Effects of toroidal plasma current on divertor power depositions on Wendelstein 7-X

Gao, Yu; Geiger, J.; Jakubowski, M.; Drewelow, P.; Endler, M.; Rahbarnia, K.; Bozhenkov, S.; Otte, M.; Suzuki, Y.; Feng, Y.; Niemann, H.; Pisano, F.; Ali, Adnan; Sitjes, A. Puig; Zanini, M.; Laqua, H. P.; Stange, T.; Marsen, S.; Szepesi, T.; Zhang, D.; Killer, C.; Hammond, K. C.; Lazerson, S.; Cannas, B.; Thomsen, H.; Andreeva, T.; Neuner, U.; Schilling, J.; Knieps, A.; Rack, M.; Liang, Yun-Feng

doi:10.1088/1741-4326/ab32c2

Cited by 32 publications

(39 citation statements)

References 39 publications

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“…For a reduced island size, connection lengths increase, the closed field line region around the O point becomes larger, and the LCFS moves outwards. A similar effect to reduced island sizes is observed when the rotational transform is slighty increased due to the toroidal plasma current [50], here showcased for a situation with 𝐼 𝑝 =6 kA. In this situation, the island moves inwards, away from the divertor (due to the low shear profile of W-7X [14]), resulting in longer connection lengths and a larger confined region around the O point.…”

Section: Magnetic Field Geometrysupporting

confidence: 70%

Reciprocating probe measurements in the test divertor operation phase of Wendelstein 7-X

Killer,

Drews,

Grulke

et al. 2021

Preprint

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Reciprocating probes are a classic and widespread tool for the investigation of the edge and Scrape-Off Layer of magnetic fusion plasmas. In the Wendelstein 7-X (W7-X) stellarator, the Multi-Purpose Manipulator serves as a multi-user platform for probe measurements of various kinds. This paper presents a review on reciprocating probe operation during the first operation phase of W7-X with a test divertor (2017)(2018). It gives an overview of the diverse zoo of probe heads and presents lessons learned about probe operation in complex magnetic geometries, operation safety, and probe head design. A few examples of probe measurements with a focus on unexpected observations are presented.

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Section: Magnetic Field Geometrysupporting

confidence: 70%

Reciprocating probe measurements in the test divertor operation phase of Wendelstein 7-X

Killer,

Drews,

Grulke

et al. 2021

Preprint

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“…Such correction has been validated through flux surface mapping of the plasma last closed flux surface and divertor strike line positioning. These two methods suggest a small level of rotational transform correction between 0 and −250 A, once toroidal current is accounted for [25]. Additionally, divertor Langmuir probe measurements from the divertor and the multi-purpose manipulator measurements confirm these findings.…”

Section: Discussionmentioning

confidence: 56%

Tuning of the rotational transform in Wendelstein 7-X

et al. 2019

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The control of rotational transform in Wendelstein 7-X (W7-X) is key to both the island divertor operation and safety of plasma facing components. The island divertor concept in W7-X relies on an edge flux surface with rotational transform of ι -= 1 resonating with an intrinsic n/m = 5/5 resonance to form a five lobed island chain. This island chain intersects with divertor plates to give rise to the island divertor. Changes in the relative position of the rational surface and the divertor plates can result in changes in divertor performance, thus the control of the rotational transform is essential to operation of the W7-X device. During the first divertor campaign electromagnetic loads resulted in elastic deformations of the shaped modular stellarator coils. Such deformations made these coils more planar, reducing the vacuum rotational transform, subsequently shifting the ι -= 1 resonance outward.

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“…The eroded area ranges from about -320 mm to 0 mm and is relatively wide. This is due to the movement of the strike line by toroidal currents [22]. In addition to the large erosion at the strike line at around -90 mm a second line of enhanced erosion is observed at about -210 mm: This is probably due to a second strike line which was already observed by thermography and appears at higher plasma currents [22].…”

Section: Erosion/deposition Patternmentioning

confidence: 70%

Material erosion and deposition on the divertor of W7-X

et al. 2020

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The net erosion and deposition pattern of carbon from the Test Divertor Unit (TDU) of the stellarator W7-X was determined. Special target elements with marker layers consisting of about 300 nm molybdenum and 5-10 µm carbon on top were used during the operation phase OP 1.2a. The thicknesses of the marker layers were determined by elastic backscattering spectrometry (EBS) using 2.5 MeV protons before and after plasma exposure and laser-induced breakdown spectroscopy (LIBS) on selected target elements after exposure. Scanning electron microscopy (SEM) was used for investigating the surface morphology before and after exposure. Massive erosion of up to 20 µm carbon was observed at the strike line, in total 48±14 g carbon were eroded from the 10 TDUs. The erosion was laterally nonuniform on the micro-scale. Strongly eroded surfaces were considerably smoother as compared to the original material. Only very little deposition of carbon is observed on the TDU: This means that the TDU is a large net erosion source.

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Effects of toroidal plasma current on divertor power depositions on Wendelstein 7-X

Cited by 32 publications

References 39 publications

Reciprocating probe measurements in the test divertor operation phase of Wendelstein 7-X

Reciprocating probe measurements in the test divertor operation phase of Wendelstein 7-X

Tuning of the rotational transform in Wendelstein 7-X

Material erosion and deposition on the divertor of W7-X

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