Sawtooth-free Ohmic discharges in ASDEX and aspects of neoclassical ion transport

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Abstract
Sawtooth-free Ohmic discharges can serve as a model case of a quiescent tokamak plasma. The properties and global parameters of such discharges as observed in ASDEX are discussed as well as the mechanism apparently responsible for stabilization of the sawtooth instability. Stationary Ohmic discharges were used to investigate particle, impurity and energy transport in the absence of the sawtooth instability. Particular emphasis was placed on comparing these results with the predictions of neoclassical theories. The level of the ion energy transport is found to be that predicted by neoclassical theory. Particle transport and impurity transport are explained in terms of neoclassical inward drift velocities and diffusion coefficients with the same small anomalous contributions. In the central region of the plasma, where the power flux is low, the values of the electron heat conductivity were found to be very low.