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The conversion of methane into transportable and storable materials is crucial in the petrochemical sector. In this study, a specially constructed AC-driven dielectric barrier discharge (DBD) that has charge injector pyramids on one of the electrodes and runs at ambient temperature and pressure was used to evaluate noncatalytic methane conversion. The obtained result was compared with the traditional flat electrode DBD. It was discovered that the product selectivity in direct nonoxidative methane conversion depended on the discharge conditions. Pyramid electrode plasma sources convert methane up to 50 (Formula presented.) more than flat electrode plasma due to the appearance of more microdischarges. Pyramid electrode plasma generally has a greater production efficiency than flat electrode plasma, while requiring more operational power. The turnkey solutions offered by the sustainable methane coupling method discussed here may be advantageous for the long-term small-scale ethylene exploration scenario.

The induced primary emission leads to changes in the primary emission of a device and the induced secondary emission leads to changes in the propagation of supraharmonics in the adjacent phase due to the connection of single-phase loads spread over three phases in an installation. The induced primary emission and induced secondary emission are shown to give a significant contribution to the total emission measured at a given point in an installation. The induction of the emission is caused by the inductive and capacitive coupling among the conductors within the cables. This paper presents an analysis of four parameters that impact the magnitude of the induced emissions. Simulations carried out in COMSOL, show that the type of cable used impacts the induced emission and studies show that shielded cable with a stranded conductor with the shield grounded will lead to a reduction in the induced emissions. Among the other parameters, i.e., the load and transformer impedance and the length of the cable, the length of the cable is dominating in deciding the magnitude of the induced emissions. Analysis is carried out using Monte Carlo simulation and varying parameters stochastically. For all investigated parameters there is a strong frequency dependency. The stochastic variation of the load impedance in one phase causes a variation of 5% whereas the change in length of the cable leads to a maximum 40% variation in the considered frequency range for induced primary emission. Measurement results are presented to validate the results., Validerad;2023;Nivå 2;2023-08-07 (joosat);Licens fulltext: CC BY LicenseThis article has previously appeared as a manuscript in a thesis.

The induced primary emission leads to changes in the primary emission of a device and the induced secondary emission leads to changes in the propagation of supraharmonics in the adjacent phase due to the connection of single-phase loads spread over three phases in an installation. The induced primary emission and induced secondary emission are shown to give a significant contribution to the total emission measured at a given point in an installation. The induction of the emission is caused by the inductive and capacitive coupling among the conductors within the cables. This paper presents an analysis of four parameters that impact the magnitude of the induced emissions. Simulations carried out in COMSOL, show that the type of cable used impacts the induced emission and studies show that shielded cable with a stranded conductor with the shield grounded will lead to a reduction in the induced emissions. Among the other parameters, i.e., the load and transformer impedance and the length of the cable, the length of the cable is dominating in deciding the magnitude of the induced emissions. Analysis is carried out using Monte Carlo simulation and varying parameters stochastically. For all investigated parameters there is a strong frequency dependency. The stochastic variation of the load impedance in one phase causes a variation of 5% whereas the change in length of the cable leads to a maximum 40% variation in the considered frequency range for induced primary emission. Measurement results are presented to validate the results., Validerad;2023;Nivå 2;2023-08-07 (joosat);Licens fulltext: CC BY LicenseThis article has previously appeared as a manuscript in a thesis.

The air concentrations of organophosphate esters (OPEs) were studied in a network of six remote high-mountain areas of the Pyrenees located along an altitudinal profile between 1619 m and 2453 m above sea level on a restricted planar surface to assess their vertical distribution based on long-range atmospheric transport and temperature gradients. Polyurethane foam passive samplers were used in five periods spanning over three years (September 2017-October 2020). The sum of concentrations of five OPEs were between 5.3 and 100 pg m-3, averaging 16-53 pg m-3 across campaigns at the different locations. These concentrations were much lower than those observed in areas under anthropogenic influence but also than those found in low altitude remote continental sites. A significant progressive change in predominant compounds was observed along the altitudinal gradient, with prevalence of tris(1-chloro-2-propyl) phosphate (TCIPP) or tris(2-chloroethyl) phosphate (TCEP) below or above 2300 m above sea level, respectively. This trend was consistent with the higher volatility of TCEP, which was retained at greater extent at lower environmental temperatures (higher altitude). A significant temperature dependence of the gas phase concentrations was observed for TCEP, TCIPP and triphenyl phosphate (TPHP), which could be explained by retention in the cold periods, predominantly adsorbed in snow, and their release to the atmosphere during snowmelt. This mechanism was consistent with the good agreement found between the vaporization enthalpies measured under laboratory conditions and the experimental values obtained from the slopes of the significant linear regressions when representing the vertical gradients.

We use numerical simulations to study the dynamics of surface discharges, which are common in high-voltage engineering. We simulate positive streamer discharges that propagate towards a dielectric surface, attach to it, and then propagate over the surface. The simulations are performed in air with a two-dimensional plasma fluid model, in which a flat dielectric is placed between two plate electrodes. Electrostatic attraction is the main mechanism that causes streamers to grow towards the dielectric. Due to the net charge in the streamer head, the dielectric gets polarized, and the electric field between the streamer and the dielectric is increased. Compared to streamers in bulk gas, surface streamers have a smaller radius, a higher electric field, a higher electron density, and higher propagation velocity. A higher applied voltage leads to faster inception and faster propagation of the surface discharge. A higher dielectric permittivity leads to more rapid attachment of the streamer to the surface and a thinner surface streamer. Secondary emission coefficients are shown to play a modest role, which is due to relatively strong photoionization in air. In the simulations, a high electric field is present between the positive streamers and the dielectric surface. We show that the magnitude and decay of this field are affected by the positive ion mobility.

