Gas exhaust in the Wendelstein 7-X stellarator during the first divertor operation

Wenzel, U.; Schlisio, G.; Drewelow, P.; Krychowiak, M.; König, R.; Pedersen, T. S.; Bozhenkov, S.; Haak, Victoria M; Kharwandhikar, Amit; Lazerson, S.; Naujoks, D.; Perseo, V.; Winters, V.

doi:10.1088/1741-4326/ac7ac4

Cited by 6 publications

(12 citation statements)

References 19 publications

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“…In both devices much lower sub-divertor pressures were found due to a relatively low electron density in the divertor. As an example, the maximum sub-divertor pressure in W7-X was 0.15 Pa in the high-iota configuration [5], more than one order of magnitude less than in ASDEX Upgrade. The loss of plasma pressure conservation along flux tubes due to enhanced cross-field transport is the reason for that [6].…”

Section: (Some Figures May Appear In Colour Only In the Online Journal)mentioning

confidence: 92%

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Ultrahigh neutral pressures in the sub-divertor of the Large Helical Device

Wenzel,

Motojima,

Kobayashi

et al. 2024

Nucl. Fusion

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In the Large Helical Device (LHD) a low temperature mode (LTM) of the helical divertor was discovered. It combines particle detachment and very large sub-divertor pressures up to 1.4 Pa. During the LTM, the electron temperature in the divertor was in the range from 0.25 to 0.42 eV so that volume recombination occurred. This result is remarkable because in the stellarators LHD and Wendelstein 7-X (W7-X) only low sub-divertor pressures (0.03 - 0.3 Pa) were expected and measured up to now due the loss of pressure conservation along flux tubes by an enhanced cross-field transport (three-dimensional effect). It demonstrates that the more complex, three-dimensional divertors of stellarators can achieve a similar performance with respect to particle exhaust and detachment like the geometrically simpler poloidal divertors in tokamaks even if the favorable effect of flux amplification is absent. The LTM of the helical divertor depends, however, on the magnetic configuration, i.e. on geometry. It was only observed in the inward shifted configuration with Rax = 3.55 m, but not in the more frequently studied configuration with R<sub>ax</sub = 3.6 m. A nuclear fusion reactor based on the heliotron concept (DEMO) would benefit from the LTM by the very compact divertor configuration and the excellent performance.

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Section: (Some Figures May Appear In Colour Only In the Online Journal)mentioning

confidence: 92%

“…The ratio of the flux through the pumping gap to the flux to the divertor targets is called particle collection efficiency [5]. After the transition to the LTM at 3.5 s, this efficiency was much higher.…”

Section: (Some Figures May Appear In Colour Only In the Online Journal)mentioning

confidence: 99%

Ultrahigh neutral pressures in the sub-divertor of the Large Helical Device

Wenzel,

Motojima,

Kobayashi

et al. 2024

Nucl. Fusion

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“…The CCPG has the advantage over conventional pressure gauges in that the cylindrical geometry of the cathode rod, and its low work function for electrons, functions even in strong magnetic fields and resists the usually disruptive Lorentz force. This makes it a key diagnostic for scrape-off-layer (SOL) physics in fusion devices, like W7-X: placed in front of the pumping ducts in the sub-divertor volume, the pressure measurement is a direct indicator of the exhaust rate [8].…”

Section: Neutral Pressure Gauges With Lab 6 Cathodesmentioning

confidence: 99%

“…The electrodes, including a control electrode of the pressure gauge form a typical triode, which is arranged along the magnetic field lines (figure 9). The gauge has already been successfully used in operation phase 1.2 in W7-X in 2018 [8].…”

Section: Neutral Pressure Gauges With Lab 6 Cathodesmentioning

confidence: 99%

“…All of the diagnostics installed in the plasma vessel will be exposed to magnetic fields of up to 2.5 T (W7-X) [6] and 8 T (ITER) [7] for detectors at the divertor, must withstand the strong Lorentz force and require a specific characterization in respect to the magnetic field. For example, the field strength at the location of the pressure gauges in W7-X ranges from 1.64 to 2.19 T [8]. Especially the targeted long pulse and continuous mode operation of the fusion devices places high requirements on the detectors.…”

Section: Introductionmentioning

confidence: 99%

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D-Mag — a laboratory for studying plasma physics and diagnostics in strong magnetic fields

et al. 2023

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We have set up a diagnostic magnet (D-Mag) laboratory for a wide range of applications in plasma physics. It consists of a superconducting magnet for field strengths of up to 5.9 T. The main purpose is to provide an experimental environment for the development of plasma diagnostics for nuclear fusion studies and the investigation of dusty plasmas in strong magnetic fields. We describe in the article the setup and operation of the D-Mag. Some applications are presented for the development of plasma diagnostics, such as neutral pressure gauges and Langmuir probes that have to be operated in strong magnetic fields. Among the examples is the test of the long-pulse capability and stability of the diagnostic pressure gauge (DPG) for the ITER device.

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Overview over the neutral gas pressures in Wendelstein 7-X during divertor operation under boronized wall conditions

Haak

Bozhenkov

Feng

et al. 2023

Plasma Phys. Control. Fusion

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During the first test divertor campaign of Wendelstein 7-X, 13 neutral gas pressure gauges collected data in different locations in the plasma vessel, enabling a detailed analysis of the neutral gas pressures, the compression ratios and the particle exhaust rates in different magnetic field configurations. In Wendelstein 7-X, the edge magnetic islands are intersected by the divertor target plates and used to create a plasma-wall interface. As the number and position of the islands varies in different magnetic configurations, the position of the strike line on the target plates and the neutral gas pressure in the subdivertor differs between the configurations.Neutral gas pressures on the order of few 10e-04 mbar were measured in the subdivertor region.The highest neutral gas pressure of 1.75*10e-03 mbar was obtained in high iota configuration featuring 4 edge magnetic islands per cross section. The neutral particle flux through the pumping gaps into the subdivertor volume was provided by EMC3-EIRENE simulations and allowed to analyze the relation between the particle flux and the pressure distribution in the subdivertor.Finite element simulations in ANSYS provide a detailed picture of the pressure distribution in the subdivertor and agree with the neutral gas pressure measurements in the standard configuration featuring an island chain of 5 edge magnetic islands.High neutral gas pressures that were not predicted by the simulation were measured in the subdivertor region away from the main strike line for discharges in standard configuration. While the pressure ratio between the two sections of the subdivertor volume, the low and high iota section, is 0.06 in high iota configuration, a ratio of 2-5 was obtained in other configurations, indicating significant particle loads and exhaust rates on the high iota section of the subdivertor in magnetic configurations with the main strike line on the low iota divertor targets.

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Gas exhaust in the Wendelstein 7-X stellarator during the first divertor operation

Cited by 6 publications

References 19 publications

Ultrahigh neutral pressures in the sub-divertor of the Large Helical Device

Ultrahigh neutral pressures in the sub-divertor of the Large Helical Device

D-Mag — a laboratory for studying plasma physics and diagnostics in strong magnetic fields

Overview over the neutral gas pressures in Wendelstein 7-X during divertor operation under boronized wall conditions

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