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[ES] En los últimos años han proliferado los nuevos sistemas de satélites, sobre todo las grandes constelaciones en las órbitas terrestres bajas. Casi todos los satélites transmiten señales digitales con diversas modulaciones y niveles de potencia. Y no sólo eso, el modelo de negocio exige un rápido despliegue de los satélites, lo que impone enormes restricciones a los proveedores de equipos de carga útil de microondas. Un área de riesgo clave para estos equipos sigue siendo la avería del multipactor bajo niveles de potencia de moderados a altos. Debido a la aleatoriedad inherente al fenómeno multipactor, los clientes tienden a añadir márgenes de diseño adicionales para los componentes de microondas de alta potencia. Esto se traduce en costes más elevados, dispositivos más voluminosos y más tiempo para las pruebas. A partir de la experiencia personal realizando ensayos de multipactor, la principal motivación del trabajo descrito en la tesis ha sido emprender una revisión exhaustiva de este fenómeno y desarrollar capacidades de ensayo multipactor de vanguardia. Proporcionar medios para la prueba rápida de multipactores bajo una variedad de señales moduladas de banda ancha. La tesis demuestra que las modulaciones analógicas y digitales tienen un impacto significativo en el umbral multipactor. También se analizan los regímenes multipactor a corto y largo plazo, regímenes que, en algunos casos, presentan umbrales multipactor muy diferentes para el mismo hueco crítico. La necesidad de reducir el peso de la carga útil de microondas convierte a la multiportadora en una excelente opción para los diseñadores. Al encaminar varias señales a través del mismo dispositivo, el peso de la carga útil se reduce drásticamente. Las soluciones comerciales para pruebas multicarrier no son adecuadas debido a los altos niveles de potencia requeridos. Se presentan varias estrategias para implementar bancos de pruebas multiportadora con parámetros controlables. Los resultados demuestran que la señal generada es precisa y estable en el tiempo. Por último, se propone un novedoso sistema de detección de multipactores para hacer frente a la detección de multipactores cuando se utilizan señales moduladas y multiportadora de cualquier ancho de banda. Este método tiene la misma sensibilidad que el conocido anulador de microondas para señales de onda continua y la supera para señales moduladas. El procesamiento digital de señales utilizado para detectar los patrones multipactor proporciona un método de detección totalmente autónomo., [CA] En els darrers anys han proliferat els nous sistemes de satèl·lits, sobretot les grans constel·lacions a les òrbites terrestres baixes. Gairebé tots els satèl·lits transmetten dades digitals amb diverses modulacions i nivells de potència. I no només això, el model de negoci exigeix un ràpid desplegament dels satèl·lits, cosa que imposa enormes restriccions als proveïdors de càrrega útil de microones. Una àrea de risc clau per a aquests equips continua sent la descarrega de multipactor sota nivells de potència de moderats a alts. A causa de l'aleatorietat inherent al fenomen multipactor, els clients tendeixen a afegir marges de disseny addicionals per als components de microones d'alta potència. Això es tradueix en costos més elevats, dispositius més voluminosos i més temps per a les proves. A partir de l'experiència personal realitzant assajos de multipactor, la motivació principal del treball descrit a la tesi ha estat emprendre una revisió exhaustiva d'aquest fenomen i desenvolupar capacitats d'assaig multipactor d'avantguarda. Proporcionar mitjans per a la prova ràpida de multipactors sota una varietat de senyals modulats de banda ampla. La tesi demostra que les modulacions analògiques i digitals tenen un impacte significatiu al llindar multipactor. També s'analitzen els règims multipactor a curt i llarg termini, règims que, en alguns casos, presenten llindars multipactor molt diferents per al buit crític mateix. La necessitat de reduir el pes de la càrrega útil de microones fa de la transmissií multiportadora en una excel·lent opció per als dissenyadors. Encaminant diverses senyals a través del mateix dispositiu, el pes de la càrrega útil es redueix dràsticament. Les solucions comercials per a proves multicarrier no són adequades a causa dels alts nivells de potència requerits. Es presenten diverses estratègies per implementar bancs de proves multiportadora amb paràmetres controlables. Els resultats demostren que el senyal amb què s'alimenta el dispositiu sotmès a proves és precís i estable en el temps. Finalment, es proposa un nou sistema de detecció de multipactors per fer front a la detecció de multipactors quan s'utilitzen senyals modulats i multiportadors de qualsevol amplada de banda. Aquest mètode té la mateixa sensibilitat que el conegut anul·lador de microones per a senyals d'ona contínua i la supera per a senyals modulats. El processament digital de senyals utilitzat per detectar els patrons multiactor proporciona un mètode de detecció totalment autònom., [EN] In the recent past, there has been a proliferation of new satellite systems, especially the large constellations in the Low Earth Orbits (LEOs). Nearly all satellites now carry digital traffic with a variety of modulations and power levels. Not only that, the business model requires rapid deployment of satellites, putting enormous constraints for the suppliers of microwave payload hardware. A key risk area for such equipment remains the multipactor breakdown under moderate to high power levels. Owing to the inherent randomness of the multipactor phenomenon, customers tend to add extra design margins for the high power microwave components. This results in higher costs, bulkier devices and longer time for testing. Based on personal experience in multipactor testing, the prime motivator for the work described in the thesis has been to undertake a comprehensive review of this phenomenon and develop cutting edge multipactor test capabilities, providing means for the rapid multipactor testing under a variety of wide-band modulated signals. The thesis dissertation shows that analog and digital modulations have a significant impact in the multipactor threshold. The short and long-term multipactor regimes are also analyzed, regimes that, in some cases, have very different multipactor thresholds for the same critical gap. The need to reduce the microwave payload weight by using multicarriers in a single transponder provides an excellent option for designers. By routing several signals through the same device, the payload weight is dramatically reduced. Commercial solutions for multicarrier testing are not suitable because of the high power levels required. Several strategies to implement multipactor test benches with controllable parameters are presented. Results prove that the signal being fed to the device under tests is accurate and stable over time. Finally, a novel multipactor detection system is proposed to cope with multipactor detection when modulated and multicarrier signals of any bandwidth are used. This method has the same sensitivity as the well known microwave nulling for continuous wave signals and surpasses it for modulated signals. The digital signal processing used to detect the multipactor patterns provides a full autonomous detection method.