We use numerical simulations to study the dynamics of surface discharges, which are common in high-voltage engineering. We simulate positive streamer discharges that propagate towards a dielectric surface, attach to it, and then propagate over the surface. The simulations are performed in air with a two-dimensional plasma fluid model, in which a flat dielectric is placed between two plate electrodes. Electrostatic attraction is the main mechanism that causes streamers to grow towards the dielectric. Due to the net charge in the streamer head, the dielectric gets polarized, and the electric field between the streamer and the dielectric is increased. Compared to streamers in bulk gas, surface streamers have a smaller radius, a higher electric field, a higher electron density, and higher propagation velocity. A higher applied voltage leads to faster inception and faster propagation of the surface discharge. A higher dielectric permittivity leads to more rapid attachment of the streamer to the surf

We use numerical simulations to study the dynamics of surface discharges, which are common in high-voltage engineering. We simulate positive streamer discharges that propagate towards a dielectric surface, attach to it, and then propagate over the surface. The simulations are performed in air with a two-dimensional plasma fluid model, in which a flat dielectric is placed between two plate electrodes. Electrostatic attraction is the main mechanism that causes streamers to grow towards the dielectric. Due to the net charge in the streamer head, the dielectric gets polarized, and the electric field between the streamer and the dielectric is increased. Compared to streamers in bulk gas, surface streamers have a smaller radius, a higher electric field, a higher electron density, and higher propagation velocity. A higher applied voltage leads to faster inception and faster propagation of the surface discharge. A higher dielectric permittivity leads to more rapid attachment of the streamer to the surf

[EN] The power handling capability of helical resonator filters is studied by means of the parallel plate model (employed in the European Cooperation for Space Standardisation) and more rigorous modelling techniques (like the one available in the commercial software tool SPARK3D (TM)) as well as through an experimental test campaign. The results indicate that the parallel plate model provides conservative power handling capabilities for this class of filters, while rigorous modelling can better capture the impact of the geometrical features on multipactor evolution. Although the accuracy of the estimated power handling depends on the knowledge of the practical secondary emission yield values, the use of such rigorous modelling tools enables the design of helical resonator filters with improved power handling capability by exploiting the large gap approach, therefore opening opportunities to avoid additional dielectric fillings.

[EN] The power handling capability of helical resonator filters is studied by means of the parallel plate model (employed in the European Cooperation for Space Standardisation) and more rigorous modelling techniques (like the one available in the commercial software tool SPARK3D (TM)) as well as through an experimental test campaign. The results indicate that the parallel plate model provides conservative power handling capabilities for this class of filters, while rigorous modelling can better capture the impact of the geometrical features on multipactor evolution. Although the accuracy of the estimated power handling depends on the knowledge of the practical secondary emission yield values, the use of such rigorous modelling tools enables the design of helical resonator filters with improved power handling capability by exploiting the large gap approach, therefore opening opportunities to avoid additional dielectric fillings.

Hundreds of concurrent collisions per bunch crossing are expected at future hadron colliders. Precision timing calorimetry has been advocated as a way to mitigate the pileup effects and, thanks to their excellent time resolution, microchannel plates (MCPs) are good candidate detectors for this goal. We report on the response of MCPs, used as secondary emission detectors, to single relativistic particles and to electromagnetic showers. Several prototypes, with different geometries and characteristics, were exposed to particle beams at the INFN-LNF Beam Test Facility and at CERN. Their time resolution and efficiency are measured for single particles and as a function of the multiplicity of particles. Efficiencies between 50% and 90% to single relativistic particles are reached, and up to 100% in presence of a large number of particles. Time resolutions between 20 ps and 30 ps are obtained

We present a method for imaging depletion layers using the gaseous secondary electron detector (GSED) employed in environmental scanning electron microscopes. GSED images of a p-np-n junction were obtained from a Si P+PNP+PN power diode. Behavior of the junction contrast as a function of imaging conditions is unrelated to reported GSED contrast formation mechanisms [ A. L. Fletcher, B. L. Thiel, and A. M. Donald, J. Phys. D 30, 2249 (1997)]. Optimum imaging conditions are presented, and the contrast behavior is interpreted in terms of a previously unreported induced current component in GSED images. The presented technique is unique as it will enable imaging of depletion layers in uncoated semiconductor/oxide devices in controlled gaseous environments at elevated specimen temperatures.

We present a method for imaging depletion layers using the gaseous secondary electron detector (GSED) employed in environmental scanning electron microscopes. GSED images of a p-np-n junction were obtained from a Si P+PNP+PN power diode. Behavior of the junction contrast as a function of imaging conditions is unrelated to reported GSED contrast formation mechanisms [ A. L. Fletcher, B. L. Thiel, and A. M. Donald, J. Phys. D 30, 2249 (1997)]. Optimum imaging conditions are presented, and the contrast behavior is interpreted in terms of a previously unreported induced current component in GSED images. The presented technique is unique as it will enable imaging of depletion layers in uncoated semiconductor/oxide devices in controlled gaseous environments at elevated specimen temperatures.

Development of MUSCAT (Multi-Utility Spacecraft Charging Analysis Tool) had started in November 2004 as a quantitative spacecraft charging analysis tool in Japan. In the middle of development term, the beta version of MUSCAT has been released on March 2006 as the first version of integrated software. The integrated GUI (Graphical User Interface) tool of MUSCAT, called 'Vineyard' had been developed, which conducts the MUSCAT simulation on local Windows (trademark) PC. Functions of 'Vineyard' have parameter input panels including 3D satellite model, data converter from parameters in the GUI format into those in the solver format. As the development of the physical functions, fundamental physical elements such as photoelectron emission, secondary electron emission, auroral electrons had been included. As a result, the solver enables fundamental charging analyses at GEO (Geostationary Orbit), LEO (Low Earth Orbit) and PEO (Polar Earth Orbit), which makes MUSCAT feasible for multi-utility use. Parallelization and tuning of the code have almost been achieved, and eight-CPUs (Central Processing Unit) parallel computation can calculate absolute potential of a large-scale satellite model in a half size of maximum computation region of 256 x 64 x 128 in two days. Experiments for the code validation were made at LaSEINE (Laboratory of Spacecraft Environment Interaction Engineering) in KIT (Kyushu Institute of Technology). Spatial distribution of electric potential around the electrode of a Langmuir probe and IV (Current-Voltage) characteristic curve were measured, and we had good agreement in experimental results and the numerical ones. These results show that the physical functions of MUSCAT simulate charging processes quite well. For a function of plasma plume analysis of the MUSCAT solver, we consider a model of active emission of ions, which employs a fixed analytical beam ion profile and electrons of Boltzmann distribution. Distributions of CEX (Charge Exchange) ions are, JAXA Special Publication, 宇宙航空研究開発機構特別資料

We report on the response of microchannel plates (MCPs) to single relativistic particles and to electromagnetic showers. Particle detection by means of secondary emission of electrons at the MCP surface has long been proposed and is used extensively in ion time-of-flight mass spectrometers. What has not been investigated in depth is their use to detect the ionizing component of showers. The time resolution of MCPs exceeds anything that has been previously used in calorimeters and, if exploited effectively, could aid in the event reconstruction at high luminosity colliders. Several prototypes of photodetectors with the amplification stage based on MCPs were exposed to cosmic rays and to 491 MeV electrons at the INFN-LNF Beam-Test Facility. The time resolution and the efficiency of the MCPs are measured as a function of the particle multiplicity, and the results used to model the response to high-energy showers.

