164 research outputs found
Bosonization Theory of Excitons in One-dimensional Narrow Gap Semiconductors
Excitons in one-dimensional narrow gap semiconductors of anti-crossing
quantum Hall edge states are investigated using a bosonization method. The
excitonic states are studied by mapping the problem into a non-integrable
sine-Gordon type model. We also find that many-body interactions lead to a
strong enhancement of the band gap. We have estimated when an exciton
instability may occur.Comment: 4pages, 1 figure, to appear in Phys. Rev. B Brief Report
Anomalous resistance of the fractal current-carrying corona of Z-pinch
An effect of the random plasma inhomogeneity onto the scenario of ion-acoustic anomalous resistivity is considered. It is shown that such an inhomogeneity could be more efficient than nonlinear effects to determine the turbulent resistivity. In application to Z-pinches, some peculiarities of the skin-effect are considered, in particular, subsequent inhomogeneity of the current penetration into the conducting medium
Magnetic Helicity Conservation and Inverse Energy Cascade in Electron Magnetohydrodynamic Wave Packets
Electron magnetohydrodynamics (EMHD) provides a fluid-like description of
small-scale magnetized plasmas. An EMHD wave (also known as whistler wave)
propagates along magnetic field lines. The direction of propagation can be
either parallel or anti-parallel to the magnetic field lines. We numerically
study propagation of 3-dimensional (3D) EMHD wave packets moving in one
direction. We obtain two major results: 1. Unlike its magnetohydrodynamic (MHD)
counterpart, an EMHD wave packet is dispersive. Because of this, EMHD wave
packets traveling in one direction create opposite traveling wave packets via
self-interaction and cascade energy to smaller scales. 2. EMHD wave packets
traveling in one direction clearly exhibit inverse energy cascade. We find that
the latter is due to conservation of magnetic helicity. We compare inverse
energy cascade in 3D EMHD turbulence and 2-dimensional (2D) hydrodynamic
turbulence.Comment: Phys. Rev. Lett., accepted (4pages, 4 figures
Turbulence and Particle Heating in Advection-Dominated Accretion Flows
We extend and reconcile recent work on turbulence and particle heating in
advection-dominated accretion flows. For approximately equipartition magnetic
fields, the turbulence primarily heats the electrons. For weaker magnetic
fields, the protons are primarily heated. The division between electron and
proton heating occurs between and (where
is the ratio of the gas to the magnetic pressure), depending on unknown
details of how Alfv\'en waves are converted into whistlers on scales of the
proton Larmor radius. We also discuss the possibility that magnetic
reconnection could be a significant source of electron heating.Comment: 17 pages (Latex), incl. 2 Figures; submitted to Ap
Theory and Simulations of Whistler Wave Propagation
A linear theory of whistler wave is developed wihtin the paradigm of a two
dimensional incompressible electron magnetohydrodynamics model. Exact analytic
wave solutions are obtained for a small amplitude whistler wave that exhibit
magnetic field topological structures consistent with the observations and our
simulations in linear regime. In agreement with experiment, we find that the
parallel group velocity of the wave is large compared to its perpendicular
counterpart. Numerical simulations of collisional interactions demonstrate that
the wave magnetic field either coalesces or repels depending upon the polarity
of the associated current. In the nonlinear regime, our simulations demonstrate
that the evolution of wave magnetic field is governed essentially by the
nonlinear Hall force
Transition from the chaotic turbulence to the turbulent structures
Weak turbulence, similar to incoherent light, may be represented as an ensemble of quasi-free quanta or Fourier harmonics. Unlike it, strongly turbulent state should be based on nonlinear structures. In particular, strong plasma turbulence may be constructed of discrete
formations, viz., Langmuir solitons. Instead for ‘infrared catastrophe’ typical of the weakly turbulent regime, one deals with the ‘relay race’ model providing the proper direction of the energetic flux over scales from the source towards the leakage
Electric fields in plasmas under pulsed currents
Electric fields in a plasma that conducts a high-current pulse are measured
as a function of time and space. The experiment is performed using a coaxial
configuration, in which a current rising to 160 kA in 100 ns is conducted
through a plasma that prefills the region between two coaxial electrodes. The
electric field is determined using laser spectroscopy and line-shape analysis.
Plasma doping allows for 3D spatially resolved measurements. The measured peak
magnitude and propagation velocity of the electric field is found to match
those of the Hall electric field, inferred from the magnetic-field front
propagation measured previously.Comment: 13 pages, 13 figures, submitted to PR
Generalised relativistic Ohm's laws, extended gauge transformations and magnetic linking
Generalisations of the relativistic ideal Ohm's law are presented that
include specific dynamical features of the current carrying particles in a
plasma. Cases of interest for space and laboratory plasmas are identified where
these generalisations allow for the definition of generalised electromagnetic
fields that transform under a Lorentz boost in the same way as the real
electromagnetic fields and that obey the same set of homogeneous Maxwell's
equations
On the Possibility of Development of the Explosion Instability in a Two-Component Gravitating System
We obtain an expression for the energy of the density wave propagating in a
multicomponent gravitating medium in the form well known from electrodynamics.
Using the above, the possibility of "triple production" of the quasi-particles,
or waves, with their energies summing up to zero, in a non-equilibrium medium
is demonstrated. That kind of resonance wave interaction is shown to result in
the development of an explosion instability. By the method developed in plasma
physics, the characteristic time of the instability is evaluated.Comment: 15 pages, 3 figures, accepted for publication (JETP
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