Papers by Venugopal Chandu
Dust Acoustic Dromions in a Magnetized, Five-Component Cometary Plasma
IEEE Transactions on Plasma Science
Indian Journal of Physics, 2013
We have studied the stability of magnetosonic wave in a plasma, where the ions and electrons are ... more We have studied the stability of magnetosonic wave in a plasma, where the ions and electrons are described by anti-loss cone (ALC) distributions. Our studies indicate that the magnetosonic waves produced by ions and electrons with ALC distributions are in the higher frequency end within the range of frequencies, as observed by the Combined Release and Radiation Effects Satellite spacecraft. They are weakly damped and can, therefore, travel long distances. These waves are expected to play an important role in the acceleration of radiation belt electrons.
A comparative study of night-time enhancement in TEC during sudden commencement storms with those during quiet nights - latitudinal and seasonal aspects
There have been very few detailed studies on nighttime enhancements in total electron content (TE... more There have been very few detailed studies on nighttime enhancements in total electron content (TEC) during magnetic storms. Therefore, in the present study, the main characteristics of nighttime enhancements during sudden commencement (SC) storms were compared with those during quiet nights for different seasons by considering stations of low-, mid-, and high latitudes which fell under the same longitudinal sector for a high solar activity year, 1989. The interdependence of these characteristics was also analysed. We als o investigated the effect that the intensity of a storm could have on the characteristics of nighttime enhancements. During 1989, the mean amplitudes at low- and mid- latitudes during SC storms were greater than those during quiet nights. Surprisingly, the mean amplitude and half-amplitude durations during quiet nights were greater than those during SC storms for the high latitude station. For low-, mid- and high latitude stations the percentages of occurrence of ni...
Relation between shear-zone thickness, boundary layer instability and plasmoids in the geo-magnetosphere
A study of the dependence of shear-zone thickness on the growth rate and frequency of Kelvin-Helm... more A study of the dependence of shear-zone thickness on the growth rate and frequency of Kelvin-Helmholtz instability (KHI) in the shear-zone between low latitude boundary layer (LLBL) and central plasma sheet (CPS) is carried out. It is found that the growth rate and frequency are maximum for a shear-zone of minimum thickness. The amplitude of plasma sheet (PS) oscillation is found to be positive as the PS thickness increases and is maximum when PS thickness is 2RE (IRE= 6378 km) for a shear-zone of minimum thickness. This perturbation generates tearing mode instability (TMI) which leads to the formation of plasmoids.
In this paper, the stability of ion-cyclotron waves in multi-ion plasma consisting of electrons, ... more In this paper, the stability of ion-cyclotron waves in multi-ion plasma consisting of electrons, positively and negatively charged oxygen ions and hydrogen ions are examined by simulations. In order to identify the modes in a mixed plasma and to gain physical insight into the nature of the instability, cold plasma theory is used, while the warm plasma theory accounts for finite temperature effects. The expression for the frequencies of lower hybrid and ion-ion hybrid modes are derived and solved by numerical methods From the simulation studies it is concluded that lower hybrid mode is a weakly unstable mode while the ion-ion hybrid mode is almost freely propagating.
Optical gain studies in sodium fluorescein: rhodamine B and sodium fluroscein: cresyl violet dye pairs
Asian Journal of Spectroscopy
Indian Journal of Physics
We have studied the stability of the ion-acoustic wave in multi-ion plasma consisting of a lighte... more We have studied the stability of the ion-acoustic wave in multi-ion plasma consisting of a lighter ion component (hydrogen) and positively and negatively ionised heavier ion component of oxygen. This model approximates very well the plasma environment of the coma of comet Halley. Coupled equations have been derived for the dispersion relation as well as the growth/damping rate for oblique propagation of ion-acoustic waves; these equations were solved by numerical methods. Various aspects of wave stability with regard to angle of propagation, number densities and species temperatures have been considered. While for all combinations of compositions the wave growth is a maximum for parallel propagation, the heavier species (irrespective of its charge) either aids/damps the instability depending on whether they are hotter/colder than the lighter hydrogen ions.