3D mesostructures with a height of up to 1 mm and micrometer feature size are fabricated employing a writing speed of 1 cm s-1 via direct laser writing utilizing a novel functional photoresist based on the radical coupling reaction of thiols and alkynes. The refractive index of the resist - consisting of a tetrafunctional thiol, a tetrafunctional alkyne and a photoinitiator - is tailored to be compatible with the employed high numerical aperture (NA) objective lens, thus enabling a Dip-in configuration. Mesostructures are characterized by scanning electron microscopy, optical photography, and nondestructive 3D time-of-flight secondary ion mass spectrometry. Woodpile photonic crystals are fabricated as benchmark structures in order to investigate the axial resolution. Verification of the chemical fabrication mechanism is achieved via transmission Fourier transform infrared (FTIR) spectroscopy of fabricated cuboid structures by monitoring the decrease of corresponding thiol and alkyne absorption peaks. Postmodification reactions, namely the thiol-Michael addition and the copper-catalyzed azide alkyne cycloaddition, are conducted employing residual thiols and alkynes throughout the cuboid structures. Successful dual and orthogonal modification throughout the structure and on the surface is achieved and verified utilizing transmission FTIR spectroscopy and time-of-flight secondary ion mass spectrometry. Reactive 3D mesostructures with micrometer feature size are fabricated via dip-in direct laser writing employing the radical thiol-yne coupling reaction. Axial resolution and the polymerization process of the photoresist are investigated. Residual thiols and alkynes are exploited for postmodification reactions, namely thiol-Michael addition and copper-catalyzed azide alkyne cycloaddition, demonstrating successful dual functionalization throughout the structure and on the surface. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report on the response of microchannel plates (MCPs) to single relativistic particles and to electromagnetic showers. Particle detection by means of secondary emission of electrons at the MCP surface has long been proposed and is used extensively in ion time-of-flight mass spectrometers. What has not been investigated in depth is their use to detect the ionizing component of showers. The time resolution of MCPs exceeds anything that has been previously used in calorimeters and, if exploited effectively, could aid in the event reconstruction at high luminosity colliders. Several prototypes of photodetectors with the amplification stage based on MCPs were exposed to cosmic rays and to 491 MeV electrons at the INFN-LNF Beam-Test Facility. The time resolution and the efficiency of the MCPs are measured as a function of the particle multiplicity, and the results used to model the response to high-energy showers., SCOPUS: ar.j, info:eu-repo/semantics/published

Although nowadays the use of cluster ion sources seems to enhance the secondary ion emission for nearly all materials, the technique of metal-assisted SIMS can still give further insights in the secondary ion emission process. In this study, the metallization for static SIMS analysis was performed in situ. The combination of a detailed morphology study by SEM, TEM and the secondary yield enhancements in time-of-flight SIMS allows to develop a model explaining the secondary yield enhancement in metal-assisted SIMS. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

El efecto multipactor de ruptura en RF ha sido objeto de numerosos estudios desde hace más de 80 años, a partir del desarrollo de los primeros aceleradores de partículas en la primera mitad del siglo XX. A mediados de ese siglo, con el desarrollo de fuentes de alta potencia para aplicaciones radar y la llegada de los satélites artificiales, la investigación del multipactor cobró una considerable relevancia, al convertirse este fenómeno en un riesgo determinante para costosos proyectos comerciales. Las guías de onda con secciones rectas canónicas, como las rectangulares o las coaxiales, han sido tradicionalmente las más utilizadas en dispositivos de microondas. Sus principales ventajas son que sus campos electromagnéticos pueden resolverse analíticamente, lo que permite su aplicación directa en diseños complejos, y la simplicidad de su fabricación. Pero las capacidades de computación y las prestaciones de los algoritmos se han multiplicado con los años, lo que ha permitido ampliar el espectro de posibles topologías a geometrías casi arbitrarias, ofreciendo al diseñador una mayor libertad creativa. En todo caso, gran parte de los dispositivos de microondas actuales siguen confiando en la madurez y fiabilidad de las tecnologías de guía de onda tradicionales, que no requieren una inversión adicional en equipos de fabricación. La supresión del efecto multipactor es la motivación para arriesgarse a probar topologías de guía de onda innovadoras, como la guía en forma de cuña. Es en este contexto donde este trabajo de doctorado pretende ofrecer una contribuci'on. En primer lugar, se ha desarrollado un modelo numérico para predecir el efecto multipactor de ruptura en guías de onda huecas en forma de cuña. Esta herramienta ha permitido la identificación de criterios óptimos de diseño. Así mismo, se ha adaptado un método de síntesis de filtros paso-banda en guía rectangular para poder realizar un diseño similar pero basado en la nueva topología. Como culminación, las estructur, The multipactor RF breakdown effect has been object of numerous studies for over 80 years, since the development of the first particle accelerators in the beginning of the 20th century. Around the middle of that century, with the development of high power sources for radar applications and with the emergence of the artificial satellites, a new impulse was given to the multipactor research, since it became a risk for expensive commercial projects. Traditionally, waveguides with canonical cross sections, like rectangular or coaxial ones, have been the building blocks of most microwave devices. Their main advantages are that their electromagnetic fields can be solved analytically, enabling their direct application in complex designs, as well as their manufacturing simplicity. But over the years the computation capabilities and algorithms have continuously evolved, which has broadened the spectrum of possible topologies to almost arbitrary geometries, offering the designer more room for creativity. However, most of the current microwave devices still trust on the mature canonical waveguide technologies, which do not require an additional investment in manufacturing equipment. The suppression of the multipactor effect is the motivation for considering an innovative waveguide topology, like the wedge-shaped waveguide. It is within this context where this PhD work aims to offer a contribution. On the one hand, a numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides has been developed. This tool has aided in the derivation of optimised design criteria. On the other hand, a bandpass filter synthesis method for rectangular waveguide has been adapted in order to calculate a similar design based on the new topology. As a culmination, the designed structures have been manufactured and tested, in order to verify their electromagnetic performance and their multipactor sensibility. A patent was also filed to protect these new filters. In

