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    Dispersion of electromagnetic waves in coaxial cylindrical rippled-wall waveguide including plasma layer
    (2022-01-01)
    Asadiamiri, F.
    ;
    Chaudhary, K.
    ;
    Ali, J.
    ;
    Bahadoran, M.
    ;
    Nejati, Malihe
    Electronic technologies, especially in the microwave and terahertz frequency ranges, including plasma show better interaction efficiency and higher output power as compared to apparatus with the vacuum. Also, in these frequency ranges, the plasma-filled high-power waveguides can support TE and TM modes. Therefore, in this study, the dispersion relation of electromagnetic (EM) waves in a new rippled-wall waveguide structure contain the plasma layer and coaxial dielectric geometry is numerically studied. The Maxwell equations and boundary conditions are employed to investigate and analyze the dispersion relation in TM mode for coaxial geometry dielectric rippled-wall waveguide contain the plasma layer. High-frequency radiations are observed from the proposed configuration. It is found that the frequency of the wave increases with a decrease in the corrugation amplitude and period. Moreover, a decrease in frequency is observed with an increase in dielectric radius and a decrease in plasma radius.
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    Dispersion characteristics of terahertz transverse electric mode in a smooth-wall cylindrical waveguide with a degenerate plasma layer
    (2020-05-01)
    Asadiamiri, F.
    ;
    Nejati, M.
    ;
    Chaudhary, K.
    ;
    Baboli, M.
    ;
    Ali, J.
    The propagation of transverse electric mode in a cylindrical metallic smooth-wall waveguide contains a dielectric rod and a cold collisionless unmagnetized degenerate plasma layer is analytically investigated in the terahertz frequency region. The dispersion relations of fast and slow waves for this mode are derived and solved numerically. The effects of geometrical and physical parameters such as dielectric, plasma and metal radii, and dielectric permittivity on the dispersion characteristics of terahertz transverse electric mode and its frequency spectrum are studied. It is shown that the decrease of dielectric permittivity and metal radius, and the increase of degenerate plasma radius leads to higher frequency fast waves. It is also indicated that an increase in the dielectric radius results in a decrease in the frequency of fast waves. In addition, it is found that by reducing the dielectric rod radius and with increasing metal radius, the frequency is increased in the slow waves. Finally, it is shown that the increase in dielectric permittivity causes a decrease in the frequency of both fast and slow waves.
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    Terahertz cherenkov radiation excited by an electron beam in a cylindrical metallic rippled-wall waveguide
    (2020-04-01)
    Asadiamiri, F.
    ;
    Ali, J.
    ;
    Bahadoran, M.
    ;
    Chaudhary, K.
    ;
    Yupapin, P. P.
    The Cherenkov excitation of terahertz (THz) radiation by the interaction of an electron beam with the transverse magnetic modes of electromagnetic waves in a new configuration of cylindrical metallic rippled-wall waveguide (CMRWW) including an unmagnetized degenerate plasma layer and a dielectric rod is studied. In addition, the electric field profiles and the growth rates of these waves are investigated by deriving the wave equation and the dispersion relation for the proposed configuration. The effects of physical parameters such as dielectric and plasma radii, corrugation amplitude, and corrugation period on the dispersion relation, electric field profiles and growth rates of the terahertz radiation are discussed. It is shown that by choosing appropriate parameters of the electron beam and the waveguide, one can generate high power radiation in the terahertz range.
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    Laser-induced graphite plasma kinetic spectroscopy under different ambient pressures
    (2015-04-01)
    Chaudhary, K.
    ;
    Rosalan, S.
    ;
    Aziz, M. S.
    ;
    Bohadoran, M.
    ;
    Ali, J.
    The laser induced plasma dynamics of graphite material are investigated by optical emission spectroscopy. Ablation and excitation of the graphite material is performed by using an 1064nm Nd:YAG laser in different ambient pressures. Characteristics of graphite spectra as line intensity variations and signal-to-noise ratio are presented with a main focus on the influence of the ambient pressure on the interaction of laser-induced graphite plasma with an ambient environment. Atomic emission lines are utilized to investigate the dynamical behavior of plasma, such as the excitation temperature and electron density, to describe emission differences under different ambient conditions. The excitation temperature and plasma electron density are the primary factors which contribute to the differences among the atomic carbon emission at different ambient pressures. Reactions between the plasma species and ambient gas, and the total molecular number are the main factors influencing molecular carbon emission. The influence of laser energy on the plasma interaction with environment is also investigated to demonstrate the dynamical behavior of carbon species so that it can be utilized to optimize plasma fluctuations.
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    Kinetic model for carbon species distribution in arc discharge plasma
    (2015-01-12)
    Roslan, M. S.
    ;
    Chaudhary, K.
    ;
    Aziz, M. S.
    ;
    Ali, J.
    ;
    Yupapin, P. P.
    In present work, numerical integration for density distribution of carbon species in arc discharge plasma is presented. The model incorporates two-body collision effects using continuity equation of density in conservation mass rate law. Plasma species in inter-electrode gap are accelerated by the electric field across the gap and produced high density plasma. Electrons with high energy in arc discharge plasma cause extended ionization, excitation, recombination, and dissociation process due to particle collision which leads to enrichment of density in spatial and temporal mode. The extrapolation of species dominant in arc discharge process is critical issue to predict carbon nanostructure production. A chemical kinetic models and distribution of carbon ions and neutrals species based on collision in thermal plasma condition is developed. The reaction process of carbon species are identified in the between electrodes region. The electron-ion recombination cross section is analyzed to understand the density evolution.
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    Analysis of optical ring resonator
    (2015-01-01)
    Afroozeh, A.
    ;
    Amiri, I. S.
    ;
    Chaudhary, K.
    ;
    Ali, J.
    ;
    Yupapin, P. P.
    Microring resonators (MRR) are defined as filters with characteristics similar to Fabry-Perot filters. However, they offer an advantage as the injected and reflected signals are separated in individual waveguides. In addition, their design does not require any facets or gratings and is thus practically simple. In this chapter, analyses of microrings based on three configurations are presented.