Development of Remote Handling Technologies Tolerant to Operation Ready Fusion Reactor Conditions

The International Thermonuclear Experimental Reactor (ITER) will be the next step towards fusion power plants, featuring deuterium-tritium plasma to generate 500 MW of fusion power. Using tritium will result in the activation of the vacuum vessel materials, requiring robotic manipulators to carry out the maintenance of the machine. One of these robots must perform inspection tasks, such as carrying the ITER In-Vessel Viewing System (IVVS), and will need to be deployed in conditions as close as possible to the operating machine; the vacuum inside the vessel should be kept clean, the wall temperature and radiation level will be high, and the toroidal magnetic field should still be on. The robot should be able to place the probe within view of a good percentage of the plasma-facing wall covering the whole vacuum vessel. This study aims to provide technical solutions for every system of a robotic manipulator in this environment. The effects of the magnetic field on the different systems of a robot will be investigated, from the fundamentals of theory to practical experimentation, using a specially designed magnetic field generator. Solutions for actuation, sensing, logic system, and command that are tolerant of the magnetic field or actively use it to enhance the performance of the robotic manipulator are provided. A preliminary design of a robot using the technical solutions developed in this thesis as per the specifications of the IVVS is presented. The design is meant to demonstrate the feasibility of a robotic manipulator featuring multiple degrees of freedom within the constraints considered. Guidelines for geometry, actuation, sensing and logic systems design are provided that should allow the robotic manipulator to place its probe for it to view more than 99% of the first wall. Finally, a summary of the major contributions of the thesis is given in conclusion. The major effects of a magnetic field on robot components are listed with guidelines on how to cope with them in the design. This chapter also sums up the different technologies, their advantages, and their limitations

Surface-Mounted Metal-Organic Frameworks as the Platform for Surface Science: Photoreactivity, Electroreactivity, and Thermal Reactivity

Bisher haben Forscher Modellsysteme wie Einkristallmetalle oder Metalloxide entwickelt, um reale Pulversysteme besser zu verstehen. Es bestehen jedoch immer noch Fragen hinsichtlich der Oberflächenstruktur und Reaktivität von MOFs (Metall-organische Gerüstverbindungen). Glücklicherweise bieten oberflächenorientierte SURMOFs (surface-oriented SURMOFs) einen alternativen Ansatz für den Aufbau von Modellplattformen zur Untersuchung dieser grundlegenden Aspekte von MOFs. Diese Arbeit konzentriert sich auf die organische Photochemie, Elektrokatalyse und thermische Pyrolyse von MOFs aus einer physikalisch-chemischen Perspektive unter Verwendung von Oberflächenwissenschaftstechniken und SURMOF-Plattformen. Das Ziel dieser Arbeit besteht nicht nur darin, das Wissen über MOFs und SURMOFs zu erweitern, sondern auch die Leistungsfähigkeit von Oberflächenwissenschaftstechniken und -methoden im Bereich chemischer Reaktionen zu demonstrieren. Zu diesem Zweck verwendet die Arbeit eine hochmoderne UHV-IRRAS-Apparatur (Ultra-High-Vacuum Infrared Reflection Absorption Spectroscopy). Ein auf der Oberfläche montiertes MOF (SURMOF) Modellsystem mit Azid-Seitenketten wurde erfolgreich hergestellt und genau überwacht, um chemische Veränderungen während des Betriebs zu erfassen. Die umfassenden Ergebnisse, die durch die Kombination von IRRAS mit in situ XRD, MS und XPS erzielt wurden, zeigen, dass die Photoreaktion von Azid durch die Bildung von hochaktiven Nitren-Gruppen initiiert wird, die anschließend mit benachbarten C=C-Bindungen des Gerüsts reagieren und Pyrrol-Derivate durch intramolekulare Aminierung erzeugen. Ein hochwertiges ZIF-67-SURMOF wurde in einem Flüssigphasen-Schicht-für-Schicht-Verfahren hergestellt und erstmals in der Sauerstoffentwicklungskatalyse (OER) eingesetzt. Die katalytisch aktiven Spezies, CoOOH, in den SURMOF-Derivaten wurden identifiziert, was Einblicke in die Mechanismen der strukturellen Transformation und die Struktur-Leistung-Beziehungen bietet. Durch Zugabe von Ni und B wurde die Überspannung auf 375 mV bei 10 mA/cm2 reduziert. Zusätzlich wurden in situ IRRAS und XPS verwendet, um die strukturellen Übergänge von ZIF-67 zu kohlenstoffhaltigen Materialien mit Stickstoffelementen zu enthüllen. NEXAFS-Daten zeigen eine abschließende graphitische Struktur der kohlenstoffhaltigen Materialien nach Pyrolyse bei 900 K. Hoffentlich kann diese Arbeit das grundlegende Verständnis und die Anwendungsfelder von auf MOF und SURMOF basierenden Materialien erweitern

