Edge topology and flows in the reversed-field pinch (Abstract/Comunicazione in atti di convegno)

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Label
  • Edge topology and flows in the reversed-field pinch (Abstract/Comunicazione in atti di convegno) (literal)
Anno
  • 2011-01-01T00:00:00+01:00 (literal)
Alternative label
  • Spizzo G.; Agostini M.; Scarin P.; Vianello N.; White R. B.; Cappello S.; Puiatti M. E.; Valisa M. (2011)
    Edge topology and flows in the reversed-field pinch
    in 5th International Workshop on Stochasticity in Fusion Plasmas, Julich, Germany, April 11-14, 2011
    (literal)
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  • Spizzo G.; Agostini M.; Scarin P.; Vianello N.; White R. B.; Cappello S.; Puiatti M. E.; Valisa M. (literal)
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  • http://www2.fz-juelich.de/sfp/ (literal)
Note
  • Comunicazione (literal)
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  • 1 Consorzio RFX, Euratom-ENEA Association, Padova - Italy; 2 Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543. (Spizzo G. 1; Agostini M. 1; Scarin P. 1; Vianello N. 1; White R. B. 2; Cappello S. 1; Puiatti M. E. 1; Valisa M. 1) (literal)
Titolo
  • Edge topology and flows in the reversed-field pinch (literal)
Abstract
  • Edge topology and plasma flow deeply influence transport in the RFX-mod reversed field pinch, playing an important role in many practical aspects of plasma performances, such as access to enhanced confinement regimes 1, the impact on global power balance and operative limits, like the density limit2. In our analysis a central role is played by the edge electric field, which is determined by the ambipolar constraint guaranteeing quasi-neutrality in a sheath next to the plasma wall. Its radial component is experimentally determined in RFX over the whole toroidal angle by means of a diagnostic set measuring edge plasma potential and flow with different techniques 1. The measured radial electric field is a guess for describing the potential in the form V ( p, ?, ?) ( p radial coordinate, ?, ? angles), by means of the Hamiltonian guiding center code Orbit3. In numerical simulations we included a schematic treatment of a realistic wall with recycling. Simulations show that a proper functional form of the potential, worked out from the experimental guess, is sufficient to balance the differential radial diffusion of electrons and ions subject to magnetic island O- and X-points. These islands are naturally present in the RFP edge, due to the vanishing of q at the reversal surface4. Electrons spend more time in the X-points of such islands than in O-points; ions have comparatively larger drifts and their radial motion is more uniform over the toroidal angle. The final spatial distribution of V ( p, ?, ?) results in a complex 3D pattern, with convective cells that close onto the wall. This condition, for some threshold values of parameters as q(a) and n/nG (nG Greenwald density), as well as of the boundary electron density and temperature (that depend on wall conditioning), can degenerate to more pathologic situations, such as the development of a stagnation point for electron density (precursor of the density limit2). (literal)
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