Experimental results from the dynamic ergodic divertor (DED) at TEXTOR are given, describing the complex structure of the edge plasma and the properties of the divertor as well as its influence on ...the plasma rotation.
During the static 6/2 DED (dynamic ergodic divertor) experiments at TEXTOR, a significant impact of the edge resonant magnetic perturbation (RMP) on the blob transport in the scrape-off layer (SOL) ...has been observed. In ohmic discharges without the RMP, the turbulence intermittency extends deep into the SOL with a radially-outward speed of ∼1
km/s and ejects large turbulent flux. The fraction of the blob-carried to total turbulent flux is enhanced with increasing plasma density and reaches about 60% of the total flux in the SOL in high density discharges. With the application of the RMP, the blob size and their radially moving velocity are both reduced, resulting in a suppression of the blob transport in the SOL. It has been found that the suppression effect of the RMP on blobs is independent of the change of edge equilibrium profiles and the phasing variation of the RMP as well. The physical mechanisms appear to be consistent with the radial interchange motions of the blob structures.
The dynamic ergodic divertor (DED) produces the perturbation field, which destroys the magnetic flux surfaces and creates an open chaotic system. The plasma boundary of the TEXTOR-DED contains two ...different domains: an ergodic and a laminar one. In this work we study the power deposition patterns produced by the DED on the divertor target plates by means of the thermography. The observed heat flux patterns consist of stripes parallel to the DED coils, which changes with the degree of ergodization. Each strike zone splits up into two parts at higher level of ergodization. The structure of the power fluxes is defined by the topology of the magnetic field in the edge.
Methods of integration of the Vlasov equation along characteristics in one and two dimensions are discussed, in connection with the problem of the formation of a charge separation at a plasma edge. ...Application of these methods to the problem in which the Vlasov equation is integrated in a cylindrical geometry to calculate the electric field at a plasma edge, is presented.
The first results of the Dynamic Ergodic Divertor in TEXTOR, when operating in the m/n=3/1 mode configuration, are presented. The deeply penetrating external magnetic field perturbation of this ...configuration increases the toroidal plasma rotation. Staying below the excitation threshold for the m/n=2/1 tearing mode, this toroidal rotation is always in the direction of the plasma current, even if the toroidal projection of the rotating magnetic field perturbation is in the opposite direction. The observed toroidal rotation direction is consistent with a radial electric field, generated by an enhanced electron transport in the ergodic layers near the resonances of the perturbation. This is an effect different from theoretical predictions, which assume a direct coupling between rotating perturbation and plasma to be the dominant effect of momentum transfer.
In this contribution, we report on experimental results on edge transport in limiter H-mode plasmas in TEXTOR under the influence of the Dynamic Ergodic Divertor (DED). These plasmas are ...characterized by a pedestal structure mainly visible in the electron density, resulting in increased electron pressure gradients of up to 30
kPa/m over a pedestal width of 25
mm at high pedestal collisionalities
(
ν
e
∗
=
1
-
10
)
, and with high frequency ELMs in the range of 300–1500
Hz. Under the influence of DED the pedestal pressure is gradually reduced and completely collapses to L-mode when the laminar zone extends all the way across the pedestal width. Toroidal plasma rotation is maintained at H-mode levels by the torque introduced by DED in the stochastic region. The perturbed magnetic topology has been optimized to access conditions with a density pump-out which are strongly governed by wall pumping capabilities in TEXTOR.
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