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The aim of this article is to establish a general and practical analytical model of the one-sided multipactor on a dielectric of a metal surface and analyze the resonant multipactor effect for the recent growing interest in spacecrafts. A theoretical multipactor model involving a normal static electric field, a radio frequency (RF) electric field with both tangential and normal components, and the influence of the desorption gas is proposed. The kinetic properties and the resonant condition of the electron are studied by analytical calculations. The results show that the transit time of the electron decreases with the increase in the normal static electric field and the pressure of the desorption gas. The emission phase of the electron is the paramount factor that has a direct influence on the occurrence of the resonant multipactor. If the resonant multipactor effect could appear, the emission phase of the electron should be larger than a critical phase, and the ratio between the amplitude of the normal component of the RF electric field and the normal static electric field should be larger than a specific value as well.

RF window which serves as a barrier between the vacuum and air sides is a very important device for RF cavity of cyclotron. But the performances of a basic RF window are not good in impedance matching characteristics and service life. In this paper, two kinds of RF window are developed to improve performances from three candidate designs as impedance matching optimization, thermal consideration during RF operation, and multipactor effect analysis. The multiple comparisons indicate that one of the designed RF windows is far better than the others, and a low-power test has verified its impedance matching characteristic. This optimal RF window may be widely used in other low energy cyclotron and similar devices.

[EN] The objective of this paper is to advance the state of the art in the characterization of the multipactor effect in dielectric materials. The materials studied are the most commonly used dielectrics in space applications, namely, Alumina, Rexolite, Rogers RT5870, Rohacell, Teflon, and Ultem 1000. In this paper, a new family of coaxial waveguide components, covering the L- and S-bands, with a wideband, low-pass response has been designed, and six different prototypes have been specifically optimized and manufactured. The six prototypes have then been used to simulate and measure the multipactor breakdown susceptibility charts for the six dielectric materials investigated. Finally, the simulation results are compared with the results of the measurement campaign indicating good agreement., This work was supported in part by the European Space Agency through Research Project "Novel Investigation in Multipactor Effect in Ferrite and Other Dielectrics Used in High Power RF Space Hardware" under Grant AO 1-7551/13/NL/GLC and in part by MINECO (Spanish Government) through Research and Development Project under Grant TEC2016-75934-C4-1-R. This paper is an expanded version from the IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes IMWS-AMP 2017, Pavia, Italy, September 20-22, 2017.

International audience; Characterized by a very fast growth of the electron population in vacuum of Radio-Frequency (RF) devices, the multipactor effect has been widely studied during the past decades. As it limits the transmitted RF power and may degrade RF devices, its understanding is primordial. Multipactor simulation tools give accurate results in the simplest cases, but are less accurate for advanced configurations: complex geometries, dielectric materials, presence of magnetic fields, etc. In such cases, an accurate modelling of the electron emission phenomena becomes essential. We extended a one-dimension electron emission (EE) model to three dimensions. The obtained model is compared to measured electron emission yields. The impact of this new model on the simulated multipactor threshold of parallel plane wave-guide is also investigated.

The aim of this paper is the study of the RF multipactor breakdown in coaxial transmission lines excited by a single carrier with a digitally modulated signal. Employing an in-house developed code, numerical simulations are performed to determine the RF multipactor voltage threshold for several digitally modulated signals under different modulations schemes: quadrature phase-shift keying, 16-quadrature amplitude modulation, 16-amplitude and phase-shift keying, and 32-amplitude and phase-shift keying. Moreover, a coarse method based on the envelope integration to determine the RF multipactor voltage threshold when involving arbitrary digital modulations is also presented. These results are also compared with the 20-gap-crossing rule used in the space standard document ECSS-E20-1A. In order to validate the theoretical results, a test campaign was performed for realistic modulated signals, finding good agreement between theoretical predictions and experimental data., This work was supported in part by the European Space Agency through the EXPRO Project entitled Development of a Software Tool for the Study of RF Breakdown for Realistic Scenarios: Multicarrier and Modulated Signals under Contract 4000111147/14/NL/GLC and in part by the European High RF Power Space Laboratory of European Space Agency and Val Space Consortium for contributing with its installations Laboratory through the European Regional Development Fund, A way of Making Europe. The review of this paper was arranged by Editor M. Thumm.

The multipactor effect is a discharge phenomenon which may occur when secondary electron emission (SEE) is in resonance with an electric field under certain vacuum conditions [1]. Liberated electrons will oscillate between two surfaces driven by a radio frequency (RF) field; this discharge cultivates and sustains itself by SEE through reoccurring impacts with the surface. This can lead to deterioration of vacuum RF electronics' performance [2]. To suppress the multipactor effect, the secondary electron yield (SEY) must be reduced.

