Finite Wall Conductivity Research Articles

Excitation Equations for Irregular Waveguides Taking into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 1

Excitation Equations for Irregular Waveguides Taking into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 1

Excitation Equations for Irregular Waveguides Taking into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 2. Relativistic Klynotron

Excitation Equations for Irregular Waveguides Taking into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 2. Relativistic Klynotron

Excitation Equations for Irregular Waveguides Taking Into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 2. Relativistic Klynotron

Excitation Equations for Irregular Waveguides Taking Into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 2. Relativistic Klynotron

Excitation Equations for Irregular Waveguides Taking into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 1

Excitation Equations for Irregular Waveguides Taking into Account the Finite Wall Conductivity and Their Application for Ultrahigh-Power Microwave Problems. Part 1

Resistive wall impedance in elliptical multilayer vacuum chambers

The resistive wall impedance of a vacuum chamber with elliptic cross section is of particular interest for circular particle accelerators as well as for undulators in free electron lasers. By using the electric field of a point charge and of a small dipole moving at arbitrary speed in an elliptical vacuum chamber, expressed in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls by means of the surface impedance, and evaluate the longitudinal and transverse driving and detuning impedances for any beam velocity. We also extend the definition of the Yokoya form factors, valid in the thick wall regime, at any beam energy, and show that, in the ultra-relativistic limit, they coincide with the ones that are found in literature. The method is also extended to the multilayer vacuum chamber case. Under conditions generally satisfied with particle accelerator beam pipes, the classical transmission line theory can be used to modelling the impedance seen by a bunch in a vacuum chamber with several layers as an equivalent circuit with the same number of load impedances, giving, as result, a surface impedance that can be used in combination with the fields of the elliptic geometry to obtain the resistive wall impedance in an elliptical multilayer vacuum chamber. The results are also compared with a more time consuming 3D electromagnetic code and with solutions for known cases of circular and flat beam pipe.

Numerical simulations of time-dependent Hunt flows with finite wall conductivity

Numerical simulations of time-dependent Hunt flows with finite wall conductivity

Eigenanalysis of Electromagnetic Structures Based on the Finite Element Method

This article presents a review of our research effort on the eigenanalysis of open radiating waveguides and closed resonating structures. A two dimensional (2-D) hybrid Finite Element method in conjunction with a cylindrical harmonics expansion is established to formulate the open waveguide generalized eigenvalue problem. The key element of this approach refers to the adoption of a vector Dirichlet-to-Neumann map to rigorously enforce the continuity of the two field expansions along a truncation surface. The resulting algorithm was able to evaluate both surface and leaky eigenmodes. The eigenanalysis of three dimensional (3-D) structures involves vast research challenges, especially when they are electrically large and open-radiating. The effort herein is focused on the electrically large case including the losses due to the finite conductivity of metallic walls and objects as well as the loading material losses. The former is introduced through impedance or Leontovich boundary condition, resulting to a non-linear-polynomial generalized eigenvalue problem. A straightforward linearization solution is adopted along with a more efficient alternative technique which mimics analytical approaches. For this one the linear eigenproblem formulated assuming metals as perfect electric conductors is initially solved and their finite conductivity is accounted through impedance boundary conditions enforced locally on the resulting eigenvectors. Finally, some numerical results are presented to verify the performance of these methodologies along with a discussion on their possibilities for extension to open 3D structures as well as to characteristic modes eigenanalysis.

Longitudinal impedance and shielding effectiveness of a resistive beam pipe for arbitrary energy and frequency

The longitudinal coupling impedance of a cylindrical beam pipe for arbitrary relativistic gamma(0) and mode frequency is obtained analytically for finite wall conductivity and finite wall thickness. Closed form expressions for the electromagnetic fields excited by a beam perturbation are derived analytically. General expressions for the resistive-wall impedance in the presence of a metallic shield and for the rf shielding effectiveness of the beam pipe have been obtained and then compared with approximate expressions. The results are applied to the GSI synchrotron SIS, where the thickness of the vacuum chamber in the dipole magnets is much smaller than the skin depth at injection energy.

