Masters Degrees (Physics)

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Beam generated instabilities in space plasma.
(1999) Misthry, Surversperi Suryakumari.; Bharuthram, Ramesh.
Electrostatic instabilities associated with a model applicable to the auroral acceleration region consisting of an ion beam, precipitating electrons and stationary background electrons are theoretically investigated. The kinetic dispersion relation is solved numerically without approximations. It is shown that two low-frequency plasma instabilities are present and these may generate the low-frequency electric field fluctuations (LEFs) that have been observed in the acceleration region. A parameter variation study is carried out in order to reveal the features of the instabilities. The model is adapted to suit two possible regions of study: (1) drifting cool ions and (2) drifting cool ions and counter-streaming hot electrons. The slow ion-acoustic instability which dominates at low ion beam drift velocities is studied by varying plasma parameters such as the propagation angle, ky/k, the wavenumber, k, the cold background electron density, nco, the hot electron temperature and the cool ion beam temperature. The second mode, the modified two-stream instability, which dominates at larger ion beam drift velocities and at oblique angles of propagation is investigated in a similar manner. To complete the study of these two instabilities, the effect of drifting hot electrons is examined briefly through a similar parameter variation study.
The crossfield current-driven ion acoustic instability in a two-ion plasma.
(1987) Govender, Jagathesan.; Bharuthram, Ramesh.
The behaviour of the crossfield current-driven ion acoustic instability in a plasma containing two ion species is theoretically examined. In our model the electrons are assumed to be hot and the ions cold, i.e. Tₑ »Tᵢ (~ 0), where both ion species are given the same temperature. The length and time scales are such that the electrons are magnetized and the ions unmagnetized. The linearised Vlasov equation is used to set up a dispersion relation for electrostatic waves for Maxwellian equilibrium velocity distributions of the electrons and ions. For the ion acoustic wave, a study is made of the dependence of the critical electron drift velocity (Vͨₒ) required to excite an instability on several parameters. The parameters include light ion fraction, heavy to light ion mass ratio, magnetic field strength and the propagation angle. In general the maximum value of Vͨₒ is found to be smaller than that for an unmagnetized plasma. Approximate analytic solutions of the dispersion relation are used to make comparisons with solutions from the full dispersion relation. The effect of drifts due to inhomogeneities in external magnetic field, perpendicular electron temperature and electron density on the growth rate of the ion acoustic instability are investigated in the ion rest frame. Finally, in a reference frame in which the electrons are stationary, both ion species are given external drifts. The effects of the ion drift velocities (both equal and unequal), electron to ion temperature ratio, light ion fraction, and heavy to light ion mass ratio on the growth rate of the ion acoustic instability are then studied.
Low frequency electrostatic instabilities in a two-dust component plasma.
(1999) Maharaj, Shimul Kumar.; Bharuthram, Ramesh.
The kinetic dispersion relation for a magnetized dusty plasma comprising of ions, electrons and massive, charged dust particles is solved for low frequency electrostatic instabilities in the dust plasma frequency regime. The free energy is provided by the drifting ion beam. The effect of varying parameters such as ion drift speed, particle densities, ion temperature and magnetic field strength on the real frequency and growth rate is examined. Initially light and heavy dust species of different charge are separately considered. This procedure is then repeated for a four-component plasma in an attempt to study the effect of the presence of both the dust species on low frequency electrostatic phenomena. Using a different plasma model, instabilities generated by an equal E x B drift of both the magnetized ions and electrons relative to the unmagnetized dust grains of both the heavy and light dust species is also investigated. The latter instabilities are applicable to the planetary ring plasmas of Saturn. Throughout our studies, numerical solutions of the full dispersion relation for the real frequency and growth rate are compared with approximate analytical solutions.
A study of the interaction of strong electromagnetic waves and anisotropic ion beams with a background plasma.
(1989) Singh, Pravin.; Bharuthram, Ramesh.
The interaction of an anisotropic (in velocity space) ion beam with an isotropic background hydrogen plasma is theoretically investigated. The length and time scales are such that both the ions and electrons are magnetized. Using linear theory, the electrostatic dispersion relation is derived, and solved fully, using no approximations. It is shown that the anisotropy can significantly enhance the instability growth rates as compared to the isotropic case. The importance of ion magnetization is illustrated. Comparisons are made with unmagnetized plasma results. The modulational instability of an arbitrarily-large-amplitude electron cyclotron wave along the external magnetic field is investigated, taking into account the relativistic electron quiver velocity and the relativistic ponderomotive force. Three types of plasma slow responses, the forced-Raman, quasistatic and forced-quasistatic, are considered and a parameter study of the instability growth rates is carried out.

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Browsing Masters Degrees (Physics) by Author "Bharuthram, Ramesh."