El efecto multipactor de ruptura en RF ha sido objeto de numerosos estudios desde hace más de 80 años, a partir del desarrollo de los primeros aceleradores de partículas en la primera mitad del siglo XX. A mediados de ese siglo, con el desarrollo de fuentes de alta potencia para aplicaciones radar y la llegada de los satélites artificiales, la investigación del multipactor cobró una considerable relevancia, al convertirse este fenómeno en un riesgo determinante para costosos proyectos comerciales. Las guías de onda con secciones rectas canónicas, como las rectangulares o las coaxiales, han sido tradicionalmente las más utilizadas en dispositivos de microondas. Sus principales ventajas son que sus campos electromagnéticos pueden resolverse analíticamente, lo que permite su aplicación directa en diseños complejos, y la simplicidad de su fabricación. Pero las capacidades de computación y las prestaciones de los algoritmos se han multiplicado con los años, lo que ha permitido ampliar el espectro de posibles topologías a geometrías casi arbitrarias, ofreciendo al diseñador una mayor libertad creativa. En todo caso, gran parte de los dispositivos de microondas actuales siguen confiando en la madurez y fiabilidad de las tecnologías de guía de onda tradicionales, que no requieren una inversión adicional en equipos de fabricación. La supresión del efecto multipactor es la motivación para arriesgarse a probar topologías de guía de onda innovadoras, como la guía en forma de cuña. Es en este contexto donde este trabajo de doctorado pretende ofrecer una contribuci'on. En primer lugar, se ha desarrollado un modelo numérico para predecir el efecto multipactor de ruptura en guías de onda huecas en forma de cuña. Esta herramienta ha permitido la identificación de criterios óptimos de diseño. Así mismo, se ha adaptado un método de síntesis de filtros paso-banda en guía rectangular para poder realizar un diseño similar pero basado en la nueva topología. Como culminación, las estructur, The multipactor RF breakdown effect has been object of numerous studies for over 80 years, since the development of the first particle accelerators in the beginning of the 20th century. Around the middle of that century, with the development of high power sources for radar applications and with the emergence of the artificial satellites, a new impulse was given to the multipactor research, since it became a risk for expensive commercial projects. Traditionally, waveguides with canonical cross sections, like rectangular or coaxial ones, have been the building blocks of most microwave devices. Their main advantages are that their electromagnetic fields can be solved analytically, enabling their direct application in complex designs, as well as their manufacturing simplicity. But over the years the computation capabilities and algorithms have continuously evolved, which has broadened the spectrum of possible topologies to almost arbitrary geometries, offering the designer more room for creativity. However, most of the current microwave devices still trust on the mature canonical waveguide technologies, which do not require an additional investment in manufacturing equipment. The suppression of the multipactor effect is the motivation for considering an innovative waveguide topology, like the wedge-shaped waveguide. It is within this context where this PhD work aims to offer a contribution. On the one hand, a numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides has been developed. This tool has aided in the derivation of optimised design criteria. On the other hand, a bandpass filter synthesis method for rectangular waveguide has been adapted in order to calculate a similar design based on the new topology. As a culmination, the designed structures have been manufactured and tested, in order to verify their electromagnetic performance and their multipactor sensibility. A patent was also filed to protect these new filters. In

El efecto multipactor de ruptura en RF ha sido objeto de numerosos estudios desde hace más de 80 años, a partir del desarrollo de los primeros aceleradores de partículas en la primera mitad del siglo XX. A mediados de ese siglo, con el desarrollo de fuentes de alta potencia para aplicaciones radar y la llegada de los satélites artificiales, la investigación del multipactor cobró una considerable relevancia, al convertirse este fenómeno en un riesgo determinante para costosos proyectos comerciales. Las guías de onda con secciones rectas canónicas, como las rectangulares o las coaxiales, han sido tradicionalmente las más utilizadas en dispositivos de microondas. Sus principales ventajas son que sus campos electromagnéticos pueden resolverse analíticamente, lo que permite su aplicación directa en diseños complejos, y la simplicidad de su fabricación. Pero las capacidades de computación y las prestaciones de los algoritmos se han multiplicado con los años, lo que ha permitido ampliar el espectro de posibles topologías a geometrías casi arbitrarias, ofreciendo al diseñador una mayor libertad creativa. En todo caso, gran parte de los dispositivos de microondas actuales siguen confiando en la madurez y fiabilidad de las tecnologías de guía de onda tradicionales, que no requieren una inversión adicional en equipos de fabricación. La supresión del efecto multipactor es la motivación para arriesgarse a probar topologías de guía de onda innovadoras, como la guía en forma de cuña. Es en este contexto donde este trabajo de doctorado pretende ofrecer una contribuci'on. En primer lugar, se ha desarrollado un modelo numérico para predecir el efecto multipactor de ruptura en guías de onda huecas en forma de cuña. Esta herramienta ha permitido la identificación de criterios óptimos de diseño. Así mismo, se ha adaptado un método de síntesis de filtros paso-banda en guía rectangular para poder realizar un diseño similar pero basado en la nueva topología. Como culminación, las estructur, The multipactor RF breakdown effect has been object of numerous studies for over 80 years, since the development of the first particle accelerators in the beginning of the 20th century. Around the middle of that century, with the development of high power sources for radar applications and with the emergence of the artificial satellites, a new impulse was given to the multipactor research, since it became a risk for expensive commercial projects. Traditionally, waveguides with canonical cross sections, like rectangular or coaxial ones, have been the building blocks of most microwave devices. Their main advantages are that their electromagnetic fields can be solved analytically, enabling their direct application in complex designs, as well as their manufacturing simplicity. But over the years the computation capabilities and algorithms have continuously evolved, which has broadened the spectrum of possible topologies to almost arbitrary geometries, offering the designer more room for creativity. However, most of the current microwave devices still trust on the mature canonical waveguide technologies, which do not require an additional investment in manufacturing equipment. The suppression of the multipactor effect is the motivation for considering an innovative waveguide topology, like the wedge-shaped waveguide. It is within this context where this PhD work aims to offer a contribution. On the one hand, a numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides has been developed. This tool has aided in the derivation of optimised design criteria. On the other hand, a bandpass filter synthesis method for rectangular waveguide has been adapted in order to calculate a similar design based on the new topology. As a culmination, the designed structures have been manufactured and tested, in order to verify their electromagnetic performance and their multipactor sensibility. A patent was also filed to protect these new filters. In