Indian Journal of Physics
Wc have quantified the effect of geomagnetic storms on ionospheric scintillations observed at a f... more Wc have quantified the effect of geomagnetic storms on ionospheric scintillations observed at a few Indian low latitude stations. Total .vtniv ihree siorins were studied and classified into different categories to see the type of activity in the ionosphere on, before or after each category I siorni To show the effect of geomagnetic storms in each category on the occurrence of scintillations, we selected five individual non-recurrent stoims. mostly severe ones, having different sudden storm commencement times It is noted that for intense geomagnetic storms, both (jniillaiion and ionosphere data yield identical results which demonstrate that spatial irregularities of electron density in the ionosphere may be iiinbiJicd lo magnetic storms and associated perturbations A study of storm time N^F" h'F and scintillation, was earned out to understand the Physics l)chm d ihc inggering / suppression of scintillation activity. It is found that during the main phase, N^F^ shows peak values while it decreases sharply km^ the rcLovery phase Any enhancement during recovery time in N^F, along with a rise in h'F. implies cither an irregularity formation or strong pnssibiliiY ut occurrence of scintillation. It is also found that during solar maximum years, equatorial scintillations are totally inhibited during recurrent storms for all season.s while no such rule holds good fur non-recurrent storms. The study reveals that F-region response to geomagnetic uiriiis IS interplay of the electromagnetic dnft and rise in h'F associated with storm time electric field.
Latitude variations of storm time ionospheric response
Indian Journal of Physics
Indian Journal of Physics
The dependence of the ionospheric response on the sudden commencement(SC) and the intensity of th... more The dependence of the ionospheric response on the sudden commencement(SC) and the intensity of the geomagnetic storms have been investigated by considering the total electron content data for 68 SC-type geomagnetic storms at a low latitude station, Palehua[19.700N,157.20W] during the period 1985-89. The ionospheric response was found to be influenced by the local time of SC. The time delays associated with peak positive responses were short for day time SCs and long for nighttime SCs whereas the opposite applies for negative responses. The time delays were inversely proportional to the intensities of geomagnetic storms irrespective of their nature as positive or negative. There was a positive correlation between the strength of ionospheric response and the intensity of the geomagnetic storms. However, this study shows that the strength of both positive and negative storms decreases with increase in magnetic activity index Ap for very severe storms. The results are discussed in the l...
Latitudinal variations of strength of ionospheric storms and its correlation with intensity of magnetic storms
Photo quenching mechanism in rigid (CV) and non-rigid (FDS) dye systems
Indian Journal of Physics
IOURNA L OF lliE Spectroscopic parameters of Nd 3+ ion in phosphate glasses
The optical absorption spectrum of Nd 3+ ions in phosphate glasses of varying matrix environments... more The optical absorption spectrum of Nd 3+ ions in phosphate glasses of varying matrix environments has been recorded in the ultra violet, visible and near infrared region. From the absorption spectra, various spectroscopic parameters such as Slater-Condon (F 2, F 4 and F6), spin-orbit (fay), Racah (E 1, E 2 and E3), nephelauxetic (/3), bonding (3) and Judd-Ofelt (J-O) (02, ~' ~4 and /26) intensity parameters were evaluated. Electric dipole S~d and magnetic dipole (Sma) line strengths were evaluated with the help of J-O intensity parameters. The observed and calculated oscillator strengths (f) are found to be in reasonable agreement with one another. Using J-O parameters and calculated matrix U (a) radiative transition probabilities (A), total radiative transition probability (AT), radiative lifetime (rRA D) branching ratios (fiR) and integrated absorption cross-sections for stimulated emission ((r a) between the metastable 4F3/2 and terminal 411 levels were calculated. The analys...
Stability of Electrostatic Waves in a Multi-Ion Permeating Plasma
We have studied the stability of electrostatic waves in a multi-ion, permeating plasma. We consid... more We have studied the stability of electrostatic waves in a multi-ion, permeating plasma. We consider a neutral solar wind consisting of hydrogen ions and electrons flowing into a pair ion cometary plasma composed of positively and negatively charged oxygen ions and cometary electrons. The dispersion relation obtained is a polynomial equation of order 8. We find that the growth rate of the wave increases with increasing drift velocity of hydrogen ions. It, however, decreases with increasing hydrogen and oxygen ion densities
Dust Ion Acoustic Solitary Waves in a Pair-Ion Plasma with Super Thermal Electrons
Dust ion acoustic solitons is studied in a plasma composed of pair-ions (positively and negativel... more Dust ion acoustic solitons is studied in a plasma composed of pair-ions (positively and negatively charged hydrogen ions), dust (positively and negatively charged) and electrons (cold and super thermal). The non-linear studies are done by using the reductive perturbation method. The K-dV equation and its solution, thus obtained, are numerically analyzed by using the parameters observed at comet Halley by the Vega spacecraft. The results show that only rarefactive solitons can exist in such a plasma environment. The characteristics of the soliton is sensitive to the densities of positive ion and positive dust and its charge number than the concentrations of negative ions and negative dust. The soliton amplitude increases with an increase in spectral index (κ) of the hot electrons.
