A large divertor manipulator for ASDEX Upgrade

Herrmann, A.; Jakšić, N.; Leitenstern, P.; Greuner, H.; Krieger, K.; Marné, P. de; Oberkofler, M.; Rohde, V.; Schall, G.

doi:10.1016/j.fusengdes.2015.02.007

Cited by 33 publications

(24 citation statements)

References 5 publications

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“…15), which leads to a corresponding small shift of the power flux maximum, is neglected in this approximation. The spatial profile is described by expression (2) in [36], which consists of a convolution of an exponential profile in the SOL region with a Gaussian to describe cross-field diffusion across the separatrix into the PFR [37]: (1) where E0 denotes the energy scaling factor, sOSP the strike point position, λ the SOL heat flux profile decay length and S the divertor spreading factor.…”

Section: Power Flux To the Outer Target Platementioning

confidence: 99%

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

et al. 2018

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Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II (DIM-II) system [1]. Designed as near replicas of the geometries used also in separate experiments on the JET tokamak [2-4], the samples featured a misaligned leading edge and a sloped ridge respectively. Both structures protrude above the default target plate surface thus receiving an increased fraction of the parallel power flux. Transient melting by ELMs was induced by moving the outer strike point to the sample location. The temporal evolution of the measured current flow from the samples to vessel potential confirmed transient melting. Current magnitude and dependency from surface temperature provided strong evidence for thermionic electron emission as main origin of the replacement current driving the melt motion. The different melt patterns observed after exposures at the two sample geometries support the thermionic electron emission model used in the MEMOS melt motion code, which assumes a strong decrease of the thermionic net current at shallow magnetic field to surface angles [5]. Post exposure ex-situ analysis of the retrieved samples show recrystallization of tungsten at the exposed surface areas to a depth of up to several mm. The melt layer transport to less exposed surface areas leads to ratcheting pile up of re-solidified debris with zonal growth extending from the already enlarged grains at the surface.

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Section: Power Flux To the Outer Target Platementioning

confidence: 99%

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

et al. 2018

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“…It is worth to mention that a wide tile with steel clamp was temporarily mounted on the divertor manipulator [11] and it developed deep cracks after less than 100 shots (two weeks operation). Furthermore, it should be pointed out that in 5 positions out of 13, the edges of the HPM tiles reveal signs of melting and thermally induced cracks.…”

Section: Outcome Of First Inspectionmentioning

confidence: 99%

Cracks avoidance with a modified solid tungsten divertor in ASDEX Upgrade

Zammuto

Herrmann

et al. 2018

Fusion Engineering and Design

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To clarify the suitability of solid tungsten as plasma facing material, a new divertor, DIV-III, entered in operation in ASDEX Upgrade (AUG) in 2014. Since the first experimental campaign, AUG divertor tiles faced crack issues. Trying to identify the reasoning, a new set of tiles was installed in 2016: many precautions were taken to reduce the stresses possibly causing the cracks. The AUG campaign 2017 started in March and the first results were collected during the short summer opening in 2017. This paper reports on the modification of the tile setup, based on Finite Element Modelling, and on the progress achieved in the first operation phase.

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“…After the encouraging results of the HHF test in GLADIS one D185 tile was mounted in AUG using the divertor manipulator (DIM II) [9]. This unique device allows the exposure of two complete tiles (which could be elaborately instrumented or even actively heated/cooled) for single experimental days or for long experimental periods.…”

Section: Exposure In the Asdex Upgrade Divertormentioning

confidence: 99%

Investigations on tungsten heavy alloys for use as plasma facing material

Neu

Maier

Balden

et al. 2017

Fusion Engineering and Design

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An alternative solution for tungsten as a plasma facing material could be the use of W heavy alloys as they are produced commercially by several companies. They consist of up to 97% W and Ni/Fe (or Ni/Cu) admixtures, they are readily machinable and considerably cheaper than bulk tungsten. Their major drawbacks in view of the application in fusion experiments are the rather low melting temperature and their magnetic properties (in case of a Ni/Fe binder phase). In a first step W heavy alloys from two manufacturers were investigated concerning their thermal and magnetic properties and subjected to screening tests and cyclic loading in the high heat flux test facility GLADIS with up to 20 MWm −2 and surface temperatures of up to 2200 • C, showing no macroscopic failure. SEM investigations show a segregation of Ni and Fe at the top surface after the thermal overloading, but no signs of microcracking. The long-term behaviour of a W-Ni/Fe tile under plasma and electromagnetic load was investigated in ASDEX Upgrade using its divertor manipulator. The tile was exposed in discharges with record values of injected energy and power. Despite the observed surface modifications (Ni/Fe segregation) the W heavy alloys seem to provide a pragmatic and cost-effective alternative to bulk W tiles in the divertor of ASDEX Upgrade.

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A large divertor manipulator for ASDEX Upgrade

Cited by 33 publications

References 5 publications

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade

Cracks avoidance with a modified solid tungsten divertor in ASDEX Upgrade

Investigations on tungsten heavy alloys for use as plasma facing material

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