124 research outputs found
Kinetic theory of electromagnetic ion waves in relativistic plasmas
A kinetic theory for electromagnetic ion waves in a cold relativistic plasma
is derived. The kinetic equation for the broadband electromagnetic ion waves is
coupled to the slow density response via an acoustic equation driven by
ponderomotive force like term linear in the electromagnetic field amplitude.
The modulational instability growth rate is derived for an arbitrary spectrum
of waves. The monochromatic and random phase cases are studied.Comment: 7 pages, 4 figures, to appear in Physics of Plasma
Ion structure in warm dense matter: benchmarking solutions of hypernetted-chain equations by first-principle simulations
We investigate the microscopic structure of strongly coupled ions in warm dense matter using ab initio simulations and hypernetted chain (HNC) equations. We demonstrate that an approximate treatment of quantum effects by weak pseudopotentials fails to describe the highly degenerate electrons in warm dense matter correctly. However, one-component HNC calculations for the ions agree well with first-principles simulations if a linearly screened Coulomb potential is used. These HNC results can be further improved by adding a short-range repulsion that accounts for bound electrons. Examples are given for recently studied light elements, lithium and beryllium, and for aluminum where the extra short-range repulsion is essential
Quantum kinetic theory of the filamentation instability
The quantum electromagnetic dielectric tensor for a multi species plasma is
re-derived from the gauge invariant Wigner-Maxwell system and presented under a
form very similar to the classical one. The resulting expression is then
applied to a quantum kinetic theory of the electromagnetic filamentation
instability. Comparison is made with the quantum fluid theory including a Bohm
pressure term, and with the cold classical plasma result. A number of
analytical expressions are derived for the cutoff wave vector, the largest
growth rate and the most unstable wave vector
Swimming suppresses correlations in dilute suspensions of pusher microorganisms
Active matter exhibits various forms of non-equilibrium states in the absence
of external forcing, including macroscopic steady-state currents. Such states
are often too complex to be modelled from first principles and our
understanding of their physics relies heavily on minimal models. These have
mostly been studied in the case of "dry" active matter, where particle dynamics
are dominated by friction with their surroundings. Significantly less is known
about systems with long-range hydrodynamic interactions that belong to "wet"
active matter. Dilute suspensions of motile bacteria, modelled as
self-propelled dipolar particles interacting solely through long-ranged
hydrodynamic fields, are arguably the most studied example from this class of
active systems. Their phenomenology is well-established: at sufficiently high
density of bacteria, there appear large-scale vortices and jets comprising many
individual organisms, forming a chaotic state commonly known as bacterial
turbulence. As revealed by computer simulations, below the onset of collective
motion, the suspension exhibits very strong correlations between individual
microswimmers stemming from the long-ranged nature of dipolar fields. Here we
demonstrate that this phenomenology is captured by the minimal model of
microswimmers. We develop a kinetic theory that goes beyond the commonly used
mean-field assumption, and explicitly takes into account such correlations.
Notably, these can be computed exactly within our theory. We calculate the
fluid velocity variance, spatial and temporal correlation functions, the fluid
velocity spectrum, and the enhanced diffusivity of tracer particles. We find
that correlations are suppressed by particle self-propulsion, although the
mean-field behaviour is not restored even in the limit of very fast swimming.Comment: 23 pages, 9 figure
Dispersion and damping of potential surface waves in a degenerate plasma
Potential (electrostatic) surface waves in plasma half-space with degenerate
electrons are studied using the quasi-classical mean-field kinetic model. The
wave spectrum and the collisionless damping rate are obtained numerically for a
wide range of wavelengths. In the limit of long wavelengths, the wave frequency
approaches the cold-plasma limit with
being the plasma frequency, while at short wavelengths, the wave
spectrum asymptotically approaches the spectrum of zero-sound mode propagating
along the boundary. It is shown that the surface waves in this system remain
weakly damped at all wavelengths (in contrast to strongly damped surface waves
in Maxwellian electron plasmas), and the damping rate nonmonotonically depends
on the wavelength, with the maximum (yet small) damping occuring for surface
waves with wavelength of , where is the
Thomas-Fermi length.Comment: 22 pages, 6 figure
Heat exchange mediated by a quantum system
We consider heat transfer between two thermal reservoirs mediated by a