Power loss for multimode waveguides and its application to beam-waveguide system

The conventional way of expressing power loss in decibels/meter for a multimode waveguiding system with finite wall conductivity (such as a beam-waveguide (BWG) system with protective shroud) can be incorrect and misleading. The power loss (in decibels) for a multimode waveguiding system is, in general, not linearly proportional to the length of the waveguide. New power-loss formulas for multimode system are derived in this paper for arbitrarily shaped conducting waveguide tubes. In these formulas, there are factors such as [exp(jx)-1]/(jx), where x=(/spl beta//sub a/-/spl beta//sub b/)l, with /spl beta//sub a/ and /spl beta//sub b/ being the propagation constants of the different propagating modes and l being the distance from the source plane to the plane of interest along the guide. For a large BWG supporting many propagating modes, /spl beta//sub a/'s are quite close to /spl beta//sub b/'s, thus the mode coupling terms remain important for a very long distance from the source plane. The multimode power loss formula for a large circular conducting tube has been verified by experiments. This formula was also used to calculate the additional noise temperature contribution due to the presence of a protective shroud surrounding a millimeter-wave BWG system.

Thermal pulse propagation and dispersion in laminar flow within conduits of finite wall conductivity

The temporal and spatial characteristics of thermal pulses travelling in conduits of finite wall conductivity are studied using a multiple time scale expansion. Values for the effective dispersion coefficient of these pulses for parabolic laminar flows within both tubes and parallel plate channels are derived and some experimental observations are made to confirm the prediction that the pulses propagate at a sub-mean flow velocity. Several analogues are drawn between the presently reported results and know phenomena in chromatography.

Electrodynamics as a problem of eigenvalues. III. Maxwell operator and perturbation theory

This part of the work deals with perturbation theory. The standard technique permits us to solve problems of volume disturbances in free space, waveguides, and cavities, of disturbances of boundary conditions caused by finite conductivity of walls, and of disturbances of the boundary shape. Expressions for frequency and wave number shifts caused by the perturbation are obtained by the unified method. Several examples are presented: wave amplification in the waveguide filled with a resonant medium like an electron beam in a longitudinal magnetic field, the frequency shift (and increment/decrement) of a cavity loaded by an electron beam, and the field disturbance in the waveguide caused by finite conductivity of the walls.

Analysis of waveguide directional filters by the moment method (invited article)

AbstractAnalysis of a waveguide directional filter with N cavities is formulated in terms of the moment method. Electric fields on coupling apertures, being unknown, rigorously coupled integral equations, are established by using dyadic Green's functions. In this analysis, a virtual cavity technique is introduced as well as an approximate method to incorporate finite conductivity of cavity walls. Numerical results are also shown. © 1993 John Wiley & Sons, Inc.

Conservation of complex power technique for waveguide junctions with finite wall conductivity

Scattering at the junction of two waveguides with finite wall conductivity is rigorously treated using E-field mode matching and the conservation of complex power technique. At the transverse junction discontinuity between the two waveguides, the complex power absorbed by the junction wall is taken into account along with the usual transfer of complex power from one guide to the other. This leads to a generalized form of the scattering matrix (S) of the lossy junction which incorporates the surface impedance Z/sub m/ of the transverse metallic wall, assumed to be a good conductor. The specific case of a copper transverse diaphragm with centered circular iris in an X-band guide is considered and the equivalent TE/sub 10/ shunt admittance is computed. Numerical results are also given for lossy X-band cavity resonators with circular coupling holes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Temperature is as important as cavity size in controlling spontaneous emission

We present a simple and general derivation for a quality function describing the spontaneous emission rate in a cavity with finite wall conductivity. Our main finding is the importance of wall temperature, and therefore electron scattering rate, for controlling the spontaneous emission process. It is as effective as changing the geometry of the cavity.

