Diagnostic setup for the divertor manipulator at wendelstein 7-X

Hubeny, Michael; Höschen, D.; Rack, M.; Neubauer, O.; Bozhenkov, S.; Czymek, G.; Unterberg, B.; König, R.; Hathiramani, D.; Brezinsek, S.; Linsmeier, Ch.

doi:10.1016/j.nme.2018.11.028

Cited by 7 publications

(6 citation statements)

References 16 publications

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“…The position of this structure correlates with the application of He-ECWC, but to make a conclusion a more deep investigation would be required. With the new divertor manipulator [26] available in the next operation phases it will become possible to introduce material samples to investigate this assumption in detail.…”

Section: Morphology and Chemical Compositionmentioning

confidence: 99%

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: Morphology and Chemical Compositionmentioning

confidence: 99%

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

et al. 2020

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“…Moreover, LIBS also has great potential for depth analysis of multilayer samples based on laser ablation and atomic emission spectroscopy [10]. With these special benefits, LIBS had been installed in several tokamak devices and proposed for future application in W7-X for PWI research including fuel retention and erosion/deposition studies [11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Quantification of erosion pattern using picosecond-LIBS on a vertical divertor target element exposed in W7-X

De-you¹,

Yi²,

Eksaeva³

et al. 2020

Nucl. Fusion

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A set of dedicated marker samples consisting of fine-grain graphite as substrate, an interlayer of 0.2–0.4 μm molybdenum (Mo) employed as marker, and a 5–10 μm thick carbon (C) marker layer on top were installed in Wendelstein 7-X (W7-X) to investigate locally the C erosion and deposition. In this study, a set of five individual marker tiles, installed in a vertical divertor element of the test divertor unit in half-module 50, and exposed to about 40 min of plasma predominant in the standard magnetic divertor configuration in the first year of divertor operation in W7-X (OP1.2A), were retrieved from the vessel for post-mortem analysis. Picosecond laser induced breakdown spectroscopy (ps-LIBS) was applied on these marker tiles in order to determine the local erosion/deposition pattern caused by plasma impact. The general erosion/deposition pattern on the vertical target element was studied with the aid of depth-profiling by Mo line emission due to ps-LIBS with the number of applied laser pulses (355 nm, 2.3 J cm−2, 35 ps) at one probing location. Several potential asymmetry factors which avoid a perfect layer-by-layer ablation process in the laser ablations are proposed and discussed when a rough layered structure sample with a rough surface is analysed by the ps-LIBS technique. Thereby, a simulation model was developed to correct the measurement error of the ps-LIBS method caused by the non-perfect rectangle profile of the applied laser beam. The depth resolution of the applied ps-LIBS system was determined by quantification of the laser ablation rates of the different layers and the C substrate which were measured utilising profilometry and cross comparison with the thicknesses of the C and Mo marker layers determined by a combined focused ion beam and scanning electron microscopy technique. For the first time, the erosion/deposition pattern on the vertical target was mapped and quantified by ps-LIBS technique. A relatively wide net erosion zone with a poloidal extend of about 200 mm was identified which can be correlated to the main particle interaction zone at the magnetic strike-line of the dominantly applied standard magnetic divertor configuration. At the position of peak erosion, not only 7.6 × 1019 C atoms/cm2 but also 2 × 1018 Mo atoms/cm2 which results can be extrapolated to total 15 × 1019 C atoms/cm2, were eroded due to plasma fuel particle (H, He) and impurity (O, C) ion impact.

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“…The MPM can perform fast plunges with an acceleration of up to 30 m s −2 of up to 350 mm into the plasma. The island chain and the LCFS can be crossed in all magnetic configurations, but it is not typically done due to negative side effects for the plasma [19].…”

Section: Multi Purpose Manipulatormentioning

confidence: 99%

Analysis of hydrogen fueling, recycling, and confinement at Wendelstein 7-X via a single-reservoir particle balance

et al. 2022

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A single-reservoir particle balance for the main plasma species hydrogen has been established for Wendelstein 7-X (W7-X). This has enabled the quantitative characterization of the particle sources in the standard island divertor configuration for the first time. Findings from attached scenarios with two different island sizes with a boronized wall and turbo molecular pumping are presented. Fueling efficiencies, particle flows and source locations were measured and used to infer the total particle confinement time $\tau_{\rm{p}}$. Perturbative gas injection experiments served to measure the effective particle confinement time $\tau_{\rm{p}}^*$. Combining both confinement times provides access to the global recycling coefficient $\bar{R}$. Hydrogen particle inventories have been addressed and the knowledge of particle sources and sinks reveals the core fueling distribution and provides insight into the capability of the magnetic islands to control exhaust features. Measurements of hydrogen fueling efficiencies were sensitive to the precise fueling location and measured between 12~\% and 31~\% with the recycling fueling at the strike line modeled at only 6~\%, due to much higher densities. 15~\% of the total \SI{5.2E+22}{a/s} recycling flow ionizes far away from the recycling surfaces in the main chamber. It was shown that 60~\% of recycled particles ionize above the horizontal and 18~\% above the vertical divertor target, while the remainder of the recycling flow ionizes above the baffle (7~\%). Combining these source terms with their individual fueling efficiencies resolves the core fueling distribution. Due to the higher fueling efficiency in the main chamber, up to 51~\% of the total \SI{5.1E+21}{1/s} core fueling particles are entering the confined plasma from the main chamber. $\tau_{\rm{p}}$ values in the range of 260 ms were extracted for these discharges. Together with $\tau_{\rm{p}}$, the global recycling coefficient $\bar{R}$ was resolved for every $\tau_{\rm{p}}^*$ measurement and a typical value close to unity was obtained. An increase of the island size, resulted in no change of $\tau_{\rm{p}}$, but doubled $\tau_{\rm{p}}^*$, indicating the feasibility of the control coils as an actuator to control exhaust features without affecting core confinement properties.

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Diagnostic setup for the divertor manipulator at wendelstein 7-X

Cited by 7 publications

References 16 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

Quantification of erosion pattern using picosecond-LIBS on a vertical divertor target element exposed in W7-X

Analysis of hydrogen fueling, recycling, and confinement at Wendelstein 7-X via a single-reservoir particle balance

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