Browsing by Author "Bharuthram, Ramashwar"

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    The effect of a warm electron beam on slow electron-acoustic solitons
    (AIP Publishing, 2018) Mbuli, L.N.; Bharuthram, Ramashwar; Maharaj, S.K.
    The effects of the inclusion of finite drift speed of a warm electron component on the existence of arbitrary amplitude slow electron-acoustic solitons are investigated in a model with ions and cool, warm, and hot electrons. All plasma species are treated as adiabatic fluids. For fixed densities of the cool, warm, and hot electrons, the admissible Mach number ranges of the supported negative potential solitons are found to widen with increasing warm electron beam speed, up to a maximum value of vdbwo = 0.7. Beyond this maximum value, the soliton Mach number ranges become narrower and vanish completely at vdbwo = 1.084 where a switch to positive polarity solitons occurs. For a fixed value of the drift speed of the warm electrons, the cool electron density value at which the switch to positive polarity soliton occurs is the lowest when there is no streaming of the warm electrons but increases with increasing drift speed.
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    Existence domains of dust-acoustic solitons and supersolitons
    (AIP Publishing, 2013) Maharaj, S.K.; Bharuthram, Ramashwar; Singh, S. V.; Lakhina, G. S.
    Using the Sagdeev potential method, the existence of large amplitude dust-acoustic solitons and supersolitons is investigated in a plasma comprising cold negative dust, adiabatic positive dust, Boltzmann electrons, and non-thermal ions. This model supports the existence of positive potential supersolitons in a certain region in parameter space in addition to regular solitons having negative and positive potentials. The lower Mach number limit for supersolitons coincides with the occurrence of double layers whereas the upper limit is imposed by the constraint that the adiabatic positive dust number density must remain real valued. The upper Mach number limits for negative potential (positive potential) solitons coincide with limiting values of the negative (positive) potential for which the negative (positive) dust number density is real valued. Alternatively, the existence of positive potential solitons can terminate when positive potential double layers occur.
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    The effects of ion beams on nonlinear electrostatic waves in space plasmas
    (Universty of the Western Cape, 2024) Maxengana, Mihlali; Bharuthram, Ramashwar
    The effect of ion beams on linear and nonlinear low frequency electrostatic ion-acoustic waves is examined in multi-species plasma models, which are regularly observed in the terrestrial magnetosphere. These models comprise two thermal (adiabatic) ions and one or two Boltzmann electron species, with different temperatures in the latter case. One or both ions are regarded as drifting (beam) species. The linear study reveals the existence of two linear ion-acoustic modes: slow and fast ion-acoustic modes. The slow ion-acoustic modes emerge in models with at least one beam, while fast modes occur in beam and beamless plasma models. The slow ion-acoustic modes are found to be highly sensitive to variations in ion beam speed, becoming unstable to the ion beam instability for intermediate speeds. In the nonlinear regime, the ion-acoustic modes evolve into nonlinear structures such as solitons and double layers, which are pulse like disturbances in potential, commonly known as electrostatic solitary waves. A critical value of the beam speed must be exceeded for the existence of the slow ion-acoustic solitons of which the one slow mode propagates above and the second below the critical acoustic speed associated with the corresponding linear wave.