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@ARTICLE{Spizzo:190031,
author = {Spizzo, G. and Vianello, N. and White, R. B. and Abdullaev,
Sadrilla and Agostini, M. and Cavazzana, R. and Ciaccio, G.
and Puiatti, M. E. and Scarin, P. and Schmitz, O. and
Spolaore, M. and Terranova, D.},
title = {{E}dge ambipolar potential in toroidal fusion plasmas},
journal = {Physics of plasmas},
volume = {21},
number = {5},
issn = {1089-7674},
address = {[S.l.]},
publisher = {American Institute of Physics},
reportid = {FZJ-2015-02994},
pages = {056102},
year = {2014},
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.},
cin = {IEK-4},
ddc = {530},
cid = {I:(DE-Juel1)IEK-4-20101013},
pnm = {132 - Tokamak physics for ITER and beyond (POF2-132)},
pid = {G:(DE-HGF)POF2-132},
typ = {PUB:(DE-HGF)16},
UT = {WOS:000337107200099},
doi = {10.1063/1.4872173},
url = {https://juser.fz-juelich.de/record/190031},
}