Hydrogen pellet ablation and acceleration by current in high temperature plasmas

Kuteev, B. V.

doi:10.1088/0029-5515/35/4/i05

Cited by 58 publications

(51 citation statements)

References 28 publications

(13 reference statements)

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“…Deviations from this assumption can arise because the heat flux and the areal ablation rate are larger on pellet surface elements normal to the magnetic field lines than those that are tangential. As pointed out by Kuteev,16 the pellet would become progressively more oblate or ''lentil'' shaped. The heat flux asymmetry also imparts a nonuniform ablation recoil pressure at the pellet surface ͑rocket effect͒.…”

Section: Gϭmentioning

confidence: 91%

“…The rollover in r pellet begins when the changing pellet shape starts to bring p A and p B closer together, which in turn lessens the shear stress causing deformation. On the other hand, the thickness z pellet continually decreases due to ablation ͑lentil effect 16 ͒. Figures 14͑a͒ and 14͑b͒ show the (z,t) and (r,t) trajectories, respec- tively, of the pellet, sonic, and shock surfaces.…”

Section: Ablation With Anisotropic Heatingmentioning

confidence: 99%

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Two-dimensional simulation of pellet ablation with atomic processes

et al. 2004

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A two-dimensional hydrodynamic simulation code CAP has been developed in order to investigate the dynamics of hydrogenic pellet ablation in magnetized plasmas throughout their temporal evolution. One of the properties of the code is that it treats the solid-to-gas phase change at the pellet surface without imposing artificial boundary conditions there, as done in previous ablation models. The simulation includes multispecies atomic processes, mainly molecular dissociation and thermal ionization in the ablation flow beyond the pellet, with a kinetic heat flux model. It was found that ionization causes the formation of a quasistationary shock front in the supersonic region of the ablation flow, followed by a ''second'' sonic surface farther out. Anisotropic heating, due to the directionality of the magnetic field, contributes to a nonuniform ablation ͑recoil͒ pressure distribution over the pellet surface. Since the shear stress can exceed the yield strength of the solid for a sufficiently high heat flux, the solid pellet can be fluidized and flattened into a ''pancake'' shape while the pellet is ablating and losing mass. The effect of pellet deformation can shorten the pellet lifetime almost 3ϫ from that assuming the pellet remains rigid and stationary during ablation.

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Section: Gϭmentioning

confidence: 91%

Section: Ablation With Anisotropic Heatingmentioning

confidence: 99%

Two-dimensional simulation of pellet ablation with atomic processes

et al. 2004

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“…As a result of this configuration, the pellet ablation process may become two-dimensional and the pellet form may deviate from purely spherical [18,41,42].…”

Section: Wwwcpp-journalorgmentioning

confidence: 99%

“…-Kuteev [18] developed an ablation model in which, in addition to accounting for shielding by the plasma cloud and treating the electron energy depletion process by kinetic calculations, two-dimensional effects, i.e. the lateral heating of the pellet and its cloud by hot electrons and ions whose gyro-radii exceed the cloud dimension, are also taken into account.…”

Section: Wwwcpp-journalorgmentioning

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 ablation rate of the pellet, originally derived by Parks and Turnbull [36] and modified for hydrogen pellets by Kuteev [37] is given as (in atoms/s) where n e is the background plasma density in cm À3 , T e is the background plasma electron temperature in eV, M i is the atomic mass number in atomic units, and n m = 2.63 · 10 22 /cm 3 is the molecular density of frozen hydrogen. The density source term arises from the ablation of the pellet and is written in terms of number density, (i.e., atoms per unit volume per unit time) as S n ¼ _ N dðx À x p Þ, where the delta function is approximated as a Gaussian distribution centered over the pellet with a characteristic size equal to 10r p .…”

Section: Pellet Injectionmentioning

confidence: 99%