El efecto multipactor de ruptura en RF ha sido objeto de numerosos estudios desde hace más de 80 años, a partir del desarrollo de los primeros aceleradores de partículas en la primera mitad del siglo XX. A mediados de ese siglo, con el desarrollo de fuentes de alta potencia para aplicaciones radar y la llegada de los satélites artificiales, la investigación del multipactor cobró una considerable relevancia, al convertirse este fenómeno en un riesgo determinante para costosos proyectos comerciales. Las guías de onda con secciones rectas canónicas, como las rectangulares o las coaxiales, han sido tradicionalmente las más utilizadas en dispositivos de microondas. Sus principales ventajas son que sus campos electromagnéticos pueden resolverse analíticamente, lo que permite su aplicación directa en diseños complejos, y la simplicidad de su fabricación. Pero las capacidades de computación y las prestaciones de los algoritmos se han multiplicado con los años, lo que ha permitido ampliar el espectro de posibles topologías a geometrías casi arbitrarias, ofreciendo al diseñador una mayor libertad creativa. En todo caso, gran parte de los dispositivos de microondas actuales siguen confiando en la madurez y fiabilidad de las tecnologías de guía de onda tradicionales, que no requieren una inversión adicional en equipos de fabricación. La supresión del efecto multipactor es la motivación para arriesgarse a probar topologías de guía de onda innovadoras, como la guía en forma de cuña. Es en este contexto donde este trabajo de doctorado pretende ofrecer una contribuci'on. En primer lugar, se ha desarrollado un modelo numérico para predecir el efecto multipactor de ruptura en guías de onda huecas en forma de cuña. Esta herramienta ha permitido la identificación de criterios óptimos de diseño. Así mismo, se ha adaptado un método de síntesis de filtros paso-banda en guía rectangular para poder realizar un diseño similar pero basado en la nueva topología. Como culminación, las estructur, The multipactor RF breakdown effect has been object of numerous studies for over 80 years, since the development of the first particle accelerators in the beginning of the 20th century. Around the middle of that century, with the development of high power sources for radar applications and with the emergence of the artificial satellites, a new impulse was given to the multipactor research, since it became a risk for expensive commercial projects. Traditionally, waveguides with canonical cross sections, like rectangular or coaxial ones, have been the building blocks of most microwave devices. Their main advantages are that their electromagnetic fields can be solved analytically, enabling their direct application in complex designs, as well as their manufacturing simplicity. But over the years the computation capabilities and algorithms have continuously evolved, which has broadened the spectrum of possible topologies to almost arbitrary geometries, offering the designer more room for creativity. However, most of the current microwave devices still trust on the mature canonical waveguide technologies, which do not require an additional investment in manufacturing equipment. The suppression of the multipactor effect is the motivation for considering an innovative waveguide topology, like the wedge-shaped waveguide. It is within this context where this PhD work aims to offer a contribution. On the one hand, a numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides has been developed. This tool has aided in the derivation of optimised design criteria. On the other hand, a bandpass filter synthesis method for rectangular waveguide has been adapted in order to calculate a similar design based on the new topology. As a culmination, the designed structures have been manufactured and tested, in order to verify their electromagnetic performance and their multipactor sensibility. A patent was also filed to protect these new filters. In

Chemicals that are persistent in the atmosphere can be transported long distances and across international boundaries. Therefore, information about the fraction of local versus imported air pollution is required to formulate regulations aimed at controlling pollutant levels. The objective of this work is to illustrate the capabilities of a dynamic global-scale multimedia model to calculate source-receptor relationships for persistent organic pollutants that cycle between air, water, soil and vegetation in the global environment. As exemplary case studies, we present model calculations of time-evolving source-receptor relationships for PCB28, PCB153, alpha-HCH and beta-HCH over the duration of their usage, phase-out and a post-ban period. Our analysis is geographically explicit, and elucidates the role of primary versus secondary sources in controlling the levels of air pollution. Our case studies consider source-receptor relationships between the four regions defined by the Convention on Long-range Transboundary Air Pollution Task Force on Hemispheric Transport of Air Pollution, as well as the Arctic as a remote receptor region. We find source-receptor relationships that are highly variable over time, and between different regions and chemicals. Air pollution by PCBs in North America and Europe is consistently dominated by local emissions, whereas in East-and South-Asia extra-regional sources are sometimes major contributors. Emissions of alpha-HCH peak at different times in the four regions, which leads to a phase of high self-pollution in each region, and periods when pollution enters mainly from outside. Compared to alpha-HCH, air pollution with the less volatile and more persistent beta-HCH is more strongly determined by secondary emissions near source areas throughout its use history. PCB concentrations in Arctic air are dominated by emissions transported from North America and Europe from 1930 to 2080, whereas for HCHs each of the source regions contributes a, AuthorCount:3

In recent years, novel ion sources have been designed and developed that have enabled focused ion beam machines to go beyond their use as nano-fabrication tools. Secondary electrons are usually taken to form images, for their yield is high and strongly dependent on the surface characteristics, in terms of chemical composition and topography. In particular, the secondary electron yield varies characteristically with the angle formed by the beam and the direction normal to the sample surface in the point of impact. Knowledge of this dependence, for different ion/atom pairs, is thus the first step toward a complete understanding of the contrast mechanism in scanning ion microscopy. In this article, experimentally obtained ion-induced secondary electron yields as a function of the incidence angle of the beam on flat surfaces of Al and Cr are reported, for usual conditions in Ga+ and He+ microscopes. The curves have been compared with models and simulations, showing a good agreement for most of the angle range; deviations from the expected behavior are addressed and explanations are suggested. It appears that the maximum value of the ion-induced secondary electron yield is very similar in all the studied cases; the yield range, however, is consistently larger for helium than for gallium, which partially explains the enhanced topographical contrast of helium microscopes over the gallium focused ion beams., IST/Imaging Science and Technology, Applied Sciences

In recent years, novel ion sources have been designed and developed that have enabled focused ion beam machines to go beyond their use as nano-fabrication tools. Secondary electrons are usually taken to form images, for their yield is high and strongly dependent on the surface characteristics, in terms of chemical composition and topography. In particular, the secondary electron yield varies characteristically with the angle formed by the beam and the direction normal to the sample surface in the point of impact. Knowledge of this dependence, for different ion/atom pairs, is thus the first step toward a complete understanding of the contrast mechanism in scanning ion microscopy. In this article, experimentally obtained ion-induced secondary electron yields as a function of the incidence angle of the beam on flat surfaces of Al and Cr are reported, for usual conditions in Ga+ and He+ microscopes. The curves have been compared with models and simulations, showing a good agreement for most of the angle range; deviations from the expected behavior are addressed and explanations are suggested. It appears that the maximum value of the ion-induced secondary electron yield is very similar in all the studied cases; the yield range, however, is consistently larger for helium than for gallium, which partially explains the enhanced topographical contrast of helium microscopes over the gallium focused ion beams., IST/Imaging Science and Technology, Applied Sciences

In order to simulate the magnetized plasma thruster devices (such as CHT, DCF etc) we have developed a multi-scale numerical code that is based on coupling of a PIC/MCC analysis of neutrals and ions in a general 2D domain (or 3D) and a 1D kinetic full PIC treatment of electrons along magnetic fields. The implementation of such a two-way coupling allows calculation of the electron transport in the real physical domain while significantly reducing the computational time associated with 2D full kinetic simulations. The objective of this study was to identify the individual contribution to transport from factors such as collisions, surface roughness, secondary electron emission, and plasma oscillations. Multi-scale model of the magnetized plasma thruster discharge in which a kinetic treatment was used for the electron component while a 2D (or 3D) macroscopic model will be employed for ion and neutral component analysis. Initial coupling of the microscopic and macroscopic model was performed via axial electric field, electron fluxes to the wall and electron cross-field transport. This model demonstrated improved prediction of electron mobility., The original document contains color images.

