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Spilios Riyopoulos - One of the best experts on this subject based on the ideXlab platform.

  • THEORY OF MAGNETIZED, COUPLED, RF-DRIVEN Plasma Sheaths IN ONE DIMENSION
    Physical Review E, 1999
    Co-Authors: Spilios Riyopoulos
    Abstract:

    A set of equations for magnetized Plasma Sheaths in rf capacitance discharges is developed within the adiabatic electron, fluid ion framework. It differs from previous approaches in that (a) ion demagnetization, i.e., the detachment of the ion flow from the magnetic lines caused by electrostatic gradients, is introduced self-consistently, (b) the ion injection velocity from the presheath is reevaluated to ensure the ion-electron flux balance, and (c) two symmetrically opposed coupled Sheaths are driven by a sinusoidal driving voltage instead of a sinusoidal current. It is found that the sheath potential and thickness increase considerably with increasing magnetic inclination {theta} relative to the electric field compared to the unmagnetized results; the latter are recovered at the parallel magnetic field limit. Also, the ion injection velocity along the magnetic lines is subsonic and depends on the magnetic inclination. Finally, a sinusoidal ac voltage drives an anharmonic sheath current, while a sinusoidal current drives anharmonic voltage. {copyright} {ital 1999} {ital The American Physical Society}

  • effects of static magnetic fields on rf driven Plasma Sheaths
    Physics of Plasmas, 1996
    Co-Authors: Spilios Riyopoulos
    Abstract:

    The physics of sheath formation during rf capacitor discharges in magnetized Plasmas is examined, for arbitrary angle between the dc magnetic field and the oscillating rf electric field. Observations from particle simulations show that the induced dc sheath potential under given rf drive increases with increasing angle between the electric and magnetic fields, reaching a maximum nearly twice the unmagnetized dc potential for nearly perpendicular E and B. Analytic study of the ion dynamics in the time‐averaged sheath field reveals that the ion motion is unstable, yielding unbound ion transport across the magnetic lines. The effective ion mass m*, employed for the acceleration along the electric field, is obtained as a function of the magnetic angle and the relative magnetic strength. The magnetized presheath ions are partially demagnetized inside the sheath. The ratio of the effective masses mB/m*, where mB stands for fully magnetized ions, parametrizes the sheath potential and sheath thickness. The sheath...

  • anomalous ion heating via parametric resonance in rf driven Plasma Sheaths
    Physical Review Letters, 1992
    Co-Authors: Spilios Riyopoulos
    Abstract:

    A novel mechanism for strong ion heating inside magnetized Sheaths, formed at Plasma-wall interfaces in radio-frequency-driven Plasmas, is studied. The ion gyration frequency is modulated by the oscillating charge density inside the sheath, resulting in a Hill-type parametric equation of motion. The gyration velocity is unstable when the time-averaged gyrofrequency Ω is near a subharmonic nω/2 of the rf frequency. Large energy absorption occurs within only a few gyrations because of the initial exponential growth

Xiaohua Deng - One of the best experts on this subject based on the ideXlab platform.

  • a terahertz signal propagation model in hypersonic Plasma sheath with different flight speed
    Physics of Plasmas, 2019
    Co-Authors: Kai Yuan, Rongxin Tang, Mingyang Mao, Yuhao Wang, Xiaohua Deng
    Abstract:

    A hypersonic Plasma sheath could shield communication signals, which results in the so-called “blackout.” Hypersonic flights in near space used to suffer from the “blackout.” Terahertz (THz) communication is considered to be a potential solution to the blackout problem. On the other hand, it is still not clear that how the complex flight conditions impact the THz communication channel conditions in the Plasma sheath. The relation between the occurrence of communication blackout and the flight conditions is unclear either. In the present study, the relation between the THz signal attenuation in Plasma Sheaths and the hypersonic flight speed was investigated using the numerical hypersonic hydrodynamic model. According to this study, the thickness of the Plasma sheath decreases with the increasing flight speed. The electron density and the electron collision frequency increase with the flight speed. As a result, the THz signal attenuation increases with the flight speed. In addition, a new estimation model, which is able to predict the THz signal attenuation in the Plasma sheath for arbitrary flight speed, was developed on the basis of the numerical study. The estimation model, in which the hypersonic hydrodynamics is absent, could help to significantly reduce the time consumption in predicting the THz communication channel conditions as well as the occurrence of the blackout.

