TJ-II: Perpendicular plasma flow asymmetries in different iota magnetic configurations measured by Doppler reflectometry

Experimental campaign

Spring 2021

Proposal title

Perpendicular plasma flow asymmetries in different iota magnetic configurations measured by Doppler reflectometry

Name and affiliation of proponent

T. Estrada, E. Maragkoudakis, D. Carralero, J. Martínez

Laboratorio Nacional de Fusión, CIEMAT

Details of contact person at LNF

N/A

Description of the activity

Enter description here , including motivation/objectives and experience of the proponent (typically one-two pages)

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]. Recently, poloidal asymmetries in the rotation velocity have been detected at low k⊥. This effect appears to be more pronounced at the plasma edge under ion-root conditions and could be related to the tilt of the turbulent structures produced by sheared flows [5]. In order to investigate the possible link between this asymmetry and the tilt of turbulent structures, further experiments are needed to characterize the asymmetry and tilt angle simultaneously. We propose to study high density ECH plasmas or NBI discharges with density control, in the standard magnetic configuration and in a higher iota configuration. To properly measure with the Doppler reflectometry at different k⊥ 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. Pinzón, et al., Plasma Phys. Control. Fusion 61 (2019) 105009

International or National funding project or entity

FIS2017-88892-P

Description of required resources

Required resources:

• Number of plasma discharges or days of operation: 3 days
• Essential diagnostic systems: Doppler reflectometer, microwave interferometer, Thomson scattering, ECE, Hα detectors, diamagnetic loop, Rogosky and Mirnov coils
• Type of plasmas (heating configuration): high density ECH plasmas or NBI discharges with density control
• Specific requirements on wall conditioning if any: fresh Li coating
• External users: need a local computer account for data access: 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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