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| Hauptseite > Publikationsdatenbank > Edge ambipolar potential in toroidal fusion plasmas |
| Hauptseite > Publikationsdatenbank > Edge ambipolar potential in toroidal fusion plasmas |
| Journal Article | FZJ-2015-02994 |
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2014
American Institute of Physics
[S.l.]
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Please use a persistent id in citations: http://hdl.handle.net/2128/18174 doi:10.1063/1.4872173
Abstract: A series of issues with toroidally confined fusion plasmas are related to the generation of 3D flow patterns by means of edge magnetic islands, embedded in a chaotic field and interacting with the wall. These issues include the Greenwald limit in Tokamaks and reversed-field pinches, the collisionality window for ELM mitigation with the resonant magnetic perturbations (RMPs) in Tokamaks, and edge islands interacting with the bootstrap current in stellarators. Measurements of the 2D map of the edge electric field Er(r=a,θ,ϕ) in the RFX reversed-field pinch show that Er has the same helicity of the magnetic islands generated by a m/n perturbation: in fact, defining the helical angle u=mθ−nϕ+ωt , maps show a sinusoidal dependence as a function of u, Er=E˜rsin u . The associated E × B flow displays a huge convective cell with v(a)≠0 which, in RFX and near the Greenwald limit, determines a stagnation point for density and a reversal of the sign of Er . From a theoretical point of view, the question is how a perturbed toroidal flux of symmetry m/n gives rise to an ambipolar potential Φ=Φ˜sin u . On the basis of a model developed with the guiding center code ORBIT and applied to RFX and the TEXTOR tokamak, we will show that the presence of an m/n perturbation in any kind of device breaks the toroidal symmetry with a drift proportional to the gyroradius ρ, thus larger for ions (ρ i ≫ ρ e ). Immediately, an ambipolar potential arises to balance the drifts, with the same symmetry as the original perturbation.
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