Vitesse de dérive (électricité)

Résumé

En électricité, la vitesse de dérive (aussi appelée « vitesse de drift », de l'anglais drift velocity), vd, est la vitesse moyenne d'une particule chargée, en général un électron, qu'elle atteint sous l'effet d'un champ électrique (E). Métal Un métal ne possède qu'un seul type de porteur de charge (dans la majorité des cas des électrons, plus rarement des trous). En l'absence de champ électrique, ces porteurs de charge dans un conducteur électrique à température ambiante, de par l'agitation thermique, se déplacent de façon aléatoire à la vitesse de Fermi. Leur direction étant aléatoire, leur mouvement global est nul, il n'y a pas de création de courant électrique. Lorsqu'on applique un champ électrique à ce conducteur, les électrons gagnent une vitesse nette dans la direction du champ (mais en sens opposé), créant un courant électrique. Cette vitesse est cependant réduite à cause des collisions des électrons dans leur environnement, en particulier les phonons. Un simple a

Source officielle

https://fr.wikipedia.org/wiki/Vitesse_de_d%C3%A9rive_(%C3%A9lectricit%C3%A9)

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Publications associées (26)

Implementation of drift velocities and currents in SOLEDGE2D-EIRENE

Davide Galassi, Nicolas Mellet, Eric Serre

In order to improve cross-field transport description, drifts and currents have been implemented in SOLEDGE2D-EIRENE. The derivation of an equation for the electric potential is recalled. The resolution of current equation is tested in a simple slab case. WEST divertor simulations in forward-B and reverse-B fields are also discussed. A significant increase of ExB shear is observed in the forward-B configuration that could explain a favorable L-H transition in this case. (C) 2017 Elsevier Ltd.

2017

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The coupling between dilatation and vorticity, two coexisting and fundamental processes in fluid dynamics (Wu et al., 2006, pp. 3, 6) is investigated here, in the simplest cases of inviscid 2D isotropic Burgers and pressureless Euler Coriolis fluids respectively modeled by single vortices confined in compressible, local, inertial and global, rotating, environments. The field equations are established, inductively, starting from the equations of the characteristics solved with an initial Helmholtz decomposition of the velocity fields namely a vorticity free and a divergence free part (Wu et al., 2006, Sects. 2.3.2, 2.3.3) and, deductively, by means of a canonical Hamiltonian Clebsch like formalism (Clebsch, 1857, 1859), implying two pairs of conjugate variables. Two vector valued fields are constants of the motion: the velocity field in the Burgers case and the momentum field per unit mass in the Euler Coriolis one. Taking advantage of this property, a class of solutions for the mass densities of the fluids is given by the Jacobian of their sum with respect to the actual coordinates. Implementation of the isotropy hypothesis entails a radial dependence of the velocity potentials and of the stream functions associated to the compressible and to the rotational part of the fluids and results in the cancellation of the dilatation-rotational cross terms in the Jacobian. A simple expression is obtained for all the radially symmetric Jacobians occurring in the theory. Representative examples of regular and singular solutions are shown and the competition between dilatation and vorticity is illustrated. Inspired by thermodynamical, mean field theoretical analogies, a genuine variational formula is proposed which yields unique measure solutions for the radially symmetric fluid densities investigated. We stress that this variational formula, unlike the Hopf-Lax formula, enables us to treat systems which are both compressible and rotational. Moreover in the one-dimensional case, we show for an interesting application that both variational formulas are equivalent. (C) 2014 Elsevier B.V. All rights reserved.

Elsevier Science Bv2014

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Characterizing time intermittency in non-diffusive fast ion transport through plasma turbulence

Marcelo Baquero Ruiz, Oulfa Chellaï, Ambrogio Fasoli, Ivo Furno, Fabian Manke, Paolo Ricci

Turbulent fast ion transport has been investigated in astrophisycal, laboratory and fusion plasmas. When gyro- and drift-averaging across plasma structures manifest as non-markovian and non-local effects, this results in generally non-diffusive transport. The intermittency of the formation of these plasma structures, such as blobs, can potentially be reflected in the transport of the fast ions as well. In the TORPEX basic plasma device, a toroidal beam of suprathermal Li-6 ions is injected into electrostatic plasma turbulence. Conditional sampling techniques confirm turbulent E × B-drifts as physical driving mechanism of radial fast ion transport, which features sub-, super- or quasi-diffusive regimes depending on the fast ion energy and propagation time. To address the question of how far local intermittency is associated with each regime, we analyze characteristics of time-intermittency on an extensive set of local fast ion time-series across all observed regimes. Modeling the time-average fast ion profiles as the result of a meandering smaller instantaneous beam allows us to predict the skewness of such time-series based on their time-average. Comparisons with the skewness of simple two-valued time-series can yield relative indications towards certain transport regimes in our specific system, based on the differences in the size of the instantaneous fast ion beam.

2019

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Elsevier Science Bv2014