International audience; In this paper, we study the appearance of the multipactor in a simple system with a bottom plate holding a static potential Vd. We developed a numerical model to compute the evolution of the multipactor threshold as a function of the potential. We identify the nature of the resonant modes that appear at different Vd using resonance theory. Then, we use it to compute the theoretical threshold of the structure. As we use a very simplistic electron emission model to identify the multipactor modes, we compute the threshold in a more realistic configuration in a second step.

[ES] El efecto multipactor es un fenómeno no deseado que ocurre bajo condiciones específicas, como el alto vacío y la presencia de una señal electromagnética de alta potencia, y es causado por los electrones libres que son generados por la emisión secundaria de electrones. Este efecto es relevante para las aplicaciones espaciales, donde las posibles consecuencias oscilan entre el empeoramiento de la calidad de una señal transmitida y el completo fallo del sistema. Para entender cuándo ocurre el efecto multipactor, es necesario medir el número de electrones libres presentes en un dispositivo de radiofrecuencia que se encuentra en las condiciones anteriormente mencionadas. El método tradicional de evaluación de la cantidad de electrones libres involucra una sonda que se inserta en el dispositivo. Dicho método tiene una eficiencia y precisión baja, por lo que es difícil producir resultados precisos. Este proyecto pretende evaluar con precisión el número de electrones libres que se encuentran en un dispositivo RF (un cable coaxial) en un instante dado mediante la polarización del conductor interno y la medida de la corriente generada. Para conseguir esto, van a ser diseñados y probados varios prototipos de un circuito polarizador, utilizando optoacopladores como principal elemento. Posteriormente, el diseño definitivo se fabricará y se evaluará su funcionamiento., [EN] The multipactor effect is an unwanted phenomenon which occurs under specific conditions, such as high vacuum and the presence of a high-power electromagnetic signal, and it is caused by free electrons which are generated due to secondary electron emission. This effect is relevant to space applications, where its possible consequences range from the deterioration of a transmitted signal to a complete breakdown of the system. To understand when the multipactor effect happens, it is necessary to measure the number of free electrons which are present in an RF device in the cited vacuum environment. The traditional method of evaluating the quantity of free electrons involves a probe which is inserted into the device. This method, however, has low efficiency and precision, making it difficult to provide accurate results. This project aims to accurately estimate the number of free electrons located in an RF device (a coaxial cable) at a given time by polarizing its internal conductor and measuring the generated current. To achieve this, several prototypes of a polarization circuit will be designed and tested, using optocouplers as a key component, after which a final design will be manufactured and evaluated.

