A New Paradigm for Radial Ion Plasma Transport in Axisymmetric Magnetic Field

A series of basic transport physics experiments on the anomalous ion thermal conduction due to ion temperature gradient instabilities are performed in Columbia Linear Machine. The CLM results like most tokamak experimental data results indicate dependence of the ion thermal conductivity on the isotopic mass close to _{[perpendicular]} ~ A_i^-0.5, i.e., inverse gyro-Bohm, where A_i is the mass number of the isotope of hydrogen. This is in stark contradiction to most present theoretical models predicting Bohm (A_i⁰) or gyro-Bohm (A_i^0.5) scaling.

We now report another series of experiments designed to explore the physics basis of this scaling which appears to lead to a new model for this scaling based on 3-wave coupling of two ion temperature gradient radial harmonics and an ion acoustic wave. The resulting isotopic scaling of transport is ~ A_i^-0.5 dictated primarily by the ion acoustic damping. This basic physics is deemed to be extrapolatable to other experiments resolving the paradox and is tantamount to new paradigm for plasma turbulent transport.