Measurement of the edge ion temperature in W7-X with island divertor by a retarding field analyzer probe

Li, Y.; Henkel, Malte; Liang, Yun-Feng; Knieps, A.; Drews, P.; Killer, C.; Nicolai, D.; Cosfeld, J.; Geiger, J.; Feng, Y.; Effenberg, F.; Zhang, D.; Hacker, P.; Höschen, D.; Satheeswaran, G.; Liu, Shaocheng; Grulke, O.; Jakubowski, M.; Brezinsek, S.; Otte, M.; Neubauer, O.; Schweer, B.; Xu, Guo Sheng; Cai, Jianqing; Huang, Zhuo

doi:10.1088/1741-4326/ab3a79

Cited by 11 publications

(15 citation statements)

References 33 publications

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“…It is now possible to extract the heat flux onto the divertor for its corresponding measurement point in the SOL, which is displayed in figure 5. For T i ≃ T e in the vicinity of the divertor, which is to be expected, considering that usually this condition is already met at the vicinity of the LCFS [56], ion reflection is considered negligible (which is typically the case for a carbon target) and the usual sheath entrance condition v s = c s is taken, the heat flux entering the sheath in front of the wall, q t can be expressed in terms of the plasma parameters as in [57]:…”

Section: Therein)mentioning

confidence: 67%

On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas

Maragkoudakis¹,

Carralero²,

Estrada³

et al. 2022

Nucl. Fusion

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The formation of the radial electric field, Er in the SOL has been experimentally studied for attached divertor conditions in stellarator W7-X. The main objective of this study is to test the validity in a complex 3D island divertor of simple models, typically developed in tokamaks, relating Er in the SOL to the sheath potential drop gradient at the target. Additionally, we investigate the effect of the edge Er shear on the reduction of density fluctuation amplitude, a well-established phenomenon according to the existing bibliography. The main diagnostic for measurements in the SOL is a V-band Doppler reflectometer that can provide the measurement of the Er and density fluctuations with good spatial resolution. Three-dimensional measurements of divertor parameters have been carried out using infrared cameras, with the exponential decay length of the divertor heat flux (λq) resulting a suitable proxy for the model-relevant λT, the exponential decay length of the temperature at the divertor. In the investigated attached regimes, it is shown for the first time that the formation of the Er in the SOL depends on parameters at the divertor, following a Er ∝ Te/λq qualitatively similar to that found in a tokamak. Then, from the analyzed plasmas, the observed Er shear at the edge is linked to a moderate local reduction of the amplitude of density fluctuations.

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Section: Therein)mentioning

confidence: 67%

On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas

Maragkoudakis¹,

Carralero²,

Estrada³

et al. 2022

Nucl. Fusion

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“…Whether the ion temperature is actually higher than the electron temperature at the observed locations in the divertor region remains an open issue. Interestingly, RFA probe measurements indicate T i > T e [3] further upstream.…”

Section: Discussionmentioning

confidence: 98%

“…Thus, many sightlines or diagnostic locations in case of probes are required for satisfactory boundary characterisation. In a recent example, a retarding field analyzer (RFA) probe on a reciprocating manipulator has been used around the midplane of W7-X to measure the T i edge profile through an island [3]. However, these measurements are locally restricted and do not provide temperatures close to the targets, where plasma parameters drastically change during detachment [4].…”

Section: Introductionmentioning

confidence: 99%

2D coherence imaging measurements of C²⁺ ion temperatures in the divertor of Wendelstein 7-X

et al. 2021

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For the first time, 2D ion temperature values are derived from coherence imaging spectroscopy (CIS) fringe contrast measurements by taking Zeeman line broadening effects into account during the analysis procedure of a spatial-heterodyne CIS instrument. This allowed 2D images of C 2+ ion temperatures (T i ) across the 3D-shaped island divertor of the Wendelstein 7-X stellarator. Ion temperatures ranging from 10 to 20 eV are observed for the C 2+ impurity species in the region above the divertor targets. During the transition from the attached to the detached plasma state, the C 2+ radiation zone moves from close to the divertor target towards the last closed flux surface. Within this radiation zone, C 2+ temperature does not decrease significantly. Experimentally, the coherence imaging measurements were cross-calibrated at one poloidal cross-section using a high resolution Echelle spectrometer, that shared its sightlines with the coherence imaging diagnostic. The spectra demonstrated that, apart from Doppler broadening, the Zeeman effect significantly contributes to the spectral line broadening and cannot be neglected when analyzing the CIS contrast data for T i extraction in the edge and scrape-off-layer of Wendelstein 7-X (W7-X), due to the relatively low temperatures (T i < 100 eV) and high magnetic fields (B ≈ 2.5 T).

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“…When the ion and electron energy exchange is introduced, based on the two-point model including the ion temperature [20], the f t equation could be extended to…”

Section: Estimation Of Upstream and Downstream Electron Temperature R...mentioning

confidence: 99%

“…The effect of the ion temperature is barely considered in the theoretical simulation [17]. While in some experiments, the upstream ion temperature T iu has been measured to be much larger than the upstream electron temperature T eu , and their ratio τ u = T iu /T eu is strongly dependent on the plasma density and collisionality [18][19][20][21]. This implies that the effect of upstream ion temperature may play indirectly an important role on the W erosion in the downstream area of the divertor.…”

Section: Introductionmentioning

confidence: 99%

Effect of edge ion temperature on the divertor tungsten sputtering in WEST

Fedorczak

et al. 2023

Nucl. Fusion

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The influence of upstream ion temperature in the scrape-off layer (SOL) on the tungsten (W) sputtering in the divertor is studied in the WEST tokamak. For an almost constant power into the SOL, the upstream ion temperature and its ratio over the electron temperature gradually increase with the decrease of electron density in the SOL. This increment is observed to enhance the energy transfer from ions to electrons. This increases the downstream electron temperature and by coupling of electrons and ions, the impact energy of ions causing W sputtering in the divertor. This enhancement mechanism may become crucial to sputtering the W material for high upstream Ti/Te ratio since the impact energy of ions in the divertor would increase accordingly.

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Measurement of the edge ion temperature in W7-X with island divertor by a retarding field analyzer probe

Abstract: The Ti edge profile has been successfully measured at W7-X in an island divertor configuration using a retarding field analyzer (RFA) probe on a reciprocating manipulator.

Cited by 11 publications

References 33 publications

On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas

On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas

2D coherence imaging measurements of C²⁺ ion temperatures in the divertor of Wendelstein 7-X

Effect of edge ion temperature on the divertor tungsten sputtering in WEST

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Measurement of the edge ion temperature in W7-X with island divertor by a retarding field analyzer probe

Abstract: The Ti edge profile has been successfully measured at W7-X in an island divertor configuration using a retarding field analyzer (RFA) probe on a reciprocating manipulator.

Cited by 11 publications

References 33 publications

On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas

On the interaction between the island divertor heat fluxes, the scrape-off layer radial electric field and the edge turbulence in Wendelstein 7-X plasmas

2D coherence imaging measurements of C2+ ion temperatures in the divertor of Wendelstein 7-X

Effect of edge ion temperature on the divertor tungsten sputtering in WEST

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2D coherence imaging measurements of C²⁺ ion temperatures in the divertor of Wendelstein 7-X