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Title: Improved Confinement due to Open Ergodic Field Lines Imposed by the Dynamic Ergodic Divertor in TEXTOR

Abstract

The ergodization of the magnetic field lines imposed by the dynamic ergodic diverter (DED) in TEXTOR can lead both to confinement improvement and to confinement deterioration. The cases of substantial improvement are in resonant ways related to particular conditions in which magnetic flux tubes starting at the X points of induced islands are connected with the wall. This opening process is connected with a characteristic modification of the heat deposition pattern at the divertor target plate and leads to a substantial increase and steepening of the core plasma density and pressure. The improvement is tentatively attributed to a modification of the electric potential in the plasma carried by the open field lines. The confinement improvement bases on a spontaneous density built up due to the application of the DED and is primarily a particle confinement improvement.

Authors:
; ; ; ; ; ; ; ; ; ; ;  [1]; ; ;  [2];  [3];  [1];  [4];  [5]
  1. Trilateral Euregio Cluster, Institut fuer Plasmaphysik, Forschungszentrum Juelich, EURATOM Association, D-52425 Juelich (Germany)
  2. FOM Institute for Plasma Physics Rijnhuizen, EURATOM Association, Postbus 1207, NL-3430 BE Nieuwegein (Netherlands)
  3. Department of Electrical Engineering and Computer Sciences, Graduate School of Engineering, University of Hyogo, 2167, Shosha, Himeji, 671-2280 Hyogo (Japan)
  4. (Germany)
  5. Institut fuer Theoretische Physik, Heinrich-Heine Universitaet Duesseldorf, D-40225 Duesseldorf (Germany)
Publication Date:
OSTI Identifier:
20955449
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevLett.98.065001; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DEPOSITION; DIVERTORS; ELECTRIC POTENTIAL; MAGNETIC FIELDS; MAGNETIC FLUX; MAGNETIC ISLANDS; PLASMA; PLASMA CONFINEMENT; PLASMA DENSITY; TEXTOR TOKAMAK

