Integration of uncooled scraper elements and its diagnostics into Wendelstein 7-X

Integration of uncooled scraper elements and its diagnostics into Wendelstein 7-X

•Uncooled scraper element in front of island divertor.•Shielding of divertor edges versus loss of neutrals pumping.•Fast installation procedure to minimise oprataional break.•Simple in-vessel plug design to connect diagnostics. The modular stellarator Wendelstein 7-X in Greifswald (Germany) was succ...

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Bibliographic Details
Published in:Fusion engineering and design Vol. 124; no. C; pp. 226 - 230
Main Authors: Fellinger, Joris, Loesser, Doug, Neilson, Hutch, Lumsdaine, Arnie, McGinnis, Dean, Lore, Jeremy, Wurden, Glen, Wendorf, Jörg, Klose, Sören, Wenzel, Uwe, Grosser, Klaus, Rummel, Kerstin, Hölbe, Hauke, Pedersen, Thomas Sunn, Mitchell, John, Sibilia, Marc, Zhang, Han, Titus, Peter
Format: Journal Article
Language:English
Published: Amsterdam Elsevier B.V 01-11-2017
Elsevier Science Ltd
Elsevier
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Cables
Fusion
Heat
Heat loads
Iridium
Langmuir probes
Magnetic Fusion Energy
Manometers
Neutral gas manometer
Neutral gases
Overloading
Plasma
Plasmas
Scraper element
Strike lines
Thermocouples
Wendelstein 7-X
Strike lines
Heat loads
Scraper element
Langmuir probes
Neutral gas manometer
Wendelstein 7-X
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Description
Summary:•Uncooled scraper element in front of island divertor.•Shielding of divertor edges versus loss of neutrals pumping.•Fast installation procedure to minimise oprataional break.•Simple in-vessel plug design to connect diagnostics. The modular stellarator Wendelstein 7-X in Greifswald (Germany) was successfully taken into operation in 2015. In the next experimental campaign in 2017, divertor plasmas are planned up to 80MJ input power limited by the largely uncooled first wall. In 2020, long pulse plasmas are foreseen once the water cooled first wall has been completed. In long pulses, bootstrap currents gradually develop in the plasma, which causes a shift of the strike lines onto the relatively poorly cooled edge of the divertor. To prevent overloading of these edges, a so-called scraper element can be positioned in front of the divertor, intersecting those strike lines that would otherwise hit the divertor edges. As a result, these edges are protected but as a drawback the pumping efficiency of neutrals is also reduced. To assess the impact, two uncooled scraper elements will be installed in the mid-break of the next campaign, one at the top of module 5 and one at the bottom of module 3. The divertor and scraper elements are monitored with Langmuir probes, neutral gas manometers, thermocouples and IR and VIS cameras viewing the plasma facing surface. This paper describes the integration of the uncooled scraper elements and their diagnostics in Wendelstein 7-X. A dedicated low power plasma scenario was developed to evaluate the uncooled scraper element, allowing for reduced heat loads and design simplifications. It is demonstrated that the diagnostics are still capable of measuring the impact of the scraper element. An easily accessible socket to plug in the cables of the diagnostics integrated in the scraper was designed and installed up front to allow for a fast and simple installation of the scraper element in the short mid-break.
Bibliography:USDOE Office of Science (SC)
LA-UR-17-27939
AC05-00OR22725; 633053; AC52-06NA25396
USDOE Office of Science (SC). Fusion Energy Sciences (FES) (SC-24)
ISSN:0920-3796
1873-7196
DOI:10.1016/j.fusengdes.2017.05.115