Characterization of Quantum Efficiency and Robustness of Cesium-Based Photocathodes

High quantum efficiency, robust photocathodes produce picosecond-pulsed, high-current electron beams for photoinjection applications like free electron lasers. In photoinjectors, a pulsed drive laser incident on the photocathode causes photoemission of short, dense bunches of electrons, which are then accelerated into a relativistic, high quality beam. Future free electron lasers demand reliable photocathodes with long-lived quantum efficiency at suitable drive laser wavelengths to maintain high current density. But faced with contamination, heating, and ion back-bombardment, the highest efficiency photocathodes find their delicate cesium-based coatings inexorably lost. In answer, the work herein presents careful, focused studies on cesium-based photocathodes, particularly motivated by the cesium dispenser photocathode. This is a novel device comprised of an efficiently photoemissive, cesium-based coating deposited onto a porous sintered tungsten substrate, beneath which is a reservoir of elemental cesium. Under controlled heating cesium diffuses from the reservoir through the porous substrate and across the surface to replace cesium lost to harsh conditions -- recently shown to significantly extend the lifetime of cesium-coated metal cathodes. This work first reports experiments on coated metals to validate and refine an advanced theory of photoemission already finding application in beam simulation codes. Second, it describes a new theory of photoemission from much higher quantum efficiency cesium-based semiconductors and verifies its predictions with independent experiment. Third, it investigates causes of cesium loss from both coated metal and semiconductor photocathodes and reports remarkable rejuvenation of full quantum efficiency for contaminated cesium-coated surfaces, affirming the dispenser prescription of cesium resupply. And fourth, it details continued advances in cesium dispenser design with much-improved operating characteristics: lower temperature and cleaner operation. Motivated by dispenser integration with semiconductor coatings, initial fabrication of those coatings are reported on dispenser-type substrates with measurement of quantum efficiency and analysis of thermal stability. Detailed investigations are performed on dispenser substrate preparation by ion beam cleaning and on dispenser pore structure by electron microscopy and focused ion beam milling. The dissertation concludes by discussing implications of all results for the demonstration and optimization of the future high quantum efficiency cesium dispenser photocathode

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

Low resistance metal semiconductor contacts : low power nano-electronics and sensing

