Admittance of an infinite cylindrical antenna immersed in a lossy, compressible plasma

1969 ◽  
Vol 47 (20) ◽  
pp. 2129-2135 ◽  
Author(s):  
Richard L. Monroe
Keyword(s):  
Plasma Frequency ◽  
Propagation Constant ◽  
Plasma Temperature ◽  
Particle Collision ◽  
Low Loss ◽  
Compressible Plasma ◽  
Cylindrical Antenna ◽  
Electroacoustic Wave ◽  
Gap Width ◽  
Good Agreement

An expression is derived for the driving point admittance of an infinite, perfectly conducting cylindrical antenna excited by a finite uniform gap and immersed in a lossy, compressible, isotropic plasma. This expression is based on the twin assumptions that the gap width is much smaller than the wavelength of the plasma (electroacoustic) wave and that the radius of the antenna is much smaller than the wavelength of the electromagnetic wave; it is similar in form to the corresponding expression for an infinite antenna in free space, and it is obtained in much the same manner. Conductance and susceptance curves computed from the admittance function are in good agreement with those obtained numerically by other authors for f ≥ 0.7 fP. The behavior of the admittance function at frequencies in the neighborhood of the plasma frequency depends mainly on the electron – neutral particle collision frequency, not the plasma temperature. In general, the effect of the temperature is quite small, although a temperature-related effect can produce large admittance values in very low-loss plasmas at frequencies well below the plasma frequency (f ~ 0.03 fP for T = 1500 °K). This investigation supports the view that the propagation constant of the current along a cylindrical antenna in a compressible plasma is nearly equal to the plane-wave propagation constant in an incompressible plasma.

Current distribution on a thin cylindrical antenna immersed in an isotropic compressible plasma

1968 ◽  
Vol 46 (8) ◽  
pp. 1013-1017 ◽  
Author(s):  
Richard L. Monroe
Keyword(s):  
Current Distribution ◽  
Integrodifferential Equation ◽  
Free Space ◽  
Plasma Frequency ◽  
Propagation Constant ◽  
Wave Number ◽  
Compressible Plasma ◽  
Cylindrical Antenna ◽  
Space Wave

An integrodifferential equation is derived for the current distribution along a thin, hollow, center-driven, cylindrical, perfectly conducting antenna immersed in an isotropic, compressible plasma. On the basis of this equation it is shown that the current distribution approaches sinusoidal form as the radius of the antenna approaches zero. The propagation constant for this current is approximately equal to the free-space wave number for most frequencies greater than the plasma frequency.

Infinite cylindrical antenna in a uniaxial compressible plasma

1968 ◽  
Vol 46 (24) ◽  
pp. 2846-2849
Author(s):  
Edmund K. Miller
Keyword(s):  
Significant Influence ◽  
Plasma Frequency ◽  
Compressible Plasma ◽  
Cylindrical Antenna

Numerical values are given for the admittance of an infinite cylindrical antenna in a uniaxial plasma, taking into account both plasma compressibility and a vacuum sheath. The susceptance is found to exhibit no significant sheath or compressibility dependence above the plasma frequency (ƒp) and only a slight dependence on these factors below ƒp. The conductance behavior shows no significant influence of compressibility or sheath in the range centered about ƒp, in which it is relatively constant in value except for a slight minimum at ƒp.

Effect of Focusing Plane on Laser Blow-off Shock Waves from Confined Aluminum and Copper Foils

2021 ◽  
Author(s):  
Nagaraju Guthikonda ◽  
Sai Shiva S ◽  
E. Manikanta ◽  
Kameswari P S L D ◽  
V. R. Ikkurthi ◽  
...  
Keyword(s):  
Laser Energy ◽  
Plasma Temperature ◽  
Laser Pulses ◽  
Ambient Air ◽  
Rear Side ◽  
Hydrodynamic Simulations ◽  
Enhanced Absorption ◽  
532 Nm ◽  
Lower Plasma Density ◽  
Good Agreement

Abstract We present results on the dynamics of laser-induced blow-off shockwave generation from the rear side of 20 µm thick aluminum and copper foil confined with a glass (BK7) substrate. These foils are irradiated by 10 ns, 532 nm laser pulses of energy 25 – 200 mJ corresponding to the intensity range 0.2 – 10 GW/cm2. The plasma temperature at the glass-foil interface is observed to play an important role in the coupling of laser energy to the foil. From our experiments and 1D hydrodynamic simulations, we confirm that moving the glass-foil interface away from the focal plane led to (a) enhanced absorption of the laser beam by the foil resulting in ~ 30 % higher blow-off shock velocities (b) significant changes in the material ejection in terms of increased blow-off mass of the foil (c) lower plasma density and temperatures. The material ejection as well as blow-off shock velocity is higher for Al compared to Cu. The simulated shock evolution in ambient air shows a reasonably good agreement with the experimental results.

