skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The Optimization of the Ergodic Structure of the Dynamic Ergodic Divertor In The TEXTOR Tokamak

Abstract

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 the 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 tomore » the calculated structures.« less

Authors:
; ; ; ; ; ; ; ;  [1]
  1. Institut fuer Plasmaphysik, Forschungszentrum Juelich, Association Euratom-FZJ, Trilateral Euregio Cluster, D-52425 Juelich (Germany)
Publication Date:
OSTI Identifier:
20797895
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 812; Journal Issue: 1; Conference: PLASMA 2005: International conference on research and applications of plasmas; 3. German-Polish conference on plasma diagnostics for fusion and applications; 5. French-Polish seminar on thermal plasma in space and laboratory, Opole-Turawa (Poland), 6-9 Sep 2005; Other Information: DOI: 10.1063/1.2168821; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; A CODES; BOUNDARY LAYERS; COMPUTERIZED SIMULATION; CONTROL; DECOUPLING; ELECTRIC CURRENTS; ELECTRON TEMPERATURE; ELECTRONS; ERGODIC DIVERTORS; HEAT TRANSFER; MAGNETIC FIELDS; OPTIMIZATION; PLASMA; PLASMA PRESSURE; PLASMA SIMULATION; RADIATION TRANSPORT; TEXTOR TOKAMAK; TOPOLOGY

Citation Formats

Jakubowski, M. W., Abdullaev, S. S., Finken, K. H., Kikuchi, Y., Kraemer-Flecken, A., Lehnen, M., Schmitz, O., Unterberg, B., and Wolf, R. C. The Optimization of the Ergodic Structure of the Dynamic Ergodic Divertor In The TEXTOR Tokamak. United States: N. p., 2006. Web. doi:10.1063/1.2168821.
Jakubowski, M. W., Abdullaev, S. S., Finken, K. H., Kikuchi, Y., Kraemer-Flecken, A., Lehnen, M., Schmitz, O., Unterberg, B., & Wolf, R. C. The Optimization of the Ergodic Structure of the Dynamic Ergodic Divertor In The TEXTOR Tokamak. United States. doi:10.1063/1.2168821.
Jakubowski, M. W., Abdullaev, S. S., Finken, K. H., Kikuchi, Y., Kraemer-Flecken, A., Lehnen, M., Schmitz, O., Unterberg, B., and Wolf, R. C. Sun . "The Optimization of the Ergodic Structure of the Dynamic Ergodic Divertor In The TEXTOR Tokamak". United States. doi:10.1063/1.2168821.
@article{osti_20797895,
title = {The Optimization of the Ergodic Structure of the Dynamic Ergodic Divertor In The TEXTOR Tokamak},
author = {Jakubowski, M. W. and Abdullaev, S. S. and Finken, K. H. and Kikuchi, Y. and Kraemer-Flecken, A. and Lehnen, M. and Schmitz, O. and Unterberg, B. and Wolf, R. C.},
abstractNote = {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 the 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.},
doi = {10.1063/1.2168821},
journal = {AIP Conference Proceedings},
number = 1,
volume = 812,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • 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 ofmore » 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.« 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
  • 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.
  • For ergodization and rotation of the plasma edge region it is proposed to install a set of 16 helical soils on the inboard side of the liner in the vacuum vessel of TEXTOR 94. The coils will be fed by a 4-phase (rotating) current with a peak value of 15 kA. The system is optimized for the following four frequencies: DC, 50 Hz, 1 kHz, and 10 kHz. To reduce the skin effect the coil conductor consists of 42 insulated wires. Each coil is enclosed in a stainless steel tube of 0.2 mm thickness. The maximum coil temperature is 200more » C, and the coolant is water at a pressure of 2.5 MPa. The coils will be supplied by eight switch mode power supply units with IGBT technology. A transformer matches the power supply to the coil parameters. The reactive power is compensated. Operation with DC-current is made possible by use of additional rectifiers.« less