Papers by Chandu Venugopal
Pramana, Jul 1, 1983
The propagation of the electromagnetic ion-cyclotron wave in a fusion plasma described by a loss-... more The propagation of the electromagnetic ion-cyclotron wave in a fusion plasma described by a loss-cone structure is discussed. The wavelength is assumed to be much larger than the ion Larmour radius and the ion plasma frequency ≫ the ion-cyclotron frequency. The two modes that propagate in the plasma interact strongly and fuse together under certain conditions making the plasma unstable. The coalescence of the modes is found to decrease with an increase in electron temperature.
Journal of Non-Crystalline Solids, 1997
Title: Spectroscopic parameters of Nd3+ ion in phosphate glasses. Authors: Ajith Kumar, G. Public... more Title: Spectroscopic parameters of Nd3+ ion in phosphate glasses. Authors: Ajith Kumar, G. Publication: Journal of Non-Crystalline Solids, vol. 221, issue 1, pp. 47-58. Publication Date: 11/1997. Origin: CROSSREF. DOI: 10.1016/S0022-3093(97)00266-4. ...
IEEE Transactions on Plasma Science
Journal of Astrophysics and Astronomy, May 23, 2020
We studied dust acoustic solitary waves (DASW) in a five component cometary plasma by deriving th... more We studied dust acoustic solitary waves (DASW) in a five component cometary plasma by deriving the Kadomstev-Petiashvili (KP) equation. The five components consist of two components of electrons described by kappa distributions with different temperatures and spectral indices, a lighter (hydrogen) and a heavier (oxygen) ion component, both ion components are described by Maxwellian distributions. Dust particles, with varying charge, constitute the fifth component. The system supports rarefactive DASWs whose amplitudes are larger when the charges on the dust particles vary. The amplitudes also increase with increasing z d0 n d0 (product of equilibrium charge number and density of dust) and increasing ion densities. It, however, decreases with increasing spectral indices of the electrons.
Journal of Astrophysics and Astronomy, Sep 30, 2022
We investigate the effect of drifting ions on compressive and rarefactive solitary waves in a fiv... more We investigate the effect of drifting ions on compressive and rarefactive solitary waves in a five component plasma. Heavier pair ions, two components of electrons and drifting lighter ions form the five components. We use the pseudo-potential method to investigate the conditions for the existence of solitary waves. We find that both the Sagdeev potential and amplitudes of solitary waves are dependent on the velocities of the drifting ions: the amplitude of both compressive and rarefactive solitary waves increases with increasing drifting velocities of the lighter ions.
Plasma Physics Reports, May 1, 2020
We have investigated the propagation characteristics of Ion-Acoustic Solitary Waves (IASWs) in a ... more We have investigated the propagation characteristics of Ion-Acoustic Solitary Waves (IASWs) in a magnetized, cometary plasma consisting of hydrogen ions, positively and negatively charged oxygen ions, kappa described hot solar electrons, and slightly colder cometary electrons. The effects of q-nonextensive distributions, on both lighter and heavier ions have been studied by deriving the Zakharov-Kuznetsov (ZK) equation. The basic features of IASWs such as amplitude, width, and phase speed have been extensively studied by a numerical analysis of the ZK equation. It is found that superthermality of the electrons and nonextensivity of ions significantly modify the characteristics of the solitary waves. The amplitudes of the solitary waves seem to be well correlated to the presence of water molecules in a cometary plasma and the associated photoionization processes.
Physica Scripta, May 1, 2014
The stability of the kinetic Alfven wave (KAW) has been studied in a plasma composed of electrons... more The stability of the kinetic Alfven wave (KAW) has been studied in a plasma composed of electrons, hydrogen and positively and negatively charged oxygen ions. Using the two potential theory of Hasegawa, we have derived an expression for the frequency and growth/damping rate of the KAW. The dispersion relation derived in this paper is a generalization of the dispersion relation of Hasegawa on two counts: (i) we use a more generalized distribution function and show that our relation reduces to the dispersion relation of Hasegawa in the limiting case, and (ii) it is applicable to a multi-ion plasma containing lighter ions and positively and negatively charged heavier ions. We find the growth rate of the wave increases with increasing drift velocities of the electrons. Negatively charged oxygen ions (O-) decrease the growth rate; however, the growth rate is very sensitively dependent on O- ion density, especially when its density is greater than that of the positively charged oxygen ions (O+). Interestingly, the dispersion characteristics of KAWs can be made insensitive to the presence of the heavier ions by an appropriate choice of their densities and temperatures.