Stability of the lower hybrid drift wave in a multi-ion plasma
Indian Journal of Physics
We have investigated the stability of the lower hybrid drift (LHD) wave in a plasma containing hy... more We have investigated the stability of the lower hybrid drift (LHD) wave in a plasma containing hydrogen and positively and negatively oxygen ions. In our model, for the length and time scales of the fluctuations the electrons are treated as magnetised, while all the ions are treated as unmagnetised. The instability is driven by the equilibrium diamagnetic current associated with the hydrogen ions. The growth/damping rate is modified by a factor dependent directly on the number densities, square of the charges and masses of the oxygen ions. In the presence of the positive oxygen ions, the wave tends to stabilize due to the increased damping by the electrons. On the other hand, the negative oxygen ions tend to aid the instability due to the decreased damping by the electrons.
Advances in Space Research, 2015
The two potential theory of Hasegawa has been used to derive the dispersion relation for the kine... more The two potential theory of Hasegawa has been used to derive the dispersion relation for the kinetic Alfven wave (KAW) in a plasma composed of hydrogen, oxygen and electrons. All three components have been modeled by ring distributions (obtained by subtracting two Maxwellian distributions with different temperatures) with the hydrogen and electrons drifting, respectively, with velocities V dH and V de. For the most general case, the dispersion relation is a polynomial equation of order five; it reduces to a relation which supports only one mode when V dH = 0. For typical parameters at comet Halley, we find that both V dH and V de can drive the wave unstable; the KAW is thus driven unstable in a current-less plasma. Such an instability was found for the ion acoustic wave by Vranjes et al. (2009).
Solitary waves in a plasma with oppositely charged dust (heavier, pair ions) and kappa modeled lighter ions and electrons
Physica Scripta, 2015
ABSTRACT Solitary waves in a plasma with oppositely charged dust (heavier, pair ions) and kappa m... more ABSTRACT Solitary waves in a plasma with oppositely charged dust (heavier, pair ions) and kappa modeled lighter ions and electrons Abstract We investigate the existence of compressive and rarefactive solitary waves in a five-component plasma. Positively and negatively multiply charged heavier ions (dust), kappa function described photo-electrons, hot electrons and ions form the five components. The pseudo-potential approach is used to determine the existence of a soliton. We find that the Sagdeev potential as well as the amplitude of the solitary wave for both compressive and rarefactive solitons increases with increasing spectral indices of the kappa distributions describing the cometary species. The magnitude of the amplitude of the solitary wave increases with increasing positively charged ion densities and charge numbers, but decreases with increasing charge numbers of the negative ions for both type of solitons.
Journal of Astrophysics, 2013
We have, in this paper, studied the stability of the ion-acoustic wave in a plasma composed of hy... more We have, in this paper, studied the stability of the ion-acoustic wave in a plasma composed of hydrogen, positively and negatively charged oxygen ions, and electrons, which approximates very well the plasma environment around a comet. Modelling each cometary component (H+, O+, and O−) by a ring distribution, we find that ion-acoustic waves can be generated at frequencies comparable to the hydrogen ion plasma frequency. The dispersion relation has been solved both analytically and numerically. We find that the ratio of the ring speed (u⊥s) to the thermal spread (vts) modifies the dispersion characteristics of the ion-acoustic wave. The contrasting behaviour of the phase velocity of the ion-acoustic wave in the presence of O− ions for u⊥s>vts (and vice versa) can be used to detect the presence of negatively charged oxygen ions and also their thermalization.
OALib, 2014
We study the stability of the ion-acoustic (IA) wave in a collisional plasma composed of hydrogen... more We study the stability of the ion-acoustic (IA) wave in a collisional plasma composed of hydrogen, positively and negatively charged oxygen ions, electrons and neutral atoms. This composition approximates very well the plasma environment around a comet. A solution of the dispersion relation yields a frequency for the IA wave at around the hydrogen plasma frequency. The growth/ damping rate is sensitively dependent on the ring parameters s u ⊥ (the ring speed) and ts v (the thermal spread). The growth rate of the wave, which decreases with increasing collisional frequencies, is larger when s ts u v ⊥ <. In the presence of negatively charged oxygen ions, the phase and group velocities of the IA wave behave in a contrasting manner when s ts u v ⊥ < (and viceversa). We propose that this behaviour be exploited as a diagnostic tool for the detection of these ions and also their thermalization.
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Papers by Venugopal Chandu