Characterization of edge profiles and fluctuations in discharges with type-II and nitrogen-mitigated edge localized modes in ASDEX Upgrade

Wolfrum, E.; Bernert, M.; Boom, J.; Burckhart, A.; Classen, I. G. J.; Eich, T.; Fischer, R.; Gude, A.; Herrmann, A.; Luhmann, Neville C.; Maraschek, M.; McDermott, R. M.; Park, H. K.; Pütterich, T.; Vicente, J.; Wieland, B.; Willensdorfer, M.

doi:10.1088/0741-3335/53/8/085026

Cited by 44 publications

(64 citation statements)

References 22 publications

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“…Similar neutron rates (not shown) are found in comparable discharges with and without N 2 puff. At given heating power, the higher plasma temperature in the presence of N compensates the loss in neutron yield due to increased D dilution in the case with N seeding [11]. Within the resolution of the MSE diagnostic, q-profiles for comparable discharges with and without N are identical.…”

Section: Detailed Study Of Nitrogen Seeded Improved H-modesmentioning

confidence: 90%

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

Schweinzer¹,

Sips²,

Tardini³

et al. 2011

Nucl. Fusion

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: Detailed Study Of Nitrogen Seeded Improved H-modesmentioning

confidence: 90%

“…For completeness also the electron collisionality (same definition of € ν e * as in [11]) is plotted in fig. 5.…”

Section: Detailed Study Of Nitrogen Seeded Improved H-modesmentioning

confidence: 99%

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

Schweinzer¹,

Sips²,

Tardini³

et al. 2011

Nucl. Fusion

131

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“…In order to find the origin of the off-mid-plane fluctuation, a comparison will be made to the T e oscillations observed in type-II ELMs, which show similar behaviour [31]. Combining the ECEI measurements of filaments during the temperature collapse phase with measurements from (visual ligth) cameras, Langmuir probes and e.g.…”

Section: Discussionmentioning

confidence: 99%

2D ECE measurements of type-I edge localized modes at ASDEX Upgrade

et al. 2011

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The installation of a 2D electron cyclotron emission imaging (ECEI) diagnostic on ASDEX Upgrade has provided a new means to observe the nature of Edge Localized Modes (ELMs). For a series of ELMs in a typical type-I ELMy H-mode (with q 95 = 4.7), the 2D dynamics have been characterized. Firstly, a clear distinction between so-called 'fast' and 'slow' ELMs was found to be the occurrence of an off-mid-plane fluctuation in case of the latter. This mode has its amplitude strongest off-midplane and its poloidal and toroidal mode numbers are m ~ 110 and n ~ 30. Secondly, prior to the onset of the ELM's temperature collapse, a mode is observed that covers the whole ECEI observation window. Here, the estimated poloidal and toroidal mode numbers are m ~ 75 and n ~ 20. These have been seen to increase towards the ELM crash, simultaneously with a velocity increase of the mode (in poloidal direction). Finally, filaments have been identified during the temperature collapse phase and their motion could be followed in the vertical direction. Contrary to both the off-mid-plane fluctuation and the ELM onset mode, which only have been seen rotating in the electron diamagnetic drift direction, the first few filaments have sometimes been observed to move in the opposite direction as well.

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“…A transition from a Type I to a pure Type II ELMy regime is observed on AUG in single null configurations [41]. This transition is achieved by applying strong fuelling to exceed a collisionality threshold.…”

Section: Elm Characterisationmentioning

confidence: 95%

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

Leyland¹,

Beurskens²,

Frassinetti³

et al. 2013

Nucl. Fusion

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We present the results from a new fuelling scan database consisting of 14 high triangularity ( ~ 0.41), Type I ELMy H-mode JET plasmas. As the fuelling level is increased from low, ( D ~ 0.2x10 22 el/s, n e,ped /n gw =0.7), to high dosing ( D ~ 2.6x10 22 el/s, n e,ped /n gw =1.0) the variation in ELM behaviour is consistent with a transition from 'pure Type I' to 'mixed Type I/II' ELMs [1]. However, the pulses in Scattering (HRTS) system. We continue by presenting, for the first time, the role of pedestal structure, as quantified by a least squares mtanh fit to the HRTS profiles, on the performance across the fuelling scan. A key result is that the pedestal width narrows and peak pressure gradient increases during the ELM cycle for low fuelling plasmas, whereas at high fuelling the pedestal width and peak pressure gradient saturates towards the latter half of the ELM cycle. An ideal MHD stability analysis shows that both low and high fuelling plasmas move from stable to unstable approaching the ideal ballooning limit of the finite peeling ballooning stability boundary. Comparison to EPED predictions show on average good agreement with experimental measurements for both pedestal height and width however when presented as a function of pedestal density, experiment and model show opposing trends. The measured pre-ELM pressure pedestal height increases by ~ 20% whereas EPED predicts a decrease of 25% from low to high fuelling. Similarly the measured pressure pedestal width widens by ~ 55%, in poloidal flux space, whereas EPED predicts a decrease of 20% from low to high fuelling. We give two possible explanations for the disagreement. First, it may be that EPED under-predicts the critical density, which marks the transition from kink-peeling to ballooning limited plasmas. Second, the stronger broadening of the experimental pedestal width than predicted by EPED is an indication that other transport related processes contribute to defining the pedestal width such as enhanced inter-ELM transport as observed at high fuelling, for mixed Type I/II ELMy pulses.M. Leyland

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Characterization of edge profiles and fluctuations in discharges with type-II and nitrogen-mitigated edge localized modes in ASDEX Upgrade

Cited by 44 publications

References 22 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

2D ECE measurements of type-I edge localized modes at ASDEX Upgrade

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

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