Asian Journal of Research and Reviews in Physics, Dec 31, 2022
A widely used measure of entropy to quantify uncertainity in an open system is the Boltzmann-Gibb... more A widely used measure of entropy to quantify uncertainity in an open system is the Boltzmann-Gibbs (B-G) entropy. It, however, cannot describe non-equilibrium systems with large variability and multi-fractality. A generalisation of the B-G entropy is the Tsallis' entropy. The values of the horizontal components of the Earth's magnetic field, observed at various stations in India in 2002 were used. During the years 2000-2002, solar cycle 23 reached its maximum. Data from Ettaiyapuram (ETT, latitude = 9 0 10' N, longitude = 78 0 01' E, geomagnetic latitude = 0.13
The heating process of the plasma in the central plasma sheet (CPS) has been found to be increasi... more The heating process of the plasma in the central plasma sheet (CPS) has been found to be increasing with decreasing plasma pressure and increasing plasma density. The specific entropy of CPS changes in accordance with the temperature T of CPS and plasma beta-parameter. The thermal energy in the CPS increases whereas its density decreases with increase of plasma beta-parameter. There
Journal of physics, May 31, 2017
Ion-Acoustic (IA) shock waves are studied in a magnetized, five component cometary plasma consist... more Ion-Acoustic (IA) shock waves are studied in a magnetized, five component cometary plasma consisting of positively and negatively charged oxygen ions, kappa described hydrogen ions, hot solar electrons and slightly colder cometary electrons. The Korteweg-de Vries-Burgers (KdVB) equation is derived and the variation of the shock profile is studied. It is found that the obliqueness of shock wave propagation significantly varies the basic properties like amplitude and width of the shock.
Annales Geophysicae, Nov 30, 2002
The main characteristics of night-time enhancements in TEC during magnetic storms are compared wi... more The main characteristics of night-time enhancements in TEC during magnetic storms are compared with those during quiet nights for different seasons and solar activity conditions at Palehua, a low latitude station during the period 1980-1989. We find that the mean amplitude has both a seasonal and solar activity dependence: in winter, the values are higher for weak storms as compared to those during quiet nights and increase with an increase in solar activity. In summer, the mean amplitude values during weak storms and quiet nights are almost equal. But during equinox, the mean amplitude values for quiet nights are greater than those during weak storms. The mean half-amplitude duration is higher during weak storms as compared to that during quiet nights in summer. However, during winter and equinox, the durations are almost equal for both quiet and weak storm nights. For the mean half-amplitude duration, the quiet night values for all the seasons and equinoctial weak storm values increase with an increase in solar activity. The occurrence frequency (in percent) of TEC enhancement during weak storms is greater than during quiet nights for all seasons. The mean amplitude, the mean half-amplitude duration and the occurrence frequency (in percent) of TEC enhancement values are higher during major storms as compared to those during quiet nights. The above parameters have their highest values during pre-midnight hours. From the data analysed, this behaviour is true in the case of major storms also.
Journal of Advances in Physics, Jun 26, 2014
Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory pl... more Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of Alfven waves in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species has been modeled by drifting distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution is simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures. We find that for frequencies * cH * , cO cO (cO being the oxygen ion gyro-frequencies) the region of wave growth increases with increasing negatively charged oxygen ion densities.
Journal of physics, May 31, 2017
We investigate solitary waves in a multicomponent plasma of positively and negatively charged lig... more We investigate solitary waves in a multicomponent plasma of positively and negatively charged lighter and heavier ionsand electrons ofsolar and cometary origin; the electron components are modeled by kappa distributions. The solitary wave solution of the Zakharov-Kuznetsov (ZK) equation is plotted for parameters of comet Halley; physical variables like densities and temperatures of negatively charged lighter ions significantly affect the width and amplitude of the solitary waves.
