Main chamber sources and edge transport of tungsten in H-mode plasmas at ASDEX Upgrade

Dux, R.; Janzer, A.; Pütterich, T.

doi:10.1088/0029-5515/51/5/053002

Cited by 78 publications

(111 citation statements)

References 33 publications

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“…In an H-mode, the edge transport barrier provides a zone of good confinement, and the inward transport of tungsten is regulated by the ELMs. Thus, a higher ELM frequency is beneficial for reducing the tungsten concentration [3]. The ELM frequency increases with the amount of additional heating, the edge q 95 and the applied gas puff level.…”

Section: Comparison Of Iphm In the All-w Aug With Results From Previomentioning

confidence: 99%

Confinement of ‘improved H-modes’ in the all-tungsten ASDEX Upgrade with nitrogen seeding

Schweinzer¹,

Sips²,

Tardini³

et al. 2011

Nucl. Fusion

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131

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Abstract. In ASDEX Upgrade the compatibility of improved H-modes with an all-W wall has been demonstrated. Under boronized conditions light impurities and the radiated power fraction in the divertor were reduced, requiring N seeding to cool the divertor plasma. The impurity seeding does not only protect the divertor tiles but also considerably improves the performance of improved H-mode discharges by up to 25%. The energy confinement increases to H 98 -factors up to 1.3 and thereby exceeds the best values in the carbon-dominated AUG at the same density and collisionality. This improvement is due to higher edge temperatures rather than to peaking of the electron density profile. Higher temperatures are reached at the pedestal top leading, via profile stiffness, to an increase of the total plasma pressure. There is no change to R/L Te,i in the plasma core. The dilution at the plasma edge by nitrogen seems to play an important role since it allows higher ion temperatures at the same edge ion pressure as in the unseeded case. The dilution of the core plasma remains moderate.PACS number: 52.55.Fa

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Section: Comparison Of Iphm In the All-w Aug With Results From Previomentioning

confidence: 99%

Confinement of ‘improved H-modes’ in the all-tungsten ASDEX Upgrade with nitrogen seeding

Schweinzer¹,

Sips²,

Tardini³

et al. 2011

Nucl. Fusion

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131

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“…It is clear that by increasing the gas puff level not only the ELM frequency changes, but also the erosion source in the divertor during as well as in-between the ELMs. Furthermore there is a reduction of the ionisation length as well as an increase of the prompt redeposition of W + ions, calling for a consistent modelling, which is provided in [41]. In the frame of the ongoing melting experiments performed with dedicated melt probes in the divertor [44,45] the divertor retention has been reassessed using the 3D transport code EMC-3 [46].…”

Section: W Transport and Contentmentioning

confidence: 96%

“…If the W content is high enough it can even influence the transport in the background plasma by changing the electron temperature profile through the radiation losses. For keeping the overall W content in H-Modes low it is essential to provide an edge instability which regularly diminishes the large edge impurity density gradient due to neoclassical effects [41]. The flushing could be provided by natural or stimulated ELMs [42,34] or by a change in the edge transport by magnetic perturbation coils [2].…”

Section: W Transport and Contentmentioning

confidence: 99%

Overview on plasma operation with a full tungsten wall in ASDEX Upgrade

Neu¹,

Kallenbach²,

Balden³

et al. 2013

Journal of Nuclear Materials

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113

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Operation with all tungsten plasma facing components has become routine in ASDEX Upgrade. The conditioning of the device is strongly simplified and short glow discharges are used only on a daily basis. The long term fuel retention was reduced by more than a factor of 5 as demonstrated in gas balance as well as in post mortem analyses. Injecting nitrogen Preprint submitted to Elsevier 23 November 2012for radiative cooling, discharges with additional heating power up to 23 MW have been achieved, providing good confinement (H98 y2 = 1), divertor power loads around 5 MW m −2 and divertor temperatures below 10 eV. ELM mitigation by pellet ELM pacemaking or magnetic perturbation coils reduces the deposited energy during ELMs, but also keeps the W density at the pedestal low. As a recipe to keep the central W concentration sufficiently low, central (wave) heating is well established and low density H-Modes could be re-established with the newly available ECRH power of up to 4 MW. The ICRH induced W sources could be strongly reduced by applying boron coatings to the poloidal guard limiters.

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“…In general, no disruption occurred if the auxiliary heating was maintained, whereas switching off the NBI power in such a case could lead to disruption by radiation collapse event. The increase of the NBI power combined with strong deuterium gas puffing rate (above 10 22 Ds −1 ) opened up the operating space by increasing central transport and the ELM frequency and therefore the flushing out tungsten from the bulk plasma (see also Sec.3.4), as seen in AUG [42,43]. Since both the increase of the loss power (power crossing the separatrix) and the gas puffing contribute to expell tungsten by increasing the ELM frequency, it was also found that the minimum gas puffing rate decreases with the loss power.…”

Section: Baseline H-mode Scenariomentioning

confidence: 99%

First operation with the JET International Thermonuclear Experimental Reactor-like wall

et al. 2013

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AbstrAct.To consolidate ITER design choices and prepare for its operation, JET has implemented ITER's plasma facing materials, namely Be at the main wall and W in the divertor. In addition, protection systems, diagnostics and the vertical stability control were upgraded and the heating capability of the neutral beams was increased to over 30 MW. First results confirm the expected benefits and the limitations of all metal plasma facing components (PFCs), but also yield understanding of operational issues directly relating to ITER. H-retention is lower by at least a factor of 10 in all operational scenarios compared to that with C PFCs. The lower C content (Section 1factor 10) have led to much lower radiation during the plasma burn-through phase eliminating breakdown failures.Similarly, the intrinsic radiation observed during disruptions is very low, leading to high power loads and to a slow current quench. Massive gas injection using a D 2 /Ar mixture restores levels of radiation and vessel forces similar to those of mitigated disruptions with the C wall. Dedicated L-H transition experiments indicate a reduced power threshold by 30%, a distinct minimum density and pronounced shape dependence. The L-mode density limit was found up to 30% higher than for C allowing stable detached divertor operation over a larger density range. Stable H-modes as well as the hybrid scenario could be only re-established when using gas puff levels of a few 10 21 es −1. On average the confinement is lower with the new PFCs, but nevertheless, H factors up to 1 (H-Mode) and 1.3 (at b N ≈ 3, hybrids) have been achieved withWconcentrationswell below themaximum acceptable level.

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Main chamber sources and edge transport of tungsten in H-mode plasmas at ASDEX Upgrade

Cited by 78 publications

References 33 publications

Confinement of ‘improved H-modes’ in the all-tungsten ASDEX Upgrade with nitrogen seeding

Confinement of ‘improved H-modes’ in the all-tungsten ASDEX Upgrade with nitrogen seeding

Overview on plasma operation with a full tungsten wall in ASDEX Upgrade

First operation with the JET International Thermonuclear Experimental Reactor-like wall

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