PSFC / JA - 10 - 2 Trajectories , orbit squeezing , and residual zonal flow in a tokamak pedestal

Particle orbits and the Rosenbluth-Hinton residual zonal flow are evaluated for the case of a strong equilibrium radial electric field ( ) / r E d d φ ψ ψ = − ∇ as observed in a tokamak pedestal. The ordering used is p i ~ / r E B v c where p B is the poloidal field and i v is the ion thermal speed. The earlier calculations of Kagan and Catto for this regime [Kagan G and Catto P J 2009 Phys. Plasmas 16 056105] correctly describes the effect of a uniform / d d φ ψ , but not the “orbit squeezing” effects associated with electric field shear 2 2 / d d φ ψ [Kagan G and Catto P J 2009 Phys. Plasmas 16 099902]. The present work gives the corrected dependence on electric field shear for a quadratic equilibrium potential ( ) φ ψ . Analytical results are given for the largeaspect-ratio limit, and a numerical approach is outlined for performing calculations at finite aspect ratio.