Physics of Plasmas, Dec 1, 2015
Multi-ion plasma is found in many regions of space like the earth's ionosphere, mesosphere, solar... more Multi-ion plasma is found in many regions of space like the earth's ionosphere, mesosphere, solar atmosphere, commentary environments, etc. Of this commentary plasma is of particular interest among researchers due to the presence of a wide variety of many species of ions: besides electrons and protons of solar origin, photoionization causes the production of H + and O + from water molecules present in the commentary atmosphere in addition to the associated photo-electrons [1]. Also, several positively charged hot lighter and heavier ions have been observed at comet Halley [2-5]. Further, the observation of negatively charged ions by spacecraft Giotto with energies between 0.03 to 3.0 keV and mass peaks in the range 7-19, 22-65 and 85-110 amu in comet Halley gave a new dimension to the investigations on plasma where negatively charged ion species act as an ion pair [6]. Later, many investigations were done where both positively and negatively charged dust particles coexist in the same plasma environment [7] in which former would be smaller and latter would be larger in size [8]. In recent decade, there were extensive studies on different nonlinear propagations of waves in different plasma environments [9-14]. This includes plasmas with cold dust and electrons and/or ions described by kappa distribution functions [15] and cold dust, adiabatic fluid ions and kappa described electrons [16]. Photo-ionization in commentary plasma environments causes the production of photo-electrons which in turn act as a major second electron component, apart from the typical solar hot electrons. For example, Zwickl et al. [17] , observed such photo-electrons from photo-ionization of commentary neutrals at comet Giacobini-Zinner by the electron spectrometer on the spacecraft ICE. Also, Bhardwaj observed the production of energetic photo-electrons in a study related to the gas production rates in comets [18]. It is a fact that the presence of high energetic particles in plasma deviate from typical Maxwellian to a non Maxwellian type "kappa distribution". Such a kind of distribution was first predicted by Vasyliunas using energetic solar wind data [19] ; this distribution has since been used to model a number of space and astrophysical environments. We, therefore study the characteristics of dust ion-acoustic solitary waves in this five component plasma, in which the electrons are modeled by kappa distributions. We find that different heavier ions significantly affect the amplitude and width of the solitary waves. BASIC EQUATIONS We are interested in solitary waves in five component plasma. The heavier ions (dust) and lighter (hydrogen) ion components ABSTRACT We investigate the influence of ions of different masses on oblique solitary waves in five component plasma consisting of positively and negatively charged heavier ions (dust), hydrogen ions and hotter and colder electrons. Of these, the heavier ions and colder photo-electrons are of commentary origin while the other two are of solar origin; the electrons being described by kappa distributions. The K-dV equation is derived and different attributes of the soliton such as amplitude and width are plotted for parameters relevant to that of comet Halley. We find that heavier ions strongly influence the amplitude and width of the solitary waves.
Annales Geophysicae, Feb 28, 2002
A detailed nonlinear time series analysis of the hourly data of the geomagnetic horizontal intens... more A detailed nonlinear time series analysis of the hourly data of the geomagnetic horizontal intensity H measured at Kodaikanal (10.2 • N; 77.5 • E; mag: dip 3.5 • N) has been carried out to investigate the dynamical behaviour of the fluctuations of H. The recurrence plots, spatiotemporal entropy and the result of the surrogate data test show the deterministic nature of the fluctuations, rejecting the hypothesis that H belong to the family of linear stochastic signals. The low dimensional character of the dynamics is evident from the estimated value of the correlation dimension and the fraction of false neighbours calculated for various embedding dimensions. The exponential decay of the power spectrum and the positive Lyapunov exponent indicate chaotic behaviour of the underlying dynamics of H. This is also supported by the results of the comparison of the chaotic characteristics of the time series of H with the pseudo-chaotic characteristics of coloured noise time series. We have also shown that the error involved in the short-term prediction of successive values of H , using a simple but robust, zero-order nonlinear prediction method, increases exponentially. It has also been suggested that there exists the possibility of characterizing the geomagnetic fluctuations in terms of the invariants in chaos theory, such as Lyapunov exponents and correlation dimension. The results of the analysis could also have implications in the development of a suitable model for the daily fluctuations of geomagnetic horizontal intensity.
Physica Scripta, 2022
The characteristics of nonlinear electron-acoustic waves such as shocks and solitons, are investi... more The characteristics of nonlinear electron-acoustic waves such as shocks and solitons, are investigated in a three component, dense laser produced plasma consisting of ions and two distinct groups of electrons, using the quantum hydrodynamic model and the standard reductive perturbation method. The modified Korteweg-deVries (mKdV) and Korteweg-deVries-Burgers (KdVB) equations have been derived for the electron-acoustic waves in the plasma. The dependence of both shocks and solitons on various parameters has been extensively studied. It is observed that whenever the density crosses the limit from the classical to the quantum range, the effective potential remains invariant for the solitary profiles; but shows a slight variation for the shock profiles. The collisional effect plays a significant role in the dissipation of solitary waves and the dissipation is larger for higher values of collision frequencies. The results obtained could prove helpful for understanding the parametric depe...
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Papers by Chandu Venugopal