N. S. Saini
Guru Nanak Dev University
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Featured researches published by N. S. Saini.
Physics of Plasmas | 2009
M. A. Hellberg; R. L. Mace; T. K. Baluku; Ioannis Kourakis; N. S. Saini
A recent paper [L.-N. Hau and W.-Z. Fu, Phys. Plasmas 14, 110702 (2007)] deals with certain mathematical and physical properties of the kappa distribution. We comment on the authors’ use of a form of distribution function that is different from the “standard” form of the kappa distribution, and hence their results, inter alia for an expansion of the distribution function and for the associated number density in an electrostatic potential, do not fully reflect the dependence on κ that would be associated with the conventional kappa distribution. We note that their definition of the kappa distribution function is also different from a modified distribution based on the notion of nonextensive entropy.
Physics of Plasmas | 2010
T. K. Baluku; M. A. Hellberg; Ioannis Kourakis; N. S. Saini
Dust ion acoustic solitons in an unmagnetized dusty plasma comprising cold dust particles, adiabatic fluid ions, and electrons satisfying a κ distribution are investigated using both small amplitude and arbitrary amplitude techniques. Their existence domain is discussed in the parameter space of Mach number M and electron density fraction f over a wide range of values of κ. For all κ>3/2, including the Maxwellian distribution, negative dust supports solitons of both polarities over a range in f. In that region of parameter space solitary structures of finite amplitude can be obtained even at the lowest Mach number, the acoustic speed, for all κ. These cannot be found from small amplitude theories. This surprising behavior is investigated, and it is shown that fc, the value of f at which the KdV coefficient A vanishes, plays a critical role. In the presence of positive dust, only positive potential solitons are found.
Physics of Plasmas | 2009
N. S. Saini; Ioannis Kourakis; M. A. Hellberg
Velocity distribution functions with an excess of superthermal particles are commonly observed in space plasmas, and are effectively modeled by a kappa distribution. They are also found in some laboratory experiments. In this paper we obtain existence conditions for and some characteristics of ion-acoustic solitary waves in a plasma composed of cold ions and -distributed electrons, where 3 / 2 represents the spectral index. As is the case for the usual Maxwell–Boltzmann electrons, only positive potential solitons are found, and, as expected, in the limit of large one recovers the usual range of possible soliton Mach numbers, viz., 1M 1.58. For lower values of , modeling the presence of a greater superthermal component, the range of accessible Mach numbers is reduced. It is found that the amplitude of the largest possible solitons that may be generated in a given plasma corresponding to the highest allowed Mach number for the given plasma composition falls off with decreasing , i.e., an increasing superthermal component. On the other hand, at fixed Mach number, both soliton amplitude and profile steepness increase as is decreased. These changes are seen to be important particularly for 4, i.e., when the electrons have a “hard” spectrum.
Physics of Plasmas | 2008
N. S. Saini; Ioannis Kourakis
A study is presented of the nonlinear self-modulation of low-frequency electrostatic (dust acoustic) waves propagating in a dusty plasma, in the presence of a superthermal ion (and Maxwellian electron) background. A kappa-type superthermal distribution is assumed for the ion component, accounting for an arbitrary deviation from Maxwellian equilibrium, parametrized via a real parameter κ. The ordinary Maxwellian-background case is recovered for κ→∞. By employing a multiple scales technique, a nonlinear Schrodinger-type equation (NLSE) is derived for the electric potential wave amplitude. Both dispersion and nonlinearity coefficients of the NLSE are explicit functions of the carrier wavenumber and of relevant physical parameters (background species density and temperature, as well as nonthermality, via κ). The influence of plasma background superthermality on the growth rate of the modulational instability is discussed. The superthermal feature appears to control the occurrence of modulational instability, ...