This work presents a novel low-pass filter based on using dielectric materials, in the critical areas of the structure, to prevent high-power space condition adverse effects, like multipactor breakdown. It is shown that the use of dielectric pieces in the inverters of the filter leads to increased gaps between metallic parts in the irises. In addition, by completely filling up the air space in critical gaps, the multipactor breakdown thresholds can be increased. Moreover, they also lead to a volume reduction, increasing compactness of the structure. To demonstrate the proposed concept, a prototype has been manufactured with an aluminum housing and a Teflon dielectric material, and tested for multipactor effect at ESA-VSC Laboratory. Tests confirmed that the manufactured filter has good electrical performance with cut-off frequency 13.6 GHz, insertion losses 0.32 dB, return losses better than 15 dB, and additionally does not show multipactor breakdown up to the maximum power tested in the experimental facility (5.5 kW). This research work has been financially supported by the Spanish Ministerio de Ciencia e Innovación in the frame of the project “Green an Efficient Technologies for Advanced Telecommunication Systems (GRETAS)” with Ref. TPID2019-103982RB-C42.

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.

This work demonstrates the design of an E-band waveguide duplexer and the fabrication process based on micromachining technology. To make the proposed solution practical, the error tolerance analysis and multipactor effect simulation were carried out. Compared with state-of-art technologies, three distinctive advancements have been achieved: (1) the design of a high-performance E-band duplexer and the corresponding fabrication process based on micromachining technology; (2) the demonstration of the RF performance simulation and the error tolerance analysis of the proposed fabrication process; and (3) the illustration of the multipaction phenomena and the counter measures to inhibit the effect. As such, the proposed portfolio of micromachining fabrication process and suppression scheme of multipaction can offer a practical approach for E-band waveguide duplexers.