An experimental setup was designed and implemented for the study of the multipactor effect in a rectangular waveguide under high vacuum. The experiment and test piece were constructed using WR 284 waveguide sections operating at S- Band frequencies. Multipactor effects are to be detected via an Electron Multiplier Tube (EMT). The test setup includes sections of standard WR 284 waveguide which will be in line with a custom test piece. Design of the test setup incorporates a standard piece of waveguide with a custom steel collar which can be used to insert different tapers, and even periodic structures into the hollowed out broadside wall. A solid state RF transmitter with 2.8 kW peak power and a center frequency of 2.85 GHz is used to inject an RF signal into the test section.

[EN] Secondary electron emission has an important role on the triggering of the multipactor effect; therefore, its study and characterization are essential in radio-frequency waveguide applications. In this paper, we propose a theoretical model, based on equivalent circuit models, to properly understand charging and discharging processes that occur in dielectric samples under electron irradiation for secondary electron emission characterization. Experimental results obtained for Pt, Si, GaS, and Teflon samples are presented to verify the accuracy of the proposed model. Good agreement between theory and experiments has been found., The authors would like to thank the European High Power Space Materials Laboratory for its contribution-a laboratory funded by the European Regional Development Fund-a way of making Europe. Many thanks to the University of Valencia (Spain) for supporting this research activity with the internal program "Assistance for temporary stays of invited researchers within the framework of the Subprogramme Attraction of Talent 2015".

Multipactor effect in a coaxial transmission line was studied theoretically and numerically. The results show that significant radio frequency breakdown likely originates from gas desorption in the material and further gas ionization induced by electrons. The multipactor effect using different surface gas pressures was analyzed with particle-in-cell simulations. The simulation results indicate that plasma originating from locally desorbed gas causes significant power reflection and absorption. At the same time, plasma electrons play a more significant role than plasma ions in the multipactor process. A numerical method such as the one used here can thus be used to predict whether radio frequency breakdown can be caused by the multipactor effect.

The aim of this paper is the analysis of the multipactor effect in a parallel-plate waveguide when a ferrite slab, transversally magnetized by a static magnetic field parallel to the waveguide walls, is present. Employing an in-house developed code, numerical simulations are performed to predict the multipactor radio frequency voltage threshold in such a ferrite-loaded waveguide. Variations of the ferrite magnetization field strength and the ferrite slab height are analyzed. Effective electron trajectories are also shown for a better understanding of the breakdown phenomenon, finding different multipactor regimes.

In this paper, the multipactor RF breakdown in a parallel-plate waveguide partially filled with a ferrite slab magnetized normal to the metallic plates is studied. An external magnetic field is applied along the vertical direction between the plates in order to magnetize the ferrite. Numerical simulations using an in-house 3-D code are carried out to obtain the multipactor RF voltage threshold in this kind of structures. The presented results show that the multipactor RF voltage threshold at certain frequencies becomes considerably lower than for the corresponding classical metallic parallel-plate waveguide with the same vacuum gap, This work was supported in part by the European Space Agency under Novel Investigation in Multipactor Effect in Ferrite and other Dielectrics used in high power RF Space Hardware under Contract AO 1-7551/13/NL/GLC, in part by the Spanish Government under Coordinated R&D Project TEC2013- 47037-5-R and Project TEC2014-55463-C3-3-P, and in part by the European Commission (ERDF). The review of this paper was arranged by Editor R. Carter.

Multipactor discharges in waveguides with wedge- shaped cross section are studied both analytically and by means of numerical simulations. It is shown that similar to the case of a rectangular waveguide, a trapped electron trajectory is possible in a wedge-shaped waveguide; however, this trajectory is unstable with respect to small deviations of launch time and initial position of the electrons. Numerical simulations have been carried out taking into account a spread of the electron initial velocity and the action of the radio frequency magnetic field on the electron motion. The simulation results show that growth of the multipactor avalanche is possible in the wedge-shaped waveguide; however, the multipactor threshold in terms of the transmitted power is higher than for the rectangular waveguide with the same propagation constant and cross-section area.

The main goal of this letter is the analysis of the multipactor effect within a coaxial waveguide excited by an RF pulsed signal. The variation of the multipactor RF voltage thresholdwiththe ON interval length of the pulse has been analyzed. To reach this aim, an in-house multipactor simulation code based on the Monte-Carlo algorithm has been implemented. The numerical simulations show that the multipactor RF voltage threshold increases as the ON pulse interval diminishes. In addition, an experiment was carried out to validate the proposed theoretical model, and demonstrating the excellent agreement between the theory and the experimental data. Finally, the results are compared with the 20-gap-crossing rule used in the space standard document (ECSS-E20-1A)., The work of O. Monerris Belda was supported by the European Regional Development Fund. The review of this letter was arranged by Editor A. Ortiz-Conde.

