Pellet ablation theory and experiments

Pégouriè, B.; Picchiottino, J M

doi:10.1088/0741-3335/35/sb/012

Cited by 12 publications

(6 citation statements)

References 19 publications

(3 reference statements)

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“…The corresponding calculations were provided in [31,43,44] and confirmed, in further analyses, by Pégourié [2,45]) by means of one-dimensional single-fluid numerical MHD modelling. The first numerical results applicable to reactore-grade plasmas were obtained with the help of a resisitve MHD code about 15 years ago [13].…”

Section: Wwwcpp-journalorgmentioning

confidence: 52%

Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Lengyel

Schneider

Kardaun

et al. 2008

Contrib. Plasma Phys.

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This work is aimed at the analysis of pellet injection experiments by means of a magnetohydrodynamic code that computes the processes of pellet ablation, expansion, ionization, and magnetic confinement of the ablated substance. In particular, experimental pellet injection scenarios stemming from the tokamak ASDEX-Upgrade (D2 pellets) and the stellarator W7-AS (carbon pellets) are analyzed by means of this time-dependent quasithree-dimensional MHD pellet code. Pellet penetration depths measured in ASDEX-Upgrade at LFS (lowfield-side) and HFS (high-field-side) pellet injection, are compared with computational results.It was found that the penetration depths of deuterium pellets observed in about twenty randomly selected LFS and HFS injection scenarios could accurately be reproduced by a single code in which drift effects were intentionally ignored. This may be understood as an indication of the negligible effect drift exerts on the ablation process. At the same time, the distribution of the ablated and partially ionized substance may very well be affected by the drift of the ionized particles in the direction of the decreasing magnetic field.With the help of the Dα radiation patterns observed, the magnitudes of the heat fluxes affecting the pellet and the ablation cloud were estimated. The calculations show that the thermal heat fluxes (electron and ion) acting along the magnetic field lines are not sufficient to explain the size of the radiating filaments observed.The effect of extra-thermal electrons on the ablation history of pellets injected in W7-AS is demonstrated: the particle end energy fluxes causing measured pellet ablation profiles are determined.Based on a statistically well-designed computational data set, an empirical scaling of the penetration depths in terms of the background plasma parameters was attempted. It is shown that the form of the temperature profile of the background plasma cannot be ignored while deriving scaling laws; the specification of the central or the bulk temperature alone is insufficient.Quantitative data are provided for the magnitudes of various additional processes such as the anomalous thermal conduction across the field lines or the grad(B)-induced drift of the shielding cloud surrounding the pellet.The modelling of supersonic gas jets, a fuelling method that appears to be an alternative to pellet injection, is also considered. Since the massive stream of a cold gas represents a disturbance for the recipient plasma similar to that of a pellet, its dynamics can be described by the same means as the evolution of pellet clouds.

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Section: Wwwcpp-journalorgmentioning

confidence: 52%

Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Lengyel

Schneider

Kardaun

et al. 2008

Contrib. Plasma Phys.

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“…In the SOL, perpendicular transport is defined by the diffusivities at the separatrix; longitudinal transport follows Braginskii's approximation. HPI2 determines the pellet particle source by application of a pellet ablation model which is based on the neutral gas and plasmoid shielding description [23]. The E × B drift of the cloudlets can be taken into account following a four-fluid Lagrangian model for the plasmoid homogenization process [18].…”

Section: Jintracmentioning

confidence: 99%

Integrated simulation of ELM triggered by a pellet through energy absorption and transport enhancement

Hayashi¹,

Parail²,

Koechl³

et al. 2011

Nucl. Fusion

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Abstract. Two integrated core / scrape-off-layer (SOL) / divertor transport codes TOPICS-IB and JINTRAC with links to MHD stability codes have been coupled with models of pellet injection to clarify effects of pellet on the behavior of edge localized modes (ELMs). The energy absorption by pellet and its further displacement due to ExB drift as well as transport enhancement by the pellet were found to be able to trigger the ELM. The ablated cloud of pellet absorbs the background plasma energy and causes the radial redistribution of pressure due to the subsequent ExB drift. On the other hand, the sharp increase in local density and temperature gradients in the vicinity of ablated cloud could cause transient enhancement of heat and particle transport. Both mechanisms produce a region of an increased pressure gradient in the background plasma profile within the pedestal, which triggers the ELM. The mechanisms have the potential to explain a wide range of experimental observations.

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“…A simple picture of the way the perpendicular expansion of the cloud is stopped by the j × B force once the ablatant is ionized can be found in [57]. It is illustrated in figure 7: as long as it is neutral, the ablation cloud, which expands at velocity v 0 , follows the pellet and moves across the plasma with velocity v p .…”

Section: Ablation Models-recent Developmentsmentioning

confidence: 99%

Review: Pellet injection experiments and modelling

Pégouriè

2007

Plasma Phys. Control. Fusion

126

158

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During the last decade, significant progress has been made in the field of pellet injection with (1) the identification of the drift of the deposited material in the inhomogeneous magnetic field that opened the possibility of fuelling efficiently the plasmas from the high-field side of the torus, (2) the technique to mitigate ELMS in H-mode discharges with shallow pellet injection at high frequency and (3) with the development of high density, high performance scenarios close to the ITER requirements. Both the experimental and theoretical aspects of this domain are reviewed in this paper.

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Pellet ablation theory and experiments

Cited by 12 publications

References 19 publications

Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Integrated simulation of ELM triggered by a pellet through energy absorption and transport enhancement

Review: Pellet injection experiments and modelling

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