[ES] El propósito de la presente tesis es desarrollar una herramienta informática para la predicción del efecto multipactor tanto en líneas de transmisión coaxiales como en guías circulares. Esta herramienta está pensada para ser complementaria de las de diseño asistido por ordenador Computer-Aided Design (CAD) en el caso de dispositivos de comunicaciones a implementar en estas tecnologías de ondas guiadas. En el caso de guías coaxiales, se desarrollará un modelo numérico para la predicción de los umbrales de potencia del fenómeno de multipactor. Este método ha sido validado con medidas experimentales, así como validado con otros estudios teóricos realizados. En este tipo de guía se ha considerado tres tipos de señal de radio frecuencia (RF), la onda incidente, la onda estacionaria pura y las ondas estacionarias en general (combinación de ondas incidente y reflejada de distintas amplitudes). Así pues, se ha analizado y obtenido los umbrales de potencia para cada una de las diferentes señales consideradas y observado los efectos que se producen. En las guías circulares, se ha demostrado en primer lugar la existencia del fenómeno de multipactor bajo la excitación del modo fundamental de la guía circular TE11. El interés en estas guías se debe al amplio uso en la fabricación de componentes pasivos, tanto en cavidades resonantes como el uso de irises que conectan las cavidades, empleados tanto en aceleradores de partículas como en diferentes subsistemas de comunicaciones en satélites. Por tanto, además de observar la existencia del efecto multipactor hemos calculado una carta de susceptibilidad para dicho fenómeno, inicialmente en el caso de que sólo se transmita una única polarización, en concreto la polarización vertical. Una vez hemos demostrado que el efecto multipactor es posible en estas guías circulares, se ha realizado un estudio teniendo en consideración la coexistencia de las dos polarizaciones del modo fundamental TE11. Para una mejor comprensión del fenómeno, se ha analizado inicialmente para órdenes de multipactor más bajos en función de la excentricidad de la elipse de polarización. Prestando especial atención para el caso de la polarización lineal y circular, aunque también se ha analizado otras combinaciones más generales., [CA] El propòsit de la present tesi és desenvolupar una eina informàtica per a la predicció de l'efecte multipactor tant en línies de transmissió coaxials com en guies circulars. Aquesta eina està pensada per a ser complementària de les de disseny assistit per ordinador Computer- Aided Design (CAD) en el cas de dispositius de comunicacions a implementar en aquestes tecnologies d'ones guiades. En el cas de guies coaxials, es desenvoluparà un model numèric per a la predicció dels llindars de potència del fenomen de multipactor. Aquest mètode ha sigut validat amb mesures experimentals, així com validat amb altres estudis teòrics realitzats. En aquesta mena de guia s'ha considerat tres tipus de senyal de ràdio freqüència (RF), l'ona incident, l'ona estacionària pura i les ones estacionàries en general (combinació d'ones incident i reflectida de diferents amplituds). Així doncs, s'ha analitzat i obtingut els llindars de potència per a cadascuna dels diferents senyals considerats i observat els efectes que es produeixen. En les guies circulars, s'ha demostrat en primer lloc l'existència del fenomen de multipactor sota l'excitació de la manera fonamental de la guia circular TE11. L'interés en aquestes guies es deu a l'ampli ús en la fabricació de components passius, tant en cavitats ressonants com l'ús d'irises que connecten les cavitats, emprats tant en acceleradors de partícules com en diferents subsistemes de comunicacions en satèllits. Per tant, a més d'observar l'existència de l'efecte multipactor hem calculat una carta de susceptibilitat per a aquest fenomen, inicialment en el cas que només es transmeta una única polarització, en concret la polarització vertical. Una vegada hem demostrat que l'efecte multipactor és possible en aquestes guies circulars, s'ha realitzat un estudi tenint en consideració la coexistència de les dues polaritzacions de la manera fonamental TE11. Per a una millor comprensió del fenomen, s'ha analitzat inicialment per a ordres de multipactor més baixos en funció de l'excentricitat de l'ellipse de polarització. Prestant especial atenció per al cas de la polarització lineal i circular, encara que també s'ha analitzat altres combinacions més generals., [EN] The main goal of this PhD thesis is to develop a computer tool for the prediction of the multipactor effect, both in coaxial transmission lines and in circular guides. This tool is intended to be complementary to the available Computer-Aided Design (CAD) versions, in particular for the case of communication devices to be implemented in the cited guided wave technologies. In the case of coaxial guides, a numerical model is developed to predict the power thresholds of the multipactor phenomenon. This method has been validated with experimental measurements, as well as with other theoretical studies carried out. In this type of guide, three types of radio frequency (RF) signals have been considered, i.e. the incident wave, the pure standing wave and the standing waves in general (a combination of incident and reflected waves of different amplitudes). Thus, the power thresholds for each of the different signals considered have been analyzed and obtained, and the corresponding effects that occur have been observed. In circular guides, the existence of the multipactor phenomenon under the excitation of the TE11 fundamental mode of the circular guide has been demonstrated first. The interest in these guides is due to their wide use in the manufacture of passive components, both in resonant cavities and within irises that connect the cavities, used both in particle accelerators and in different satellite communications subsystems. Therefore, in addition to observing the existence of the multipactor effect, we have calculated a susceptibility chart for this phenomenon, initially in the case that only a single polarization is transmitted, specifically the vertical polarization. Once we have shown that the multipactor effect is possible in these circular guides, a study has been carried out taking into account the co-existence of the two polarizations of the TE11 fundamental mode. For a better understanding of the phenomenon, it has been initially analyzed for lower multipactor orders as a function of the eccentricity of the polarization ellipse. Special attention has been paid to the case of linear and circular polarization, although other more general combinations have also been analyzed., This work was supported in part by Ministerio de Educación y Ciencia, Spanish Government, under the coordinated Research Project TEC 2007/67630-C03-01 and in part by Generalitat Valenciana (Spain) under Projects IIARC0/2004/20, IIARC0/2004/21 and IIARC0/2004/22. This work has been supported by Ministerio de Ciencia e Innovación, Spanish Government, under Research Project TEC2007-67630-C03-01.

