An ultraviolet-visible-near infrared overview spectroscopy for divertor plasma diagnosis on Wendelstein 7-X

Wei, Y. L.; Wang, E.; Liang, Yun-Feng; Brezinsek, S.; Schweer, B.; Krychowiak, M.; Neubauer, O.; König, R.; Sereda, S.; Linsmeier, Ch.; Team, W X

doi:10.1063/1.5033371

Cited by 5 publications

(5 citation statements)

References 9 publications

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“…For the remote PFCs erosion processes for boron would be one order of magnitude slower, but still taking place due to the erosion by charge exchange neutrals and residual ions. The overview spectrometer system [16] was used as the main tool to characterize the effects of boronizations on impurity sources at the main PFCs.…”

Section: Experimental Approachmentioning

confidence: 99%

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Impact of boronizations on impurity sources and performance in Wendelstein 7-X

et al. 2020

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The low-Z oxygen and carbon were the main plasma impurities in the Wendelstein 7-X (W7-X) stellarator in the last experimental campaign with the passively cooled graphite divertor. To tackle this issue boronization [1] was applied, which has led to one of the main achievements of the campaign: plasma operation at high core densities of more than 10 20 m -3 in hydrogen fueled plasmas due to the reduced radiation-induced density limit. In total three boronizations were applied. After the first boronization the oxygen to hydrogen flux ratio (normalized influx of oxygen) at the divertor substantially decreased by a factor of 10 and the carbon to hydrogen flux ratio (normalized influx of carbon) decreased by a factor of 4 as obtained from spectroscopy. In the same time, boron emission appeared in the spectra. Between the boronizations oxygen and carbon normalized influxes increased but never reached the pre-boronization values. With each subsequent boronization O level decreased even more, reaching the lowest values after the third boronization which were more than a factor of 100 lower than before the first boronization. Such a decrease in low-Z impurity concentration significantly extended the operation window of W7-X in terms of line-integrated electron density (from 4‧10 19 m -2 to more than 1‧10 20 m -2 ) and diamagnetic energy (from 330 kJ up to 510 kJ). Zeff decreased from 4.5 down to values close to 1.2 as obtained from bremsstrahlung measurements. The above mentioned values are given for the two reference discharges before and after boronization.

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Section: Experimental Approachmentioning

confidence: 99%

“…The overview spectrometer system [16] was used as the main tool to characterize the effects of boronizations on impurity sources at the main PFCs. In this case the overview spectrometer was connected to the endoscope at the AEJ51 port [17,18] of W7-X at the toroidal angle φ = 302.9 • .…”

Section: Experimental Approachmentioning

confidence: 99%

Impact of boronizations on impurity sources and performance in Wendelstein 7-X

et al. 2020

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“…2. The other one was an overview spectroscopy (Avantes: ULS2048L) which was attached to the endoscope using quartz fibers (NA=0.22) with a diameter 800 μm [10], LOS of which was tangential as shown in Fig. 2.…”

Section: Experimental Set-upmentioning

confidence: 99%

Impurity sources and fluxes in W7-X: from the plasma-facing components to the edge layer

Wang¹,

Brezinsek²,

Sereda³

et al. 2020

Phys. Scr.

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Wendelstein 7-X (W7-X) is a nearly full-carbon machine with graphite divertors, baffles and shields in Operation Phase 1.2b (OP 1.2b). Divertor spectrometer measurements showed that an amount of helium and oxygen impurities existed in the predominately hydrogen plasma, which resulted in a high carbon impurity level by enhanced physical and chemical sputtering by these impurities in comparison with the pure impinging proton yields. In order to improve the wall conditions, especially to reduce the oxygen content, boronizations were applied in OP1.2b. After the boronization, an oxygen decrease by more than an order of magnitude was observed. Helium disappeared in comparison with OP1.2a due to reduced application of helium wall conditioning after introduction of boronizations. The overall radiation normalized to line integrated density was reduced by a factor of six. In addition, local CH4 injection was applied in the divertor in order to quantify the chemical sputtering by hydrogen on divertor plates. The experimentally determined effective D/XB of the A-X band of CH resulting from CH4 was [ 𝐷 𝑋𝐵 ] 𝐴 2 ∆→𝑋 2 Π 𝐶𝐻 4 →𝐶𝐻 = 16 at Te ≈ 20 eV and ne ≈ 5e18 m -3 . It was applied to determine the hydrocarbon fluxes and further to deduce the particle flux ratio Г CH4 /Г H on divertor plates.

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“…Carbon and oxygen are believed to have been the dominant edge radiators during OP1.2a. Both show up on spectroscopic diagnostics [32], and the co-deposited layers found after PFC extraction consist of a homogeneous mixture of O and C in combination with a high H fraction. Moreover, the edge temperatures were in the range where both species radiate very effectively.…”

Section: First Operation With Pellet Fueling and Observations Of Deta...mentioning

confidence: 99%

First results from divertor operation in Wendelstein 7-X

Pedersen

König

Krychowiak

et al. 2018

Plasma Phys. Control. Fusion

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Wendelstein 7-X is a highly optimized stellarator that went into operation in 2015. With a 30 cubic meter volume, a superconducting coil system operating at 2.5 T, and steady-state heating capability of eventually up to 10 MW, it was built to demonstrate the benefits of optimized stellarators at parameters approaching those of a fusion power plant. We report here on the first results with the test divertor installed, during the second operation phase, which was performed in the second half of 2017. Operation with a divertor, and the addition of several new fueling systems, allowed higher density operation in hydrogen as well as helium. The effects that higher density operation had on both divertor operation and global confinement will be described. In particular, at high densities detachment was observed, and the highest fusion triple product for a stellarator was achieved.

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An ultraviolet-visible-near infrared overview spectroscopy for divertor plasma diagnosis on Wendelstein 7-X

Cited by 5 publications

References 9 publications

Impact of boronizations on impurity sources and performance in Wendelstein 7-X

Impact of boronizations on impurity sources and performance in Wendelstein 7-X

Impurity sources and fluxes in W7-X: from the plasma-facing components to the edge layer

First results from divertor operation in Wendelstein 7-X

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