PhD

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Study of Collective Interactions in Low Beta Dense Plasmas
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2022) Ayesha Rehman; CIIT/SP15-PPH-004/LHR; Dr. Muhammad Jamil; LHR TP 8173
The low-beta plasmas reflect the strong magnetic pressure in the comparison of thermal statistical pressure which affects the plasma characteristics and the wave propagation. The collective interactions in low beta plasmas, for the reason of its micro and nano scale applications in the latest technological era, is studied in this research thesis. The electrostatic and electromagnetic modes, their instabilities and growth rates to study new horizon of frequency spectrum is focused in this dissertation. Whenever two charged particles mutually interact, it is done through Coulomb interaction. Though the separation distance among two particles becomes greater than the mean separation distance of particles and as a result the particles immediately interact with many other charged particles in its surroundings and causes collective interactions in plasma. In dense plasmas the charged particles act as a Fermi gas, so the quantum mechanical effects due to significant associated de Broglie length become important while studying the dynamics of charge carriers. The quantum hydrodynamic (QHD) model is helpful for the study of collective interactions in dense plasmas that works well for low beta. The QHD is comparatively simple and captures many of the essential properties of plasma dynamics. This thesis contains three papers. The first paper discussion reveals novel aspects of dusty plasmas as the dust particles can coagulate and grow in size ranging from tens of nanometers to about hundreds of microns size. A semi classical Quantum Hydrodynamic Model (QHD) is employed which includes the quantum effects for plasma electrons in the terms of statistical degenerate pressure, Landau quantization, exchange-correlation potential, and tunneling potential. The low beta plasma characteristics provides the opportunity for the usage of two potential theory in order to derive a complex equation of dispersion of the shear Alfvén wave in quantum dusty magneto plasmas. Analytical simplification of dispersion equation provides the damping rate of the shear Alfvén wave which is verified graphically for a typical set of parameters. It is noticed that the damping rate depends upon the quantum properties of Landau quantization, exchange-correlation, and tunneling potential in addition to the dust radius which modifies the floating potential of the dust particles. Secondly, a system of single wall carbon nano-tubes is considered to study dispersive properties of plasma waves in the presence of uniform axial magnetic field. The impact of quantum characteristics of plasma electrons on the growth rate in the carbon nano- tubes are studied. It is noticed that wave-guide configuration of the plasma system plays a significant role in the growth rate. The graphical analysis depicts the significant role of axial magnetic field in the Landau quantization. Thirdly, an electrostatic wave in a bounded geometry is studied for e-p-i quantum plasmas. The quantum hydrodynamic model is employed to find the dispersion relation xi of waveguide mode. The complex frequency leads to the growth rate and the phase speed in the cylindrical geometry.
Study on Metal Ions Mediated Structural Properties of Bio-Glass Matrix
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Saira Saif; CIIT/SP20-RPH-019/LHR; Dr. Junaid Amjad; LHR TP 7713
Study on Metal Ions Mediated Structural Properties of Bio-Glass Matrix Rare earth Bioglass materials show promise for biomedical uses. In this study, Yb3+ ions and CuO were co-doped in borophosphate glass, and new glass with varied characteristics was created using the melt-quenching approach. The intensities of rare earth 4f intraband transitions changed when metallic Cu nanoparticles (NPs) were added. Advanced techniques, such as Raman and UV are used to study the optical characteristics of these glasses. The results demonstrate absorption and luminescence spectroscopy, as well as the excited state lifetime, which influences the optical characteristics of the glass.
Study of Nonlinear Interactions in Dense Plasmas
(Library Information Services, COMSATS University Islamabad, Lahore Campus, 2021) Zahid Mir; CIIT/FA14-PPHY-004/LHR; Dr. Muhammad Jamil; LHR TP 7539
It is intended here in this thesis to study the nonlinear interactions evolved from the interaction of linear modes in dense plasmas like astrophysical objects, laser produced plasmas and semiconductor plasmas, etc. The dense plasma systems in focus contain electrons, ions and negatively charged dust grains. The constituent modes are electrostatic and electromagnetic in nature. In addition to the coupling mechanism, an electron beam is also considered as an energy source. A multi-fluid model consisting upon momentum balancing equation, equation of continuity, Poisson’s equation and set of Maxwell equations for quantum plasmas is used to diagnose the plasmas analytically. The thesis is composed of two-fold studies of nonlinear interactions based upon the published papers. Firstly, excitation of a beat wave generated by the parametric coupling of two modes of slightly different wavelengths is discussed. The linear analysis of the dispersive nature of the incident (pump) and scattered (sideband) is carried out. A derivation of the nonlinear dispersion expression is carried out due to the linear coupling of the pump and sideband in the assembly of a homogeneous dense dusty magneto-plasmas. This leads to the growth rate of the parametric instability of three waves. Secondly, the nonlinear growth of the parametric instability of electrostatic electron Langmuir wave, produced by the coupling of two waves with slightly different frequencies in semiconductor plasma is discussed. The linearity behaviour of an electrostatic pump (upper-hybrid wave) and electromagnetic sideband (O-mode) in semiconductor quantum plasma is studied. The second order convective term couples the fields of pair modes to derive the nonlinear beat frequency of the resultant perturbation leading to three waves parametric instability in semiconductor quantum plasma system. In both the cases the quantum mechanical effects arising due to degenerate pressure of Fermi gas, quantum tunneling effect, and exchange-correlation potential have been incorporated for the fermions. The instability is analyzed graphically for both cases on varying different parameters.

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