quantum system using the generalized quantum Langevin equation. The thermal
reservoirs are treated as ensembles of oscillators within the framework of the
Drude-Ullersma model. General expressions for the heat current and thermal
conductance are obtained for arbitrary coupling strength between the reservoirs
and the mediator and for different temperature regimes. As an application of
these results we discuss the origin of Fourier's law in a chain of large, but
finite subsystems coupled to each other by the quantum mediators. We also
address a question of anomalously large heat current between the STM tip and
substrate found in a recent experiment. The question of minimum thermal
conductivity is revisited in the framework of scaling theory as a potential
application of the developed approach.Comment: 16 pages, 6 figure
Bimodality and hysteresis in systems driven by confined L\'evy flights
We demonstrate occurrence of bimodality and dynamical hysteresis in a system
describing an overdamped quartic oscillator perturbed by additive white and
asymmetric L\'evy noise. Investigated estimators of the stationary probability
density profiles display not only a turnover from unimodal to bimodal character
but also a change in a relative stability of stationary states that depends on
the asymmetry parameter of the underlying noise term. When varying the
asymmetry parameter cyclically, the system exhibits a hysteresis in the
occupation of a chosen stationary state.Comment: 4 pages, 5 figures, 30 reference
Nonlinear relaxation field in charged systems under high electric fields
The influence of an external electric field on the current in charged systems
is investigated. The results from the classical hierarchy of density matrices
are compared with the results from the quantum kinetic theory. The kinetic
theory yields a systematic treatment of the nonlinear current beyond linear
response. To this end the dynamically screened and field-dependent
Lenard-Balescu equation is integrated analytically and the nonlinear relaxation
field is calculated. The classical linear response result known as Debye -
Onsager relaxation effect is only obtained if asymmetric screening is assumed.
Considering the kinetic equation of one specie the other species have to be
screened dynamically while the screening with the same specie itself has to be
performed statically. Different other approximations are discussed and
compared.Comment: language correction
Colloquium: Nonlinear collective interactions in quantum plasmas with degenerate electron fluids
The current understanding of some important nonlinear collective processes in
quantum plasmas with degenerate electrons is presented. After reviewing the
basic properties of quantum plasmas, we present model equations (e.g. the
quantum hydrodynamic and effective nonlinear Schr\"odinger-Poisson equations)
that describe collective nonlinear phenomena at nanoscales. The effects of the
electron degeneracy arise due to Heisenberg's uncertainty principle and Pauli's
exclusion principle for overlapping electron wavefunctions that result in
tunneling of electrons and the electron degeneracy pressure. Since electrons
are Fermions (spin-1/2), there also appears an electron spin current and a spin
force acting on electrons due to the Bohr magnetization. The quantum effects
produce new aspects of electrostatic (ES) and electromagnetic (EM) waves in a
quantum plasma that are summarized in here. Furthermore, we discuss nonlinear
features of ES ion waves and electron plasma oscillations (ESOs), as well as
the trapping of intense EM waves in quantum electron density cavities.
Specifically, simulation studies of the coupled nonlinear Schr\"odinger (NLS)
and Poisson equations reveal the formation and dynamics of localized ES
structures at nanoscales in a quantum plasma. We also discuss the effect of an
external magnetic field on the plasma wave spectra and develop quantum
magnetohydrodynamic (Q-MHD) equations. The results are useful for understanding
numerous collective phenomena in quantum plasmas, such as those in compact
astrophysical objects, in plasma-assisted nanotechnology, and in the
next-generation of intense laser-solid density plasma interaction experiments.Comment: 25 pages, 14 figures. To be published in Reviews of Modern Physic
Shielding of a moving test charge in a quantum plasma
The linearized potential of a moving test charge in a one-component fully
degenerate fermion plasma is studied using the Lindhard dielectric function.
The motion is found to greatly enhance the Friedel oscillations behind the
charge, especially for velocities larger than a half of the Fermi velocity, in
which case the asymptotic behavior of their amplitude changes from 1/r^3 to
1/r^2.5. In the absence of the quantum recoil (tunneling) the potential reduces
to a form similar to that in a classical Maxwellian plasma, with a difference
being that the plasma oscillations behind the charge at velocities larger than
the Fermi velocity are not Landau-damped.Comment: 9 pages, 11 figures. v3: Fixed typo, updated abstrac
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