1,721,052 research outputs found
Reflection and transmission of electromagnetic waves from a nonlinear anisotropic slab between two linear isotropic media
No full textIn this paper, the author has studied the reflection from and transmission through a homogenous nonlinear anisotropic slab (anisotropy being due to an external magnetic field) bounded by two linear isotropic media. Nonlinear equations describing the growth of the two modes of propagation of an electromagnetic wave in the direction of the magnetic field, in an anisotropic nonlinear medium, have been set up and solved; the solutions have been used to obtain expressions for the reflected and transmitted components of the incident wave. The simpler problem of the reflection and transmission from an isotropic nonlinear slab has also been discussed as a special case
Optical mixing by mobile carriers in semiconductors
No full textIt is shown that certain nonlinearities associated with the energy dependence of the carrier-momentum relaxation time in semiconductors make contributions to the optically mixed output, which may be larger than the ones considered by earlier workers
Nonlinear trapped electron mode and anomalous heat transport in Tokamaks
No full textWe take the phenomenological point of view that the anomalous electron thermal conductivity produced by the nonlinear trapped electron mode should also influence the stability properties of the mode itself. Using a model equation, we show that this effect makes the mode self-stabilizing. A simple expression for the anomalous thermal conductivity is derived, and its scaling properties are discussed
Stability of vortex flows in magnetized plasmas. II. Boltzmann vortices
No full textThe stability of elliptical vortex flow to the excitation of low-frequency electrostatic drift waves is investigated. It is demonstrated that finite ellipticity of flow drives the secondary instability of drift/drift-acoustic waves. When flow ellipticity is small, certain matching conditions between the rotation frequency and secondary wave frequency are needed for instability to occur. The case of large eccentricity is solved by asymptotic methods and gives a growth rate for the instability that depends logarithmically on eccentricity. Such secondary instability mechanisms can act as a sink of vortex energy (limiting the vortex condensation at the long-wavelength end) and thereby help in our understanding of nonlinear saturation of low-frequency instabilitie
Anomalous absorption of radio waves by electrojet irregularities
No full textThe enhanced absorption of radio waves (with a frequency close to the upper hybrid frequency) in the equatorial electrojet by resonant coupling to electrojet irregularities and damped upper hybrid modes is investigated. It is found that, under normal ionospheric conditions, the absorption coefficient for such radio waves may be increased by a factor of as large as 100
Nonlinear effects of laser propagation in dense plasmas
No full textTwo nonlinear effects of laser propagation in dense plasmas have been analytically investigated, viz., laser penetration into an overdense plasma and the self-focusing of a laser beam. It is concluded that for laser powers currently being used, both these effects can be quite important
An interpretation for the power spectrum of spread F irregularities
No full textThe k-2 power spectrum of long scale length spread F irregularities is interpreted in terms of a two-step theory. The analysis is carried out by using a mode-mode coupling approach for the two-step process instead of a 'linear' one as used earlier. This results in a better physical understanding of the process and shows that it does not take place on certain modes, for example, drift waves
Instability of elliptical vortex cores in electron clouds
No full textWe investigate the stability of a magnetized electron cloud equilibrium with an elliptical E × B vortex core to the excitation of high frequency electrostatic waves. It is demonstrated that the finite ellipticity of the flow drives the instability of oblique electron plasma oscillations. When the flow ellipticity is small, certain matching conditions between the near rotation frequency of the vortex and the oscillation frequency of the plasma wave are needed. For larger ellipticities, the instability domain is shown to be much broader. Equilibria with elliptic vortex cores are therefore likely to be found with considerable electrostatic noise which will contribute to the transport of the electron fluid across field lines
Optimum second-harmonic generation in nondegenerate semiconductors using dc electric fields
No full textIn this paper the author has analytically investigated the use of dc electric fields of arbitrary strength, for the generation of second harmonics of high-frequency electromagnetic waves in a nondegenerate semiconductor. Boltzmann equation techniques have been employed to describe the motion of free carriers inside the semiconductor; the only form of carrier scattering considered is acoustic phonon scattering. The curve of second-harmonic intensity vs dc field exhibits a maximum, thus illustrating that there is an optimum value of the dc field for which the generation can be most efficient
Collisional instabilities in a dusty plasma with recombination and ion-drift effects
No full textInstabilities of dust acoustic waves in a plasma with a significant background pressure of neutrals have been investigated. A long wavelength mode is found to be unstable due to recombination of electrons and ions on the surface of dust particles. At short wavelengths, a dissipative instability driven by relative drift between ions and the dust particles is found to be important. Nonlinearly, the short wavelength modes lead to the formation of K-dV solitons whereas the long wavelength end is dominated by modulational instabilities
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