scholarly journals Analytic modelling of a planar Goubau line with circular conductor

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Tobias Schaich ◽  
Daniel Molnar ◽  
Anas Al Rawi ◽  
Mike Payne
Keyword(s):  
Numerical Simulations ◽  
Propagation Constant ◽  
Finite Thickness ◽  
Approximate Equation ◽  
Dielectric Substrate ◽  
Transverse Magnetic ◽  
Wave Mode ◽  
Velocity Measurements ◽  
Low Loss ◽  
Transverse Magnetic Mode

AbstractPlanar Goubau lines show promise as high frequency, low-loss waveguides on a substrate. However, to date only numerical simulations and experimental measurements have been performed. This paper analytically investigates the surface wave mode propagating along a planar Goubau line consisting of a perfectly conducting circular wire on top of a dielectric substrate of finite thickness but infinite width. An approximate equation for the propagation constant is derived and solved through numerical integration. The dependence of the propagation constant on various system parameters is calculated and the results agree well with full numerical simulations. In addition, the spatial distribution of the longitudinal electric field is reported and excellent agreement with a numerical simulation and previous studies is found. Moreover, validation against experimental phase velocity measurements is also reported. Finally, insights gained from the model are considered for a Goubau line with a rectangular conductor. The analytic model reveals that the propagating mode of a planar Goubau line is hybrid in contrast to the transverse magnetic mode of a classic Goubau line.

THE ADMITTANCE OF AN INFINITE CYLINDRICAL ANTENNA IN A LOSSY INCOMPRESSIBLE, ANISOTROPIC PLASMA

1967 ◽  
Vol 45 (12) ◽  
pp. 4019-4038 ◽  
Author(s):  
Edmund K. Miller
Keyword(s):  
Magnetic Field ◽  
Free Space ◽  
Cyclotron Frequency ◽  
Plasma Frequency ◽  
Floating Potential ◽  
Space Layer ◽  
Cylindrical Antenna ◽  
Warm Plasma ◽  
Positive Ion ◽  
Uniform Plasma

A numerical investigation of the admittance of an infinite, circular cylindrical antenna excited at a circumferential gap of nonzero thickness, and immersed in a lossy incompressible magnetoplasma with the antenna parallel to the static magnetic field is described. A concentric free-space layer (the vacuum sheath) which separates the antenna from the external uniform plasma is included in the analysis to approximate the positive ion sheath which may form about a body at floating potential in a warm plasma. The numerical results for the antenna admittance show that: (1) in the absence of a sheath, a sharp admittance maximum is found at the electron cyclotron frequency, with the maximum more pronounced when the plasma frequency exceeds the cyclotron frequency than for the converse case; (2) the vacuum sheath shifts upward in frequency and reduces in amplitude the admittance maximum which occurs for the sheathless case at the cyclotron frequency; (3) a kink or minimum in the admittance is found at the plasma frequency.

Photoelastic Waveguides In Sige/Si Heterostructures And Bulk Si

1997 ◽  
Vol 486 ◽  
Author(s):  
E. Lea ◽  
B. L. Weiss ◽  
H. Rho ◽  
H. E. Jackson
Keyword(s):  
Transverse Strain ◽  
Bulk Silicon ◽  
Low Loss ◽  
Good Agreement

AbstractPhotoelastic waveguides in bulk Si and SiGe/Si heterostructures have been modelled and characterised. The calculated transverse strain profiles of photoelastic waveguide structures in SiGe/Si heterostructures and bulk silicon are in good agreement with those obtained by microRaman experiments. The waveguide characteristics are also found to be in good agreement with those obtained from the strain modelling and demonstrate that low loss waveguides can be fabricated using these structures

scholarly journals Large-amplitude electromagnetic waves in magnetized relativistic plasmas with temperature

2014 ◽  
Vol 21 (1) ◽  
pp. 217-236 ◽  
Author(s):  
V. Muñoz ◽  
F. A. Asenjo ◽  
M. Domínguez ◽  
R. A. López ◽  
J. A. Valdivia ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thermal Effects ◽  
Large Amplitude ◽  
Plasma Frequency ◽  
Plasma Temperature ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Background Magnetic Field ◽  
Cold Case ◽  
Effective Plasma Frequency

