Two-component ion distributions in tokamak hot ion plasmas

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Abstract
The two‐component ion distribution observed with active charge‐exchange measurements on the tokamak PDX are explained using the Fokker–Planck drift‐kinetic equation and assuming that ion self‐collisions are dominant for energy scattering. The energetic tail of the distribution, which is diffusing outwards in radius and down in energy, must retain an approximately constant effective temperature TH≡(−∂ ln f i/m∂ε)−1. The discontinuity in the slope of ln f i is shown to be the boundary between the inward and outward diffusion parts of f i and is a form of contact discontinuity. Energy‐scattering collisions with electrons or circulating beam ions, when important, modify the constancy of TH.