Classification of Particle Orbits near the Magnetic Axis in a Tokamak by Using Constants of Motion

概要

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A classification of particle orbits near the magnetic axis in a tokamak is presented in a space of constants of motion (COM), which is important to apply Lagrangian formulation of neoclassical transport theory to the region near the axis. Orbit types are distinguished by the number of the turning points of σ_<||> = v_<||>/|v_<||>| and σ_θ = θ/|θ| on each orbit, where v_<||> is the velocity parallel to the magnetic field, and 0 is the poloidal angular velocity. As a set of COM, (ε, μ, <r>) is taken, where ε is the energy of a particle, ~ is the magnetic moment, and (r) is the bounce-averaged minor radius position of a particle orbit. Compared with a familiar set of COM (v, ζ_s, r_s), where v is the particle velocity, rs is the minor radius at which an orbit crosses the mid-plane, and ~ = viiIv evaluated at the crossing point, the set of COM (ε, μ, <r>) is more suitable in practice for Lagrangian formulation of neoclassical transport theory, in which the particle diffusion is described by the change of average position of particles <r> by collisions. Near the magnetic axis, it is found that there are overlaps in regions of orbit types in the (ε, μ, <r>) space and that <r> has a minimum value for a given ε. These features should be treated when applying Lagrangian representation of neoclassical transport theory.
社団法人プラズマ・核融合学会の論文
2001-06-25