Abstract. Propagation of large-amplitude waves in plasmas is subject to several sources of nonlinearity due to relativistic effects, either when particle quiver velocities in the wave field are large, or when thermal velocities are large due to relativistic temperatures. Wave propagation in these conditions has been studied for decades, due to its interest in several contexts such as pulsar emission models, laser-plasma interaction, and extragalactic jets. For large-amplitude circularly polarized waves propagating along a constant magnetic field, an exact solution of the fluid equations can be found for relativistic temperatures. Relativistic thermal effects produce: (a) a decrease in the effective plasma frequency (thus, waves in the electromagnetic branch can propagate for lower frequencies than in the cold case); and (b) a decrease in the upper frequency cutoff for the Alfvén branch (thus, Alfvén waves are confined to a frequency range that is narrower than in the cold case). It is also found that the Alfvén speed decreases with temperature, being zero for infinite temperature. We have also studied the same system, but based on the relativistic Vlasov equation, to include thermal effects along the direction of propagation. It turns out that kinetic and fluid results are qualitatively consistent, with several quantitative differences. Regarding the electromagnetic branch, the effective plasma frequency is always larger in the kinetic model. Thus, kinetic effects reduce the transparency of the plasma. As to the Alfvén branch, there is a critical, nonzero value of the temperature at which the Alfvén speed is zero. For temperatures above this critical value, the Alfvén branch is suppressed; however, if the background magnetic field increases, then Alfvén waves can propagate for larger temperatures. There are at least two ways in which the above results can be improved. First, nonlinear decays of the electromagnetic wave have been neglected; second, the kinetic treatment considers thermal effects only along the direction of propagation. We have approached the first subject by studying the parametric decays of the exact wave solution found in the context of fluid theory. The dispersion relation of the decays has been solved, showing several resonant and nonresonant instabilities whose dependence on the wave amplitude and plasma temperature has been studied systematically. Regarding the second subject, we are currently performing numerical 1-D particle in cell simulations, a work that is still in progress, although preliminary results are consistent with the analytical ones.

The admittance of an infinite cylindrical antenna in a lossy, compressible, anisotropic plasma

1968 ◽  
Vol 46 (9) ◽  
pp. 1109-1118 ◽  
Author(s):  
Edmund K. Miller
Keyword(s):  
Plasma Parameter ◽  
Cyclotron Frequency ◽  
Plasma Frequency ◽  
Fourier Integral ◽  
Dipole Antenna ◽  
Cylindrical Antenna ◽  
Axis Parallel ◽  
E Region ◽  
Antenna Surface ◽  
Parameter Values

An analysis of the current on an infinite cylindrical dipole antenna which is excited across a circumferential gap of nonzero thickness and immersed in a lossy, compressible magnetoplasma with its axis parallel to the static magnetic field is described. Some numerical results are presented for the antenna admittance for the sheathless case, where the uniform magnetoplasma is in contact with the antenna surface. The admittance values are obtained from a numerical integration of the Fourier integral for the antenna current, and are given for plasma parameter values typical of the E region of the ionosphere.The admittance values obtained exhibit a maximum slightly above the electron cyclotron frequency, and in this regard are similar to the admittance when the magnetoplasma is incompressible but separated from the antenna by a free-space layer (the vacuum sheath). In addition, the admittance is found to have a slight minimum at the plasma frequency and to have a more pronounced minimum at the upper hybrid frequency where also the susceptance changes sign, these minima not being significantly affected by the plasma compressibility or vacuum sheath. These features of the calculated admittances are found to have a qualitative resemblance to experimental results obtained from antenna measurements in the ionosphere.

Experimental and Computational Assessment of Windage Losses in Rotating Machinery

1996 ◽  
Vol 118 (1) ◽  
pp. 116-122 ◽  
Author(s):  
P. M. Wild ◽  
N. Djilali ◽  
G. W. Vickers
Keyword(s):  
Shear Stress ◽  
Aspect Ratio ◽  
Axial Distribution ◽  
End Effects ◽  
Taylor Vortices ◽  
Functional Relations ◽  
Azimuthal Shear ◽  
Radial Gap ◽  
Gap Width ◽  
Good Agreement

A combined experimental and computational investigation of the flow between a rotating cylinder and a fixed enclosure is presented. The configuration considered is related to the design of a centrifugal desalinator, and includes the flow in the annular as well as in the axial gap regions. The computed flowfield shows significant variations in the axial distribution of the azimuthal shear stress due to the secondary flow associated with Taylor vortices. The averaged azimuthal shear stress (or torque) is however not very sensitive to the number of vortices. Computational results also show that, where the aspect ratio of the annulus (rotor length to radial gap width) is relatively small, this azimuthal variation results in a higher average azimuthal shear stress than for the case where the aspect ratio of the annulus is relatively large. Various functional relations for windage torque of infinite cylinders, developed by other researchers on the basis of power law relations or assuming a log-law velocity distribution, are evaluated. Three such relations are found to be in good agreement with the experimental results when coupled with a correction for end effects. These relations are also the most useful with respect to the design of rotating equipment.

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