Gyroradius Scaling of Electron and Ion Transport

The scaling of heat diffusion with relative gyroradius ρ* is measured on the DIII-D tokamak using dimensionally similar discharges. For the first time, a two-fluid transport analysis allows the ρ* scaling of the electron and ion fluids to be determined separately. The electron diffusivity is found to scale like χₑ∝χBρ*^1.1±0.3 (gyro-Bohm-like) while the ion diffusivity is found to scale like χᵢ∝χBρ*^-0.5±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.