Anomalous thermal confinement in ohmically heated tokamaks

A model is proposed for explaining the behaviour of the gross energy confinement time in ohmically heated tokamak plasmas. The analysis takes into account the effect of the anomalous thermal conductivity due to small scale turbulence and the effect of the macroscopic MHD behaviour which provides some constraints on the temperature profile. The results indicate that the thermal conductivity associated with the dissipative trapped-electron mode can account for Neo-Alcator scaling and the thermal conductivity associated with the ion temperature gradient mode can account for the saturation of the energy confinement time with density. Comparisons with experimental results show reasonable agreement.