The impact of divertor detachment on carbon sources in JET L-mode discharges

Brezinsek, S.; Meigs, A.; Jachmich, S.; Stamp, M.; Rapp, J.; Felton, R.; Pitts, R.A.; Philipps, V.; Huber, A.; Pugno, R.; Sergienko, G.; Pospieszczyk, A.; Contributors, Jet

doi:10.1016/j.jnucmat.2009.01.100

Cited by 16 publications

(13 citation statements)

References 11 publications

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“…Potential counter measures required for reliable and safe long pulse operation in W7-X are (a) reduction of the C source by operation with cold, detached divertor [63], (b) optimised wall conditioning techniques to avoid carbon layer formation with high fuel content [64], and (c) ultimately change of the PFC material to e.g. tungsten [65].…”

Section: Discussionmentioning

confidence: 99%

Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

et al. 2021

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W7-X completed its plasma operation in hydrogen with island divertor and inertially cooled test divertor unit (TDU) made of graphite. A substantial set of plasma-facing components (PFCs), including in particular marker target elements, were extracted from the W7-X vessel and analysed post-mortem. The analysis provided key information about underlying plasma–surface interactions (PSI) processes, namely erosion, transport, and deposition as well as fuel retention in the graphite components. The net carbon (C) erosion and deposition distribution on the horizontal target (HT) and vertical target (VT) plates were quantified and related to the plasma time in standard divertor configuration with edge transform ι = 5/5, the dominant magnetic configuration of the two operational phases (OP) with TDU. The operation resulted in integrated high net C erosion rate of 2.8 mg s−1 in OP1.2B over 4809 plasma seconds. Boronisations reduced the net erosion on the HT by about a factor 5.4 with respect to OP1.2A owing to the suppression of oxygen (O). In the case of the VT, high peak net C erosion of 11 μm at the strike line was measured during OP1.2B which converts to 2.5 nm s−1 or 1.4 mg s−1 when related to the exposed area of the target plate and the operational time in standard divertor configuration. PSI modelling with ERO2.0 and WallDYN-3D is applied in an interpretative manner and reproduces the net C erosion and deposition pattern at the target plates determined by different post-mortem analysis techniques. This includes also the 13C tracer deposition from the last experiment of OP1.2B with local 13CH4 injection through a magnetic island in one half module. The experimental findings are used to predict the C erosion, transport, and deposition in the next campaigns aiming in long-pulse operation up to 1800 s and utilising the actively cooled carbon-fibre composite (CFC) divertor currently being installed. The CFC divertor has the same geometrical design as the TDU and extrapolation depends mainly on the applied plasma boundary. Extrapolation from campaign averaged information obtained in OP1.2B reveals a net erosion of 7.6 g per 1800 s for a typical W7-X attached divertor plasma in hydrogen.

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Section: Discussionmentioning

confidence: 99%

Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

et al. 2021

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“…7) and first attempts of coupling the line ratios, the electron density and ADAS photon emission coefficient ratios to determine the electron temperature failed. Previous work using the Paschen continuum step showed temperatures in the carbon machine of 1-4eV [9]. Work is ongoing to reproduce the temperature results using both line ratio's and the continuum steps.…”

Section: Balmer/stark Spectroscopy In the Divertormentioning

confidence: 97%

Deuterium Balmer/Stark spectroscopy and impurity profiles: First results from mirror-link divertor spectroscopy system on the JET ITER-like wall

Meigs¹,

Brezinsek²,

Clever³

et al. 2013

Journal of Nuclear Materials

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For the ITER-like wall, the JET mirror link divertor spectroscopy system was redesigned to fully cover the tungsten horizontal strike plate with faster time resolution and improved near-UV performance. Since the ITER-like wall project involves a change in JET from a carbon dominated machine to a beryllium and tungsten dominated machine with residual carbon, the aim of the system is to provide the recycling flux, equivalent, to the impinging deuterium ion flux, the impurity fluxes (C, Be, O) and tungsten sputtering fluxes and hence give information on the tungsten divertor source. In order to do this self-consistently, the system also needs to provide plasma characterization through the deuterium Balmer spectra measurements of electron density and temperature during high density. L-Mode results at the density limit from Stark broadening/line ratio analysis will be presented and compared to Langmuir probe profiles and 2D-tomography of low-n Balmer emission [1]. Comparison with other diagnostics will be vital for modelling attempts with the EDGE2D-EIRENE code[2] as the best possible data sets need to be provided to study detachment behaviour.

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“…Thus, even though D.R. excitation of CH probably does generate some photons in the CH 4 puffs in detached plasma at JET (T e ∼ 2 eV) [37] and DIII-D (T e = 2.0 eV) [38], it might be a marginal process. Further research is needed to conclusively answer this question.…”

Section: Ch A-level Excitation Probabilities Of the Different Dissoci...mentioning

confidence: 99%

Dissociative recombination and electron-impact de-excitation in CH photon emission under ITER divertor-relevant plasma conditions

Swaaij

Bystrov

Borodin

et al. 2012

Plasma Phys. Control. Fusion

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For understanding carbon erosion and redeposition in nuclear fusion devices, it is important to understand the transport and chemical break-up of hydrocarbon molecules in edge plasmas, often diagnosed by emission of the CH A 2 ∆-X 2 Π Gerö band around 430 nm. The CH A-level can be excited either by electronimpact or by dissociative recombination (D.R.) of hydrocarbon ions. These processes were included in the 3D Monte Carlo impurity transport code ERO. A series of methane injection experiments was performed in the high-density, low-temperature linear plasma generator Pilot-PSI, and simulated emission intensity profiles were benchmarked against these experiments. It was confirmed that excitation by D.R. dominates at T e < 1.5 eV. The results indicate that the fraction of D.R. events that lead to a CH radical in the A-level and consequent photon emission is at least 10%. Additionally, quenching of the excited CH radicals by electron impact de-excitation was included in the modeling. This quenching is shown to be significant: depending on the electron density, it reduces the effective CH emission by a factor of 1.4 at n e = 1.3 * 10 20 m −3 , to 2.8 at n e = 9.3 * 10 20 m −3 . Its inclusion significantly improved agreement between experiment and modeling.

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The impact of divertor detachment on carbon sources in JET L-mode discharges

Cited by 16 publications

References 11 publications

Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

Plasma–surface interaction in the stellarator W7-X: conclusions drawn from operation with graphite plasma-facing components

Deuterium Balmer/Stark spectroscopy and impurity profiles: First results from mirror-link divertor spectroscopy system on the JET ITER-like wall

Dissociative recombination and electron-impact de-excitation in CH photon emission under ITER divertor-relevant plasma conditions

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