Anomalous ion thermal transport in hot ion plasmas by the ion temperature gradient mode

摘要

Experiments show that the observed radial profiles of the ion thermal conductivity (chi)(sub i) have the opposite shapes with those obtained from the ion temperature gradient mode ((eta)(sub i) mode) turbulence model by the traditional mixing length estimate. In this work, this radial profile problem is reconsidered with an electromagnetic study of the linear stability of the toroidal (eta)(sub i) mode and a new rule for choosing the mixing length. It is first shown that the electromagnetic effect gives a significant stabilizing effect on the toroidal (eta)(sub i) mode, and that the observed reduction of (chi)(sub i)(r) in the core region can be explained by this electromagnetic effect. Secondly, in view of earlier numerical simulations showing the transfer of fluctuation energy to larger scales that those for the fastest growth rate, as well as fluctuation measurements indicating longer radial correlation lengths, a new mixing length formula is proposed to explain the radial increase of the (chi)(sub i). It is shown the new formula fits well the observed (chi)(sub i)(r) profiles in two TFTR supershot discharges and also gives the scaling law in the current and the magnetic field which agrees better with experiment than the conventional formula.