Direct measurements of the plasma potential in ELMy H-mode plasma with ball-pen probes on ASDEX Upgrade tokamak

Adámek, Jiřı́; Rohde, V.; Müller, Hans; Herrmann, A.; Ioniţă, C.; Schrittwieser, R.; Mehlmann, F.; Ştöckel, J.; Horáček, J.; Brotánková, J.

doi:10.1016/j.jnucmat.2009.01.286

Cited by 31 publications

(25 citation statements)

References 8 publications

(5 reference statements)

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“…The ball pen probe BPP was exposed to the SOL of a mid size tokamak for the first time. It consists of four protruding pins and four retracted ball pen pins which allow for a direct measurement of the plasma potential V pl [17]. The protruding pins are also 2 mm long with a diameter of 0.9 mm, while the ball pen pins have a diameter of 4 mm.…”

Section: Methodsmentioning

confidence: 99%

Latest investigations on fluctuations, ELM filaments and turbulent transport in the SOL of ASDEX Upgrade

et al. 2011

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Abstract. This paper presents turbulence investigations in the scrape off layer (SOL) of ASDEX Upgrade in Ohmic, L-mode and H-mode discharges using electrostatic and electromagnetic probes. Detailed studies are performed on small scale turbulence and on ELM filaments. Simultaneous measurements of floating and plasma potential fluctuations revealed significant differences between these quantities. Large errors can occur when the electric field is extracted from floating potential measurements, even in Ohmic discharges. Turbulence studies in Ohmic plasmas show the existence of density holes inside the separatrix and blobs outside. Close to the separatrix a reversal of the poloidal blob propagation velocity occurs. Investigations on the Reynolds stress in the scrape-off layer show its importance for the momentum transport in L-mode while its impact for momentum transport during ELMs in H-mode is rather small. In the far SOL the electron density and temperature were measured during type-I ELMy H-mode at ASDEX Upgrade resolving ELM filaments. Strong density peaks and temperatures of several 10 eV were detected during the ELM events. Additional investigations on the ions in the filaments by a retarding field analyzer indicate ion temperatures of 50-80 eV. ELMs expel also current concentrated in filaments into the scrape off layer. Furthermore discharges with small ELMs were studied. In N 2 seeded discharges the type-I ELM frequency rises and the ELM duration decreases. For discharges with small type-II ELMs the mean turbulent radial particle flux is increased over the mean particle flux in type-I ELM discharges at otherwise similar plasma parameters.

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Section: Methodsmentioning

confidence: 99%

Latest investigations on fluctuations, ELM filaments and turbulent transport in the SOL of ASDEX Upgrade

et al. 2011

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“…More details on this probe are published in [24]. An important feature of this probe is the possibility to measure V pl directly using the BP tips.…”

Section: Methodsmentioning

confidence: 99%

Towards Fast Measurement of the Electron Temperature in the SOL of ASDEX Upgrade Using Swept Langmuir Probes

Müller

Adámek

Horáček

et al. 2010

Contrib. Plasma Phys.

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On ASDEX Upgrade first experiments were made using single probes with a voltage sweep frequency up to 100kHz. Possibilities and limitations using fast swept probes with a standard diagnostic and analysis tools are discussed. A good agreement between the data derived from fast swept single probe characteristics and floating as well as saturation current measurements was found. In a stationary (non ELMing) plasma the data of the fast swept probe are compared to standard slow swept probes (kHz range) showing an improvement of the measurement by faster sweeping. While ELM filaments already could be resolved the access of electron temperature fluctuations in small scale turbulence still has to be improved. Further comparisons are done in ELMy H-mode with combined ball-pen probe/floating potential measurements which can deliver electron temperatures with 25 μs time resolution at reduced spatial resolution compared to pin probes. During ELMs the electron temperatures derived from the ball-pen probe and fast swept single probes agreed.

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“…A recent experiment in AUG, in which V p was assessed by two independent techniques, demonstrates the feasibility of such measurements. In this experiment, which will be presented in a future paper, the RPM was equipped with a probe head consisting of a ball pen probe (BPP) which measures a potential close to V p [10,11], and an electrically floating LP. As shown in figure 4, at the turning point of the reciprocation, the LP reaches the temperature at which it undergoes a transition to an EP, providing additional measurements of V EP ≈ V p during the probe outward motion.…”

Section: The Importance and Feasibility Of Direct Plasma Potential Mementioning

confidence: 99%

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

et al. 2013

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Abstract.We report the latest results of turbulence and transport studies in the ASDEX Upgrade scrapeoff layer (SOL). Dissimilarity between the plasma and the floating potential fluctuations is studied experimentally and by gyrofluid simulations. Measurements by a retarding field analyzer reveal that both, ELM and turbulent filaments convey hot ions over large radial distances in the SOL. The measured far SOL ELM ion temperature increases with the ELM energy, consistent with earlier observations that large ELMs deposit a large fraction of their energy outside the divertor. In the SOL, the ELM suppression by magnetic perturbations (MPs) results into lower ELM ion energy in the far SOL. At the same time, large filaments of ion saturation current are replaced by more continuous bursts. Splitting of the divertor strike zones observed by the infrared imaging in H-mode with MPs agree with predictions from the EMC3-Eirene simulations. This suggests that the 'lobe' structures due to perturbation fields observed near the X-point are not significantly affected by plasma screening, and can be described by a vacuum approach, as in the EMC3-Eirene. Finally, some effects of the MPs on the L-mode SOL are addressed.

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Direct measurements of the plasma potential in ELMy H-mode plasma with ball-pen probes on ASDEX Upgrade tokamak

Abstract: Experimental investigations of the plasma potential and electric field were performed for

Cited by 31 publications

References 8 publications

Latest investigations on fluctuations, ELM filaments and turbulent transport in the SOL of ASDEX Upgrade

Latest investigations on fluctuations, ELM filaments and turbulent transport in the SOL of ASDEX Upgrade

Towards Fast Measurement of the Electron Temperature in the SOL of ASDEX Upgrade Using Swept Langmuir Probes

Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

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