Fast Ion Non-adiabaticity in Spherical Tokamaks

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Transport processes of fast ions in axisymmetric low-aspect-ratio spherical torus (ST) plasmas are investigated, which are induced by the non-conservation of the magnetic moment {mu}. The reason for non-conservation of {mu} of fast ions in ST's is the relatively large adiabaticity parameter epsilon typically exceeding the value 0.1 (epsilon = ratio of ion gyroradius to the gradient scale length of the magnetic field). Both analytical and numerical evaluations of the magnitude of nonadiabatic variations of {mu} are performed. Nonadiabaticity effects are shown to be most significant for fast ions for which the bounce oscillations are in resonance with the gyromotion, ... continued below

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Yavorskij, V.A.; Darrow, D.; Goloborod'ko, V.Ya.; Reznik, S.N.; Holzmueller-Steinacker, U.; Gorelenkov, N. et al. August 1, 2002.

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Description

Transport processes of fast ions in axisymmetric low-aspect-ratio spherical torus (ST) plasmas are investigated, which are induced by the non-conservation of the magnetic moment {mu}. The reason for non-conservation of {mu} of fast ions in ST's is the relatively large adiabaticity parameter epsilon typically exceeding the value 0.1 (epsilon = ratio of ion gyroradius to the gradient scale length of the magnetic field). Both analytical and numerical evaluations of the magnitude of nonadiabatic variations of {mu} are performed. Nonadiabaticity effects are shown to be most significant for fast ions for which the bounce oscillations are in resonance with the gyromotion, i.e., for ions with omega(subscript)B - lomega(subscript)b = 0, where omega(subscript)B and omega(subscript)b represent the bounce-averaged gyrofrequency and the bounce frequency, respectively, and l is an integer. The critical threshold of the adiabaticity parameter, epsilon(subscript)cr, to be exceeded for the transition to stochastic behavior of fast ions in axisymmetric ST's is inspected. Nonadiabatic variations of {mu} are shown to lead to collisionless transformation of trapped orbits into circulating ones and vice versa. For the case of strong nonadiabaticity, epsilon > epsilon(subscript)cr, we assess the transport coefficients describing intense collisionless pitch-angle diffusion, whereas, in the case of weak nonadiabaticity, epsilon > epsilon(subscript)cr, the more substantial coefficients of enhanced collisional radial diffusion and convection of fast ions gyrating resonantly with the bounce oscillations are estimated.

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2.1 Megabytes pages

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INIS; OSTI as DE00808380

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  • Other Information: PBD: 1 Aug 2002

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  • Report No.: PPPL-3733
  • Grant Number: AC02-76CH03073
  • DOI: 10.2172/808380 | External Link
  • Office of Scientific & Technical Information Report Number: 808380
  • Archival Resource Key: ark:/67531/metadc739287

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  • August 1, 2002

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  • Oct. 18, 2015, 6:40 p.m.

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  • April 15, 2016, 9:19 p.m.

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Yavorskij, V.A.; Darrow, D.; Goloborod'ko, V.Ya.; Reznik, S.N.; Holzmueller-Steinacker, U.; Gorelenkov, N. et al. Fast Ion Non-adiabaticity in Spherical Tokamaks, report, August 1, 2002; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc739287/: accessed September 19, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.