Modelling of the field line penetration and force transfer by the dynamic ergodic divertor of TEXTOR

Abstract

For describing the penetration of the external dynamic ergodic divertor magnetic field into the plasma, a single fluid magnetohydrodynamic model has been applied which contains all three components of the magnetic and electric field, the electrical currents and the flow pattern. The set of equations is solved numerically. The analysis shows that the external magnetic field penetrates nearly unperturbed into the plasma edge; at the resonance layer, where the external coils are parallel to the internal magnetic field lines, a strong shielding current is generated. Depending on the frequency difference between the external field and the plasma, the width and the amplitude of the shielding current varies: With increasing frequency, the amplitude and the width of the resonant layer grows while with decreasing frequency both quantities are diminished. The model predicts that the shielding current is connected with a localized flow of the plasma. The force transfer function is calculated from the integration of the j × B term. Differences between the expected edge and core interactions are discussed.