  • Impact of Reentry Speed on the Transmission of Obliquely Incident THz Waves in Realistic Plasma Sheaths
    IEEE Transactions on Plasma Science, 2018
    Co-Authors: Kai Yuan, Jiamin Chen, Linfang Shen, Xiaohua Deng, Lujun Hong
    Abstract:

    Nowadays, the terahertz (THz) communication is believed to be a potential solution to the communication blackout for reentry vehicles. In this paper, a numerical hypersonic fluid model was introduced to obtain the realistic Plasma Sheaths. The onboard antenna which is installed on the wall was assumed to be conformal. The transmission of obliquely incident THz waves in the Plasma Sheaths was analyzed. According to this paper, the power transmission coefficient decreases with the increase of reentry speed since both the electron density and the electron collision frequency near the onboard antenna increase with the reentry speed. In addition, the relation between the wave transmission and the reentry speed is revealed. The power transmission coefficient decreases with the increase of incident angle, because the conformal antenna cannot receive the field component which is perpendicular to the wall. Two supplemental schemes to enhance the transmission rate for THz signals were discussed based on this paper.

  • Studies on the transmission of sub-THz waves in magnetized inhomogeneous Plasma sheath
    Physics of Plasmas, 2018
    Co-Authors: Kai Yuan, Linfang Shen, Xiaohua Deng, Ming Yao, Zhou Chen, Lujun Hong
    Abstract:

    There have been many studies on the sub-terahertz (sub-THz) wave transmission in reentry Plasma Sheaths. However, only some of them have paid attention to the transmission of sub-THz waves in magnetized Plasma Sheaths. In this paper, the transmission of sub-THz waves in both unmagnetized and magnetized reentry Plasma Sheaths was investigated. The impacts of temporal evolution of the Plasma sheath on the wave transmission were studied. The transmission of “atmospheric window” frequencies in a magnetized Plasma sheath was discussed in detail. According to the study, the power transmission rates (Tp) for the left hand circular (LHC) and the right hand circular modes in the magnetized Plasma sheath are obviously higher and lower than those in the unmagnetized Plasma sheath, respectively. The Tp of LHC mode increases with both wave frequency and external magnetic field strength. Also, the Tp of LHC mode in both magnetized and unmagnetized Plasma Sheaths varies with time due to the temporal evolution of the pla...

Kai Yuan - One of the best experts on this subject based on the ideXlab platform.

  • a terahertz signal propagation model in hypersonic Plasma sheath with different flight speed
    Physics of Plasmas, 2019
    Co-Authors: Kai Yuan, Rongxin Tang, Mingyang Mao, Yuhao Wang, Xiaohua Deng
    Abstract:

    A hypersonic Plasma sheath could shield communication signals, which results in the so-called “blackout.” Hypersonic flights in near space used to suffer from the “blackout.” Terahertz (THz) communication is considered to be a potential solution to the blackout problem. On the other hand, it is still not clear that how the complex flight conditions impact the THz communication channel conditions in the Plasma sheath. The relation between the occurrence of communication blackout and the flight conditions is unclear either. In the present study, the relation between the THz signal attenuation in Plasma Sheaths and the hypersonic flight speed was investigated using the numerical hypersonic hydrodynamic model. According to this study, the thickness of the Plasma sheath decreases with the increasing flight speed. The electron density and the electron collision frequency increase with the flight speed. As a result, the THz signal attenuation increases with the flight speed. In addition, a new estimation model, which is able to predict the THz signal attenuation in the Plasma sheath for arbitrary flight speed, was developed on the basis of the numerical study. The estimation model, in which the hypersonic hydrodynamics is absent, could help to significantly reduce the time consumption in predicting the THz communication channel conditions as well as the occurrence of the blackout.

  • Impact of Reentry Speed on the Transmission of Obliquely Incident THz Waves in Realistic Plasma Sheaths
    IEEE Transactions on Plasma Science, 2018
    Co-Authors: Kai Yuan, Jiamin Chen, Linfang Shen, Xiaohua Deng, Lujun Hong
    Abstract:

    Nowadays, the terahertz (THz) communication is believed to be a potential solution to the communication blackout for reentry vehicles. In this paper, a numerical hypersonic fluid model was introduced to obtain the realistic Plasma Sheaths. The onboard antenna which is installed on the wall was assumed to be conformal. The transmission of obliquely incident THz waves in the Plasma Sheaths was analyzed. According to this paper, the power transmission coefficient decreases with the increase of reentry speed since both the electron density and the electron collision frequency near the onboard antenna increase with the reentry speed. In addition, the relation between the wave transmission and the reentry speed is revealed. The power transmission coefficient decreases with the increase of incident angle, because the conformal antenna cannot receive the field component which is perpendicular to the wall. Two supplemental schemes to enhance the transmission rate for THz signals were discussed based on this paper.