[ES] Las guías de onda con paredes laterales corrugadas (en inglés Groove Gap Waveguides, GGWs) son un prometedor medio de transmisión a emplear en futuras aplicaciones espaciales, pues su fabricación resulta más sencilla tecnológicamente que las clásicas guías de onda rectangular, y son capaces de ofrecer prestaciones similares. Con el objeto de explorar su potencial uso en el entorno espacial (en cargas útiles de comunicaciones por satélite), es necesario estudiar la capacidad de manejo de potencia de las mismas en condiciones de alto vacío (mediante la estimación de la potencia umbral del efecto indeseado conocido como multipactor). En este proyecto, se pretende estudiar el citado efecto multipactor en estas nuevas guías GGWs, haciendo uso de modelos disponibles en programas informáticos comerciales. Para validar estos resultados, se diseñarán también diversos prototipos sencillos de componentes basados en dichas guías (por ejemplo adaptadores de impedancia), y se explorará también su posible fabricación y la posterior realización de medidas (tanto de respuesta eléctrica, como del citado efecto multipactor)., [EN] Groove Gap Waveguides (GGWs) are a promising transmission line to be used in future space applications, since their manufacture is more simple technologically than the classic rectangular waveguides, and are able to offer similar performance. In order to explore their potential use in the space sector (within satellite communications payloads), it is necessary to study their power handling capabilities under high vacuum conditions (i.e. the estimation of the threshold power of the undesirable effect known as multipactor). This final year work aims to study the aforementioned multipactor effect in these new GGWs, making use of models available in commercial software tools. To validate these results, several prototypes of simple components based on GGWs (for example impedance matching networks) will be designed. Their manufacture and the realization of measurements (of the electric response and the aforementioned multipactor effect) will be also explored.

Suppressing the harmful multipactor effect by, for instance, reducing secondary electron yield (SEY) is crucial in the design of RF space technologies. Therefore, improving fundamental understanding of how structural and electronic features of materials affect the SEY is necessary. In this benchmark work, we use density functional theory calculated properties to simulate, via Monte Carlo method, the SEY of simple metals copper and silver. As in these simulations the dielectric property i.e. the energy and momentum dependent energy loss function plays a major role, we focus our study on the computational procedures necessary to obtain reliable first principles data.

A planar test cell was designed and implemented to observe the multipactor effect in waveguide structures. This plug and play device allows for multiple geometries to be machined and easily replaced within the test structure. A direct detection method was used to observe the multipactor effect while the upper and lower thresholds were measured for a 2.1 mm gap at 2.85 GHz. While there is an obvious lower limit to multipactor (2 kW), there was no observable upper limit even at powers over 200 kW. This is attributed to the transverse electric field distribution in the dominant TE 10 mode which is not taken into account in most multipactor theoretical models.

A well-documented effect of cosmic and solar radiation on TWTs used in satellites is the production of secondary electrons from the bombardment of incident particles and the resultant cascade and growth of these secondaries, which in turn leads to tube failure. Our work focuses on numerical simulation of gap closure in coaxial geometry due to the multipactor effect. The secondary electron yield (SEY) is dependent not just on material properties, but also on the geometric properties of the surface and of the tube, as well as the size of the interaction space and the operating frequency. We then focus on particle-in-cell simulations of a coaxial testbed that will generate data to develop advanced models that incorporate patterned surfaces, new source geometries, and new materials developed to suppress SEY. This paper presents preliminary results from our coaxial PIC simulations utilizing the CST Design Studio and Spark3D codes.

