Cylindrical Metallic Waveguide Research Articles

Superluminal X-shaped beams propagating without distortion along a coaxial guide.

In a previous paper we showed that localized superluminal solutions to the Maxwell equations exist, which propagate down (nonevanescence) regions of a metallic cylindrical waveguide. In this paper we construct analogous nondispersive waves propagating along coaxial cables. Such new solutions, in general, consist in trains of (undistorted) superluminal "X-shaped" pulses. Particular attention is paid to the construction of finite total energy solutions. Any results of this kind may find application in the other fields in which an essential role is played by a wave equation (like acoustics, geophysics, etc.).

Nonlinear ineraction of an annular electron beam with azimuthal surface waves

A nonlinear theory is developed that describes the interaction between an annular electron beam and an electromagnetic surface wave propagating strictly transverse to a constant external axial magnetic field in a cylindrical metal waveguide partially filled with a cold plasma. It is shown theoretically that surface waves with positive azimuthal mode numbers can be efficiently excited by an electron beam moving in the gap between the plasma column and the metal waveguide wall. Numerical simulations prove that, by applying a constant external electric field oriented along the waveguide radius, it is possible to increase the amplitude at which the surface waves saturate during the beam instability. The full set of equations consisting of the waveenvelope equation, the equation for the wave phase, and the equations of motion for the beam electrons is solved numerically in order to construct the phase diagrams of the beam electrons in momentum space and to determine their positions in coordinate space (in the radial variable-azimuthal angle plane).

Ultrasound shock wave generator with one-bit time reversal in a dispersive medium, application to lithotripsy

The building of high-power ultrasonic sources from piezoelectric ceramics is limited by the maximum voltage that the ceramics can endure. We have conceived a device that uses a small number of piezoelectric transducers fastened to a cylindrical metallic waveguide. A one-bit time- reversal operation transforms the long-lasting low-level dispersed wave forms into a sharp pulse, thus taking advantage of dispersion to generate high-power ultrasound. The pressure amplitude that is generated at the focus is found to be 15 times greater than that achieved with comparable standard techniques. Applications to lithotripsy are discussed and the destructive efficiency of the system is demonstrated on pieces of chalk.

Electrodynamic Model of the Gas Discharge Sustained by Azimuthal Surface Waves

Results of studying an electrodynamical model of the plasma producer based on azimuthal surface waves (ASW) propagation both in a cylindrical metal waveguide filled by magnetoactive plasma and along metal cylindrical antenna placed into the plasma are presented. Parameters of these gas discharges are studied in the two frequency ranges where propagation of the ASW is possible and also are compared. The value of plasma density that can be achieved by this producer is calculated. The spatial distribution of the wave electromagnetic fields, dependencies of their penetration depth into plasma and angular discharge length on the discharge parameters are studied analytically and numerically. Advantages of the operation in the both frequency ranges are indicated. Possibility of resonant absorption of the ASW energy due to their conversion into the bulk upper hybrid mode is examined as well.

Electrodynamic Model of the Gas Discharge Sustained by Azimuthal Surface Waves

Results of studying an electrodynamical model of the plasma producer based on azimuthal surface waves (ASW) propagation both in a cylindrical metal waveguide filled by magnetoactive plasma and along metal cylindrical antenna placed into the plasma are presented. Parameters of these gas discharges are studied in the two frequency ranges where propagation of the ASW is possible and also are compared. The value of plasma density that can be achieved by this producer is calculated. The spatial distribution of the wave electromagnetic fields, dependencies of their penetration depth into plasma and angular discharge length on the discharge parameters are studied analytically and numerically. Advantages of the operation in the both frequency ranges are indicated. Possibility of resonant absorption of the ASW energy due to their conversion into the bulk upper hybrid mode is examined as well.

Microwave Gas Discharge Sustained by the Azimuthal Surface Waves

A theoretical model of plasma source based on azimuthal surface waves (ASW) propagation in a plasma filled cylindrical metal waveguide is presented. The ASW propagate across an external axial steady magnetic field and posses the eigenfrequencies in the range between upper hybrid frequency and the cut-off frequency for HF bulk wave. The problem is studied using a local hydrodynamic approach and taking into consideration a collisional wave damping. Spatial distributions of the ASW fields and produced plasma density are examined both analytically and numerically.

