148 research outputs found
Comment on: Thermostatistics of Overdamped Motion of Interacting Particles [arXiv:1008.1421]
In a recent paper, Phys. Rev. Lett. 105 260601 (2010) [arXiv:1008.1421],
Andrade et al., argued that classical particles confined in a parabolic trap at
T=0 distribute themselves in accordance with the Tsallis statistics. To prove
their point the authors performed molecular dynamics simulations. Here we show
that the model of Andrade et al. can be solved exactly. The distribution of
particles at T=0 has nothing to do with the Tsallis entropy and is determined
simply by the force balance
Non-equilibrium Statistical Mechanics of Two-dimensional Vortices
It has been observed empirically that two dimensional vortices tend to
cluster forming a giant vortex. To account for this observation Onsager
introduced a concept of negative absolute temperature in equilibrium
statistical mechanics. In this Letter we will show that in the thermodynamic
limit a system of interacting vortices does not relax to the thermodynamic
equilibrium, but becomes trapped in a non-equilibrium stationary state. We will
show that the vortex distribution in this non-equilibrium stationary state has
a characteristic core-halo structure, which can be predicted {\it a priori}.
All the theoretical results are compared with explicit molecular dynamics
simulations
Symmetry Breaking in d-Dimensional Self-gravitating Systems
Systems with long-range interactions, such as self-gravitating clusters and
magnetically confined plasmas, do not relax to the usual Boltzmann-Gibbs
thermodynamic equilibrium, but become trapped in quasi-stationary states (QSS)
the life time of which diverges with the number of particles. The QSS are
characterized by the lack of ergodicity which can result in a symmetry broken
QSS starting from a spherically symmetric particle distribution. We will
present a theory which allows us to quantitatively predict the instability
threshold for spontaneous symmetry breaking for a class of d-dimensional
self-gravitating systems.Comment: 5 pages, 4 figures. Accepted for publication in Physical Review
Letter
Nonlinear dynamics of electromagnetic pulses in cold relativistic plasmas
In the present analysis we study the self consistent propagation of nonlinear
electromagnetic pulses in a one dimensional relativistic electron-ion plasma,
from the perspective of nonlinear dynamics. We show how a series of Hamiltonian
bifurcations give rise to the electric fields which are of relevance in the
subject of particle acceleration. Connections between these bifurcated
solutions and results of earlier analysis are made.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Relaxation and Emittance Growth of a Thermal Charged-Particle Beam
We present a theory that allows us to accurately calculate the distribution
functions and the emittance growth of a thermal charged-particle beam after it
relaxes to equilibrium. The theory can be used to obtain the fraction of
particles, which will evaporate from the beam to form a halo. The calculated
emittance growth is found to be in excellent agreement with the simulations.Comment: 3 pages, 3 figure
Collisionless relaxation in non-neutral plasmas
A theoretical framework is presented which allows to quantitatively predict
the final stationary state achieved by a non-neutral plasma during a process of
collisionless relaxation. As a specific application, the theory is used to
study relaxation of charged-particles beams. It is shown that a fully matched
beam relaxes to the Lynden-Bell distribution. However, when a mismatch is
present and the beam oscillates, parametric resonances lead to a core-halo
phase separation. The approach developed accounts for both the density and the
velocity distributions in the final stationary state.Comment: Accepted in Phys. Rev. Let
Wave breaking and particle jets in intense inhomogeneous charged beams
This work analyzes the dynamics of inhomogeneous, magnetically focused
high-intensity beams of charged particles. While for homogeneous beams the
whole system oscillates with a single frequency, any inhomogeneity leads to
propagating transverse density waves which eventually result in a singular
density build up, causing wave breaking and jet formation. The theory presented
in this paper allows to analytically calculate the time at which the wave
breaking takes place. It also gives a good estimate of the time necessary for
the beam to relax into the final stationary state consisting of a cold core
surrounded by a halo of highly energetic particles.Comment: Accepted in Physics of Plasma Letter
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