This final technical report reviews the research activities during the period of this grant, emphasizing the final year. The effects of surface roughness on secondary electron emission were investigated for copper. The surface of copper samples were modified using a high-power Nd-YAG laser, where the degree of surface modification depended on the duration and intensity of the laser exposure. Four different levels of modification were tested, in addition to the unmodified sample. Minor modification resulted in the biggest effect, significantly reducing the secondary electron emission. However, this effect only holds true for very low electron dose, where dose is the incident charge per unit area. For higher dose levels those commensurate with technical materials in applied situations there was negligible effect of surface roughness on secondary electron emission. The data set presented here seeks to quantify the effect of surface roughness with further gradations than is accounted for in the semi-empirical formulae in the literature., The original document contains color images.

Theoretical analysis of mechanisms that excite auto-oscillations in magnetrons with secondary emission cathode without use of additional thermo-cathode is conducted. Processes of exciting auto-oscillations with the use of modulated pulse of anode voltage are studied. Conditions under which the realization of the given excitation mechanism is possible are determined.

This DEPSCoR research examined secondary electron emission (SEE) from thin films and from a warm metal material. Evidence suggests that backscattered electrons as a whole have a preferred scattering direction with a distribution that is dependent on the type of surface treatment. Secondary electron emission was studied from a chemical polished niobium sample during transient cooling from tilde 360 deg K to tilde 293 deg K. It was observed that: (1) "True" secondary electron distributions tend to exhibit a shifted Gaussian-like spatial distribution; (2) a metal structure undergoing transient cooling exhibits some small overall average tendencies on the scattering process; (3) the change in the mean number of scattered electrons seems to increase on average as the metal sample cools; and (4) the emitted backscattered electron cluster appears to be scattered normal to the sample surface for the temperature range considered. A strong AFRL/UNLV collaboration examined four different types of samples. Based on single, pulsed, emission tests, improvements in minimizing secondary electron emission count were observed with the coated copper substrates. Within experimental bounds, secondary electron emission hardening may not take place in all films. Further, the count and distribution are dependent on the primary electron beam's target angle., The original document contains color images.

This final technical report reviews the research activities during the period of this grant, emphasizing the final year. The key finding of our study is that the total incident electron dose is a critical parameter affecting secondary electron emission (SEE). A completely automated experimental set-up was implemented that allowed for measurement of secondary electron yield (SEY) as a function of beam energy, angle of incidence of primary electrons, electron dose, and time. We present SEY data for copper, plasma-sprayed boron carbide, and titanium nitride samples with principal attention given to the dose dependence. Experiments were conducted in the energy range 5 - 1000 eV using DC voltages. Modified empirical formulas are proposed that incorporate the dose effect and match the experimental measurements.

Radioactive ions injected into the decay ring of a Betabeam neutrino facility will constitute a continuous source of decay products distributed around the ring. Secondary ions from beta decays will differ in charge state from the primary ions and will follow widely off-momentum orbits. In the racetrack configuration of the ring, they will be mismatched in the long straights and may acquire large amplitudes, but the great majority of losses will be in the arcs. We describe here a comprehensive model of ion decay, secondary ion tracking, and loss detection, which has been implemented in the tracking and simulation code Accsim. Methods have been developed to accurately follow ion trajectories at large momentum deviations as well as to detect their impact coordinates on vacuum chamber walls and possibly inside magnetic elements. Using secondary-ion data from Accsim and post-processing with Mathematica, we have implemented a follow-on simulation in FLUKA with a 3D geometry of decay ring components and physics models for ion interactions in matter, allowing radiological studies and in particular the visualization and analysis of heat deposition in the dipole magnets which is a critical design factor for the ring. In our simulations we have also implemented absorber elements which are intended to localize the majority of losses outside of the dipoles. These studies provide estimates of ring performance (in terms of loss concentration and management), the effectiveness of absorbers, and the implications for successful superconducting dipole operation., QC 20100921

A model of the plasma interaction with the dielectric walls of a Hall thruster has been presented. It accounts for partial thermalization of the electron population through a single parameter 3/4 and includes a two-population, four-parameter model for SEE. Analytical expressions are obtained for the main parameters characterizing that interaction, such as the particle and energy fluxes to the walls and sheaths, which are needed as boundary conditions of quasineutral models of the full discharge. The behavior for low thermalization is shown to differ greatly from the commonly-used, high-thermalization case. This is very relevant for Hall thrusters, where there is a growing conviction that electron thermalization is low. At low thermalization, energy losses are close to its minimum, the charge saturation limit is not attainable, and the sheath potential is small; the different roles of beam and primary electrons on these characteristics have been analyzed. Significant decreases of the parallel temperature of primary electrons and, therefore, of the plasma flux into the sheath take place only at the very-low thermalization limit. The investigation of the emission model for secondary electrons has shown that the presence of a relevant fraction of elastically reflected electrons affects greatly the response. They tend to amplify the relative densities of untrapped electrons; their effect on the net primary and beam fluxes comes out from the zero electrical current balance. It is reiteratively found that the role of the sheath potential fall is to adjust the primary electron flux to wall and not vice versa. Although most of the analysis is carried out for an energy-independent yield of reflected electrons, a temperature-dependent yield expression is proposed, which avoids integrals expressions at the same time that it recovers approximately the reduction of that yield with the impact energy., The original document contains color images.

Pulsed hollow cathode discharges, used to generate kilovolt electron beams for the production of plasmas, were studied in low pressure (50-70 mTorr) backgrounds of argon, oxygen, nitrogen, SF sub 6 and mixtures thereof. Cathode currents were measured as a function of cathode voltage, duty factor, and relative gas concentration. The cathode current was found to have a dependence on all variables, with the greatest impact being operating gas for all voltages and duty factors. The ambient gas is thought to influence the production of secondary electrons at the cathode surface thereby impacting the operation of the hollow cathode discharge and electron beam production.

This final technical report summarizes the research activities over the last year of this grant. New time-dependent secondary electron yield (S.E.Y) measurements, including both true secondary emission and backscattering, have been made on materials thought to be suitable for low yield vacuum electronic applications such as collectors in High Power Microwave (HPM) tubes and beam-facing components in particle accelerators. Measurements of the angular dependence of S.E.Y. have also been performed and compared well with the literature. Boron-carbide-sprayed copper substrates, provided by Calbazas Creek Research, Inc., have also been initially characterized, and will be presented in a paper at IVEC 2005. The dependence of true secondaries on incident beam energy has been measured, but its intepretation has yet to be cormpleted. These 0pen questions will be resolved under the auspices of a follow-on grant., The original document contains color images.