  • Studies on the transmission of sub-THz waves in magnetized inhomogeneous Plasma sheath
    Physics of Plasmas, 2018
    Co-Authors: Kai Yuan, Linfang Shen, Xiaohua Deng, Ming Yao, Zhou Chen, Lujun Hong
    Abstract:

    There have been many studies on the sub-terahertz (sub-THz) wave transmission in reentry Plasma Sheaths. However, only some of them have paid attention to the transmission of sub-THz waves in magnetized Plasma Sheaths. In this paper, the transmission of sub-THz waves in both unmagnetized and magnetized reentry Plasma Sheaths was investigated. The impacts of temporal evolution of the Plasma sheath on the wave transmission were studied. The transmission of “atmospheric window” frequencies in a magnetized Plasma sheath was discussed in detail. According to the study, the power transmission rates (Tp) for the left hand circular (LHC) and the right hand circular modes in the magnetized Plasma sheath are obviously higher and lower than those in the unmagnetized Plasma sheath, respectively. The Tp of LHC mode increases with both wave frequency and external magnetic field strength. Also, the Tp of LHC mode in both magnetized and unmagnetized Plasma Sheaths varies with time due to the temporal evolution of the pla...

Lujun Hong - One of the best experts on this subject based on the ideXlab platform.

  • Impact of Reentry Speed on the Transmission of Obliquely Incident THz Waves in Realistic Plasma Sheaths
    IEEE Transactions on Plasma Science, 2018
    Co-Authors: Kai Yuan, Jiamin Chen, Linfang Shen, Xiaohua Deng, Lujun Hong
    Abstract:

    Nowadays, the terahertz (THz) communication is believed to be a potential solution to the communication blackout for reentry vehicles. In this paper, a numerical hypersonic fluid model was introduced to obtain the realistic Plasma Sheaths. The onboard antenna which is installed on the wall was assumed to be conformal. The transmission of obliquely incident THz waves in the Plasma Sheaths was analyzed. According to this paper, the power transmission coefficient decreases with the increase of reentry speed since both the electron density and the electron collision frequency near the onboard antenna increase with the reentry speed. In addition, the relation between the wave transmission and the reentry speed is revealed. The power transmission coefficient decreases with the increase of incident angle, because the conformal antenna cannot receive the field component which is perpendicular to the wall. Two supplemental schemes to enhance the transmission rate for THz signals were discussed based on this paper.

  • Studies on the transmission of sub-THz waves in magnetized inhomogeneous Plasma sheath
    Physics of Plasmas, 2018
    Co-Authors: Kai Yuan, Linfang Shen, Xiaohua Deng, Ming Yao, Zhou Chen, Lujun Hong
    Abstract:

    There have been many studies on the sub-terahertz (sub-THz) wave transmission in reentry Plasma Sheaths. However, only some of them have paid attention to the transmission of sub-THz waves in magnetized Plasma Sheaths. In this paper, the transmission of sub-THz waves in both unmagnetized and magnetized reentry Plasma Sheaths was investigated. The impacts of temporal evolution of the Plasma sheath on the wave transmission were studied. The transmission of “atmospheric window” frequencies in a magnetized Plasma sheath was discussed in detail. According to the study, the power transmission rates (Tp) for the left hand circular (LHC) and the right hand circular modes in the magnetized Plasma sheath are obviously higher and lower than those in the unmagnetized Plasma sheath, respectively. The Tp of LHC mode increases with both wave frequency and external magnetic field strength. Also, the Tp of LHC mode in both magnetized and unmagnetized Plasma Sheaths varies with time due to the temporal evolution of the pla...

Sergey Nazarenko - One of the best experts on this subject based on the ideXlab platform.

  • communication with reentry space vehicles via short pulses
    Radio Science, 1995
    Co-Authors: Sergey Nazarenko, Alan C Newell, A M Rubenchik
    Abstract:

    The resonant absorption of a short pulse of electromagnetic radiation in a Plasma slab is considered in order to examine the effectiveness of using short pulses for information transfer through the Plasma Sheaths surrounding reentry vehicles. The amplitudes of the Raman scattering (RS) on the Langmuir oscillations associated with resonant absorption and the amplitude of the Brillouin scattering (BS) on the nonlinear modifications of the Plasma profile are calculated. On-board detection of the RS and BS signals are proposed as parallel and independent channels for reading the message encoded on the electromagnetic pulse sequence. The information transfer capacity of two other nonlinear effects, the generation of the fast electrons in the wave breaking process, and the excitation of the ion-sound waves by the radiative pressure of the Langmuir oscillations are also considered.

  • communication through Plasma Sheaths via raman three wave scattering process
    Physics of Plasmas, 1994
    Co-Authors: Sergey Nazarenko, Alan C Newell, V E Zakharov
    Abstract:

    A mechanism of communication through Plasma Sheaths which surround vehicles traveling at hypersonic velocities is proposed. The idea is to place a source of an intensive, high frequency electromagnetic pump wave on the vehicle and to use the nonlinearity of the medium to create a backscattered Stokes wave through the interaction of the pump wave with the signal‐carrying wave sent by a ground transmitter. Such an interaction will be mediated by the Plasma oscillations generated in the process of the resonant absorption of the signal‐carrying wave. The advantages of this mechanism for information transfer are that the high frequency pump wave only is present in a small region near the vehicle and that the signal wave can have relatively low frequency.