We have studied nanometric high aspect ratio Ag nanopillar coatings exhibiting reduced secondary electron emission for the mitigation of multipactor effect in radio-frequency space devices of high frequency and high power. The Ag nanopillars have been grown by glancing angle deposition with DC magnetron sputtering. Some samples have been covered by a gold capping layer to reduce oxidation and aging effects. The secondary emission yield of the surfaces of these samples has been measured and compared to those of flat Ag and Au reference samples. The results show that high aspect ratio surface roughness at the nanometer scale significantly reduce the secondary emission yield of the surface. This reduction is more important for low electron energies, which is the most influencing energy range of electrons for multipactor. The multipactor region for the nanopillar coating presenting the best secondary emission yield properties has been simulated, finding practical suppression of multipactor effect. The high-frequency surface resistance of these samples has also been estimated from published computations for similar surface roughness patterns. It was found that such nanopillar coatings are compatible with the best accomplishments of present space industry., This investigation has been funded by the MINECO of Spain through the AYA2012-39832-C02-02, FIS2015-67367-C2-1-P, MAT2015-69035-REDC and MAT2014-59772-C2-1-P projects and by the Comunidad de Madrid through the NANOMAGCOST-CM Ref: P2018/NMT4321 project. One of the authors (C.M.) thanks MECD for FPU14/02020 grant. The authors also want to thank SEGAINVEX and SIdI from UAM for technical support, and to acknowledge the service from the MiNa Laboratory at IMN funded by Comunidad de Madrid (S2018/NMT-4291 TEC2SPACE), MINECO (CSIC13-4E-1794) and the European Union (FEDER, FSE).

[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.

In this work, a comparative study of the susceptibility chart in a partially dielectric-loaded rectangular wave-guide and in its equivalent partially dielectric-loaded parallel-plate wave-guide with the same height is performed. This study shows how the inhomogeneity of the electric field inside the rectangular wave-guide modifies the edges of the multipactor susceptibility chart with respect to that predicted by the parallel-plate wave-guide case. Moreover, comparisons of the evolution of the population and the trajectory of the effective electron and the DC field appearing in the wave-guide in a point well inside the multipactor region obtained with both models are performed, showing some quantitative differences in the multipactor evolution, but a similar qualitative behaviour is observed.

In this work it is investigated, in the parallel-plate waveguide case, how the 1D, 2D or 3D motion of the electrons inside the waveguide can affect the generalized susceptibility diagrams, by means of a developed model capable of tracking the exact trajectory of multiple effective electrons which includes effects such as the spreading of the secondary electron departure kinetic energies or the dependence on elastic and inelastic electrons. On the other hand, a comparative study of the susceptibility charts in a parallel-plate and in its equivalent rectangular waveguide with the same height is performed, showing how the inhomogeneity of the electric field inside the waveguide modifies the multipactor region with respect to that predicted by the parallel-plate waveguide case. The results of this study are going to be extended to a partially dielectric-loaded rectangular waveguide, which is a problem of great interest in the space industry that has not yet been rigorously investigated in the literature.

In view of the multipactor effect caused by the resonant multiplication of secondary electrons in space high-power microwave components, this paper proposes an intra-expansion trap surface to strongly suppress the emission of secondary electrons, and analyzes the suppression characteristics on multipactor via numerical simulation. We track each electrons' trajectory inside the trap to obtain secondary electron emission, and compare with a traditional straight hole trap to present its suppression effects. In addition, the influence of the structure parameters on the secondary electron emission characteristics and the power threshold of multipactor was studied. Results show that comparing with the traditional straight hole trap surface, the proposed intra-expansion trap surface performs 13% more remarkable suppression effect on secondary electron emission, and the power threshold of multipactor can be improved from 8969W to 15437W. A deeper intra-expansion trap surface can enhance the multipactor power threshold further.

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.

High-power multipactor effect always leads to high risk of passive intermodulation and electromagnetic compatibility problems. In this paper, multipactor in ferrite circulators has been simulated, analyzed, and measured. Using the Electromagnetic Particle-In-Cell method, the discharge breakdown thresholds of multipactor in circulators with electron-blocking dielectric and without electron-blocking dielectric have been predicted and verified by simulations. To improve the simulation accuracy of electron emission and collision on the ferrite dielectric, Secondary Electron Emission properties have been measured and fitted into the numerical models. Through power scanning method, transient evolution of electron numbers has been obtained and threshold predicted. Simulation results show that the threshold power of these circulators with and without electron-blocking were 1000W and 9700W, respectively. It demonstrates that multipactor breakdown power in ferrite circulators have been improved more than 900% utilizing the electron-blocking dielectric, which is promising for high-power applications, especially in space industry.

