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

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

doi:10.1002/ctpp.201010144

Cited by 23 publications

(25 citation statements)

References 23 publications

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“…Figure 11 shows n e , T e , V flt , and I ratio determined from the fast swept single probe (black data) during an ELM which starts at significantly lowered compared to the pedestal top temperature of about 600 eV. Starting at 3.9805s there is a good correlation of the n e,fl and T e,fl peaks as shown in figure 11 (see also [20] Investigations on T i in ELM filaments indicated that T i > T e . In [34].…”

Section: Elm Filament Temperaturesmentioning

confidence: 73%

“…To measure ion energies, a retarding field analyzer (RFA) [19] was operated in ELMy H-mode. For investigations where high heat loads have to be expected a Mach type probe head with ten in-plane Langmuir probes (HHF) [20] similar to flush mounted probes was exposed to the plasma. Five pins were poloidally staggered at each side of the probe.…”

Section: Methodsmentioning

confidence: 99%

“…For the first time in ASDEX Upgrade experiments were performed to measure T e of individual ELM filaments with 5-10 ìs time resolution using single probes with fast swept bias voltage (HHF probe head). In L-mode discharges the comparison of slow (kHz range) and fast swept single probes indicated that at bias sweep frequencies of 50-100 kHz the probe characteristics still can be used to determine n e and T e without being affected by the polarization current caused by the potential difference between the intersected flux tube and the surrounding plasma [20]. In a type-I ELMy H-mode plasma (#24925) with , , , electron cyclotron heating power , and , ELM filaments are detected with 10 ìs time resolution 45 mm outside the separatrix.…”

Section: Elm Filament Temperaturesmentioning

confidence: 99%

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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: Elm Filament Temperaturesmentioning

confidence: 73%

Section: Methodsmentioning

confidence: 99%

Section: Elm Filament Temperaturesmentioning

confidence: 99%

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

et al. 2011

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“…eV [17,18]. However, it should be noticed that none of these scarce e T measurements are available for the discharge parameters discussed here.)…”

Section: Retarding Field Analyzermentioning

confidence: 94%

First measurements of edge localized mode ion energies in the ASDEX Upgrade far scrape-off layer

Kočan

Herrmann

Müller

et al. 2011

Plasma Phys. Control. Fusion

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Abstract. Using the Retarding Field Analyser (RFA) technique, ion energies carried by ELM filaments have been measured for the first time in the far scrape-off layer (SOL) of the ASDEX Upgrade tokamak. Energies, ELM i E, exceeding 160 eV have been found, 5 -6 cm outside the separatrix, with a decay length of about 2 cm. The measured ELM particle ion temperature in the far SOL is in the range 80 50 − ≈ IntroductionThermal heat loads to the first wall during edge localized modes (ELMs) have been identified as one of the important issues for ITER burning plasma operation and determine the design of the ITER blanket module shaping and power handling capacity [1]. These heat loads scale with the energies carried by ELM ions to the first wall, which, in turn, depend on dissipation by parallel losses of the ELM energy to the divertor targets as the ELM particles travel across the SOL. Direct measurements of the ELM ion energies in the far SOL are, therefore, important in order to constrain the models of the ELM parallel transport in the SOL [2,3], which, in turn, increases the confidence in the model predictions towards ITER.Earlier measurements of the heat loads to the first wall in ASDEX Upgrade (AUG) revealed that up to~25% of the energy lost per ELM can be deposited on non-divertor components, indicating that ELM ions can carry relatively large fractions of the energy with which they are released into the SOL to the first wall [4,5,6]. These observations (also seen later on JET [7,8]), were consistent with increase by an order of magnitude of the tungsten influx from the outboard limiters in AUG during ELMs compared to inter-ELM periods [9]. Energetic ELM ions (impact energies exceeding 400 eV) in the far SOL (typically 2-3 characteristic SOL power widths outside the separatrix) were measured directly for the first time in JET [10] (and more recently in MAST [11]) using a Retarding Field

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“…The BPP screens the electrons by magnetic field in order to achieve α ≈ 0, because ions with larger Larmor radius can penetrate inside the hole, whilst the electrons cannot. Detailed comparison with other diagnostics demonstrated such functionality [5,3] Especially, direct comparison with 100kHz-swept Langmuir probe LP 3 shows quite good agreement [7] in absolute values up to high frequencies. It was found experimentally [3] that α bpp = 0.6 ± 0.3.…”

Section: Introductionmentioning

confidence: 99%

Interpretation of fast measurements of plasma potential, temperature and density in SOL of ASDEX Upgrade

et al. 2010

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Abstract. This paper focuses on interpretation of fast measurement of plasma density, potential and electron temperature in SOL. Steady-state radial profiles demonstrate credibility of the Ball-pen probe. Spatial and temporal scales are found consistent with expectations based on interchange driven turbulence model generating blobs. Conditionally averaged signals found for both potential and density are also consistent, however, those for temperature show unexpected short drop at the very center of a blob.

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

Cited by 23 publications

References 23 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

First measurements of edge localized mode ion energies in the ASDEX Upgrade far scrape-off layer

Interpretation of fast measurements of plasma potential, temperature and density in SOL of ASDEX Upgrade

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