Dynamical analysis of electron transport in RF cavities and photomultipliers tubes

El objetivo de este trabajo es el estudio de la dinámica de haces y corrientes de electrones en cavidades aceleradoras de radiofrecuencia (RF) y en tubos fotomultiplicadores. Por una parte, los haces de electrones presentan una gran importancia histórica tanto en aplicaciones directas (televisiones, hornos de microondas, tratamiento del cáncer), como en la generación de radiación sincrotrón. La última generación de fuentes de rayos X muy brillantes se basa en los láseres de electrones libres (XFEL). No obstante, para producir los haces de electrones que emitirán dichos rayos X como radiación sincrotrón, se necesitan campos eléctricos de gran intensidad lo que produce que, debido a la emisión de electrones por efecto de emisión de campo en las paredes de los dispositivos, se generen las llamadas corrientes oscuras. Estas corrientes no solo perturban la dinámica de los haces de electrones, sino que incluso pueden producir un daño irreparable en el dispositivo mediante un fenómeno conocido como RF breakdown. Por este motivo, es de vital importancia estudiar la emisión de efecto de campo en los dispositivos aceleradores de alto gradiente y esta es la principal motivación de este trabajo. Por otra parte, los tubos fotomultiplicadores son unos dispositivos que se usan en espectroscopía gamma desde hace más de 70 años, pero no hay prácticamente referencias donde se haya simulado su funcionamiento. Estos fotodetectores son bastante sensibles a los campos magnéticos externos. De hecho, incluso el campo magnético terrestre puede afectar a su funcionamiento. Por ello, se ha simulado un tubo fotomultiplicador con la finalidad de poder realizar en el futuro un diseño lo más adecuado posible para la realización de medidas en una habitación para el tratamiento con protonterapia.The aim of this work is the study of the dynamics of beams and electron currents in radio frequency (RF) accelerating cavities and in photomultiplier tubes. Electron beams present a great historical importance both in direct applications (tele visions, microwave ovens, cancer treatment) and in the generation of synchrotron radia tion. The latest generation of very bright X-ray sources is based on free electron lasers (XFEL). However, to produce the electron beams that will emit the X-rays as synchrotron radiation, high intensity electric fields are needed, producing the emission of electrons (called dark currents) from the walls of the devices due to the effect of field emission. These currents can disturb the dynamics of the electron beams, but can also cause an irreparable damage to the device through a phenomenon known as RF breakdown. For this reason, it is of vital importance to study the field effect emission in high gradient accelerator devices and this is the main motivation for this work. On the other hand, photomultiplier tubes are devices that have been used in gamma spectroscopy for more than 70 years, but there are practically no references where their operation has been simulated. These photodetectors are quite sensitive to external mag netic fields. In fact, even the Earth’s magnetic field can affect its operation. Hence, a photomultiplier tube has been simulated in order to be able to make a design as suitable as possible in the future for carrying out measurements in a proton treatment room

Simulación numérica de dinámica relativista de partículas cargadas en campos electromagnéticos empleando el método de Boris

Las aplicaciones basadas en la aceleración de partículas cargadas son muy diversas: colisionadores de partículas, estudios de la estructura molecular y atómica o de las propiedades de materiales, tratamientos contra el cáncer… Por ello, es necesario saber calcular cómo se mueven (y, en consecuencia, qué energía adquieren) estas partículas en presencia de campos electromagnéticos. De esta forma se podrá optimizar el diseño de la estructura aceleradora dependiendo del propósito final que tengan las partículas aceleradas. Vamos a implementar un algoritmo numérico (el método de Boris) que permite resolver numéricamente de forma sencilla la fuerza de Lorentz relativista. Utilizaremos este método para estudiar las trayectorias descritas por electrones al atravesar un solenoide finito con una densidad de corriente constante y, posteriormente, al caso ideal en el que solo tenemos un campo eléctrico oscilante temporalmente en el que demostraremos que, bajo ciertas condiciones, podemos obtener la trayectoria promedio a partir de la fuerza de Miller. Finalmente, aplicaremos el método de Boris para estudiar una estructura aceleradora real con geometría cilíndrica formada por 1.6 celdas.The range of applications based on the acceleration of charged particles is very diverse: particle colliders, studies of molecular and atomic structure or material properties, cancer treatments... Therefore, we must know how to calculate the movement of particles (and, consequently, their energy) in the presence of electromagnetic fields. In this way, the design of the accelerator structure can be optimized depending on the final purpose of the accelerated particles. We will implement a numerical algorithm (the Boris method) that solves numerically the relativistic Lorentz’s force. We will use this method to study the trajectories described by electrons when they cross a finite solenoid with a constant current density and, subsequently, to the ideal case where we only have a temporarily oscillating electric field where we will demonstrate that, under certain conditions, we can obtain the average trajectory from Miller’s force. Finally, we will apply the Boris method to study a real accelerator structure with cylindrical geometry formed by 1.6 cells

