65 research outputs found
A symplectic, symmetric algorithm for spatial evolution of particles in a time-dependent field
A symplectic, symmetric, second-order scheme is constructed for particle
evolution in a time-dependent field with a fixed spatial step. The scheme is
implemented in one space dimension and tested, showing excellent adequacy to
experiment analysis.Comment: version 2; 16 p
New foundations and unification of basic plasma physics by means of classical mechanics
The derivation of Debye shielding and Landau damping from the -body
description of plasmas requires many pages of heavy kinetic calculations in
classical textbooks and is done in distinct, unrelated chapters. Using Newton's
second law for the -body system, we perform this derivation in a few steps
with elementary calculations using standard tools of calculus, and no
probabilistic setting. Unexpectedly, Debye shielding is encountered on the way
to Landau damping. The theory is extended to accommodate a correct description
of trapping or chaos due to Langmuir waves, and to avoid the small amplitude
assumption for the electrostatic potential. Using the shielded potential,
collisional transport is computed for the first time by a convergent expression
including the correct calculation of deflections for all impact parameters.
Shielding and collisional transport are found to be two related aspects of the
repulsive deflections of electrons.Comment: 28 pages, revTeX. arXiv admin note: substantial text overlap with
arXiv:1210.154
Vlasov equation and -body dynamics - How central is particle dynamics to our understanding of plasmas?
Difficulties in founding microscopically the Vlasov equation for
Coulomb-interacting particles are recalled for both the statistical approach
(BBGKY hierarchy and Liouville equation on phase space) and the dynamical
approach (single empirical measure on one-particle
-space). The role of particle trajectories
(characteristics) in the analysis of the partial differential Vlasov--Poisson
system is stressed. Starting from many-body dynamics, a direct derivation of
both Debye shielding and collective behaviour is sketched.Comment: revTeX, 15 p
Sticky islands in stochastic webs and anomalous chaotic cross-field particle transport by ExB electron drift instability
The ExB electron drift instability, present in many plasma devices, is an
important agent in cross-field particle transport. In presence of a resulting
low frequency electrostatic wave, the motion of a charged particle becomes
chaotic and generates a stochastic web in phase space. We define a scaling
exponent to characterise transport in phase space and we show that the
transport is anomalous, of super-diffusive type. Given the values of the model
parameters, the trajectories stick to different kinds of islands in phase
space, and their different sticking time power-law statistics generate
successive regimes of the super-diffusive transport.Comment: This manuscript contains 13 Pages and 21 figure
Wave-particle interactions in a long traveling wave tube with upgraded helix
We investigate the interaction of electromagnetic waves and electron beams in
a 4 meters long traveling wave tube (TWT). The device is specially designed to
simulate beam-plasma experiments without appreciable noise. This TWT presents
an upgraded slow wave structure (SWS) that results in more precise measurements
and makes new experiments possible. We introduce a theoretical model describing
wave propagation through the SWS and validated by the experimental dispersion
relation, impedance, phase and group velocities. We analyze nonlinear effects
arising from the beam-wave interaction, such as the modulation of the electron
beam and the wave growth and saturation process. When the beam current is low,
the wave growth coefficient and saturation amplitude follow the linear theory
predictions. However, for high values of current, nonlinear space charge
effects become important and these parameters deviate from the linear
predictions, tending to a constant value. After saturation, we also observe
trapping of the beam electrons, which alters the wave amplitude along the TWT.Comment: Submitted for publicatio
VEGUETA Y CATEDRAL DESDE EL RISCO [Material gráfico]
DUPLICADO DE LA IMAGEN Nº 3029FOTO POSTAL DE "GRAN CANARIA LAS PALMAS VISTA GENERAL" (COLOREADA) IMAGEN PARECIDA A 3034Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201
Direct path from microscopic mechanics to Debye shielding, Landau damping, and wave-particle interaction
The derivation of Debye shielding and Landau damping from the -body
description of plasmas is performed directly by using Newton's second law for
the -body system. This is done in a few steps with elementary calculations
using standard tools of calculus, and no probabilistic setting. Unexpectedly,
Debye shielding is encountered together with Landau damping. This approach is
shown to be justified in the one-dimensional case when the number of particles
in a Debye sphere becomes large. The theory is extended to accommodate a
correct description of trapping and chaos due to Langmuir waves. Shielding and
collisional transport are found to be two related aspects of the repulsive
deflections of electrons, in such a way that each particle is shielded by all
other ones while keeping in uninterrupted motion.Comment: arXiv admin note: substantial text overlap with arXiv:1310.3096,
arXiv:1210.154
Long-time discrete particle effects versus kinetic theory in the self-consistent single-wave model
The influence of the finite number N of particles coupled to a monochromatic
wave in a collisionless plasma is investigated. For growth as well as damping
of the wave, discrete particle numerical simulations show an N-dependent long
time behavior resulting from the dynamics of individual particles. This
behavior differs from the one due to the numerical errors incurred by Vlasov
approaches. Trapping oscillations are crucial to long time dynamics, as the
wave oscillations are controlled by the particle distribution inhomogeneities
and the pulsating separatrix crossings drive the relaxation towards thermal
equilibrium.Comment: 11 pages incl. 13 figs. Phys. Rev. E, in pres
Analytical study of magnetic turbulence
The growth of magnetic islands considerably affects the transport properties of fusion plasmas. The Hamiltonian formalism appears as a very powerful tool to describe the onset of magnetic turbulence. This last one is associated to the blowup of the stochastic layer of the main magnetic island. Moreover, the renormalization theory developed for Hamiltonian systems explains the order of appearance of magnetic islands.La croissance d'îlots magnétiques modifie considérablement les propriétés de transport des plasmas de fusion. Le formalisme hamiltonien se révèle un outil indispensable à une bonne description de l'apparition de turbulence magnétique. Celle-ci est associée à l'explosion de la couche stochastique de l'îlot principal du système. La théorie de renormalisation développée pour les systèmes hamiltoniens permet de plus d'expliquer l'ordre d'apparition des îlots
- …