The edge CXRS system at ASDEX Upgrade has been upgraded to provide temporally and radially resolved measurements of the ion temperature, density, fluid velocity and hence Er via the radial force balance equation with unprecedented temporal resolution. The new system enables measurements with a frequency of up to 20 kHz and a radial resolution of down to 3 mm. Together with knowledge of ne, the CXRS measurements can be used to test the limit of the neoclassical prediction of the E×B velocity. A comparison between vE×B and vidia during a constant I-phase shows no deviations between the measurements within the temporal resolution of 100 s. Within the same timescale, the edge gradients and flows are found to evolve together during the whole transition from L- to H-mode. Hence, vE×B seems to be dominated by the collisional (neoclassical) contribution because a substantial contribution from turbulence induced flows should induce delays or differences between vE×B and vidia. A constant E×B shear is observed at the H-mode onset across a large database of L-H transitions under different conditions, including hydrogen and deuterium plasmas. This result is in agreement with [6, 7] and identifies Erneo as a key role for the L-H transition. Finally, Er and Erneo have been compared during an ELM cycle. Good agreement has been observed throughout the ELM cycle, except for the phase 2 to 4 ms after the ELM crash. However, due to the relatively large error bars in this phase further investigations are needed to confirm this observation.
Cavedon, M., Putterich, T., Viezzer, E., Birkenmeier, G., Dunne, M., Dux, R., et al. (2017). The role of radial electric field and neoclassical transport in the establishment and sustainment of the edge transport barrier in the ASDEX Upgrade tokamak. In 44th EPS Conference on Plasma Physics, EPS 2017. European Physical Society.
The role of radial electric field and neoclassical transport in the establishment and sustainment of the edge transport barrier in the ASDEX Upgrade tokamak
Cavedon M.;
2017
Abstract
The edge CXRS system at ASDEX Upgrade has been upgraded to provide temporally and radially resolved measurements of the ion temperature, density, fluid velocity and hence Er via the radial force balance equation with unprecedented temporal resolution. The new system enables measurements with a frequency of up to 20 kHz and a radial resolution of down to 3 mm. Together with knowledge of ne, the CXRS measurements can be used to test the limit of the neoclassical prediction of the E×B velocity. A comparison between vE×B and vidia during a constant I-phase shows no deviations between the measurements within the temporal resolution of 100 s. Within the same timescale, the edge gradients and flows are found to evolve together during the whole transition from L- to H-mode. Hence, vE×B seems to be dominated by the collisional (neoclassical) contribution because a substantial contribution from turbulence induced flows should induce delays or differences between vE×B and vidia. A constant E×B shear is observed at the H-mode onset across a large database of L-H transitions under different conditions, including hydrogen and deuterium plasmas. This result is in agreement with [6, 7] and identifies Erneo as a key role for the L-H transition. Finally, Er and Erneo have been compared during an ELM cycle. Good agreement has been observed throughout the ELM cycle, except for the phase 2 to 4 ms after the ELM crash. However, due to the relatively large error bars in this phase further investigations are needed to confirm this observation.
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