1,968 research outputs found
How to model quantum plasmas
Traditional plasma physics has mainly focused on regimes characterized by
high temperatures and low densities, for which quantum-mechanical effects have
virtually no impact. However, recent technological advances (particularly on
miniaturized semiconductor devices and nanoscale objects) have made it possible
to envisage practical applications of plasma physics where the quantum nature
of the particles plays a crucial role. Here, I shall review different
approaches to the modeling of quantum effects in electrostatic collisionless
plasmas. The full kinetic model is provided by the Wigner equation, which is
the quantum analog of the Vlasov equation. The Wigner formalism is particularly
attractive, as it recasts quantum mechanics in the familiar classical phase
space, although this comes at the cost of dealing with negative distribution
functions. Equivalently, the Wigner model can be expressed in terms of
one-particle Schr{\"o}dinger equations, coupled by Poisson's equation: this is
the Hartree formalism, which is related to the `multi-stream' approach of
classical plasma physics. In order to reduce the complexity of the above
approaches, it is possible to develop a quantum fluid model by taking
velocity-space moments of the Wigner equation. Finally, certain regimes at
large excitation energies can be described by semiclassical kinetic models
(Vlasov-Poisson), provided that the initial ground-state equilibrium is treated
quantum-mechanically. The above models are validated and compared both in the
linear and nonlinear regimes.Comment: To be published in the Fields Institute Communications Series.
Proceedings of the Workshop on Kinetic Theory, The Fields Institute, Toronto,
March 29 - April 2, 200
Nonlinear aspects of quantum plasma physics
Dense quantum plasmas are ubiquitous in planetary interiors and in compact
astrophysical objects, in semiconductors and micro-mechanical systems, as well
as in the next generation intense laser-solid density plasma interaction
experiments and in quantum x-ray free-electron lasers. In contrast to classical
plasmas, one encounters extremely high plasma number density and low
temperature in quantum plasmas. The latter are composed of electrons, positrons
and holes, which are degenerate. Positrons (holes) have the same (slightly
different) mass as electrons, but opposite charge. The degenerate charged
particles (electrons, positrons, holes) follow the Fermi-Dirac statistics. In
quantum plasmas, there are new forces associated with i) quantum statistical
electron and positron pressures, ii) electron and positron tunneling through
the Bohm potential, and iii) electron and positron angular momentum spin.
Inclusion of these quantum forces provides possibility of very high-frequency
dispersive electrostatic and electromagnetic waves (e.g. in the hard x-ray and
gamma rays regimes) having extremely short wavelengths. In this review paper,
we present theoretical backgrounds for some important nonlinear aspects of
wave-wave and wave-electron interactions in dense quantum plasmas.
Specifically, we shall focus on nonlinear electrostatic electron and ion plasma
waves, novel aspects of 3D quantum electron fluid turbulence, as well as
nonlinearly coupled intense electromagnetic waves and localized plasma wave
structures. Also discussed are the phase space kinetic structures and
mechanisms that can generate quasi-stationary magnetic fields in dense quantum
plasmas. The influence of the external magnetic field and the electron angular
momentum spin on the electromagnetic wave dynamics is discussed.Comment: 42 pages, 20 figures, accepted for publication in Physics-Uspekh
ORB5: a global electromagnetic gyrokinetic code using the PIC approach in toroidal geometry
This paper presents the current state of the global gyrokinetic code ORB5 as
an update of the previous reference [Jolliet et al., Comp. Phys. Commun. 177
409 (2007)]. The ORB5 code solves the electromagnetic Vlasov-Maxwell system of
equations using a PIC scheme and also includes collisions and strong flows. The
code assumes multiple gyrokinetic ion species at all wavelengths for the
polarization density and drift-kinetic electrons. Variants of the physical
model can be selected for electrons such as assuming an adiabatic response or a
``hybrid'' model in which passing electrons are assumed adiabatic and trapped
electrons are drift-kinetic. A Fourier filter as well as various control
variates and noise reduction techniques enable simulations with good
signal-to-noise ratios at a limited numerical cost. They are completed with
different momentum and zonal flow-conserving heat sources allowing for
temperature-gradient and flux-driven simulations. The code, which runs on both
CPUs and GPUs, is well benchmarked against other similar codes and analytical
predictions, and shows good scalability up to thousands of nodes
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