A hydrodynamic model for particle beam-driven plasmon wakefield in carbon nanotubes

Charged particles moving through a carbon nanotube may be used to excite electromagnetic modes in the electron gas produced by π and σ orbitals in the cylindrical graphene shell that makes up a nanotube wall [1]. This effect has recently been proposed as a potential novel method of short-wavelength-high-gradient particle acceleration [2, 3]. In this contribution, first we review the existing theory based on a linearised hydrodynamic model for a non-relativistic, localised point-charge propagating in a single wall nanotube (SWNT) [4]. Then we extend it to the relativistic case. In this hydrodynamic model the electron gas is treated as a plasma with additional contributions to the fluid momentum equation from specific solid- state properties of the gas. The governing set of differential equations is formed by the continuity and momentum equations for the involved species: beam charges, electrons and ions of the lattice. These equations are then coupled by Maxwell’s equations. The ions are assumed to be quasistatic and provide a neutralising background. To solve the differential equation system a modified Fourier-Bessel transform has been applied. Furthermore, a spectral analysis has been realised to determine the plasma modes able to excite a longitudinal electrical wakefield component in the SWNT to accelerate test charges. Eventually, we discuss the suitability and possible limitations of the method proposed in this study for particle acceleration

The ANTI-Vea task: analyzing the executive and arousal vigilance decrements while measuring the three attentional networks