Why do spacecraft charge in sunlight? The first reason concerns differential charging between the sunlit and dark sides. A monopole-dipole model describing the differential charging potential distribution yields interesting theoretical results. We compare the results with observations. The second reason concerns reflectance. Much attention has been paid in recent years to the effect of surface conditions on secondary emission, which plays an essential role in spacecraft charging. In comparison, little or no attention has been paid to the effect of surface condition on photoemission, which plays a dominating role in spacecraft sunlight charging. We present theoretical reasoning why highly reflective mirrors generate substantially reduced photoemission. We have calculated, by using the Langmuir orbit- limited current balance equation in 1 -D, 2-D, and 3-D, the different surface potentials of various surface materials under typical space plasma conditions, satellite surface reflectivity values, and sunlight incidence angles. We present numerical results confining that with substantially reduced photoemission, highly reflective surfaces would often charge to high negative potentials in sunlight., Published in Proceedings of Spacecraft Charging Technology Conference (9th), JAXA-SP-05-001E, JAXA, p1-10, 2005. Presented at Spacecraft Charging Technology Conference (9th), held in Tsukuba, Japan in April 2005.

High power microwave tubes are used for both civilian and military applications. Due to the power requirement, tremendous amounts of electrons (up to 100A/cm2) are extracted from the cathodes and bombard on the anodes with very high kinetic energy. Overheating, out-gassing, and formation of secondary electrons of the anode cause serious problems. Preliminary results at the AFRL suggest that carbon coating can reduce SE. We investigated the effect of carbon nanotube (CNT) coating on the anode surface. Initial experiments show that CNT is more efficient in absorbing SE compared to the reference metal at low energy. Further experiments are required to study and understand the effect at high energy.

Recent research has examined the feasibility of detecting biological warfare agents by conjugating their antibodies (receptors) with taggant nanoparticles (also known as "quantum dots"), which subsequently fluoresce upon excitation, when they are bound to a specific biowarfare agent, or its simulant. Furthermore, when they react with their target bacteria, optically excited nanoparticle-receptor conjugates generate spectra in which the intensities of primary emission peaks are diminished, while the secondary emission peaks increase in intensities, i.e., energy is transferred from major peaks to minor peaks. These optical emission spectral signatures, with emission wavelength shifts of 140 nm in some cases, strongly suggest the possibility of homogeneous (one step) assays, leading to positive detection of bacterial agents, without wash steps using nanoparticle-receptor conjugates., See also ADM001736. Proceedings for the Army Science Conference (24th) Held on 29 November - 2 December 2004 in Orlando, Florida. The original document contains color images. Prepared in cooperation with Nano Science Diagnostics(NSD), Inc, Austin, TX and Operational Technologies Corportation, San Antonio, TX.

This report results from a contract tasking CPAT as follows: The Grantee will perform theoretical modeling of point, surface, and volume high-pressure plasmas created using Micro Hollow Cathode Discharge sources. The primary goal is to better understand the fundamental physics of these discharges in order to optimize operating conditions and develop more efficient devices., Grant 033083, Universite Paul Sabatier, Toulouse, France. Annex 1: Mid-term grant rept. Annex 2: Journal article to appear in Appl Phys Lett. Annex 3: Journal article to appear in IEEE Trans Plasma Sci special issue on Images in Plasma Science. Annex 4: Conference paper to appear in the Proceedings of the Gas Disch Conf, 2005. The original document contains color images.

This paper reviews some recent advances in the onset of spacecraft charging. Current balance determines the spacecraft potential. The electron flux intercepted by an object in a plasma exceeds that of ions by orders of magnitude because of the ion-electron mass difference. Negative voltage charging occurs when the incoming electron flux exceeds the outgoing secondary and backscattered electron flux. The secondary electron emission coefficient depends on the surface material, typically exceeds unity at about 40 to-1800 eV of primary electron energy, and falls below unity at higher energies. Beyond a critical temperature T*, the incoming electron flux exceeds that of the secondary electrons, thereby negative charging occurs. Scarce evidence of T* was observed on ATS-5 and ATS-6 satellites. Recently, abundant evidence was observed on the Los Alamos National Laboratory geosynchronous satellites. The existence of T* enables accurate prediction of spacecraft charging onset. In double Maxwellian plasmas, the onset of spacecraft charging depends on the density and temperature of both distributions. We explain pedagogically the onset of charging in double Maxwellian plasmas. Triple-root jumps in spacecraft potential can occur., Pub. in proceedings of the Spacecraft Charging Technology Conference (8th), NASA Marshall Space Flight Center, Huntsville, AL.

A general theory of a method to quantitatively perform optical patternation in a particle field is developed. The general equations of optical radiation are considered, along with general methods of probing the particle field with illuminating light and general methods of performing the required measurements, in order to determine the assumptions, approximations, and conditions under which various kinds of measurements can be performed. Under conditions which exist in many practical applications, it is found that the capabilities of modern optical instrumentation allow the spatial distribution of various properties of a particle field such as particle volume or surface area concentrations to be measured, even when the measurement is complicated by attenuation of the illuminating light, attenuation of the signal light, and secondary emission. The measurements can be performed in fully three dimensional form or within a single two dimensional plane, and under certain conditions can be performed even when the particles are not spherical., Revised September 2003 to correct some incorrect symbols throughout document. This version should replace any previously-distributed versions. Actual dates covered are 01 Oct 1992 thru 04 Mar 2002.

This study characterizes the SPT-25 model with discharge chamber walls made of different materials, including the Russian BN-SiO2-type (BGP) ceramics and the AIN-BN-type and BN-type ceramics produced in France and in the United States, respectively. The first ceramic is used in modern SPT-70 and SPT-100 flight designs and the others are prospective materials for SPT discharge chamber manufacturing. These materials have good thermal resistance and, according to published data, they have different secondary electron emissions. Characterization of thrusters with discharge chamber walls made of these materials could give some indication of secondary electron emission influence on thruster operation and performance. The SPT-25 model has an external accelerating channel diameter of 25 millimeters and an acceptable performance level under discharge powers (100-200)W. To characterize its operation with discharge chamber walls made of different ceramics the authors determined the voltage-current characteristics of this model under different magnetic fields inside the accelerating channel and different mass flow rates through the channel. They also determined thrust values and other output parameters such as thrust efficiency and specific impulse, accelerated ion flow divergence, plume plasma parameters measured by cylindrical electrostatic probe, discharge voltage, and current oscillation characteristics. The results confirm a high performance level by the SPT-25 model with BGP ceramics. Total thrust efficiency was ^0,25 and specific impulse ^885s under power ^100W, and total thrust efficiency was ^0,32 and specific impulse ^1300s under power ^200W. Also, there were notable differences in voltage-current characteristics and thrust values for different ceramics under low mass flow rates and magnetic fields. Moreover, thrust and thrust efficiency were different with different materials even under similar discharge voltages and currents obtained under comparable conditions.7, Presented at the AIAA Joint Propulsion Conference held in Huntsville, AL, on 20-23 Jul 2003. Prepared in collaboration with the Russian Scientific Center, Kurchatov Institute, Moscow, Russia, and the University of Washington, Seattle, WA.

