Growth Of Electromagnetic Waves Research Articles

Electromagnetic waves in the auroral and subauroral regions of the topside ionosphere

The density and temperature of the plasma electron component and wave emission intensity in the topside ionosphere were measured by the INTERCOSMOS-19 satellite. In the subauroral ionosphere, a decrease in the plasma density correlates with an increase in the plasma electron component temperature. In this case, the additional increase in the electron component temperature was measured in regions with increased plasma density gradients during the substorm recovery phase. In a linear approximation, the electromagnetic wave growth increments are small on electron fluxes precipitating in the auroral zone. It has been indicated that Bernstein electromagnetic waves propagating in the subauroral topside ionosphere can intensify in regions with increased plasma density gradients on electron fluxes orthogonal to the geomagnetic field, which are formed when plasma is heated by decaying electrostatic oscillations of the plasma electron component. This can be one of the most important factors responsible for the intensification of auroral kilometric radiation.

Modeling Density and Anisotropy of Energetic Electrons Along Magnetic Field Lines

The electromagnetic wave growth or damping depends basically on the number density and anisotropy of energetic particles as the resonant interaction takes place between the particles and waves in the magnetosphere. The variance of both the number density and anisotropy along the magnetic field line is evaluated systematically by modeling four typically prescribed distribution functions. It is shown that in the case of ``the positive anisotropy'' (namely, the perpendicular temperature T⊥ exceeds the parallel temperature T||), the number density of energetic electrons always decreases with the magnetic latitude for a regular increasing magnetic field and the maximum wave growth is therefore generally confined to the equator where the resonant energy is minimum, and the number density is the largest. However, the ``loss-cone'' anisotropy of the electrons with a ``pancake'' distribution or kappadistribution keeps invariant or nearly invariant, whereas the ``temperature'' anisotropy with a pure bi-Maxwellian distribution or Ashour-Abdalla and Kennel's distributions decreases with the magnetic latitude. The results may provide a useful approach to evaluating the number density and anisotropy of the energetic electrons at latitudes where the observation information is not available.

A triple-wave resonance model for the emission from tokamaks of narrow-band radiation at the plasma frequency

When the distribution of electron velocities parallel to the magnetic field has a tail with a bump, a linear triple-wave resonance instability can cause the growth of electromagnetic waves at ωp. The bandwidth of the radiation depends on the ratio of the number of electrons in the tail to the total number of electrons; the smaller this ratio, the narrower the bandwidth. The instability occurs only when the mean tail velocity has a specific value. The radiation thus gives an indication of the tail structure.

Growth of electromagnetic waves on the surface of a negative differential conductance material

In order to determine the usefulness in device applications of semiconducting materials which exhibit a bulk differential negative conductivity, but which may be fabricated most easily in the form of thin sheets, a study is performed of the propagation of electromagnetic surface waves along the interface between such materials and free space. The dispersion relation of the system is determined for waves traveling with phase velocities comparable to the velocity of light, so that the quasistatic approximation is not made. rf charge concentration at the surface is accounted for in a manner similar to that used in the study of scalloped electron beams. Numerical solution of the dispersion relation is made for possible values of parameters for one relevant class of semiconducting materials, viz., compound semiconductors in which crystalline superlattices have been formed. Growth rates up to several decades of dB/cm at frequencies up to 1012 Hz are seen to occur for reasonable superlattice parameters for gallium arsenide and indium antimonide.

Field of a growing electromagnetic wave on a beam-plasma slab†

The effect of growth of electromagnetic waves on the transverse variation of the field of a wave guided along a beam-plasma slab is described. It is found that there is a component of the power flow normal to the slab. The magnitude of this normal component (directed outwards) is proportional to the imaginary part of tho propagation constant.

Growing Electromagnetic Waves

The growth of radio and other electromagnetic waves is considered in terms of the ion motions of Bailey's electromagneto-ionic theory, of a double electron stream and other factors. These conclusions are reached: (i) The electromagneto-ionic theory predicts spurious growing waves which do not correspond to any interchange of energy between gas and field but merely to the movements of the observer and emitter relative to the gas particles. It probably does not predict any real growing waves.(ii) The twelve different oscillatory modes inferred from the full dispersion equation correspond to four unreal waves and four pairs of real waves: two pairs of hydromagnetic waves (becoming radio waves as a limiting high-frequency case), one pair of modified sound waves and one pair of modified electron-sound waves.(iii) Electromagnetic wave growth may possibly result from one and only one process: the trapping of ions between potential troughs of the space-charge wave which is an integral part of some electromagnetic waves. After trapping, the ions give kinetic energy to the wave by one of two known processes.(iv) Ion drift motions may introduce important effects not indicated by the wave equations.