Within the framework of a project sponsored by the European Space Agency (ESA), we have developed a software tool to predict the occurrence of multipactor discharge in a simple radio frequency (RF) device modeled as parallel plates. The tool uses a micro-level explicit representation of the electrons (i.e., each electron in the system is modeled separately), and includes a detailed Monte Carlo model of the secondary electron emission process in the plates. Materials secondary emission yield (SEY) is described using either the usual parameter set (E/sub 1/, E/sub 2/, and /spl sigma//sub max/), or a more detailed model, where the contributions due to true secondary, backscattered or elastically reflected electrons are given their own sets of parameters, together with additional parameters for the angle dependence. The simulator has been validated using experimental data gathered at ESA and the Universidad Auto/spl acute/noma de Madrid, Madrid, Spain. The simulator helped in the selection of material coatings for the mitigation of Multipactor effect in RF transmission lines on-board satellite payloads.

The main goal of this letter is the analysis of the multipactor effect within a coaxial waveguide structure when an external axial dc magnetic field is applied. We have designed and manufactured a coaxial waveguide sample that has been immersed within a long solenoid. Numerical and experimental results confirm a significant change in the RF breakdown behavior with regard to the case without the axial dc magnetic field, as well as the existence of single- and double-surface multipactor regimes. Good agreement between theory and experimental data has been found., Manuscript received January 23, 2012; accepted January 31, 2012. Date of publication March 16, 2012; date of current version April 20, 2012. This work was supported in part by the Spanish Government through R&D project TEC2010-21520-C04-01. The review of this letter was arranged by Editor E. A. Gutierrez-D.

Multipactor effect is a resonant avalanche of secondary electrons induced by an RF electromagnetic field, which endangers high-power payloads on satellites and particle accelerator structures. The main goal of this letter is to present a multimodal network characterization of a multipactor discharge occurring in a bounded waveguide region. This will allow to perform a rigorous analysis of a complete passive component considering the presence of a discharge. In order to verify the present formulation, we have measured the power spectrum generated by a multipactor event excited in a simple microwave circuit based on rectangular waveguides, which has been compared with the theoretical results, obtaining good agreement., This work was supported by ESA/ESTEC through the NPI program and through the contract 20841/08/NL/GLC.

The multipactor effect is a constraining phenomenon in the design of RF components. Due to an increasing number of channels and power levels for multicarrier signals, specific requirements of design must be taken into account in order to prevent the multipactor effect. The current methods of analysis are based on the Hatch and Williams diagrams, which provide the multipaction threshold voltage for a parallel plate geometry as a function of the frequency gap product. However, whereas experimental results have shown good correlation with the theoretical charts for the parallel plate geometry, discrepancies have been found for complex geometries such as irises.

Based on an improved multipactor dynamic model, the multipactor phenomenon on a dielectric surface existing longitudinal RF electric field was simulated using Monte Carlo method. The temporal evolution images of the multipactor discharge were investigated. The power deposited on the dielectric surface by the multipactor was also obtained in terms of an S-band RF dielectric window. The results show that, the longitudinal RF electric field may intensify the single-surface multipactor effect, which is likely to result in dielectric crack and detrimental to RF transmission.

A numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides is presented in this paper. The computation of electromagnetic fields is based on the boundary integral–resonant mode expansion method, which provides the modal chart of hollow waveguides with any arbitrary cross section. The advantage of using wedge-shaped waveguides with respect to conventional rectangular ones is the deviation of the resonant paths of the electrons toward regions with lower voltages, thus reducing the probability of multipactor threshold for certain input power. To validate this method, our results have been compared with simulations from previous theoretical studies. Once the simulation tool is validated, it is used to predict the multipactor threshold of wedge-shaped waveguides with different symmetric inclination angles of their horizontal plates. Finally, susceptibility curves as the ones already available for rectangular waveguides are presented. These charts are useful for designing innovative waveguide geometries with improved multipactor-free working power ranges. This work was supported by the Ministerio de Ciencia e Innovación, Spain, under Research Project TEC2007-67630-C03-01/TCM.

In this paper, we present a numerical model for predicting the multipactor breakdown effect in coaxial transmission lines. To validate this method, we have first compared our results with numerical data from other theoretical studies and with experimental measurements. Then, we have investigated the multipactor phenomena in coaxial lines considering three kinds of RF signals: traveling, standing, and mixed waves. From this paper, we conclude that different breakdown thresholds are obtained for any of the considered RF excitations under high values of frequency x gap product. This effect is attributed to the existence of regions with zero (or very low levels) electric field amplitude in the propagation direction, where electrons are absorbed before the discharge occurs., This work was supported in part by Ministerio de Educacion y Ciencia, Spanish Government, under the coordinated Research Project TEC 2007/67630-CO3-01 and in part by Generalitat Valenciana (Spain) under Projects IIARCO/2004/20, IIARCO/2004/2 1, and IIARCO/2004/22.