We discuss appearance of an anode current transient which persists a maximum of 500 seconds and results in a 50% increase in the anode current during initial start-up following exposure to ambient laboratory conditions. The anode current transient is characterized by 18 kHz main discharge on/off behavior. This contrasts with the steady state behavior of a strong DC component overlaid with a low amplitude 25 kHz component. Conduction through the radial magnetic field appears to be modified during the transient period. The main discharge chamber is determined to be the source of this behavior. The anode current transient appears to be a result of water absorption on the surface layer of the boron nitride insulator. We speculate as to the connection between the absorption of water and the anode current transient. The modification of the secondary electron emission coefficient could affect near wall conductivity and produce the measured effects. The introduction of hydrogen from dissociated water could also produce these enhanced oscillations., The original document contains color images. All DTIC reproductions will be in black and white.

We have developed a numerical model for the temporal evolution of particle and photon spectra resulting from nonthermal processes at the shock fronts formed in merging clusters of galaxies. Fermi acceleration is approximated by injecting power-law distributions of particles during a merger event, subject to constraints on maximum particle energies. We consider synchrotron, bremsstrahlung, Compton, and Coulomb processes for the electrons, nuclear, photomeson, and Coulomb processes for the protons, and knock-on electron production during the merging process. The broadband radio through gamma-ray emission radiated by nonthermal protons and primary and secondary electrons is calculated both during and after the merger event. Using ROSAT observations to establish typical parameters for the matter density profile of clusters of galaxies, we find that typical merger shocks are weak and accelerate particles with relatively soft spectra. We consider the prospects for detecting nonthermal radio and gamma-ray emission from clusters of galaxies and implications for the origin of ultra-high-energy cosmic rays and the diffuse gamma-ray background. Our results suggest that only a few of the isotropically distributed unidentified EGRET sources are due to shocks formed in cluster mergers and that only a minor contribution to the diffuse extragalactic gamma-ray background can originate from cluster merger shocks. Cluster merger shocks can accelerate protons to < 10(19) eV for the standard parameters considered here. We predict that GLAST will detect several cluster mergers, and depending on the mean magnetic fields in the intracluster medium, the Low Frequency Array could detect anywhere from several to several hundred., Published in the Astrphysical Journal, v594 p709-731 2003.

This report investigates I dimensional and 2 dimensional hall effect thruster models to better understand the following physics related issues: radial structure of the plasma, lateral wall effects, physics of the subsonic region, no near-total ionization regimes, effects of secondary electron emission from the walls, and reduction of the growth rate of self oscillations.

We discuss the appearance of an anode current transient which persists a maximum of 500 seconds and results in a 50% increase in the anode current during initial start-up following exposure to ambient laboratory conditions. The anode current transient is characterized by 18 kHz main discharge on/off behavior. This contrasts with the steady state behavior of a strong DC component overlaid with a low amplitude 25 kHz component. Conduction through the radial magnetic field appears to be modified during the transient period. The main discharge chamber is determined to be the source of this behavior. The anode current transient appears to be a result of water absorption on the surface layer of the boron nitride insulator. We speculate as to the connection between the absorption of water and the anode current transient. The modification of the secondary electron emission coefficient could affect near wall conductivity and produce the measured effects. The introduction of hydrogen from dissociated water could also produce these enhanced oscillations., Pres: 38th AIAA/ASME/SAE/ASEE JPC&E, 7-10 Jul 2002, Indianapolis, IN.

John Prineas was the student supported by this AASERT. In our Progress Reports of July 31, 1998 and June 30, 1999, he described his research on radiatively coupled quantum wells with narrow excitation linewidths (^<0.6 meV) and with periods in the vicinity of half the wavelength of light in the semiconducting material (X012n 830 nm/(2x3.6) 115 nm) 1-8 John won a Dean's Fellowship, so he no longer needed AASERT support for his salary. Soon after he received an unusual invitation to spend several months at Bell Laboratories in the laboratory of Jagdeep Shah AASERT funds were used for his travel and living expenses, making possible this industrial experience and leading to very significant results described in the next section and published in Physical Review Letters. John studied the resonance Rayleigh scattering of disordered periodic semiconductor multiple quantum-well structures experimentally with Jagdeep Shah at Bell Labs. Polaritonic effects were found to dominate the secondary emission dynamics due to the coexistence of several radiant modes with different radiative decay times. They give rise to polarization beating between modes and determine rise and decay times of the resonance Rayleigh scattered signals. These results have been published in Physical Review Letters 9.

An interesting phenomenon of thermal annealing in gamma irradiated undoped, and photorefractive Cu- and Fe-doped. Z-oriented LiNbO3 crystals has been observed. Prior and alter each gamma irradiation the crystals were thermally annealed in the air at 800 deg C for a couple of hours. Optical homogeneity was investigated on the entire areas of LiNbO3 wafers by measuring distributions of birefringence, the principal azimuth, transmission, and parameters associated with birefringence dispersion, and also by measurements of additional absorption in a few wafers' points. It has been rather unexpectedly observed that the classical thermal annealing can lead to a decrease in optical homogeneity in the majority of cases. It is attributed to generation of an internal electric field by the pyroelectric effect, and to the electrooptic effect involved thereafter. On the other hand, the secondary electrons generated by gamma irradiation are believed to increase the optical homogeneity by increasing the crystal's conductivity and dissipating this field. A uniform temperature heating across the wafer generated by this irradiation is also a helpful factor in this gamma-annealing. It has been found that this effect at room temperature is small for gamma irradiation of 10(exp 5) Gy, while increasing the doses to 10(exp 6) Gy and 10(exp 7) Gy can profit in a considerable reduction of the optical inhomogeneity. A certain influence of Cu-doping on this effect has also been observed., Prepared in cooperation with the Polish Society for Crystal Growth, SPIE-The International Society for Optical Engineering in association with SPIE Poland Chapter; Institute of Electronic Materials Technology, Warsaw, Poland; Institute of Chemistry and Nuclear Technics, Warsaw, Poland. Pub. in Proc. SPIE, Vol. 4412 pp203-210, 2001. This article is from ADA399287 International Conference on Solid State Crystals 2000: Growth, Characterization, and Applications of Single Crystals Held in Zakopane, Poland on 9-12 October 2000