Homogenization of the pellet ablated material in tokamaks taking into account the ∇<i>B</i>-induced drift

Pégouriè, B.; Waller, Vincent; Nehme, H.; Garzotti, L.; Géraud, A.

doi:10.1088/0029-5515/47/1/006

Cited by 71 publications

(161 citation statements)

References 28 publications

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“…In addition to grain sizes and radial density distribution, the variables investigated with DUSTY are the inner dust shell temperature (T inner ), optical depth (specified at 10µm; τ 10µm ), dust composition, and the geometrical thickness of the dust shell, ξ = R out /R in , where R in and R out are the inner and outer radii of the dust shell, respectively. The optical constants for the dust components came from Pégourié (1988); Hanner (1998) and Draine & Lee (1984) for SiC, amorphous carbon and graphite, respectively. In nearly all cases it was possible to generate more than one model to fit the spectra, consequently we also investigate this degeneracy in parameter space and look for realistic ways to restrict it.…”

Section: Parameter Space Investigatedmentioning

confidence: 99%

Silicon Carbide Absorption Features: Dust Formation in the Outflows of Extreme Carbon Stars

Speck¹,

Corman²,

Wakeman³

et al. 2009

ApJ

101

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Infrared carbon stars without visible counterparts are generally known as extreme carbon stars. We have selected a subset of these stars with absorption features in the 10-13 µm range, which has been tentatively attributed to silicon carbide (SiC). We add three new objects meeting these criterion to the seven previously known, bringing our total sample to ten sources. We also present the result of radiative transfer modeling for these stars, comparing these results to those of previous studies. In order to constrain model parameters, we use published mass-loss rates, expansion velocities and theoretical dust condensation models to determine the dust condensation temperature. These show that the inner dust temperatures of the dust shells for these sources are significantly higher than previously assumed. This also implies that the dominant dust species should be graphite instead of amorphous carbon. In combination with the higher condensation temperature we show that this results in a much higher acceleration of the dust grains than would be expected from previous work. Our model results suggest that the very optically thick stage of evolution does not coincide with the timescales for the superwind, but rather, that this is a very short-lived phase. Additionally, we compare model and observational parameters in an attempt to find any correlations. Finally, we show that the spectrum of one source, IRAS 17534−3030, strongly implies that the 10-13 µm feature is due to a solid state rather than a molecular species.

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Section: Parameter Space Investigatedmentioning

confidence: 99%

Silicon Carbide Absorption Features: Dust Formation in the Outflows of Extreme Carbon Stars

Speck¹,

Corman²,

Wakeman³

et al. 2009

ApJ

101

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“…In [23] it is assumed that the drift ceases to exist when pressure equilibration takes place along the magnetic surfaces. It is suggested in [64,65] that the current circuit becomes closed along those magnetic field lines which connect the positively and negatively charged domains of the pellet cloud. According to this model, the current ceases first of all at magnetic surfaces with rational q values.…”

Section: Drift Motion Of the Ablated Substance: Particle Deposition Pmentioning

confidence: 99%

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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“…The latter can be utilized to advantage by optimizing the pellet injection location and it has been confirmed in tokamaks that the high field side pellet injection can improve effective pellet fueling performance [4,5]. The ∇B induced drift model is widely accepted as the mechanism of the pellet plasmoid drift toward the low magnetic field direction in tokamak devices [6][7][8], and the ITER plasma fueling system relies on the high field side pellet injection [9].…”

Section: Introductionmentioning

confidence: 99%

Observation of Cross-Field Transport of Pellet Plasmoid in LHD

Sakamoto

Yamada

2011

Plasma and Fusion Research

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A three-dimensional observation of the solid hydrogen pellet ablation has been performed by using a fast stereo imaging camera to investigate the pellet ablation dynamics. The initial velocity component of the injected pellet is maintained during ablation in a hot plasma, and the pellet penetrates to the core plasma. On the other hand, it has been observed that part of high density pellet plasmoid, which is formed around the pellet substance by ablating hydrogen pellet, intermittently breaks away from the pellet ablating position and the breakaway plasmoid is transported across a confinement field. The breakaway plasmoid recurrently develops at the rate of about 100 times per millisecond and it is non-diffusively transported approximately 0.1 m during its several 10 µs lifetime in the opposite direction to the pellet motion, namely, toward the low magnetic field side. This observation gives a reasonable explanation for the difference between the pellet ablation position and the effective particle deposition profile.

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Homogenization of the pellet ablated material in tokamaks taking into account the ∇B-induced drift

Cited by 71 publications

References 28 publications

Silicon Carbide Absorption Features: Dust Formation in the Outflows of Extreme Carbon Stars

Silicon Carbide Absorption Features: Dust Formation in the Outflows of Extreme Carbon Stars

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

Observation of Cross-Field Transport of Pellet Plasmoid in LHD

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