Coaxial cable

Coaxial cable, or coax (pronounced 'koʊ.æks), is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric (insulating material); many coaxial cables also have a protective outer sheath or jacket. The term coaxial refers to the inner conductor and the outer shield sharing a geometric axis. Coaxial cable is a type of transmission line, used to carry high-frequency electrical signals with low losses. It is used in such applications as telephone trunk lines, broadband internet networking cables, high-speed computer data busses, cable television signals, and connecting radio transmitters and receivers to their antennas. It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line. Coaxial cable was used in the first (1858) and following tran

Modeling of Long-Term Multipactor Evolution in Microwave Components Including Dielectric Layers

Apostolos Sounas

Multipactor is a resonant vacuum discharge occurring in microwave components of satellite systems as well as in particle accelerators. Due to its undesirable effects, multipactor analysis constitutes a mandatory step in the design of modern satellite components and in performance studies of particle accelerators. To this end, the development of computational techniques for multipactor prediction attracts intense interest in the scientific community. The phenomenon evolves in two distinct phases: first, a fast growth of the electron population and, second, a steady state during which the population reaches a saturation level and remains almost constant. State-of-the-art computational models focus on the precise prediction of the initial multipactor phase, which defines whether the discharge occurs or not. However, a clear overview of the phenomenon also requires the analysis of the longterm multipactor evolution. Due to the high complexity introduced by considering saturation mechanisms, long-term multipactor evolution remains still unclear for many configurations of highly practical importance. Such a case is the multipactor analysis in the presence of dielectrics, a case dealt within this thesis. Motivated by the challenging nature of analyzing the multipactor steady state, this work aims to provide its own contribution to the modeling and the analysis of long-term multipactor evolution. For this, a sophisticated computational tool has been developed for the full-3D multipactor analysis, taking into account saturation mechanisms. In order to get a fast overview of the phenomenon, a generalized single-electron model has been developed which allows a multipactor analysis in any configuration with unidirectionallike electric field. Based on this 1D model, qualitative studies considering the effect of lowenergy electron collisions and of single-sided multipactor in non-uniform coaxial fields have been performed. As a further step, a multiple-particle, full-3D model able to consider the stochastic nature of the secondary emission phenomenon has been developed. The singleelectron model nicely supplements the robust 3D analysis by providing fast estimations for the most likely cases in which multipactor occurs. Saturation mechanisms have been considered, too, for both 1D and 3D approximations. Taking into account the induced charges on the metallic boundaries, a fast analysis of longterm multipactor is provided by the 1D model for the parallel plate and coaxial line cases. The saturation study is boosted in the 3D analysis by taking into account the mutual Coulomb interaction between particles. The developed multipactor model has been properly adapted in order to study long-term multipactor in the case of dielectric-loaded waveguides. Space charge effects as well as the effect of the surface charge developed on the dielectric layer have been both considered in the analysis. Particularly, in order to efficiently take into account the effect of the induced charges, a novel image method for the evaluation of the 3D Green function in multi-layered media has been developed. For the first time, a saturation steady state is identified in parallel plates loaded with a dielectric layer.

EPFL2015

Space charge effects for multipactor in coaxial lines

Michael Mattes, Francisco Edén Sorolla Rosario, Apostolos Sounas

Multipactor is a hazardous vacuum discharge produced by secondary electron emission within microwave devices of particle accelerators and telecommunication satellites. This work analyzes the dynamics of the multipactor discharge within a coaxial line for the mono-energetic electron emission model taking into account the space charge effects. The steady-state is predicted by the proposed model and an analytical expression for the maximum number of electrons released by the discharge presented. This could help to link simulations to experiments and define a multipactor onset criterion.

American Institute of Physics2015

Modeling of Long-Term Multipactor Evolution in Microwave Components Including Dielectric Layers

Apostolos Sounas

EPFL2015

Modeling of Long-Term Multipactor Evolution in Microwave Components Including Dielectric Layers

Space charge effects for multipactor in coaxial lines

Analysis of Multipactor Effect in Coaxial Lines

Space charge effects for multipactor in coaxial lines

Analysis of Multipactor Effect in Coaxial Lines

Modeling of Long-Term Multipactor Evolution in Microwave Components Including Dielectric Layers