Physics of Plasmas | 2011
Ashkbiz Danehkar; N. S. Saini; Manfred A. Hellberg; Ioannis Kourakis
The nonlinear dynamics of electron-acoustic localized structures in a collisionless and unmagnetized plasma consisting of “cool” inertial electrons, “hot” electrons having a kappa distribution, and stationary ions is studied. The inertialess hot electron distribution thus has a long-tailed suprathermal (non-Maxwellian) form. A dispersion relation is derived for linear electron-acoustic waves. They show a strong dependence of the charge screening mechanism on excess suprathermality (through κ). A nonlinear pseudopotential technique is employed to investigate the occurrence of stationary-profile solitary waves, focusing on how their characteristics depend on the spectral index κ, and the hot-to-cool electron temperature and density ratios. Only negative polarity solitary waves are found to exist, in a parameter region which becomes narrower as deviation from the Maxwellian (suprathermality) increases, while the soliton amplitude at fixed soliton speed increases. However, for a constant value of the true Mach number, the amplitude decreases for decreasing κ.
Laser and Particle Beams | 2006
N. S. Saini; Tarsem Singh Gill
The problem of nonlinear self-focusing of elliptic Gaussian laser beam in collisionless magnetized plasma is studied using variation approach. The dynamics of the combined effects of nonlinearity and spatial diffraction is presented. With a and b as the beam width parameters of the beam along x and y directions, respectively, the phenomenon of cross-focusing is observed where focusing of a results in defocusing of b and vice versa. Although no stationary self-trapping is observed, oscillatory self-trapping occurs far below the threshold. The regularized phase is always negative.
Physics of Plasmas | 2003
Tarsem Singh Gill; Harvinder Kaur; N. S. Saini
In this research paper, the authors study the propagation of ion-acoustic solitons in a plasma consisting of warm positive and negative ions with different concentration of masses, charged states, and nonisothermal electrons. To account for the full nonlinearity of plasma equations, a quasipotential method is used here. The potential so obtained is characterized for solitons as a function of Mach number, positive and negative ions temperature, nonisothermal electrons, different concentration of negative and positive ions over a wide range of parameter space. Corresponding to isothermal case with β=1, coexistence of compressive and rarefactive solitons is obtained. For non-negative β≠1, only compressive solitons are observed. The prediction, that with introduction of negative ions there exists a critical ion concentration below which compressive solitons exist and above which rarefactive solitons exist, is ruled out for nonisothermal electrons.
Plasma Physics and Controlled Fusion | 2010
N. S. Saini; Ioannis Kourakis
The study of non-Maxwellian plasmas is crucial to the understanding of space and astrophysical plasma dynamics. In this paper, we investigate the existence of arbitrary amplitude ion-acoustic solitary waves in an unmagnetized plasma consisting of ions and excess superthermal electrons (modelled by a kappa-type distribution), which is penetrated by an electron beam. A kappa (κ-) type distribution is assumed for the background electrons. A (Sagdeev-type) pseudopotential formalism is employed to derive an energy-balance like equation. The range of allowed values of the soliton speed (Mach number), wherein solitary waves may exist, is determined. The Mach number range (allowed soliton speed values) becomes narrower under the combined effect of the electron beam and of the superthermal electrons, and may even be reduced to nil (predicting no solitary wave existence) for high enough beam density and low enough κ (significant superthermality). For fixed values of all other parameters (Mach number, electron beam-to-ion density ratio and electron beam velocity), both soliton amplitude and (electric potential perturbation) profile steepness increase as κ decreases. The combined occurrence of small-amplitude negative potential structures and larger amplitude positive ones is pointed out, while the dependence of either type on the plasma parameters is investigated.
Physics of Plasmas | 2010
A. S. Bains; Amar P Misra; N. S. Saini; Ts Gill
The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique ...
Physics of Plasmas | 2011
A. S. Bains; Mouloud Tribeche; N. S. Saini; Tarsem Singh Gill
By using the reductive perturbation method (RPM), a nonlinear Zakharov-Kuznetsov (ZK) equation for ion-acoustic solitary waves (IASWs) is derived for a magnetized plasma in which the electrons are nonextensively distributed. The combined effects of electron nonextensivity, strength of magnetic field, and obliqueness on the ion acoustic (IA) solitary profile are analyzed. Three different ranges of the nonextensive q-parameter are considered. It is observed that the system may support both compressive as well as rarefactive solitons. The magnetic field has no effect on the amplitude of solitary waves whereas the obliqueness affects both the amplitude as well as the width of the solitary wave structures.