Background and Initial Experiments with the Dynamic Ergodic Divertor on TEXTOR

Recently, the Dynamic Ergodic Divertor (DED) with 18 helically wound coils at the high field side has been installed on TEXTOR. The DED allows static and dynamic operation up to 10 kHz. The specific features of ergodization and the open laminar zone are discussed. The dynamic feature leads to induced electrical currents and to a force transfer from the external coils to the plasma. The structures due to the DED near field are described, which result in a stripelike pattern seen both in the light of recycling particles (H, impurities) and in the heat deposition pattern. The ergodization leads either to an enhanced plasma rotation - probably due to edge electric fields - or to a reduction of the central rotation if a tearing mode is excited; the result depends on the sense of DED rotation.