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 , usually denoted by $\Phi _{1}=\Phi _{1}(\theta ,\phi )$, with $\theta$ and $\phi$ 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: Failed to parse (syntax error): {\displaystyle n_{a0}=\left<n\right>\exp\left(-Z_{a}e\Phi_1/T_{a}\right)} , with Failed to parse (syntax error): {\displaystyle \left<...\right>} the flux-surface-average. In TJ-II plasmas experiments and simulations have shown that $e\Phi _{1}/T_{a}$ can take values from $O(0.01)$ to $O(0.1)$. 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 $\Phi _{1}$ the impurities of moderate to high $Z$ should experience strong variations of their densities over the flux surfaces, increasing with $Z$. These, in turn, should result in an anisotropic radiation over each flux surface and consequently a radially asymmetric radiation pattern should follow.

In the present experiment the analysis of the radial profiles and time evolution of the plasma emissivity using the TJ-II bolometry system after the inyection of some selected impurities by gas puffing is proposed. The experiment aims at studying the above-mentioned link between the radially assymetric emissivity and the measured and predicted $\Phi _{1}$. The measurement and evolution of $\Phi _{1}$ will be tracked during the discharges using the duplicated Langmuir probe system plasma floating potential measurements. Numerical calculations of $\Phi _{1}$ will be carried out with the neoclassical version of the code EUTERPE at different radial locations. The application of fluid tools is also foreseen for the comparison between simulations and with the experimental results.

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

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References

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