Multipactor is an electron discharge that may appear in particle accelerators and microwave devices such as filters, multiplexers, and RF satellite payloads in satellite on-board equipment under vacuum conditions. When some resonance conditions are satisfied, secondary electrons get synchronized with the RF fields, and the electron population inside the device grows exponentially leading to a multipactor discharge. This multipactor discharge has some negative effects that degrade the device performance: increase of signal noise and reflected power, heating of the device walls, outgassing, detuning of resonant cavities, and even the partial or total destruction of the component. The main aim of this investigation is to show a new model for the analysis of multipactor effect in partially dielectric-loaded rectangular waveguides. For this purpose, a CAD software has been developed which allows the simulation and design of these structures out of the operation points in which this undesired multipactor effect occurs, including the main factors that drive it.

The multipactor effect is an electron discharge which is exerted by a force on primary free electrons in vacuum and driven by electromagnetic fields between dielectric or metal surfaces. It will result in serious consequences such as rising noise level, damaging component surfaces, increasing voltage standing wave ratio of transmission system, and even permanent failure. Thus it becomes a bottleneck problem in developing high power microwave components (MCs) for satellite. With the higher power of satellite, it is essential that some of MCs should measure multipactor threshold due to lack of appropriate manufacture and storage on ground. Current methods for detecting multipactor are introduced and analyzed, such as close to carrier noise, harmonic noise, and microwave nulling method. Recent years, automatic and digital characteristic method for detecting multipactor as well as safety is proposed. Automatic nulling method for multipactor detection (MD) is presented.

A helicon current drive system need the high power vacuum feed-through (VFT) for the of upgraded KSTAR helicon current drive system. However, multipactor effect shows a problem of RF reflection in VFT vacuum region. So the proposed structure was to place a low electric field in the ceramic using a standing wave. The designed VFT shows the $\mathrm{E}_{\mathrm{z}}$ value close to zero and the electric field absolute value of about 1.7kV/cm when transmitting 1MW in ceramic. It showed the high Q value of transmission characteristics at 476MHz.

In this paper, the design of a 1.3GHz high power coupler cold window is presented for the Shanghai light source hard X-ray free electron laser system. The cold window consists of 3 parts: outer conductor, inner conductor and ceramic window. The multipactor effect is a resonant vacuum electron discharge that appears in components operating with high power electromagnetic field. When certain RF resonance condition is met, the secondary electrons grow exponentially, which leads to remarkable power losses and heating of the ceramic window, so that it becomes impossible to increase the fields by raising the incident power.

Secondary electron yield (SEY) is relevant for widely used characterization methods (e.g., secondary electron spectroscopy and electron microscopy) and materials applications (e.g., multipactor effect). Key quantities necessary for understanding the physics of electron transport in materials and simulation of SEY are electron mean free paths (MFPs). This paper explores the impact of alloying on MFPs and SEY for Cu-Ni, Cu-Zn, and Mo-Li alloys relative to their component metals Cu, Ni, Zn, Mo, and Li. Density functional theory calculations yield density of states, Fermi energy, work function, and frequency- and momentum-dependent energy loss function. These material properties were used to calculate MFPs and Monte Carlo simulations were performed to obtain energy dependent SEY for the alloys as well for the component metals. The results show that MFPs and SEYs of the studied alloys lie between those of component pure elements but are not a simple composition weighted average. Detailed analysis of the secondary electron generation and emission process shows that the changes in the SEY of alloys relative to the SEY of their component metals depend on the changes in both electronic structure and dielectric properties of the material.