Effect of contact resistance on steady MHD flows through circular pipes having constant conductivity and finite wall thickness

The steady flow of viscous, electrically conducting liquids through circular pipes having finite wall thickness and conductivity under an applied uniform transverse magnetic field is considered. A uniform contact resistance at the solid/liquid interface is taken into account. An exact solution and its numerical calculations are presented.

Magnetic Pressure Drop and Heat Transfer of Liquid Metal Flow in Annular Channel under Transverse Magnetic Field

Analytical solutions of the magnetic pressure drop and the heat transfer coefficient were obtained for liquid metal flow in an annular channel with perfectly conducting walls under transverse magnetic field. Numerical calculations of the magnetic pressure drop and the heat transfer coefficient were also conducted for liquid metal flow in an annular channel with finite wall conductivity under transverse magnetic field. It was assumed in the analysis and the numerical calculations that the flow was fully laminarized due to the effect of strong magnetic field and the velocity and temperature fields were fully developed. It became clear from the results of numerical calculations that the Poiseuille number increased with the Hartmann number and the wall conductivity numbers, and that the Nusselt numbers at 0 and π from the direction of magnetic field were lower than the average Nusselt number, but higher at π/2. The Poiseuille number and the Nusselt number obtained by the numerical calculations for large value...

Magnetic pressure drop and heat transfer of liquid metal flow in annular channel under transverse magnetic field.

Analytical solutions of the magnetic pressure drop and the heat transfer coefficient were obtained for liquid metal flow in an annular channel with perfectly conducting walls under transverse magnetic field. Numerical calculations of the magnetic pressure drop and the heat transfer coefficient were also conducted for liquid metal flow in an annular channel with finite wall conductivity under transverse magnetic field. It was assumed in the analysis and the numerical calculations that the flow was fully laminarized due to the effect of strong magnetic field and the velocity and temperature fields were fully developed. It became clear from the results of numerical calculations that the Poiseuille number increased with the Hartmann number and the wall conductivity numbers, and that the Nusselt numbers at 0 and π from the direction of magnetic field were lower than the average Nusselt number, but higher at π/2. The Poiseuille number and the Nusselt number obtained by the numerical calculations for large values of the wall conductivity numbers almost agreed with the analytical solutions for the case of walls with infinite conductivity.

Equilibrium of a high-current electron ring in a modified-betatron accelerator

The dynamics of an ultrahigh-current electron ring in a modified-betatron configuration is addressed. This study includes analytical and numerical results for both ‘‘cold’’ and ‘‘hot’’ rings. It has been found that the walls surrounding the ring and toroidal effects play a very important role in the dynamics of the ring, even when the wall conductivity is infinite. For finite wall conductivity, the diffusion of the ring’s self-magnetic field profoundly impacts its dynamics and in general the equilibrium could be lost if means are not provided to compensate for this effect. In addition, it has been found that the toroidal-field grad B drift is not important, except when the bounce frequency is very small. The general conclusion of these studies is that equilibrium states of ultrahigh-current rings in modified-betatron configuration exist over a wide range of parameters. These states are accessible and within the reach of existing pulsed power technology.

Stabilization of axially symmetric magnetohydrodynamic modes with wall and conductor arrays

A straight, incompressible plasma of elliptical cross-section and constant current density is examined for stability against vertical displacement. This mode.is unstable for any ellipticity in the absence of walls. A system enclosing the core plasma and surrounding vacuum, consisting of a thin resistive wall and a regular conductor array, simulates the vacuum vessel and coils used to contain and generate the plasma. The effect on stability of the finite wall and coil conductivity and their locations are examined and discussed. Criteria for the virtual stabilization of axially symmetric instabilities are given.

Determination of the electrodynamic and thermal fluctuation characteristics of a biconical cavity

A method is proposed for the design of a biconical cavity with finite wall conductivity. The quality of the resonance volume, the temperature field in its walls, and also the level of natural fluctuational thermal radiation are determined.