Eden Sorolla

An Analytical Model to Evaluate the Radiated Power Spectrum of a Multipactor Discharge in a Parallel-Plate Region

This paper is aimed at studying the electromagnetic radiation pattern of a multipactor discharge occurring in a parallel-plate waveguide. The proposed method is based on the Fourier expansion of the multipactor current in terms of time-harmonic currents radiating in the parallel-plate region. Classical radiation theory combined with the frequency domain Greens function of the problem allows the calculation of both the electric and the magnetic radiated fields. A novel analytical formula for the total radiated power of each multipactor harmonic has been derived. This formula is suitable for predicting multipactor with the third-harmonic technique. The proposed formulation has been successfully tested with a particle-in-cell code.

Multipactor saturation in parallel-plate waveguides

The saturation stage of a multipactor discharge is considered of interest, since it can guide towards a criterion to assess the multipactor onset. The electron cloud under multipactor regime within a parallel-plate waveguide is modeled by a thin continuous distribution of charge and the equations of motion are calculated taking into account the space charge effects. The saturation is identified by the interaction of the electron cloud with its image charge. The stability of the electron population growth is analyzed and two mechanisms of saturation to explain the steady-state multipactor for voltages near above the threshold onset are identified. The impact energy in the collision against the metal plates decreases during the electron population growth due to the attraction of the electron sheet on the image through the initial plate. When this growth remains stable till the impact energy reaches the first cross-over point, the electron surface density tends to a constant value. When the stability is brok...

Space charge effects for multipactor in coaxial lines

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.

Algorithm to Calculate a Large Number of Roots of the Cross-Product of Bessel Functions

This paper describes an algorithm to calculate a large number of roots of the cross-product of Bessel functions and of their first derivatives. The algorithm initially finds the roots of the zeroth order using an auxiliary function that exhibits the same roots as the original cross-products but with better behavior for numerical root search with the Newton–Raphson algorithm. In order to find the roots for higher orders, the algorithm follows a pyramidal scheme using the interlacing property of the cross-product of Bessel functions. The algorithm shows globally convergent behavior for a large range of values of the argument and of the order of the Bessel functions. The roots can be computed to any precision, limited only by the computer implementation, and the convergence is attained in six iterations per root in average, showing a much better performance than previous works for the calculation of these roots.

Globally convergent algorithm to find the zeros of the cross-product of Bessel functions

This paper shows the construction of an algorithm to calculate the roots of both, the cross-product of Bessel functions respectively of their first derivatives. The algorithm has shown globally convergent behavior for a large range of values of the argument and of the order of the Bessel functions with the desired accuracy to machine precision.

N × N coupling matrix synthesis of dissipative microwave filters

In this communication, the coupling matrix synthesis of dissipative microwave filters is analyzed and compared to the synthesis of lossless filters. A modified definition of the vector matrix product allows using the same synthesis procedure in both cases. The constraint conditions to obtain a symmetric coupling matrix are also presented in the communication. Finally, a synthesis example is presented to show how the proposed method is used.

Microwave gas breakdown in elliptical waveguides

This paper analyzes the microwave gas discharge within elliptical waveguides excited by the fundamental mode. The Rayleigh-Ritz method has been applied to solve the continuity equation. The eigenvalue problem defined by the breakdown condition has been solved and the effective diffusion length of the elliptical waveguide has been calculated, what is used to find the corona threshold. This paper extends the microwave breakdown model developed for circular waveguides and shows the better corona withstanding capabilities of elliptical waveguides. The corona breakdown electric field threshold obtained with the variational method has been compared with the one calculated with the Finite Elements Method, showing excellent agreement.

New multipactor dynamics in presence of dielectrics

A new multipactor saturation mechanism is presented for high power microwave devices in the presence of dielectrics. Recent measures have shown that the positive charge deposited on a dielectric as a consequence of the secondary electron emission causes the reduction of its secondary electron yield. This work shows a new multipactor dynamics within a partially filled parallel-plate waveguide where both the decrease of the secondary electron yield with the charge on the dielectric and the subsequent electrostatic field produced are taken into account. The results obtained show that these two mechanisms predict the multipactor saturation as well as some differences with the classical resonance theory when charged dielectrics come into play.

Modeling microwave/electron-cloud interaction

Starting from the separate codes BI-RME and ECLOUD or PyECLOUD, we are developing a novel joint simulation tool, which models the combined effect of a charged particle beam and of microwaves on an electron cloud. Possible applications include the degradation of microwave transmission in tele-communication satellites by electron clouds; the microwave-transmission tecchniques being used in particle accelerators for the purpose of electroncloud diagnostics; the microwave emission by the electron cloud itself in the presence of a magnetic field; and the possible suppression of electron-cloud formation in an accelerator by injecting microwaves of suitable amplitude and frequency. A few early simulation results are presented.

Modelling the interaction of electron clouds and microwaves

This paper deals with the interaction of electron clouds with microwaves inside beam-pipes like the one of the LHC in CERN. The details of the model and recent results are presented during the conference.