Radio-frequency sheaths physics: Experimental characterization on Tore Supra and related self-consistent modeling

During the 2011 experimental campaign, one of the three ion cyclotron resonance heating (ICRH) antennas in the Tore Supra tokamak was equipped with a new type of Faraday screen (FS). The new design aimed at minimizing the integrated parallel electric field over long field lines as well as increasing...

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Bibliographic Details
Published in:Physics of plasmas 2014-06, Vol.21 (6)
Main Authors: Jacquot, Jonathan, Milanesio, Daniele, Colas, Laurent, Corre, Yann, Goniche, Marc, Gunn, Jamie, Heuraux, Stéphane, Kubič, Martin
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Antenna design
ANTENNAS
Computer simulation
Cyclotron resonance
DESIGN
Electrical resistivity
HEAT FLUX
Heating
HEATING LOAD
ICR HEATING
LANGMUIR PROBE
LIMITERS
Parameter sensitivity
Physics
Plasma Physics
PLASMA POTENTIAL
PLASMA SCRAPE-OFF LAYER
Plasmas (physics)
Radio frequency
RADIOWAVE RADIATION
Sheaths
SIMULATION
Tokamak devices
TORE SUPRA TOKAMAK
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Summary:During the 2011 experimental campaign, one of the three ion cyclotron resonance heating (ICRH) antennas in the Tore Supra tokamak was equipped with a new type of Faraday screen (FS). The new design aimed at minimizing the integrated parallel electric field over long field lines as well as increasing the heat exhaust capability of the actively cooled screen. It proved to be inefficient for attenuating the radio-frequency (RF)-sheaths on the screen itself on the contrary to the heat exhaust concept that allowed operation despite higher heat fluxes on the antenna. In parallel, a new approach has been proposed to model self-consistently RF sheaths: the SSWICH (Self-consistent Sheaths and Waves for IC Heating) code. Simulations results from SSWICH coupled with the TOPICA antenna code were able to reproduce the difference between the two FS designs and part of the spatial pattern of heat loads and Langmuir probe floating potential. The poloidal pattern is a reliable result that mainly depends on the electrical design of the antenna while the radial pattern is on the contrary highly sensitive to loosely constrained parameters such as perpendicular conductivity that generates a DC current circulation from the private region inside the antenna limiters to the free scrape off layer outside these limiters. Moreover, the cantilevered bars seem to be the element in the screen design that enhanced the plasma potential.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4884778