Core tungsten transport in WEST long pulse L-mode plasmas

Yang, Xiaoping; Manas, P.; Bourdelle, C.; Artaud, Jean-François; Sabot, R.; Camenen, Y.; Citrin, J.; Clairet, F.; Desgranges, C.; Devynck, P.; Dittmar, T.; Fedorczak, N.; Gil, C.; Loarer, T.; Lotte, P.; Meyer, Olivier; Moralès, J.; Peret, M; Peysson, Y.; Stephens, C. D.; Urbanczyk, G.; Vezinet, D.; Zhang, Ling; Gong, Xianzu

doi:10.1088/1741-4326/ab9669

Cited by 23 publications

(44 citation statements)

References 58 publications

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“…Such ion density ratios of n 27 /n 26 are plotted in figure 10. The results are fairly in good agreement with the ratios of the ionization equilibrium model, which were calculated adopting ionization and recombination rate coefficients of atomic data and analysis structure (ADAS) database 4 and local T e and n e measured by Thomson scattering, except for radial regions where the ion densities are vanishingly small. The agreement seems to be better for the ratios obtained taking the proton collision effects into account.…”

Section: Assessment Of Tungsten Densitysupporting

confidence: 77%

“…The surpression of tungsten accumulation was observed also in Alcator C-Mod H-mode plasmas [3] with ICRH heating only. In long pulse WEST L-mode plasmas, it was reported that turblent transport manifesting at high ratios of electron temperatures to ion temperatures (𝑇𝑇 e 𝑇𝑇 i ⁄ ) mitigated tungsten accumulation [4]. Although such driving mechanisms have been identified with tokamak machines, tungsten transport is still hard to predict mainly due to the fact that subtle change in plasma profiles result in significant effects on the tungsten transport.…”

Section: Introductionmentioning

confidence: 99%

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Assessment of W density in LHD core plasmas using visible forbidden lines of highly charged W ions

Kato¹,

Sakaue²,

Murakami³

et al. 2021

Nucl. Fusion

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Visible magnetic-dipole (M1) lines can serve as a novel diagnostic mean of tungsten in ITER and future DEMO reactors. Here a local tungsten density in core plasmas of the Large Helical Device (LHD) is successfully assessed with the measurement of visible M1 lines emitted by W 26+ and W 27+ . By such a measurement, (i) the radial profile of total tungsten density in the LHD core plasmas with a line-averaged electron density of ~ 4×10 19 m -3 and central electron temperature of ~ 1 keV is found to be a hollow, and (ii) the total tungsten density is found to be decreased in the whole region with an increase in the electron temperature due to the onset of reheat mode. The scheme with visible M1 lines used in the present work can be also applied for the tungsten density measurement at the ITER edge plasma.

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Section: Assessment Of Tungsten Densitysupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Assessment of W density in LHD core plasmas using visible forbidden lines of highly charged W ions

Kato¹,

Sakaue²,

Murakami³

et al. 2021

Nucl. Fusion

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“…These improvements occurred with no changes to the LHCD power or plasma current and were concurrent with increases in the electron density and radiated power, suggesting improved confinement. A likely explanation is the suppression of ITGdriven turbulence due to main ion dilution, as observed in N2 seeding experiments in WEST [36], and/or modification of the density profile, as observed in powder injection experiments on AUG [15], W7-X [20], and LHD [22].…”

Section: Discussionmentioning

confidence: 97%

“…On the other hand, gaseous N 2 seeding experiments on WEST [36] have observed increases in confinement without density profile modification. In these experiments, fuel dilution was the dominant mechanism for turbulence suppression.…”

Section: Experimental Observations Of Improved Confinementmentioning

confidence: 99%

Initial results from boron powder injection experiments in WEST lower single null L-mode plasmas

Bodner¹,

Gallo²,

Diallo³

et al. 2022

Nucl. Fusion

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Using a recently installed impurity powder dropper (IPD), boron powder (< 150 μm) was injected into lower single null (LSN) L-mode discharges in WEST. IPDs possibly enable real-time wall conditioning of the plasma-facing components and may help to facilitate H-mode access in the full-tungsten environment of WEST. The discharges in this experiment featured Ip = 0.5 MA, BT = 3.7 T, q95 = 4.3, tpulse = 12–30 s, ne,0 ~ 4×1019 m-2, and PLHCD ~ 4.5 MW. Estimates of the deuterium and impurity particle fluxes, derived from a combination of visible spectroscopy measurements and their corresponding S/XB coefficients, showed decreases of ~ 50% in O+, N+, and C+ populations during powder injection and a moderate reduction of these low-Z impurities (~ 50%) and W (~ 10%) in the discharges that followed powder injection. Along with the improved wall conditions, WEST discharges with B powder injection observed improved confinement, as the stored energy WMHD, neutron rate, and electron temperature Te increased significantly (10–25% for WMHD and 60–200% for the neutron rate) at constant input power. These increases in confinement scale up with the powder drop rate and are likely due to the suppression of ion temperature gradient (ITG) turbulence from changes in Zeff and/or modifications to the electron density profile.

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“…It is therefore essential to understand the mechanisms for the release and transport of W into the core, either from the divertor plates or from the walls of the machine onto which W has been deposited during previous plasma operations (e.g. Dux et al 2011, Yang et al 2020. JET, with its ITER-like wall (ILW) of Be in the main chamber and W in the divertor, is ideally suited to such studies (Casson et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Observation of low temperature VUV tungsten emission in JET divertor plasmas

et al. 2022

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The properties of tungsten make it ideal for use as a plasma facing surface in the divertor of large plasma machines such as JET and ITER. However, the intense heat and particle fluxes that fall on the divertor surfaces lead to its release from these surfaces into the plasma and it is necessary to model its transport from the divertor and plasma edge into the plasma core. This requires measurement of spectral features over a wide temperature range. In large machines the W influx is often determined from W I line intensities, there being few measurements of discrete W lines from other low ionization stages. Their observation is highly desirable because the transport of neutral W differs markedly from that of the W ions. A change in the line of sight of a VUV survey spectrometer on JET to view directly into the divertor has led to the observation of numerous discrete low temperature W lines in the VUV spectral region. The spectrum of an intense influx in which W IV to W VIII features are observed has been analysed in order to provide spectral classifications so that these lines can be used for diagnostic purposes. The first observation of a VUV low temperature W magnetic dipole (M1) transition is reported for the W VIII ionization stage. The analysis shows where further line identifications are needed and that the provision of the highest quality atomic data for these ionization stages is desirable. Lines from W VI and W VII are used to illustrate their use in determining the electron temperature of the emitting plasma region and the W concentration. Dependences of the W line intensities on plasma parameters shows the optimal conditions for the W release and suggests the site of its release.

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Core tungsten transport in WEST long pulse L-mode plasmas

Cited by 23 publications

References 58 publications

Assessment of W density in LHD core plasmas using visible forbidden lines of highly charged W ions

Assessment of W density in LHD core plasmas using visible forbidden lines of highly charged W ions

Initial results from boron powder injection experiments in WEST lower single null L-mode plasmas

Observation of low temperature VUV tungsten emission in JET divertor plasmas

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