Modelling of the pellet cloud evolution and mass deposition with an account of ∇<i>B</i>induced drift

Senichenkov, I.; Veselova, I.; Rozhansky, V.; Schneider, R.

doi:10.1088/0029-5515/46/8/004

Cited by 12 publications

(17 citation statements)

References 21 publications

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“…The reduction rate of pellet radius r p by the ablation is given by the neutral gas and plasmoid shielding (NGPS) description as [11], (1) The meaning of each variable is the same as in the reference and omitted here due to the page limitation. The time derivative of detached cloud speed υ ⊥ in the R direction is given as [11][12][13], (2) The first term in right-hand-side of eq. (2) is a driving term due to the ExB drift and second and third terms are damping terms.…”

Section: Topics-ibmentioning

confidence: 99%

“…These periodic 'cloud disruptions' breed a sequence of more than ten detached clouds. The time derivative of the speed υ ⊥ of each detached cloud in the direction of major radius R is given as [8,17,18] dυ…”

Section: Topics-ibmentioning

confidence: 99%

“…and L φ = 4π 3/2 Ra/r ⊥ . The first term on the right-hand side of equation ( 2) is a driving term due to a vertical curvature and ∇B drift current induced inside the cloud by the 1/R toroidal field variation, which results in the E × B drift [8,17]. The second and third terms are damping terms due to the Alfvén wave [8,18] and the external current [18], respectively.…”

Section: Topics-ibmentioning

confidence: 99%

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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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Section: Topics-ibmentioning

confidence: 99%

Section: Topics-ibmentioning

confidence: 99%

Section: Topics-ibmentioning

confidence: 99%

See 1 more Smart Citation

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

Hayashi¹,

Parail²,

Koechl³

et al. 2011

Nucl. Fusion

View full text Add to dashboard Cite

show abstract

“…Because such a drift across the flux surfaces results in a modification of the deposition profile with respect to ablation, a modelling of the post-ablation phase-including the drift-is a mandatory complement to conventional ablation theory [6]. For understanding the physical mechanisms behind the drift displacement, ∇B-induced polarization drift models [4,5,[7][8][9][10] as well as magnetohydrodynamic (MHD) simulations [11][12][13][14] were intensively studied.…”

Section: Introductionmentioning

confidence: 99%

“…The leading term is the charge separation resulting from the opposite drift of electrons and ions in the inhomogeneous magnetic field. Two types of currents are considered that cancel this ∇B-induced polarization: internal currents [8,9], which flow inside the plasmoid, and external currents [10], which flow in the surrounding plasma. As a whole, they are analogous to the Pfirsch-Schlüter currents in MHD equilibria [24].…”

Section: Introductionmentioning

confidence: 99%

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

Matsuyama¹,

Koechl²,

Pégouriè³

et al. 2012

Nucl. Fusion

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Drift displacement during density homogenization is modelled for hydrogen pellets injected into the Large Helical Device (LHD). The pellet ablation and deposition profiles are simulated for neutral-beam injection heated plasmas and are shown to reproduce well the main characteristics of the observed drift displacement for both low-field side and high-field side (HFS) injected pellets. The model describes the parallel expansion of ionized ablated pellet particle cloudlets (plasmoid) in non-axisymmetric magnetic configurations and the associated evolution of the plasmoid drift acceleration force exerted by the average magnetic field gradient over the plasmoid length. It is shown that, during the ablation and early homogenization phases, plasmoids are strongly accelerated towards the inverse direction of the local magnetic field gradient. In the case of the LHD, its direction and magnitude depend mainly on the pellet launching location with respect to the external helical coils. While such an initial drift—induced near the ablation region—is efficiently damped by plasmoid internal currents as soon as the plasmoid length becomes comparable to a toroidal connection length, a weak drift acceleration force is maintained over the whole homogenization time, whose direction depends on whether the confining magnetic field possesses a magnetic well or hill structure. Simulations show that, in a strong magnetic hill configuration like the LHD, this small but long-term drift becomes significant and results in a radially outward displacement of the mass deposition even for pellets injected from the HFS.

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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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Modelling of the pellet cloud evolution and mass deposition with an account of ∇Binduced drift

Abstract: Modeling of the pellet ablation cloud evolution including the B ∇ induced drift motion is

Cited by 12 publications

References 21 publications

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

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

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

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

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