The X-point scrape-off plasma in jet with L- and H-modes

Harbour, P.J.; Summers, Danny; Clement, S.; Coad, J.P.; Kock, L. de; Ehrenberg, J.; Erents, K.; Gottardi, N.; Hubbard, A.E.; Keilhacker, M.; Morgan, P. D.; Snipes, J. A.; Stamp, M.; Tagle, J.A.; Tanga, A.; Behrisch, R.; Wang, Wenmin

doi:10.1016/0022-3115(89)90276-6

Cited by 60 publications

(25 citation statements)

References 3 publications

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“…Hydrogen was the principal fuelling gas for the initial campaigns , and since the hydrogen from the fuelling cannot be distinguished from hydrogen from other sources, analyses concentrated on deposited carbon and metals [1]. However, deuterium became the principal fuelling gas for the 1985 campaign, and its retention in the vessel following operations has been the principal focus of post-mortem analysis studies since that time [2][3][4][5][6][7][8][9][10][11][12]. In addition, in 1991 and 1997 there have been campaigns with deuterium-tritium fuelling, and analysis of retained tritium has also contributed to our understanding of the in-vessel retention [13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Carbon Deposition and Hydrogen Isotope Retention in JET

1999

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Hydrogen retention in tokamaks is dominated by two mechanisms: implantation into plasmafacing surfaces and trapping in deposited layers. The amount of hydrogen implantation saturates at typically ~10 21 atoms m-2 , giving ~2 x 10 23 atoms in the JET first wall (which is ~200 m 2), whilst codeposition depends firstly on the quantity of carbon deposited, and secondly on the temperature history of the deposits. Generally, codeposition has dominated the retained H inventory in JET, which was typically ~10 24 atoms. The installation of a divertor in JET has necessitated the presence of water-cooled components to protect the divertor field coils, whereas previously all plasma-facing components were normally at least 300°C. Thick carbon-based films are deposited on surfaces in the vicinity of the inner corner of the divertor on surfaces shadowed from the plasma. Because of the divertor cooling, these deposits are at low temperature and their H:C ratio is at least 0.5:1; as a result their contribution to the overall in-vessel inventory is increased. No comparable deposition is found at the outer divertor. In the Mk IIA divertor the majority of the deposition occurs on cool surfaces many centimetres from the plasma, although with a line-of-sight to the vicinity of the inner strike point, and the average amount deposited per pulse is much greater than previously observed. The number of carbon atoms forming the basis of the deposits amounts to several percent of the ion flux to the inner strike point. The build-up of material leads to spalling (probably on venting to air) The mechanism for the generation and transport of the carbon to form the films is unknown, but ELMs may have a role: it is important to fully understand the phenomenon because of the similarities between the JET and ITER divertor geometries.

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Section: Introductionmentioning

confidence: 99%

Carbon Deposition and Hydrogen Isotope Retention in JET

1999

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“…Under these conditions, the inner divertor plasma is usually colder compared to the outer divertor. As a consequence, a thermoelectric current [19] [20] flows from the plasma into the inner target, through the structure and into the outer divertor plasma. The current is maintained by a superior number of (fast) electrons reaching the target in the hotter divertor and a corresponding higher ion flux towards the target in the colder divertor.…”

Section: Introductionmentioning

confidence: 99%

Divertor power and particle fluxes between and during type-I ELMs in the ASDEX Upgrade

et al. 2008

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Abstract. Particle, electric charge and power fluxes for type-I ELMy H-modes are measured in the divertor of the ASDEX Upgrade tokamak by triple Langmuir probes, shunts, IR-thermography and spectroscopy. The discharges are in the medium to high density range, resulting in predominantly convective ELMs with moderate fractional stored energy losses of 2 % or below. Time resolved data over ELM cycles are obtained by coherent averaging of typically one hundred similar ELMs, spatial profiles from the flush-mounted Langmuir probes are obtained by strike point sweeps. Application of simple physics models is used to compare different diagnostics and to make consistency checks, e.g. the standard sheath model applied to the Langmuir probes yields power fluxes which are compared to the thermographic measurements. In between ELMs, Langmuir probe and thermography power loads appear consistent in the outer divertor, taking into account additional load due to radiation and charge exchange neutrals measured by thermography. The inner divertor is completely detached and no significant power flow by charged particles is measured. During ELMs, quite similar power flux profiles are found in the outer divertor by thermography and probes, albeit larger uncertainties in Langmuir probe evaluation during ELMs have to be taken into account. In the inner divertor, ELM power fluxes from thermography are a factor 10 larger than those derived from probes using the standard sheath model. This deviation is too large to be caused by deficiencies of probe analysis. The total ELM energy deposition from IR is about a factor 2 higher in the inner compared to the outer divertor. Spectroscopic measurements suggest a quite moderate contribution of radiation to the target power load.Shunt measurements reveal a significant positive charge flow into the inner target during ELMs. The net number of elementary charges correlates well with the total core particle loss obtained from highly resolved density profiles.As a consequence, the discrepancy between probe and IR measurements is attributed to the ion power channel via a high mean impact energy of the ions at the inner target. The dominant contributing mechanism is proposed to be the directed loss of ions from the pedestal region into the inner divertor.

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“…Harbour [4] observed current flowing from a target plate in a higher-T e divertor ("hot sheath") to a plate in a lower-T e divertor ("cold sheath") in JET, and provided a theoretical interpretation for the current based on the thermoelectric potential arising from the difference in temperature at the two sheaths. Staebler and Hinton [5] extended his analysis to include finite resistance of the SOL region connecting the two sheaths.…”

Section: Thermoelectrically Driven Solcmentioning

confidence: 99%