This work was supported by the Spanish Ministry of Economy, Industry, and Competitiveness, research project to JL [grant number PSI2017-84926-P]; and by the Secretaría de Ciencia y Tecnología from the Universidad Nacional de Córdoba, Argentina (Proyecto Estimular to FGL); FGL received PhD scholarship support from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina; FGL received a scholarship mobility by the Asociación Universitaria Iberoamericana de Posgrado (AUIP) in cooperation with the Consejería de Economía y Conocimiento de la Junta de Andalucía, España; EMA was supported by a Juan de la Cierva postdoctoral fellowship from the Spanish Ministry of Economy, Industry, and Competitiveness [IJCI-2015-23204]. Preliminary results of this work has been presented in the Spanish XI Scientific Meeting of Attention (RECA), developed from 28th to 30th of September 2017 in Baeza, Spain. This paper is part of the doctoral thesis by the first author, under the supervision of the last two authors.The vigilance decrement phenomenon has been traditionally studied by simple and monotonous behavioral tasks. Nowadays, however, there is considerable interest in measuring vigilance with more complex tasks, including independent measures of other attentional functions. In the present study, we provide evidence supporting the suitability of the Attentional Networks Test for Interactions and Vigilance – executive and arousal components (ANTI-Vea) as an appropriate method to simultaneously assess multiple attentional and vigilance components. Vigilance was examined as two dissociated components: executive vigilance –as the detection of infrequent signals– and arousal vigilance –as the sustenance of a fast reaction to stimuli without response selection–. Importantly, the executive vigilance decrement was analyzed with a novel methodological approach to particularly determine whether the sensitivity loss effect is influenced by a floor level on the false alarms. As expected, the ANTI-Vea proved to be a task suitable to assess: (a) the main effects and interactions of phasic alertness, orienting, and executive control; (b) the executive vigilance decrement as a progressive change in the response bias; and (c) the arousal vigilance decrement as a progressive slowness and variability in reaction time. We discuss some critical theoretical and empirical implications of measuring vigilance components with the ANTI-Vea task. We expect the present study to provide a suitable method to analyze the vigilance decrement phenomenon when measuring multiple attentional and vigilance functions.Tradicionalmente, el decremento de la vigilancia se ha estudiado con tareas comportamentales simples y repetitivas. Sin embargo, actualmente existe un considerable interés en evaluar la vigilancia con tareas más complejas que incluyan medidas independientes de otros procesos atencionales. En el presente estudio, nuestro objetivo fue proporcionar nueva evidencia empírica sobre la adecuación del Test de Redes Atencionales para Interacciones y Vigilancia – componentes ejecutivo y de activación (ANTI-Vea) para medir simultáneamente múltiples componentes atencionales y de vigilancia. Examinamos la vigilancia como dos componentes disociados: vigilancia ejecutiva –como la detección de señales infrecuentes– y vigilancia de activación –como el mantenimiento de una reacción rápida a los estímulos sin control sobre la respuesta–. Es importante destacar que la vigilancia ejecutiva se analizó con un novedoso método para determinar si un efecto suelo en las falsas alarmas podría influenciar una disminución en la sensibilidad. Como se esperaba, se observó que la tarea ANTI-Vea es adecuada para medir: (a) los efectos principales e interacciones de las funciones de alerta fásica, orientación, y control ejecutivo; (b) el decremento en la vigilancia ejecutiva como un cambio en la tendencia de la respuesta; y (c) el decremento en la vigilancia de activación como un enlentecimiento y variabilidad de la respuesta. Discutimos algunas implicaciones teóricas y empíricas sobre la medición de los componentes de la vigilancia con la tarea ANTI-Vea. Esperamos que el presente estudio provea un método adecuado para analizar el decremento de la vigilancia cuando se evalúan múltiples funciones atencionales y de vigilancia.Spanish Ministry of Economy, Industry, and Competitiveness PSI2017-84926-PSecretaria de Ciencia y Tecnologia from the Universidad Nacional de Cordoba, ArgentinaConsejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET)Asociacion Universitaria Iberoamericana de Posgrado (AUIP)Junta de AndaluciaJuan de la Cierva postdoctoral fellowship from the Spanish Ministry of Economy, Industry, and Competitiveness IJCI-2015-2320

Cognitive load mitigates the executive but not the arousal vigilance decrement

This study was supported by the Spanish Ministry of Economy, Industry, and Competitiveness, through research projects to JL [grants number PSI2017-84926-P and PID2020-114790GB-I00] and the Secretaría de Ciencia y Tecnología from the Universidad Nacional de Córdoba, Argentina (Proyecto Estimular to FGL). In addition, FGL received PhD scholarship support from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina and a scholarship mobility by the Asociación Universitaria Iberoamericana de Posgrado (AUIP) in cooperation with the Consejería de Economía y Conocimiento de la Junta de Andalucía, España. Funding sources had no involvement in the study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication. Preliminary results of this work has been presented in the Spanish XI Scientific Meeting of Attention (RECA), developed from 28th to 30th of September 2017 in Baeza, Spain. This study is part of the doctoral thesis by FGL, conducted under the supervision of JL and EMA.Previous research has shown opposite effects of dual tasking on the vigilance decrement phenomenon. We examined the executive (i.e., detecting infrequent critical signals) and arousal (i.e., sustaining a fast reaction to stimuli without much control on responses) vigilance decrements as a function of task load. Ninety-six participants performed either a single signal-detection (i.e., executive vigilance) task, a single reaction time (i.e., arousal vigilance) task, or a dual vigilance task with the same stimuli and procedure. All participants self-reported their fatigue’ state along the session. Exploratory analyses included data from a previous study with a triple task condition. Task load significantly modulated the executive but not the arousal vigilance decrement. Interestingly, the largest increase in mental fatigue was observed in the single executive vigilance task condition. We discuss limitations of classic vigilance theories to account for the vigilance decrement and changes in mental fatigue as a function of task load.Spanish Ministry of Economy, Industry, and Competitiveness, grants number PSI2017-84926-P and PID2020-114790GB-I00Secretaría de Ciencia y Tecnología from the Universidad Nacional de Córdoba, ArgentinaConsejo Nacional de Investigaciones Científicas y Técnicas (CONICET)Asociación Universitaria Iberoamericana de Posgrado (AUIP) in cooperation with the Consejería de Economía y Conocimiento de la Junta de Andalucía, Españ

