ANOMALOUS RESISTIVITY OF A TOROIDAL PLASMA IN THE PRESENCE OF MAGNETIC TURBULENCE

The impact of anomalous radial diffusion due to turbulent magnetic fields on the electrical conductivity of a toroidal plasma is investigated. The problem is solved by evaluating an appropriate three-dimensional response function for the current density. This yields an analytic expression of the turbulent electrical conductivity including trapped particle effects. In the pressure gradient region, the conductivity is generally enhanced with respect to the neoclassical one. This results in an anomalously low plasma resistance - a trend observed in many tokamak experiments. The analytic expression is shown to be in very good agreement with numerical calculations using a three-dimensional bounce averaged Fokker-Planck code. By a similar method, the toroidal response function for radiofrequency current drive in the presence of magnetic turbulence is also found.