Gyroradius Scaling of Electron and Ion Transport

Abstract

The scaling of heat diffusion with relative gyroradius ${\ensuremath{\rho}}_{*}$ is measured on the DIII-D tokamak using dimensionally similar discharges. For the first time, a two-fluid transport analysis allows the ${\ensuremath{\rho}}_{*}$ scaling of the electron and ion fluids to be determined separately. The electron diffusivity is found to scale like ${\ensuremath{\chi}}_{e}\ensuremath{\propto}{\ensuremath{\chi}}_{B}{\ensuremath{\rho}}_{*}^{1.1\ifmmode\pm\else\textpm\fi{}0.3}$ (gyro-Bohm-like) while the ion diffusivity is found to scale like ${\ensuremath{\chi}}_{i}\ensuremath{\propto}{\ensuremath{\chi}}_{B}{\ensuremath{\rho}}_{*}^{\ensuremath{-}0.5\ifmmode\pm\else\textpm\fi{}0.3}$ (Goldston-like). The scaling of the global confinement time and the effective diffusivity can vary from gyro-Bohm-like to Bohm-like depending upon whether the electrons or ions dominate the heat transport.