PhD ThesisMetal semiconductor (MS) contacts are essential in nearly every electronic device. High electrical contact resistance degrades device performance, especially at smaller device geometries. The contact resistance normally scales inversely with the cross-sectional area of the MS contact, and this results in poor electrical conduction in small geometries. Additionally, experiments confirm that surface effects dominate over bulk properties, especially at nanoscale geometries. These conditions impose several restrictions in implementing various device technologies. The electronic properties of metal-semiconductor contacts in some important semiconductors such as Si, Ge, GaAs, among others are found to be largely insensitive to the metal workfunction and semiconductor doping level, due to a phenomenon called Fermi level pinning (FLP). FLP can severely degrade device performance, and creates several fabrication challenges. Many semiconductors lose their applicability in mainstream electronics due to restrictions imposed by this effect. FLP effects are practically observed in many semiconductors doped below 1019 cm−3 and are most pronounced in lightly doped and (~intrinsic) pure crystals. This thesis explores material engineering methods to improve contact to semiconductors, without resorting to heavy doping. Large area metal contacts (length/ diameter (d)~ 50-300 μm) are fabricated on Si and Ge. Three key approaches are investigated: (1) Modifying interface dipoles and blocking Metal Induced Gap States (MIGS) using ~ nm thick charged oxide interlayers, implementing planar metal interlayer semiconductor (MIS) contacts (Chapter 4). (2) Exploiting geometric field enhancement in nanostructured hybrid contacts (Chapter 5) and (3) Exploiting voltage controlled non-equilibrium electron heating in island metal films. The contacts produced by these methods (2) and (3) are the first experimental demonstrations to show that limitations imposed by FLP can be overcome by modifying the contact material geometry alone, without using heavy doping. Applying mV range bias to these metallizations causes hot carrier emission from these contact’s nanostructured surfaces. Hot carriers are non-equilibrium, energetic carriers that easily overcome the FLP effect in the semiconductor. High conductivity is observed due to the hot carrier effect over a broad range of temperatures –from 4.2 K, tested up to 500 K- despite using low doping in the semiconductor (ND ~ 6.4 × 1014 cm−3). Novel transport processes are revealed by hot carrier tunnelling and emission mechanisms, which improve conductivity in semiconductors, and will potentially be applicable to other low dimensional materials as well. The results in Chapter 5 show an interesting demonstration of hot carrier edge scaling current injection used to achieve Ohmic contact to low doped n-Ge. This contact scheme presents a ii promising alternative to improving conductivity extrinsically, without using heavy doping, and in a scalable manner. Chapter 6 also contains a proof of concept demonstration. It is shown that closely spaced networks of metal nano-islands of critical dimensions are susceptible to non-equilibrium electron heating, when they receive power in the form of voltage controlled tunnel current. This leads to elevated electron temperatures (~103 K) relative to a cold lattice (at ambient temperature). Hot carriers easily overcome small (few eV) electrostatic barriers e.g. Schottky barrier. Consequently, Ohmic conduction is observed at room temperature, and near ballistic hot carrier conduction is observed at 4.2 K through the entire low doped wafer (thickness 0.5 mm, ND ~ 6.4 × 1014 cm−3). The wide scope of these findings may find promising applications in nanoelectronic engineering and applied science. There is considerable incentive to continue the research, and obtain a wider range of materials capable of similar effects, described further in the thesis outlook (Chapter 7). Advancing this research further will translate to applications in high speed switching, sensing, optoelectronics and energy harvesting. It is anticipated that these technologies will be applicable to many semiconductors and can be adapted into heterostructures, using advanced fabrication methods

NASA Tech Briefs, October 1990

Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical' Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Proceedings of the 40th Aerospace Mechanisms Symposium

The Aerospace Mechanisms Symposium (AMS) provides a unique forum for those active in the design, production and use of aerospace mechanisms. A major focus is the reporting of problems and solutions associated with the development and flight certification of new mechanisms. Organized by the Mechanisms Education Association, responsibility for hosting the AMS is shared by the National Aeronautics and Space Administration and Lockheed Martin Space Systems Company (LMSSC). Now in its 40th symposium, the AMS continues to be well attended, attracting participants from both the U.S. and abroad. The 40th AMS, hosted by the Kennedy Space Center (KSC) in Cocoa Beach, Florida, was held May 12, 13 and 14, 2010. During these three days, 38 papers were presented. Topics included gimbals and positioning mechanisms, CubeSats, actuators, Mars rovers, and Space Station mechanisms. Hardware displays during the supplier exhibit gave attendees an opportunity to meet with developers of current and future mechanism components. The use of trade names of manufacturers in this publication does not constitute an official endorsement of such products or manufacturers, either expressed or implied, by the National Aeronautics and Space Administratio

NASA Tech Briefs, August 1991

Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Fabrication and integration of metallic nano and micro cones for on-chip electron field emitters

