Sarla Sharma

Obliquely propagating ion-acoustic solitons in a multi-component magnetized plasma with negative ions

Oblique propagation of ion-acoustic solitons in a magnetized low-β plasma consisting of warm positive and negative ion species along with hot electrons is studied. Using the reductive perturbation method, a KdV equation is derived for the system, which admits an obliquely propagating soliton solution. It is found that if the ions have finite temperatures then there exist two types of modes, namely slow and fast ion-acoustic modes. The parameter determining the nature of soliton (i.e. whether the system will support compressive or rarefactive solitons) is different for slow and fast modes. For the slow mode the parameter is the relative temperature of the two ion species, whereas for the fast mode it is the relative concentraion of the two ion species. For the fast mode it is found that there is a critical value of the negative-ion concentration below which only compressive solitons exist and above which rarefactive solitons exist. To discuss the soliton solution at the critical concentration, a modified KdV equation is derived. It is found that- at the critical concentration of negative ions compressive and rarefactive solitons co-exist. The effects of temperature of different ion species, angle of obliqueness and magnetization on the characteristics of the solitons are discussed in detail

Obliquely propagating ion-acoustic solitons in a warm-ion magnetized plasma

Abstract Considering the charge separation effect, the soliton solution of the KdV equation is discussed for a warm-ion magnetized plasma with two Maxwellian electron components. The effect of ion temperature, obliqueness and magnetization on the amplitude and width of the soliton is discussed in detail. The theory is applied to the case of rarefactive solitons observed in the magnetosphere.

Modulational instability of obliquely modulated ion‐acoustic waves in a two‐ion plasma

Using the KBM perturbation technique, the stability of oblique modulation of ion‐acoustic waves in a two‐ion plasma is studied. It is found that the presence of a small amount of lighter ion impurities significantly changes the instability domain in the ω‐φ plane. The effect of the concentration and mass of impurity ions on the modulational instability is discussed in detail. The threshold amplitude for instability and nonlinear frequency shift of the wave are also calculated. The predictions of the theory are found to be in good agreement with the experimental observations.

Study of ion-acoustic rarefactive soliton in a two-electron temperature plasma

The propagation characteristics of ion-acoustic rarefactive soliton (IARS) in a two-electron temperature plasma with two cold ion species are investigated considering the nonisothermal distributions of electrons using a kinetic model and fluid model for both ion species. Using the Sagdeev potential formalism the nonlinear dispersion relation and expression for width are derived for IARS. The variation of Mach number and width of the IARS with the amplitude is studied numerically and compared with earlier theoretical results as well as experimental observations. It is found that the results are improved qualitatively as well as quantitatively with the consideration of the presence of a suitable negative ion-impurity.

Ion‐acoustic compressive and rarefactive solitons in an electron‐beam plasma system

Using the general formulation of reductive perturbation method, the Korteweg–de Vries (KdV) equation is derived for an electron‐beam plasma with hot isothermal beam and plasma electrons and warm ions. The soliton solution of the KdV equation is discussed in detail. It is found that above a critical velocity of electron‐beam two additional ion‐acoustic soliton branches appear. It is found that corresponding to two linear modes, the system supports the existence of compressive as well as rarefactive solitons depending upon the plasma parameters, while corresponding to other two wave modes, the system supports only rarefactive solitons. The effect of different parameters on the characteristics of solitons have been investigated in detail.

Effect of finite ion temperature on modulational instability of ion-acoustic waves

Abstract A nonlinear Schrodinger equation for ion-acoustic waves in a collision free plasma, consisting of warm ions and hot isothermal electrons is derived using the KBM method. It is found that for finite ion temperature these waves are modulationally unstable only in a range of wave numbers. As the ratio of ion to electron temperature increases, the range of the unstable region decreases and shifts towards small wave numbers.

Modulation instability of ion-acoustic waves in a multi-ion plasma

Abstract A nonlinear Schrodinger equation for ion-acoustic waves in a collision-free plasma, consisting of a mixture of two cold ion species and hot isothermal electrons is derived using the KBM method. It is used to discuss the modulation instability in which the effect of the light-on concentration is analysed. We find that the unstable region depends sensitively upon the fraction of light-ion concentration (α) and the ion-mass ratio. An approximate relation for α critical is derived for a given ion species in terms of the ion-mass ratio, which governs the minimum wave number, below which the carrier wave is stable against the modulational instability.

CNT-ZnO Nanocomposite Thin Films: O2 and NO2 Sensing

The CNT-ZnO nanocomposites were synthesized by addition of commercially available MWCNT during growth of ZnO nanoparticles employing a wet chemical route. These nanocomposites were then spin coated and characterized using X-ray diffraction, scanning electron microscopy, current-voltage characteristics and O2 (5-20%) / NO2 (2-20 ppm) gas sensing at 250°C operating temperature in N2 atmosphere (0.4±0.03 mbar). The addition of CNT in ZnO is found to increase the sensitivity for both O2 and NO2 gas sensing. The 0.1 wt % CNT addition in ZnO is observed to appreciably enhance the NO2 gas sensitivity while 1.0 wt % CNT addition in ZnO showed highest sensitivity for O2 gas detection.

Propagation of ion-acoustic double layer in an inhomogeneous plasma

Using the reductive perturbation technique, the propagation characteristics of ion-acoustic double layer in a spatially inhomogeneous plasma have been investigated. We have derived a modified Korteweg-de Vries (mKdV) equation with varying coefficients for an inhomogeneous plasma with two Maxwellian electron species. The double layer solution of the mKdV equation is discussed in detail. The present analysis shows that the inhomogeneous plasma density n0 does not affect the amplitude of the double layer, m, whereas its width and velocity are found to decrease as it propagates in the higher density region. It is found that the peak compressed (rarefied) ion density, n1m, corresponding to compressive (rarefactive) double layer increases as the double layer moves along the positive density gradient. The relevance of the present theory to the space plasmas is pointed out.

Obliquely propagating ion-acoustic nonlinear periodic waves in a magnetized plasma with two electron species

Obliquely propagating ion-acoustic nonlinear periodic waves in a magnetized plasma consisting of warm adiabatic ions and two Maxwellian electron species are studied. Using the reductive perturbation method, the Korteweg–de Vries (KdV) equation is derived and its cnoidal wave solution is discussed. It is found that as the amplitude of the cnoidal wave increases, so does its frequency. The effects of variations in the density and temperature ratios of the two electron species, the ion temperature, the angle of obliqueness and the magnetization on the characteristics of the cnoidal wave are discussed in detail. When the coefficient of the nonlinear term of the KdV equation, a 1 , vanishes, the modified Korteweg–de Vries equation is derived, and its periodic-wave solutions are discussed in detail. In the limiting case these periodic-wave solutions reduce to soliton or double-layer solutions.