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

Experimental campaign

2018 Spring

Proposal title

Turbulence and radial electric field asymmetries in high iota magnetic configuration measured by Doppler reflectometry

Name and affiliation of proponent

T. Estrada, E. Sánchez, D. Carralero, J. M. García-Regaña, and the TJ-II team LNF, CIEMAT

Details of contact person at LNF (if applicable)

N/A

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

Motivation 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 [1-3] 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 [4,5]. 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 [6]. 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. Differences in the turbulence intensity have been found in previous experiments when comparing the k⊥ spectra measured at poloidally separated positions in the same flux-surface, in ECH heated plasmas in the standard magnetic configuration. This behaviour remains almost unchanged in ECH plasmas with higher density and/or lower heating power. On the other hand, Er profiles obtained from the perpendicular rotation velocity measured at the two plasma regions show pronounced differences in low density plasmas, i.e. plasmas in neoclassical electron root confinement. At higher plasma densities the Er asymmetry gradually decreases and almost disappears in ion root plasmas. No asymmetries are found in NBI heated plasmas, i.e. higher density, lower electron temperature, where very similar turbulence intensity, spectral shape and Er profile are measured at both plasma regions. Finally, the asymmetry in the turbulence intensity found in the standard magnetic configuration in ECH plasmas, reverses in the magnetic configuration with high rotation transform. In order to further investigate the impact of the magnetic configuration on the turbulence and Er asymmetries we propose to cover additional plasma scenarios in the high iota magnetic configuration.

Proposal We propose to explore the magnetic configuration 42_102_69 in plasmas heated with ECH off-axis with high & low input power. To properly measured the k⊥ spectra at the two poloidally separated positions a series of about 20 similar discharges is needed in each scenario.

References

[1] M. Nadeem, et al., Phys. Plasmas 8 (2001) 4375 [2] P. Xanthopoulos, et al., Phys. Rev. X 6 (2016) 021033 [3] E. Sánchez, et al., 21st ISHW (2017) Kyoto, Japan [4] J.M. García-Regaña, et al., Nucl. Fusion 57 (2017) 056004 [5] J.M. García-Regaña, et al., 21st ISHW (2017) Kyoto, Japan [6] T. Happel, et al., Rev. Sci. Instrum. 80 (2009) 073502

If applicable, International or National funding project or entity

FIS2017-88892-P EUROfusion WP.S1

Description of required resources

Required resources:

• Number of plasma discharges or days of operation: Two experimental days are requested to cover at least two plasma scenarios
• Essential diagnostic systems:

Doppler reflectometer, Microwave interferometer, Thomson scattering, AM reflectometer, ECE, Hα detectors, Diamagnetic loop, Rogowski coils, Mirnov coils, SXR, bolometry, CX

• Type of plasmas (heating configuration): ECH heated plasmas in high iota configuration (42_102_69)
• Specific requirements on wall conditioning if any: fresh Li coates wall for a good reproducibility
• External users: need a local computer account for data access: N/A
• Any external equipment to be integrated? Provide description and integration needs: N/A

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy) June-2018 Not available in April, and on 22nd and 24th of May.