Particle transport analysis of the density build-up after the L–H transition in ASDEX Upgrade

Willensdorfer, M.; Fable, E.; Wolfrum, E.; Aho-Mantila, L.; Aumayr, F.; Fischer, R.; Reimold, F.; Ryter, F.

doi:10.1088/0029-5515/53/9/093020

Cited by 29 publications

(42 citation statements)

References 34 publications

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“…Figure 4 shows the growth rates of the main instabilities vs. k y ρ s for the two phases: in the early phase (iii) and just before the ELM crash (phase (i)). /s) that are similar to those found in the transport analysis of the density build-up after the L-H transition described in section 3 [25]. Just before the ELM crash (phase (i), figure 4b), the pressure profile is near the KBM limit.…”

Section: Elm Cycle Studies -Gyrokinetic Analysis With Genesupporting

confidence: 81%

“…However, due to the uncertainty in the neutral particle sources, the existence of a pinch cannot be confirmed by this analysis. The best agreement was found with a diffusion coefficient of 0.031 m 2 s −1 and a convective velocity of −0.5 ms −1 in the pedestal [25]. In order to determine the effect of T e on edge particle transport in the pedestal, the density build-up after the L-H transition was analyzed at different heating powers.…”

Section: Density Build-up After the L-h Transitionmentioning

confidence: 91%

“…The highly temporally resolved n e profiles after an L-H transition show a characteristic density build-up. This density build-up was modelled with the transport code ASTRA in a predictive-iterative way [25]. The convective velocity, diffusion coefficient and the particle source profiles were parameterized and their parameters were varied until the best match of the modelling to the temporal evolution of the density measurements was found.…”

Section: Density Build-up After the L-h Transitionmentioning

confidence: 99%

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Overview of recent pedestal studies at ASDEX Upgrade

et al. 2015

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Abstract. New or upgraded diagnostics of the edge transport barrier allow investigations of the dominant transport mechanisms in the pedestal. The density build-up after the L-H transition can be explained with a mainly diffusive edge transport barrier. A small inward convection term improves the agreement between modelling and experiment, but its existence cannot be confirmed due to the uncertainty in the neutral sources. Measurements of the impurity ion flow asymmetry as well as the edge current density are in agreement with neoclassical modelling. The inter-ELM pedestal recovery was traced with ideal peeling-ballooning modelling, which shows that the stability boundary moves closer to the operational point as the pedestal becomes wider. Gyrokinetic modelling of the different phases reveal that density gradient driven trapped electron modes are dominant during the early recovery, while electron temperature gradient modes or kinetic ballooning modes determine the temperature gradient in the final phase. Micro tearing modes are modelled and also experimentally determined at the top of the pedestal. Non linear coupling between modes could explain the failure of ideal linear MHD modelling. IntroductionThe edge transport barrier (ETB) is a characteristic of the high confinement mode (H-mode) of tokamaks. It is a narrow region of reduced radial transport, in which steep gradients in both density and temperature are observed, forming a pedestal for the core profiles.Extensive studies have shown that the pedestal radial electric field (E r ) profile in H-mode [1] and asymmetric density and flow profiles of impurity ions are consistent with neoclassical predictions [2]. While the ions set the background flow profile in the pedestal and their transport properties can be described by neoclassical modelling, the mechanisms which determine the electron density and temperature profiles are more varied, as electron heat and particle transport are governed by turbulence. The current emphasis of research concentrates on the determination of the driving force as well as the characteristics of the dominant transport mechanism. The understanding of the types of instabilities and the transport they create in the core plasma has been greatly advanced in recent years [3,4]. Although it has been shown that peeling ballooning (PB) theory in combination with the assumption that the pedestal width is determined by kinetic ballooning modes (KBM) [5,6] describes the pedestal top in a wide range of pedestal pressures [7], the detailed processes which determine the ion and electron heat transport as well as particle transport are not yet clearly [15] and the determination of the edge current density from a combination of magnetic measurements, edge pressure profiles and scrape-off layer (SOL) current measurements [16]. The combinations of these diagnostics deliver a set of profiles consisting of electron density (n e ), electron temperature (T e ), ion temperature (T i ), radial electric field (E r ) and edge current density (j), with temp...

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Section: Elm Cycle Studies -Gyrokinetic Analysis With Genesupporting

confidence: 81%

Section: Density Build-up After the L-h Transitionmentioning

confidence: 91%

Section: Density Build-up After the L-h Transitionmentioning

confidence: 99%

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Overview of recent pedestal studies at ASDEX Upgrade

et al. 2015

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“…Thus, D(ρ,c H ) and ν(ρ,I p ,c H ) are chosen as simple functions of ρ and c H , and it is assumed that ν = ν 0 I p /I p,0 to represent the increase of pinch at higher current, where I p,0 is the nominal plasma current, being the programmed flat-top current. An H-mode implies a reduction of transport in the plasma edge [45] and is reproduced by lower edge diffusion and a lower drift velocity for c H = 1. In Fig.…”

Section: Radial Plasma Particle Fluxmentioning

confidence: 98%

Control-oriented modeling of the plasma particle density in tokamaks and application to real-time density profile reconstruction

Blanken

Felici

Rapson

et al. 2018

Fusion Engineering and Design

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“…Recent studies analyzed the role of diffusive and convective particle transport in the pedestal during the density build-up following the transition from low confinement mode (L-mode) to H-mode (L-H transition) in ASDEX Upgrade [3]. It was shown that a diffusive ETB is required to explain the density build-up, whereas a possible particle pinch in the pedestal could neither be confirmed nor excluded.…”

Section: Introductionmentioning

confidence: 99%

Role of electron temperature in the particle transport in the pedestal during pedestal evolution

Willensdorfer

Fable

Wolfrum

et al. 2015

Journal of Nuclear Materials

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a b s t r a c tThe effect of the electron temperature (T e ) on the edge particle transport in the pedestal is analyzed during the density build-up after the L-H transition. Electron cyclotron resonance heating was used to vary the pedestal temperature during the density evolution between subsequent H-mode phases. Although the pedestal T e and its gradients could be varied by a factor of 2, almost no change in the edge density evolution is observed within the measurement uncertainties. ASTRA was used to interpret the measurements and to analyze the dependence of the pedestal particle transport on the T e profile. Thermo-diffusion seems to play a minor role in the pedestal.

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Particle transport analysis of the density build-up after the L–H transition in ASDEX Upgrade

Cited by 29 publications

References 34 publications

Overview of recent pedestal studies at ASDEX Upgrade

Overview of recent pedestal studies at ASDEX Upgrade

Control-oriented modeling of the plasma particle density in tokamaks and application to real-time density profile reconstruction

Role of electron temperature in the particle transport in the pedestal during pedestal evolution

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