Microwave Gas Discharge Sustained by the Azimuthal Surface Waves

A theoretical model of plasma source based on azimuthal surface waves (ASW) propagation in a plasma filled cylindrical metal waveguide is presented. The ASW propagate across an external axial steady magnetic field and posses the eigenfrequencies in the range between upper hybrid frequency and the cut-off frequency for HF bulk wave. The problem is studied using a local hydrodynamic approach and taking into consideration a collisional wave damping. Spatial distributions of the ASW fields and produced plasma density are examined both analytically and numerically.

Space-Charge and Cyclotron Waves in a Raman Free-Electron Laser

Effects of the wiggler field on the propagation of two types of space-charge waves in a Raman free-electron laser are studied. The relativistic electron beam is affected by an axial magnetic field and only partially fills a cylindrical metallic waveguide. Using the electrostatic approximation in the beam frame and an appropriate boundary condition a set of two equations are found as the dispersion relation. These equations are solved numerically to study the characteristics of the plasma-like and the cyclotron-like waves.

Wiggler-field effects on the space-charge waves of a Raman free-electron laser.

An analysis of the propagation of a space-charge wave through the wiggler and axial magnetic fields of a free-electron laser is presented. The relativistic electron beam is contained within and only partially fills a cylindrical metallic waveguide. A theory is developed using lab-frame Maxwell and fluid equations in a form which is equivalent to the electrostatic approximation in the beam frame. The computational method of determining the dispersion relation is described and some numerical results are presented which illustrate effects arising from the wiggler and the partially filled waveguide.

Nonlinear theory of beam excitation of azimuthal surface modes in plasma-filled cylindrical metal waveguides

It is shown that electromagnetic surface waves propagating along the azimuthal angle can be excited efficiently by an annular electron beam in a cylindrical metal waveguide partially filled with a magnetoactive plasma. A self-consistent system of differential equations is obtained to describe the nonlinear interaction between the beam particles and an azimuthal surface wave in the single-mode regime. This system of equations is analyzed numerically and the influence of the parameters of this waveguide structure on the development of the resonant beam instability is determined.

Fast-Wave Analysis of an Inhomogeneously-Loaded Helix Enclosed in a Cylindrical Waveguide

The inhomogeneously-loaded helix enclosed in a metal cylindrical waveguide operated in the fast-wave regime is field-analyzed using the tape-helix model. The inhomogeneous discrete dielectric supports have been modeled by azimuthally smoothing them out into a number of continuous, homogeneous dielectric tube regions of appropriate effective relative permittivity values determined by the relative volumes occupied by the supports in these regions. While accounting for the radial inhomogeneity, the nonuniformity of the radial propagation constant over the structure cross section is also taken into consideration. Further, structured expressions amenable to easy computation are presented with the help of the relevant recurrence relations, and a method is suggested to use them in an iterative cycle for the desired convergence accuracy. The dispersion relation developed, as a special case, passes on to that obtained elsewhere for a simpler structure in which the dielectric supports for the helix was not considered. It is observed that the dielectric-support parameters become more effective in controlling the dispersion curve than the bare helix parameters. It is also found that the effect of the controlling parameters such as the helix pitch angle on the phase velocity and interaction impedance of the structure becomes less pronounced as the helix is brought closer to the waveguide wall. The presence of the dielectric in the structure increases the value of the interaction impedance to a reasonable value over the entire operating frequency band. The results in terms of the structure parameters, namely, helix pitch angle, helix-support permittivity, helix-to-waveguide wall separation and structure inhomogeneity presented here are rather general, and can be used for the structure design and performance evaluation as well as for the control of any space harmonic of interest in a fast-wave device such as the gyro-traveling-wave amplifier.

