Gyroradius Scaling of Electron and Ion Transport

Abstract

The scaling of heat diffusion with relative gyroradius ${\rho }_{*}$ is measured on the DIII-D tokamak using dimensionally similar discharges. For the first time, a two-fluid transport analysis allows the ${\rho }_{*}$ scaling of the electron and ion fluids to be determined separately. The electron diffusivity is found to scale like ${\chi }_e\propto {\chi }_B{\rho }_{*}^{1.1\pm 0.3}$ (gyro-Bohm-like) while the ion diffusivity is found to scale like ${\chi }_i\propto {\chi }_B{\rho }_{*}^{-0.5\mathrm{}\pm 0.3}$ (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.