Citation Formats

Finken, K. H., Abdullaev, S. S., Jakubowski, M. W., Bozhenkov, S., Busch, C., Kraemer-Flecken, A., Lehnen, M., Schega, D., Schmitz, O., Unterberg, B., Wolf, R. C., Zimmermann, O., Bock, M. F. M. de, Hellermann, M. von, Jaspers, R., Kikuchi, Y., Spatschek, K. H., Institut fuer Theoretische Physik, Heinrich-Heine Universitaet Duesseldorf, D-40225 Duesseldorf, and Wingen, A. Improved Confinement due to Open Ergodic Field Lines Imposed by the Dynamic Ergodic Divertor in TEXTOR. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.065001.
Finken, K. H., Abdullaev, S. S., Jakubowski, M. W., Bozhenkov, S., Busch, C., Kraemer-Flecken, A., Lehnen, M., Schega, D., Schmitz, O., Unterberg, B., Wolf, R. C., Zimmermann, O., Bock, M. F. M. de, Hellermann, M. von, Jaspers, R., Kikuchi, Y., Spatschek, K. H., Institut fuer Theoretische Physik, Heinrich-Heine Universitaet Duesseldorf, D-40225 Duesseldorf, & Wingen, A. Improved Confinement due to Open Ergodic Field Lines Imposed by the Dynamic Ergodic Divertor in TEXTOR. United States. doi:10.1103/PHYSREVLETT.98.065001.
Finken, K. H., Abdullaev, S. S., Jakubowski, M. W., Bozhenkov, S., Busch, C., Kraemer-Flecken, A., Lehnen, M., Schega, D., Schmitz, O., Unterberg, B., Wolf, R. C., Zimmermann, O., Bock, M. F. M. de, Hellermann, M. von, Jaspers, R., Kikuchi, Y., Spatschek, K. H., Institut fuer Theoretische Physik, Heinrich-Heine Universitaet Duesseldorf, D-40225 Duesseldorf, and Wingen, A. Fri . "Improved Confinement due to Open Ergodic Field Lines Imposed by the Dynamic Ergodic Divertor in TEXTOR". United States. doi:10.1103/PHYSREVLETT.98.065001.
@article{osti_20955449,
title = {Improved Confinement due to Open Ergodic Field Lines Imposed by the Dynamic Ergodic Divertor in TEXTOR},
author = {Finken, K. H. and Abdullaev, S. S. and Jakubowski, M. W. and Bozhenkov, S. and Busch, C. and Kraemer-Flecken, A. and Lehnen, M. and Schega, D. and Schmitz, O. and Unterberg, B. and Wolf, R. C. and Zimmermann, O. and Bock, M. F. M. de and Hellermann, M. von and Jaspers, R. and Kikuchi, Y. and Spatschek, K. H. and Institut fuer Theoretische Physik, Heinrich-Heine Universitaet Duesseldorf, D-40225 Duesseldorf and Wingen, A.},
abstractNote = {The ergodization of the magnetic field lines imposed by the dynamic ergodic diverter (DED) in TEXTOR can lead both to confinement improvement and to confinement deterioration. The cases of substantial improvement are in resonant ways related to particular conditions in which magnetic flux tubes starting at the X points of induced islands are connected with the wall. This opening process is connected with a characteristic modification of the heat deposition pattern at the divertor target plate and leads to a substantial increase and steepening of the core plasma density and pressure. The improvement is tentatively attributed to a modification of the electric potential in the plasma carried by the open field lines. The confinement improvement bases on a spontaneous density built up due to the application of the DED and is primarily a particle confinement improvement.},
doi = {10.1103/PHYSREVLETT.98.065001},
journal = {Physical Review Letters},
number = 6,
volume = 98,
place = {United States},
year = {Fri Feb 09 00:00:00 EST 2007},
month = {Fri Feb 09 00:00:00 EST 2007}
}
  • The dynamic ergodic divertor (DED) in TEXTOR is designed to provide a perturbed volume in the plasma edge in order to control heat and particle exhaust. The stochastic boundary layer is generated in the outermost region of the plasma, which can be divided into ergodic and laminar regions. The topology of the magnetic field is substantial for the transport properties and plasma parameters. It is expected that the formation of the proper laminar zone allows decoupling the plasma edge from the core. Due to enhancement of the radial electron heat transport in the ergodic region the electron temperature in themore » plasma boundary is reduced. Therefore one needs to find the proper ratio of the ergodic and laminar zone, which gives optimal performance of the divertor. The structure of the perturbed volume strongly depends on the safety factor profile and the plasma pressure. At the higher level of ergodization (i.e. at higher plasma current and lower beta poloidal) the laminar zone is dominant, while at the lower level of ergodization the ergodic region is more important. The topology of the perturbed volume is modeled with the ATLAS-code and basing on the results of modeling the experiments are performed and compared to the calculated structures.« less
  • 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{sub {alpha}}, impurities) and in the heat deposition pattern. The ergodization leadsmore » 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.« less
  • Systematic measurements on the edge turbulence and turbulent transport have been made by Langmuir probe arrays on TEXTOR under various static Dynamic Ergodic Divertor (DED) configurations. Common features are observed. With the DED, in the ergodic zone the local turbulent flux reverses sign from radially outwards to inwards. The turbulence properties are profoundly modified by energy redistribution in frequency spectra and suppression of large scale eddies. The fluctuation poloidal phase velocity changes direction from electron to ion diamagnetic drift, consistent with the observed reversal of the E{sub r}xB flow. In the laminar region, the turbulence is found to react tomore » an observed reduced flow shear.« less
  • Symplectic twist mapping is proposed to model magnetic field line dynamics in the ergodic divertor at the tokamak plasma edge. The relationship between a perturbation function in the mapping and magnetic field perturbation in the tokamak is found. The mapping is specified for the Dynamic Ergodic Divertor being proposed for the Torus Experiment for Technology Oriented Research (TEXTOR-94) [Fusion Eng. Design, {bold 37}, 337 (1997)]. The spectrum of the poloidal harmonics of perturbation is assumed to be localized around the harmonics m=12. It creates the stochastic layer near the resonant magnetic surface q=3. The mapping is applied to the formationmore » of the stochastic layer and field line diffusivity at the plasma edge. For the moderate magnetic field perturbations, the ergodic layer consists of a stochastic sea with regular Kolmogorov{endash}Arnold{endash}Mozer (KAM) -stability islands. The radial profiles of the Kolmogorov lengths and the field line diffusivity are studied for different perturbations. It is shown that the behavior of open field lines at the lower boundary of the stochastic layer is subdiffusive. For large perturbations a regular convective behavior of open field lines dominates over their diffusion at the large region of the ergodic layer. {copyright} {ital 1998 American Institute of Physics.}« less
  • The Dynamic Ergodic Divertor (DED) has recently been taken into operation on the TEXTOR tokamak. One of the aims is the study of the mitigation of the heat flux by rotating the divertor strike points. After an introduction into the theory of ergodization, the design of the DED is presented. The Chirikov parameter describing the level of ergodization reaches a level of up to four if the perturbation current is applied in an optimized way. Finally the rich physics options of the DED are discussed.