Fast-Wave Analysis of an Inhomogeneously- Loaded Helix Enclosed in a Cylindrical Waveguide

The inhomogeneously-loaded helix enclosed in a metal cylindrical waveguide operated in the fast-wave regime is field-analyzed using the tape-helix model. The inhomogeneous discrete dielectric supports have been modeled by azimuthally smoothing them out into a number of continuous, homogeneous dielectric tube regions of appropriate effective relative permittivity values determined by the relative volumes occupied by the supports in these regions. While accounting for the radial inhomogeneity, the nonuniformity of the radial propagation constant over the structure cross section is also taken into consideration. Further, structured expressions amenable to easy computation are presented with the help of the relevant recurrence relations, and a method is suggested to use them in an iterative cycle for the desired convergence accuracy. The dispersion relation developed, as a special case, passes on to that obtained elsewhere for a simpler structure in which the dielectric supports for the helix was not considered. It is observed that the dielectric-support parameters become more effective in controlling the dispersion curve than the bare helix parameters. It is also found that the effect of the controlling parameters such as the helix pitch angle on the phase velocity and interaction impedance of the structure becomes less pronounced as the helix is brought closer to the waveguide wall. The presence of the dielectric in the structure increases the value of the interaction impedance to a reasonable value over the entire operating frequency band. The results in terms of the structure parameters, namely, helix pitch angle, helix-support permittivity, helix-to-waveguide wall separation and structure inhomogeneity presented here are rather general, and can be used for the structure design and performance evaluation as well as for the control of anv space harmonic of interest in a fast-wave device such as the gyro-traveling-wave amplifier.

Analysis of an anisotropically loaded helix in the fast‐wave regime for gyro‐traveling‐wave amplifiers

The dielectric-supported helix enclosed in an anisotropic metal envelope made of a metal cylindrical waveguide provided with a large number of thin metal vanes projecting radially inward from its wall is field analyzed to study its characteristics in the fast-wave regime. The tape-helix, instead of a simpler sheath-helix model, is used to consider the space-harmonic effects. Care is taken to account for the finite helix wire/tape thickness by considering a free-space gap between the mean and the outer radii. The nonuniformity of the radial propagation constant over the various cross-sectional regions of the structure is also taken into consideration in the analysis. The dispersion relation developed as a special case passes on to that obtained elsewhere for a vaneless, dielectric-absent structure as well as for a vaneless dielectric-present, structure. It is found that the parameters of the anisotropic envelope play a more dominant role in controlling the dispersion characteristics of the structure than the helix parameters. Furthermore, the effect of the controlling parameters is found to be less as the helix is brought closer to the waveguide wall. The analysis presented can be used in the design of a helix-loaded cylindrical waveguide interaction structure for a wideband fast-wave, gyro-traveling-wave amplifier. © 1997 John Wiley & Sons, Inc.

Analysis of an anisotropically loaded helix in the fast-wave regime for gyro-traveling-wave amplifiers

The dielectric-supported helix enclosed in an anisotropic metal envelope made of a metal cylindrical waveguide provided with a large number of thin metal vanes projecting radially inward from its wall is field analyzed to study its characteristics in the fast-wave regime. The tape-helix, instead of a simpler sheath-helix model, is used to consider the space-harmonic effects. Care is taken to account for the finite helix wire/tape thickness by considering a free-space gap between the mean and the outer radii. The nonuniformity of the radial propagation constant over the various cross-sectional regions of the structure is also taken into consideration in the analysis. The dispersion relation developed as a special case passes on to that obtained elsewhere for a vaneless, dielectric-absent structure as well as for a vaneless dielectric-present, structure. It is found that the parameters of the anisotropic envelope play a more dominant role in controlling the dispersion characteristics of the structure than the helix parameters. Furthermore, the effect of the controlling parameters is found to be less as the helix is brought closer to the waveguide wall. The analysis presented can be used in the design of a helix-loaded cylindrical waveguide interaction structure for a wideband fast-wave, gyro-traveling-wave amplifier. © 1997 John Wiley & Sons, Inc.