This is the author’s version of a work that was accepted for publication in Simulation Modelling Practice and Theory. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Simulation Modelling Practice and Theory, 16, 9, (2008) http://dx.doi.org/10.1016/j.simpat.2008.08.002, In this paper we present two software tools for the simulation of electron multiplication processes in radio frequency (RF) waveguides. The electric discharges are caused by the multiplication of a small initial number of electrons. These are accelerated by the RF field and produce new electrons either by collisions with the walls of the waveguide (ripping new electrons from them), or by ionization of the neutral atoms of a gas inside the device. MEST allows simulating the Multipactor effect, a discharge produced in vacuum and generated by the collision of the electrons with the walls. CEST simulates the discharge when in addition a neutral gas is present in the waveguide, at pressures lower than ground levels (often denominated Corona discharge). The main characteristic of both tools is that they implement individual-based, microscopic models, where every electron is individually represented and tracked. In the case of MEST, the simulation is discrete-event, as the trajectory of each electron can be computed analytically. In CEST we use a hybrid simulation approach. The trajectory of each electron is governed by the Langevin stochastic differential equations that take into account a deterministic RF electric force and the random interaction with the neutral atom background. In addition, wall and ionizing collisions are modelled as discrete events. The tools allow performing batches of simulations with different wall coating materials and gases, and have produced results in good agreement with experimental and theoretical data. The different output forms generated at run-time have proven to be very useful in order to analyze the different discharge processes. The tools are valuable for the selection of the most promising coating materials for the construction of the waveguide, as well as for the identification of safe operating parameters., Work sponsored by the ESA, TRP activity program 17025/03/NL/EC: Surface Treatment and Coating.

To evaluate the Dielectric-Loaded Accelerating (DLA) structure as a potential alternative high-gradient accelerator, a series of high power RF experiments have been carried-out by a joint Argonne National Laboratory/Naval Research Laboratory program. We have tested DLA structures loaded with two different ceramic materials, alumina and Mg x Ca 1-x TiO 3 . For the alumina tube, we concentrated on the study of the multipactor effect in the DLA structures under the high power rf field. In the Mg x Ca 1-x TiO 3 tests, we mainly investigate the local field enhancement that caused dielectric joint breakdown of the DLA structures. In both cases, physical models have been set up, and the corresponding engineering solutions are being implemented.

Summary form only given. Multipactor effect is a discharge phenomenon, which may occur in radio frequency circuits on board spacecraft. In an RF voltage breakdown, the electron generation mechanism is based on secondary electron emission from the conductor walls. Several approaches have been followed over the last few decades to eliminate the risk of discharge on board spacecraft. In spite of the efforts made, the threat of RF voltage breakdown is still a serious issue when designing and manufacturing RF components for space applications. The increasing demand of higher RF power amplifiers on board the payloads implies more difficulties to RF engineers when designing microwave components for space applications. Multipactor effect can cause long term erosion of component surfaces, resulting in degraded performance and even total component failure. Over the last 20 years the European Space Agency (ESA) has investigated this phenomena resulting in a significant improvement in designing, manufacturing and testing RF high power devices. However, the problem is far from being solved and the threat of an on-board RF discharge must be eliminated. Novel research activities will be implemented in ESA's research programs over the next few years to eradicate the risk of RF breakdown in future payloads. This paper shows some of these research activities and describes the test capabilities used by ESA to provide diagnostic and test support to European space programs and industry.

This paper presents the electrostatic PIC-MCC model for simulating the breakdown of dielectric surfaces illuminated by high-power microwave，and the processes of multipactor and collisional ionization in the case of vacuum and different pressures are simulated by using the code developed by ourselves. The numerical results show that the multipactor effect is the main source of electrons，and the number of the electrons oscillates in the time domain at twice the rf frequency in the case of vacuum and low pressures. In the case of high pressure，the collisional ionization is the main source of electrons.

International audience; The multipactor effect is characterized by a very fast growth of the electronic population in vacuum Radio-Frequency (RF) devices. As it limits the transmitted RF power and can severely damage RF systems, multipactor has been subject to an extensive research for the past decades. Simulation tools are relatively accurate for the simplest cases, but less reliable for advanced problems: presence of an external magnetic field, complex geometry, time or temperature-dependent materials properties, etc. A code simulating the multipactor within an infinite parallel-plate waveguide with a dielectric coating on the bottom plate has been developed. The inclusion of a realistic energy distribution for the secondary electrons and a new emission model shows a strong dependence of the multipactor threshold on the metal work function and on the dielectric electric charge.