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Author Chu, T. K.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword PLASMA PHYSICS AND FUSION ♦ TOKAMAK DEVICES ♦ TRAPPING ♦ CHARGED PARTICLES ♦ TRAJECTORIES ♦ TRAPPED ELECTRONS ♦ LARMOR RADIUS ♦ PBX DEVICES ♦ TRAPPED IONS
Abstract In tokamaks, the trajectory of a trapped particle has a pair of poloidal turning points where {ital V}{sub {ital z}} reverses direction. They form a stagnation point when coalescing on the equatorial plane. The trajectories traversing the stagnation point, because of the finite Larmor radius and hence the banana width, have a threefold degeneracy: a pinch orbit and a kidney orbit of a trapped particle, and a loop orbit of a passing particle. When traversing the stagnation point from a pinch orbit, the trajectory of a negative-{ital V}{sub {parallel}} particle must change to a loop orbit and the particle becomes passing, and that of a positive-{ital V}{sub {parallel}} particle must change to a kidney orbit and the particle remains trapped. The trapping boundary is asymmetric in {ital V}{sub {parallel}}. The percentage of trapped particles in a species in a local Maxwellian plasma depends on the radial distance {ital r} as well as on the Larmor radius of its thermal particle. At the axis the trapping ratio is finite and more ions than electrons are trapped; for typical parameters in Princeton Beta Experiment-Modification [Bell {ital et} {ital al}., Phys. Fluids B {bold 2}, 1271 (1990)], for example, 2.2{percent} of electrons and 8.6{percent} of deuterons are trapped. Up to a radial distance of {approximately}10 times the Larmor radius of a thermal particle, the trapping ratio increases as {ital r}{sup 2}. {copyright} {ital 1996 American Institute of Physics.}
ISSN 1070664X
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-09-01
Publisher Department Princeton Plasma Physics Laboratory
Publisher Place United States
Journal Physics of Plasmas
Volume Number 3
Issue Number 9
Organization Princeton Plasma Physics Laboratory


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