View source for TJ-II:Impurity density and potential asymmetries

== Experimental campaign ==
2017 Spring

== Proposal title ==
'''Impurity density and potential asymmetries'''

== Name and affiliation of proponent ==
Jose M García Regaña

== Description of the activity, including motivation/objectives and experience of the proponent (typically one-two pages)==

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
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 <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 
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>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>
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
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 <math>Z</math>.
These, in turn, should result in an anisotropic radiation over each flux surface and consequently
a radially asymmetric radiation pattern should follow.

== If applicable, International or National funding project or entity ==
Enter funding here or N/A

== Description of required resources ==
Required resources:
* Number of plasma discharges or days of operation: 
* Essential diagnostic systems:
* Type of plasmas (heating configuration):
* Specific requirements on wall conditioning if any:
* External users: need a local computer account for data access: yes/no
* Any external equipment to be integrated? Provide description and integration needs:

== Preferred dates and degree of flexibility ==
Preferred dates: (format dd-mm-yyyy)

== References ==
<references />

<hr>
[[TJ-II:Experimental proposals|Back to list of experimental proposals]]

[[Category:TJ-II internal documents]]
[[Category:TJ-II experimental proposals]]