Turbulent spectrum analysis in TFR tokamak plasmas

Abstract

Low frequency turbulence in TFR has been studied over a wide range of parameters and under many experimental conditions and a modelling of the frequency spectrum is presented. The main results are as follows. In ohmic discharges the turbulent spectrum is peaked around K_x approximately 5 cm^-1 (K_{perpendicular to} rho _i approximately 0.6) and decreases monotonically for both larger and smaller values of K_x. The decrease for small K_x values is particularly severe. No single linear dispersion relation is possible but, rather, a large domain of phase velocities is covered by the most intense waves. During auxiliary ICRF heating experiments, there is an increase of the level of turbulence which is proportional to the square root of RF power. Finally a strong increase in the turbulence after minor and major disruptions is observed.