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TJ-II:Impurity density and potential asymmetries: Difference between revisions
TJ-II:Impurity density and potential asymmetries (view source)
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Neoclassical theory predicts a non-constant portion of the electrostatic potential over the flux surfaces | Neoclassical theory predicts a non-constant portion of the electrostatic potential over the flux surfaces | ||
<ref>H. Mynick ''Calculation of the poloidal ambipolar field in a stellarator | <ref>H. Mynick ''Calculation of the poloidal ambipolar field in a stellarator | ||
and its effect on transport'' Phys. Fluids '''27'''(8) 2086 (1984)</ref>, usually denoted by | and its effect on transport'' Phys. Fluids '''27'''(8) 2086 (1984)</ref>, usually denoted by <math>\Phi_1=\Phi_1(\theta,\phi)</math>, | ||
with <math>\theta</math> and < | with <math>\theta</math> and <math>\phi</math> the poloidal and toroidal angular coordinates. | ||
When this is taken into account the equilibrium density of the different species ''a'' present in the plasma | When this is taken into account the equilibrium density of the different species ''a'' present in the plasma | ||
varies according to their adiabatic response and can be written as: < | varies according to their adiabatic response and can be written as: <math>n_{a0}=\left<n\right>\exp\left(-Z_{a}e\Phi_1/T_{a}\right)</math>, with | ||
< | <math>\left<...\right></math> the flux-surface-average. In TJ-II plasmas experiments and simulations | ||
<ref>M A Pedrosa ''et al.'', ''Electrostatic potential variations along flux surfaces in stellarators'' Nucl. Fusion '''55''' 052001 (2015) </ref> | <ref>M A Pedrosa ''et al.'', ''Electrostatic potential variations along flux surfaces in stellarators'' Nucl. Fusion '''55''' 052001 (2015) </ref> | ||
<ref>B Liu ''et al.'' ''Direct experimental evidence of potential asymmetry in magnetic flux surfaces in stellarators'' to be submitted (2017) </ref> | <ref>B Liu ''et al.'' ''Direct experimental evidence of potential asymmetry in magnetic flux surfaces in stellarators'' to be submitted (2017) </ref> | ||
<ref>J M Garcı́a-Regaña ''et al.'' ''Electrostatic potential variation on the flux surface and its impact on impurity transport'' Nuclear Fusion submitted (2017)</ref> | <ref>J M Garcı́a-Regaña ''et al.'' ''Electrostatic potential variation on the flux surface and its impact on impurity transport'' Nuclear Fusion submitted (2017)</ref> | ||
have shown that < | have shown that <math>e\Phi_1/T_{a}</math> can take values from <math>O(0.01)</math> to <math>O(0.1)</math>. Variations are predicted to be | ||
larger at the outer radii than at the inner core, and stronger in ECRH plasmas than in NBI plasmas. Under | larger at the outer radii than at the inner core, and stronger in ECRH plasmas than in NBI plasmas. Under | ||
conditions with large < | conditions with large <math>\Phi_1</math> the impurities of moderate to high <math>Z</math> should experience strong variations of their densities over the flux surfaces, | ||
increasing with < | increasing with <math>Z</math>. | ||
These, in turn, should result in an anisotropic radiation over each flux surface and consequently | These, in turn, should result in an anisotropic radiation over each flux surface and consequently | ||
a radially asymmetric radiation pattern should follow. | a radially asymmetric radiation pattern should follow. | ||