Excitation of wakefields in carbon nanotubes: a hydrodynamic model approach

The interactions of charged particles with carbon nanotubes may excite electromagnetic modes in the electron gas produced in the cylindrical graphene shell constituting the nanotube wall. This wake effect has recently been proposed as a potential novel method of short-wavelength high-gradient particle acceleration. In this work, the excitation of these wakefields is studied by means of the linearized hydrodynamic model. In this model, the electronic excitations on the nanotube surface are described treating the electron gas as a 2D plasma with additional contributions to the fluid momentum equation from specific solid-state properties of the gas. General expressions are derived for the excited longitudinal and transverse wakefields. Numerical results are obtained for a charged particle moving within a carbon nanotube, paraxially to its axis, showing how the wakefield is affected by parameters such as the particle velocity and its radial position, the nanotube radius, and a friction factor, which can be used as a phenomenological parameter to describe effects from the ionic lattice. Assuming a particle driver propagating on axis at a given velocity, optimal parameters were obtained to maximize the longitudinal wakefield amplitude.<br/

Factors Associated with Suicide Attempts and Suicides in the General Population of Andalusia (Spain)

Discrepant results have been published by studies comparing deaths by suicide with attempted suicides. This study aimed to determine factors associated with suicides and attempted suicides in Andalusia (Spain) between 2007 and 2013, comparing sex, age, year, and suicide method between these populations. A retrospective study was conducted of data on deaths by suicide and attempted suicides over a seven-year period, calculating the sex and age rates for each behavior. Adjusted Poisson regression was used to analyze the association with study variables, and incidence rate ratios were estimated. During the seven-year study period, 20,254 attempted suicides and 5202 deaths by suicide were recorded. The prevalence of attempted suicide did not differ between the sexes, whereas the prevalence of deaths by suicide was three-fold higher among males than among females and increased with higher age. The most frequently used method was the same in males and females for suicide attempts, but differed between the sexes for suicides. The combined influence of sex and age was greater in the model for death by suicide than in the model for attempted suicide. The key differentiating factor was the method used, while the finding of greatest concern was the suicide behavior among the elderly. Preventive strategies should take these differences into account

Suicide attempts in Spain according to prehospital healthcare emergency records

Objective To analyze the number and characteristics of suicide attempts by reviewing records of the public emergency healthcare service information system. Method A retrospective observational study was conducted of emergency telephone calls received between January 1 2007 and December 31 2013 throughout the Andalusia region (Southern Spain). Cases were selected based on phone operator or healthcare team labeling. Data were analyzed on the characteristics of the individuals, the timing and severity of attempts, their prioritization, and their outcome. Results Between January 1 2007 and December 31 2013, 20.942 calls related to suicide attempts were recorded, a rate of 34.7 attempts per 100,000 inhabitants. Most cases were classified by the public emergency healthcare service (Empresa Pública de Emergencias Sanitarias, EPES) as code X84 (The International Statistical Classification of Diseases, tenth revision, ICD-10) or 305(The International Statistical Classification of Diseases, ninth revision, ICD- 9). Attempts were more frequent in the 35-49-year age group and there were similar proportions of males and females. The lowest number of calls for suicide attempts were in 2007 and the highest in 2013. Calls were more frequent during the summer months, at weekends, and between 16:00 and 23:00 h. The likelihood of evacuation to the hospital emergency department was almost two-fold lower in over 65-yr-olds than in younger individuals. Significant (ƿ = 0.001) gender differences were found in call outcome and prioritization. The most influential factor for evacuation to a hospital emergency department was the code assigned by the attending healthcare team. Conclusions Information obtained from extra-hospital emergency services provides valuable data on the characteristics and timing of calls related to suicide attempts, complementing information from hospital emergency departments or population surveys. There is a need to standardize the definition and recording of a suicide attempt.The authors are grateful to the Public Enterprise of Healthcare Emergencies of Andalusia (Empresa Pública de Emergencias Sanitarias de Andalucía) for providing the data used in this study