TJ-II:Turbulence and radial electric field asymmetries in different iota magnetic configurations measured by Doppler reflectometry

Experimental campaign

2019 Autumn

Proposal title

Turbulence and radial electric field asymmetries in different iota magnetic configurations measured by Doppler reflectometry

Name and affiliation of proponent

Teresa Estrada CIEMAT

Details of contact person at LNF

N/A

Description of the activity

Experimental studies have been performed in TJ-II aiming at the verification of the spatial localization of instabilities predicted by the Gyrokinetic simulations in stellarators and the verification of the electrostatic potential variation on the flux surface as calculated by Neoclassical codes and its possible impact on the radial electric field. The experimental technique used to measure these quantities, Doppler reflectometry, allows the measurement of the density turbulence and its perpendicular rotation velocity at different turbulence scales and with good spatial and temporal resolution [1]. It can cover the radial region from ρ ≈ 0.6 to 0.9, at different perpendicular wave-numbers of the turbulence in the range k⊥ ≈ 1-14 cm-1, and at two plasma regions poloidally separated. Poloidal asymmetries in the k⊥ spectrum were found [2] and compared with linear gyrokinetic simulations obtained using the code EUTERPE [3]. Model and experiment agree in showing a poloidal asymmetry that depends on the magnetic configuration. The agreement is good in the high iota configuration but not in the standard one. Besides, poloidal asymmetries in the Er profile were found in low density plasmas [2] and compared with the contribution to the local radial electric field arising from −φ′1, φ1 being the component of the neoclassical electrostatic potential that varies over the flux surface [4]. The simulation results show variations in Er comparable to those found in the experiments, but there is a disagreement regarding the sign of the Er correction when the effect of kinetic electrons on φ1 is not considered as shown in recent simulations performed with the newly developed NC code KNOSOS [5]. In order to further investigate the impact of the magnetic configuration on the turbulence and Er asymmetries we propose to explore additional magnetic configurations covering different rotational transform values. We propose to explore magnetic configurations between the standard 100_44_64 and the high iota 42_102_69 in electron root confinement regime plasmas, heated with ECH full power on-axis at densities 0.5-0.6 1019 m-3. To properly measured the k⊥ spectra at the two poloidally separated positions a series of 16-20 similar discharges is needed in each scenario.

[1] T. Happel, et al., Rev. Sci. Instrum. 80 (2009) 073502

[2] T. Estrada, et al., Nucl. Fusion 59 (2019) 076021

[3] E. Sánchez, et al., Nucl. Fusion 59 (2019) 076029

[4] J.M. García-Regaña, et al., Plasma Phys. Control. Fusion 60 (2018) 104002

[5] J. L. Velasco, I. Calvo, F. I. Parra, and J. M. García-Regaña, Submitted, arXiv:1908.11615

International or National funding project or entity

FIS2017-88892-P

Description of required resources

Required resources:

• Number of plasma discharges or days of operation: 2-3 days
• Essential diagnostic systems: Doppler reflectometer, microwave interferometer, Thomson scattering, ECE
• Type of plasmas (heating configuration): ECH full power on-axis
• 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

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