Surface flashover at the solid dielectric/vacuum interface is a fundamental physical phenomenon, which restricts the development of pulsed power system and high voltage electrical equipment. The initiation and developing processes of surface flashover at the solid dielectric are associated with electrode-dielectric interface, dielectric surface and other external factors. Especially, the surface charges transport properties that related with surface flashover developing process are determined by the physicochemical of the dielectric surface. Therefore, the surface insulating performance can be enhanced by deposited with appropriate functional films. TiN film has a low secondary electron yield (SEY), which can help to suppress the secondary electron multipactor effect and suppress the surface flashover. In this paper, a preparation method of film contained TiCxOyNz using atmospheric pressure plasma jet (APPJ) is proposed. The experimental devices include AC power supply, plasma jet chamber and gas/precursor system. The AC power supply has a power of 1000 VA and frequency of 20 kHz. The precursor tetraethyl titanate (TTEO) is pumped into plasma jet chamber by argon gas and the working gas is nitrogen. The experimental results show that the maximum SEY of sample with TiCxOyNz film is approximately decreased to 1.5. The flashover voltage of sample with TiCxOyNz film is increased obviously. The morphology of the dielectric surface indicates that the rough surface is introduced after modification. Also, the physical processes of film deposition are investigated by the emission spectroscopic analysis.

The secondary electron emission (SEE) property of materials is closely related to the multipactor, which is one of the potential risk factors affecting the reliability of high power microwave components for space application. In the presented work, the influence of atmospheric exposure on the secondary electron yield (SEY) of the inert metal is investigated. It is found that the SEY increases gradually with exposing time, and the increase in SEY results from the surface adsorption layer consisting of carbon and oxygen elements. A two-layers SEY model is established to explain this evolution and obtain the corresponding parameters of the adsorption layer. Simulation on a C band impedance transformer shows that 45 days of exposure will result in a 7.5 dB decrease of multipactor threshold.

The reduction of the total secondary electron emission during electron-matter interactions is required to improve the maximum power limit of the vacuum RF equipments prone to multipactor discharge. In this work, a chemical deposition technique was developed to create the appropriate micron or submicron surface roughness to significantly improve the typical characteristics of the flat silver coatings used for high-power microwave devices for space applications. Rough silver coated RF filters with a high surface aspect ratio, >3, was achieved. It is found that the secondary electron emission yield (SEY) remains lower than 1 throughout the primary electron energy range and therefore multipactor electron avalanche is avoided. The influence of aging on the multipactor discharge is also drastically reduced in rough silver coatings. An experimental linear correlation was found between the multipactor power level and the minimum interaction energy for which the number of incident and emitted electrons is equal.

[EN] This paper reports on the experimental measurement of power threshold levels for the multipactor effect between samples of ferrite material typically used in the practical implementation of L-and S-band circulators and isolators. For this purposes, a new family of wideband, nonreciprocal rectangular waveguide structures loaded with ferrites has been designed with a full-wave electromagnetic simulation tool. The design also includes the required magnetostatic field biasing circuits. The multipactor breakdown power levels have also been predicted with an accurate electron tracking code using measured values for the secondary electron yield (SEY) coefficient. The measured results agree well with simulations, thereby fully validating the experimental campaign., This work was supported in part by the European Space Agency (ESA) through the Research Project 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 Ministerio de Economia y Competitividad (Spanish Government) through Research and Development under Project TEC2016-75934-C4-1-R and Project TEC2016-75934-C4-2-R, and in part by the European Regional Development Fund under Project TEC2014-55463-C3-3-P.

To study the multipactor effect on the surface of a circular waveguide window excited by the TE11 mode, the effects of the radius of the window, frequency, and style of polarization of the electromagnetic field and the reflection coefficient of the incident wave are examined in this paper using a Monte Carlo algorithm and theoretical analysis. The results show that the character of the multipactor is dominated by the longitudinal velocity of the secondary electrons, which is directly proportional to the square of their oscillatory velocity and inversely proportional to the phase velocity of the RF field. Either increasing the radius of the window disk or decreasing the field frequency leads to the aggravation of multipactor discharge. Moreover, applying the circularly polarized TE11 mode in a circular waveguide window generates electrons at a higher velocity normal to the window disk than that with linearly polarized TE11 mode transmission. In addition, the increase in the reflection coefficient of the incident wave imposes a longitudinal gradient force in the vicinity of the window disk, which also boosts the longitudinal velocity of the secondary electrons and degrades multipactor discharge upstream of the window box.