This title appears in the Scientific Report : 2006 

Influence of the wall characteristics on the development of MARFE in tokamaks
Marchuk, O.
Tokar, M. Z. / Kelly, F. A.
Institut für Plasmaphysik; IPP
Contributions to plasma physics, 46 (2006)
Weinheim Wiley-VCH 2006
10.1002/ctpp.200610072
Journal Article
Fusion
Contributions to Plasma Physics 46
J
Please use the identifier: http://dx.doi.org/10.1002/ctpp.200610072 in citations.
Multifaceted asymmetric radiation from the edge (MARFE) normally develops in fusion devices close to the density limit. MARFE is considered a result of thermal instabilities excited under critical conditions through different mechanisms: impurity radiation, recycling of neutral particles, anomalous transport of charged particles and energy. Recent experiments on tokamaks TEXTOR and JET show that plasma-wall interaction, leading to release of recycling neutrals and impurities, plays a very important role for the formation of MARFE.In the present contribution we develop further the MARFE models based on the instability of particle recycling on the tokamak wall by including a simple description for the release of recycling neutrals from the wall surface into the plasma. This development takes into account the time delay between the outflow of charged particles from the plasma and influx of neutrals. The linear stability analysis shows that this does not change the critical plasma density for the MARFE formation but modifies significantly the growth rate of unstable perturbations developing when the density exceeds the threshold. These findings are confirmed in a non-linear consideration by solving the equations for the particle, momentum and energy transfer in the plasma coupled with the wall particle balance equations. This is done in a one-dimensional approximation by taking into account the variation of the main plasma parameters in the poloidal direction and making averaging in the radial direction over the plasma edge width of the penetration depth of neutrals. The intrinsic poloidal asymmetry of the system, defining the MARFE localization, is introduced by the Shafranov shift of magnetic flux surfaces. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.