Nanotechnology enables a diversity of new effects compared to the classical physical properties of the material. The metallic wires with a dimension of less than 1 µm and a length between 10 µm to 50 µm exhibit a great aspect ratio. A high density of such wires particularly gives a great surface to volume ratio, which results in new mechanical, electrical, thermal, and chemical properties of the surfaces covered with them. These new physical and chemical effects enable a new level of more sensitive sensors like chemical, biological, gas flow, force, and inertial sensors. Also, low resistance micro switches, more efficient thermal interface materials, and room-temperature interconnects can be enabled with nanowired surfaces. The high aspect ratio of the wires enables them to be applied as a high-performance electron field emitter. For realizing these applications there is an obstacle to overcome: Vertical integration of the metallic nanowires into a 3D microsystem. This work introduces a technique for in-situ integration of nanowires into microsystems with a focus on an application in sensor technology and commercial and industry suitable fabrication. The objective of this work is to develop an on-chip electron field emitter, based on metallic nanowires, for measuring vacuum pressures less than 10^-12 mbar in cryogenic systems at temperatures below 6 K. A review of state-of-the-art technologies in vacuum measurement sets the basis for discussing possibilities to eliminate or minimize the problems of the field emitter based gauges. It is shown theoretically that using the metallic nanowires with high aspect ratio and sharp tips as an electron field emitter results in a great local electrical field enhancement, thus, a higher current emission. For fabricating the wires the so-called ion-track etch process is used. Such nanowires are also known as template grown wires because the nanowires are electrochemically synthesized in the pores of the ion-track etched template membranes. With this process, nanowires with a diameter from 30 nm to some µm and a length of 2 µm to 100 µm with different densities in the range of 10^4 cm^-2 to 10^9 cm^-2 can be realized. The development of a process for in-situ integration of the wires into a 10 mm x 30 mm surface (as 16x50 array of pads) and the developed devices and techniques are explained in detail. The process and the electrochemical deposition device are optimized to enable covering broad surfaces with nanowires. With the optimization, the nanowires can be integrated into the whole surface with 300 mm x300 mm dimensions and also industrial 12-inch wafers. Compared to cylindrical nanowires, conical structures show a much better thermomechanical performance. Therefore, the used ion-track templates are etched asymmetrically in an etching device, developed in this work including an electrical measurement process to control the apex angle of the conical pores. Theoretically, with the conical structure a stable current emission, sufficient for vacuum pressure measurement, with a significantly longer lifetime of the emitting cones is expected. These effects are experimentally explored with a large variety of samples. The field emission characteristics of the nanocones in a diode and triode setup are measured and described in detail. In a long term measurement a stable field emission current of 31 µA at an applied voltage of 290 V for 50 h and above 100 µA at an applied voltage of 338 V for 12.5 h shows the potential of this emitter structure for enough stable current emission for XHV vacuum pressure measurement. To complete the structure of an on-chip emitter, an extraction grid for applying the extraction voltage as well as transmission of the emitted current must be attached over the nanocones. A concept for an XHV suitable integration of the extraction grid is designed. This concept is pursued by the idea, which is to use nanowires as a hook and loop fastener. In this application, two surfaces are covered with nanowires. By pressing these surfaces on top of each other both surfaces are bonded at room temperature. This process takes place by entanglement and diffusion of the nanowires into each other. The development of this room temperature bonding technology and exploring the mechanical and electrical properties of the connections are discussed in detail. This new technology is presented for a heat-free bonding of semiconductors on pads down to 3 µm and pitches lower than 5 µm. Also, this technology has the potential of a wafer-wafer and die-wafer bonding in large scales and with temperatures far below 230 °C or at room temperature. In the context of this work, the company NanoWired GmbH was founded. This company transfers the developed technology to the market for applications in semiconductor, automotive, sensor, and light segments. Different conventional methods like glueing, welding, soldering, or screws can be substituted with this technology

1996 Laboratory directed research and development annual report

This report summarizes progress from the Laboratory Directed Research and Development (LDRD) program during fiscal year 1996. In addition to a programmatic and financial overview, the report includes progress reports from 259 individual R&D projects in seventeen categories. The general areas of research include: engineered processes and materials; computational and information sciences; microelectronics and photonics; engineering sciences; pulsed power; advanced manufacturing technologies; biomedical engineering; energy and environmental science and technology; advanced information technologies; counterproliferation; advanced transportation; national security technology; electronics technologies; idea exploration and exploitation; production; and science at the interfaces - engineering with atoms