Plasma rotation induced by the dynamic ergodic divertor

After introduction of the experimental options available with the Dynamic Ergodic Divertor (DED) and a discussion of the static aspects of the ergodic and laminar zones, the dynamic aspects of the rotating DED field are emphasized. The rotating perturbation field induces a shielding current which is modelled under different assumptions. Interaction of the shielding current with that of the DED coils results in a torque exerted by the coils on the plasma. The location of the maximum of this torque with respect to the frequency depends critically on the width of the shielding current, and for the TEXTOR-DED conditions it is in the frequency band of 1-30 kHz. The DED will have the option of operation with full power in this band so that the basic investigations on the field line penetration can be attempted. The force transferred to the plasma has two components, a weaker toroidal one and a dominant poloidal one. The toroidal force component has about the same value as the one from NBI; from the experience with NBI induced plasma rotation, a substantial plasma acceleration in the toroidal direction is expected. For neoclassical reasons it is not yet clear whether the dominant poloidal force component will result in a poloidal plasma rotation or a radial force. If the poloidal rotation is inhibited, a static radial electric field is estimated on the basis of a revisited neoclassical theory to be of the order of several kilovolts per metre.