Beam space-charge modes in a free-electron laser

Propagation of space-charge waves in a Raman free-electron laser is analyzed. The device under consideration consists of a cylindrical metallic waveguide filled with a relativistic electron beam which passes through a helical wiggler magnetic field and a uniform axial magnetic field. A solution of the fluid equations and Gauss’s law is developed in the form of truncated Fourier and Fourier–Bessel series. The dispersion relation is derived and the combined effects of the waveguide boundary and the wiggler and axial magnetic fields on cyclotron-like waves are studied numerically. In the limit of infinite waveguide radius, the dispersion relation yields a well-known expression in which the combined wiggler and axial fields determine an effective plasma frequency. In the limit of zero wiggler field, it reduces to the dispersion relation for axisymmetric space-charge waves which, in the beam frame, are purely electrostatic.

High-frequency waves in a plasma waveguide

An analysis of the azimuthally symmetrical, high-frequency eigenmodes of a cylindrical metallic waveguide partially filled with a magnetized plasma is presented. Equations that permit calculation of the dispersion curves for four families of electromagnetic and electrostatic modes are derived. Numerical solutions are presented to facilitate the development of devices for generation of high-power electromagnetic radiation, charged particle acceleration, and other applications of plasma waveguides. The dependence of the cutoff frequencies, and dispersion curves of various modes on the ratio of the plasma radius a to the waveguide radius R is studied in detail. Space-charge modes are found to be strongly dependent on the radius ratio a/R. The coupling of the dispersion curves of different modes and the variation of the cutoff frequencies of HE waveguide and cyclotron modes with cyclotron frequency are illustrated for the partially filled waveguide.

Magnetic field effects in a free electron laser with longitudinal electric wiggler

An analysis of the parametric instability which forms the basis for operation of a ubitron-type free electron laser with a longitudinal electric wiggler is presented. Excitation of a space charge wave and a predominantly transverse magnetic waveguide mode results from passage of a relativistic electron beam through a static spatially periodic longitudinal electric field. The beam is contained in a cylindrical metal waveguide and an axial magnetic field of arbitrary magnitude. Effects of the magnetic field on the growth rate, efficiency, radiation wavelength and the required pump wavelength are studied. Suitable values of the magnitude of the magnetic field and other parameters for generating millimetre wavelength radiation are indicated.

Temperature effects on the parametric growth of space-charge waves in a relativistic electron beam

Parametric excitation of two space-charge waves in a cylindrical metallic waveguide completely or partially filled with a relativistic electron beam is analyzed. The pump wave in the laboratory reference frame consists of a static, spatially periodic axial electric field. A theory is presented that is fully electromagnetic and allows for a radially nonuniform pump wave field and finite electron beam temperature. Effects of temperature on the frequency and growth rate of the space-charge waves are studied.

Free electron laser with longitudinal wiggler and finite axial magnetic field

An analysis of the excitation of a space charge wave and a predominantly transverse magnetic mode in a cylindrical metallic waveguide filled with a relativistic electron beam is presented. The beam is guided by a uniform, axial magnetic field of arbitrary magnitude and passes through a spatially periodic, longitudinal electric (wiggler) field. A non-linear wave equation is derived in a form which includes the coupling of TM and TE modes due to the finite axial magnetic field. For the case of a weak and purely axial wiggler field, a solution of this wave equation is developed with each of the two excited waves expressed as a sum of three partial waves. A spatial growth rate formula is derived in a form appropriate for operation infinitesimally above cut-off of the TM mode. Numerical calculations indicate that the axial magnetic field magnitude should be somewhat larger than the value which maximizes the growth rate in order to achieve high efficiency.

Parametric growth of space-charge waves using a non-uniform electric wiggler

An analysis of the excitation of two space-charge waves in a cylindrical metallic waveguide filled with a relativistic electron beam is presented. The wiggler electrostatic potential is spatially periodic along the guide axis and has a radial dependence. A formula for the growth rate in the laboratory frame is derived in terms of an appropriate radial average of the wiggler potential amplitude. Effects of finite beam electron temperature are included and extension to a partially filled waveguide is discussed.