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The increasing demand for powerful, reliable, and efficient gyrotron oscillators for Electron Cyclotron Resonance Heating (ECRH) in fusion plasma experiments requires a close look at the various factors in gyrotrons that determine gyrotron performance. In this frame, the influence of emitter surface roughness, emission inhomogeneity, and secondary electron generation on gyrotron operation is presented, with focus on Low Frequency Oscillations (LFOs) and Electron Beam Halo (EBH) generation.

Strahlsysteme --- Emitter --- Low Frequency Oscillations --- Magnetron Injection Gun --- Gyrotron --- Electron Beam Halo --- Electron Beam HaloGyrotron

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The mysteries of the universe have always fascinated people on earth. Hence, methods to observe and study it in details have been and are still being developed. Since the first detection of gravitational wave at LIGO (Laser Interferometer Gravitational-wave Obser- vatory) in 2015, a new tool to study the universe was added to the panel of existing ones. It is called gravitational wave astronomy.
However, the detection of such waves is a technical challenge as their effects are ex- tremely small. As a result, the detectors that aims to capture them must have a tremen- dous degree of precision. The various noise sources to which they are subjected must then be drastically reduced. An important one is the vibration of the detector due to seismic motion. Passive as well as active isolation systems are thus employed to isolate the detector from the ground motion.
The goal of this work is to design a type of optimal controller called linear quadratic Gaussian (LQG) controller on an existing experimental isolation platform. The design is separated into two main steps. The first is the development of a full-state observer to estimate the states of the isolation platform from its outputs. The second is the design of a linear quadratic regulator (LQR) to control the system. The two are then combined to form the LQG controller to be used as feedback in a closed-loop system with the initial plant.
The performances of this controller are finally analysed and discussed. From this analysis, it emerged that the controller allows to increase the isolation performances of the platform by about one order of magnitude between 0.1 Hz and 1 Hz and by two order of magnitudes from 1 Hz to 10 Hz. Therefore, conclusion has been made that this type of controller were appropriate to provide good isolation performances to the experimental platform in the control bandwidth [0.1,10] Hz. The next step is now to implement it experimentally to address its performances in real situations.

Active isolation --- seismic motion --- Low frequency --- LQG control --- gravitational wave --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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The gravitational wave detectors must be isolated from the Earth’s constant vibrations to be able to sense low-frequency gravitational waves. The combined performances of passive and active isolation stages allow getting close to the target requirements in terms of seismic vibration isolation. A new active platform is currently designed. Its embedded inertial sensors measure the ground motion, which is then actively canceled by actuators. The inertial sensors require a large dynamic measurement range, which can be achieved by lowering the sensor resonance frequency while increasing the resonance frequency of internal modes away from the operational range.
The leaf-spring suspension composing the gravity compensator system of a vertical inertial sensor, the Compact Interferometric Inertial Sensor (μVINS), is numerically and experimentally characterized. The end-purpose of the study is to extend the dynamic measurement range of that particular inertial sensor by evaluating the impact on its resonance frequencies of various parameters related to the leaf-spring suspension. Following the numerous studies, numerical and experimental, performed in the context of this work, design guidelines are devised, enabling the suspension to be tuned into a low resonance frequency quasi-zero stiffness mechanism. The μVINS design can be modified to be competitive with the already existing sensors, while being more compact. Optimizing the leaf-spring suspension length and clamping location enabled the resonance frequency to be decreased by one order of magnitude. The measurement bandwidth is thus also increased by one order of magnitude. With the capacity to measure lower frequency displacements, μVINS can feed a wider range of data to the active stage and ensure an effective low-frequency isolation.

Inertial sensor --- low-frequency measurements --- broad-band seismometry --- leaf-spring suspension --- quasi-zero stiffness --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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In order to understand the current-voltage behaviour of a Lithium-Ion Battery, its impedance needs to be investigated in the low-frequency domain. This work deals with measurement, modelling and model validation in that low-frequency domain and introduces the Distribution-Function-of-Differential-Capacity (DDC) as a new tool for investigating capacity contributions of different particle sizes and particle types inside of a Lithium-Ion Battery.

Lithium-Ion-Battery --- Lithium-Ionen-Batterie --- Distribution Function of Differential Capacity (DDC) --- Impedanz --- Batteriemodell --- Low-Frequency --- Verteilungsfunktion der differentiellen Kapazität (DDC) --- Battery-Model --- Niederfrequenz --- Impedance

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The major emphasis of this book is on physical mechanisms and sources of the ULF/ELF natural electromagnetic fields noises. In the course of this text, some of these mechanisms of magnetospheric origin will be treated in detail and others in a more sketchy fashion, while the global electromagnetic resonances excited by lightning activity and other sources are the priority. The interested reader is referred to the books cited in the text for details about the ULF/ELF fields of magnetospheric origin. Much emphasis is put on studies of electromagnetic phenomena caused by rock deformation/fracture including the ULF/ELF effects possibly associated with tectonic activity, earthquakes, and other natural disasters. One of the challenges of this research is to fully understand electromagnetic effects and physical processes in the rocks deep in the Earth’s crust.

ELF electromagnetic fields --- ELF electromagnetic fields. --- Environmental aspects. --- ELF fields --- Extremely low frequency electromagnetic fields --- Extremely low frequency fields --- Electromagnetic fields --- Physical geography. --- Geophysics/Geodesy. --- Atmospheric Sciences. --- Geophysics and Environmental Physics. --- Geography --- Geophysics. --- Atmospheric sciences. --- Atmospheric sciences --- Earth sciences --- Atmosphere --- Geological physics --- Terrestrial physics --- Physics