The DED is a unique new experiment, offering the opportunity of studying fundamental questions of plasma and tokamak physics, which cover aspects of both concept improvements (e.g. control of plasma transport and stability) and plasma-wall interaction (e.g. control of heat and particle exhaust). The hardware of the DED has been installed in 2001/2002 in TEXTOR.

The main objectives for the installation of the DED are:

• Reduction of heat load by distributing the heat over large areas by multiple and rotating strike points.
  
  
• Influencing of plasma transport, in particular impurities, by ergodisation of the edge magnetic field and diverting the plasma flow to the target plates in the near field with the objective of impurity screening and optimised radiation cooling.
  

Additional objectives result in particular from the effect of external rotating magnetic fields on transport and stability:

• Active influence of plasma transport by externally induced rotational shear with the possibility of triggering transport barriers. This will be complemented by heating and current drive experiments, changing heating composition, momentum transfer and current profile.
  
  
• Exploration of the applicability of external rotating magnetic fields for the suppression of MHD instabilities. This includes stabilization of neoclassical tearing modes, error field amplification and rotation damping and investigation of resistive wall modes. The aim is to extend the operational limits, also in conjunction with local heating and current drive (e.g. electron cyclotron resonance heating).
  
  
• Validation of three dimensional transport models for the description of complex edge plasmas with ergodic zones and island structures, also forming an interdisciplinary link to stellarator physics.
  
  
• The fundamental properties of stochastic plasmas might also help to understand transient phenomena, such as ELMs and disruptions.

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