correction term in the expansion of the Boltzmann scattering operator. The analysis is carried out for thin slabs where backscattering effects can be neglected and makes use of a moment approach, which leads to an infinite system of recursively coupled ordinary differential equations. The system is truncated in a consistent manner, and the effects of large angle scattering on the evolution of the moments are determined in explicit analytical form. An approximate similarity solution of the generalized Fokker-Planck equation is also found, and the results of both approaches provide a clear picture of the increased diffusive beam spreading due to large angle scattering. A comparison with previously published Monte Carlo simulation results shows good agreement.
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