Demonstration of microwave generation by a ferroelectric-cathode tube

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Gyrotrons are essential for electron cyclotron resonance heating (ECRH) in fusion reactors, making their efficient operation crucial for fusion energy. Past experiments revealed instability issues due to trapped electrons in the magnetron injection gun (MIG) region, causing undesired currents and operational failures. To address this, tight manufacturing tolerances are required for the MIG geometry~\cite{pago2}. We present findings of the TRapped Electrons eXperiment (T-REX) at the Swiss Plasma Center, desi

It was noticed long time ago that the dielectric permittivity of BaTiO3 single crystals in the rhombohedral phase varies from observation to observation, but the microstructure mechanism behind this phenomenon remained unclear. We show that the variations in susceptibility can be related to the variable domain structure introduced by different pre-treatments at higher temperatures: Electrical depoling at room temperature leads to nano-sized domains and ultrahigh susceptibility in rhombohedral phase, whereas

This paper focuses on the fabrication and evaluation of vibration energy harvesting devices by utilizing an epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin film. The high quality of the c-axis oriented PZT layer results in a high piezoelectric coefficient and a low dielectric constant, which are key parameters for realizing high performance piezoelectric energy harvesters. Different cantilever structures, with and without a Si proof mass, are realized using micro-patterning techniques optimized for the epitaxial oxi

This study aims to quantify in a holistic approach chromium (Cr) contamination in solid oxide fuel cell (SOFC) stack testing using adapted tools: i) a hot gas sampling method to analyze volatile Cr species in the air flux at the cathode inlet location; ii) a rapid quantification method for Cr as condensed matter in cathode material of post-test samples. The hot air sampling method reveals itself as a reproducible and time-resolved quantification technique for Cr trace amounts in a gas flow; this technique i

In a multi-gyrotron system such as the one presently designed for the ITER ECH & ECCD system, stray magnetic fields can significantly alter the operational capabilities of the global system. A numerical study was carried out within the European Gyrotron Consortium (EGYC) to assess the importance of the different effects and their impact on the gyrotron operation. Using the Ariadne++ 3D code, and based on the geometrical layout of the ITER-EC system, the effect of the ITER stray magnetic field combined toget

Pb(Zr, Ti)O-3 (PZT) is an interesting material for bulk acoustic wave resonator applications due to its high electromechanical coupling constant, which would enable fabrication of large bandwidth frequency filters. The major challenge of the PZT solid solution system is to overcome mechanical losses generally observed in PZT ceramics. To increase the understanding of these losses in textured thin films, thin film bulk acoustic resonators (TFBAR's) based on PZT thin films with compositions either in the tetr

A detailed study of the operational capabilities of the W7-X/1MW gyrotron operated at 126GHz/TE26,7 is presented. This study is associated with the foreseen upgrade of TCV in which it is planned to add to the present EC system 3MW of additional RF power bringing the total EC-power to 7.5MW. This study is extended to a possible operation of the gyrotron at the ITER relevant frequency of 168GHz in the TE35,9 mode without implementing any further modification neither in the gyrotron nor in the gyrotron superco

This work shows a self-consistent numerical model of ion cyclotron resonant heating (ICRH) in a plasma of arbitrary (2D or 3D) geometry. Effects of anisotropy and full shaping on both MHD equilibrium and the dielectric tensor are explored. In particular, it is shown that the dielectric tensor becomes dependent on poloidal angle. Also, the anisotropic effects dominate the dielectric tensor. Using single particle simulations it is demonstrated that anisotropy develops due to ICRH. The changing of the equilibr

Models of amorphous (HfO2)x(SiO2)(1), for varying hafnium, content x are generated by ab initio molecular dynamics. The structural properties are analyzed in terms of pair distribution functions from which typical bond lengths and coordination numbers are extracted. Electronic band gaps are calculated with a hybrid density functional and are found to decrease in a nonlinear way with increasing x, in accord with experimental observations. Static dielectric constants are evaluated through the application of a

We discuss the structural, electronic and dielectric properties of a model structure of the Si(100)-SiO2 interface that accounts for the amorphous nature of the oxide. After showing that the structural properties of this model are consistent with a variety of experimental data, we consider the variation of the valence and conduction band edges across the interface. Our calculations indicate that the width of the electronic structure transition from the substrate to the oxide is 0.7-0.8 nm. We also address t

We investigate the dielectric permittivity of SiO2 on Si(100) substrates using a first-principles approach. It is shown that both the static and high-frequency dielectric constants of the oxide overlayer increase when the oxide thickness is reduced. This behavior of the overlayer is found to be well reproduced by a classical two-layer model in which the pure oxide and the suboxide layer are treated as distinct dielectrics. Implications for interfaces between silicon and high-k gate oxides are discussed. (C)

Sol-gel process has successfully been applied for the deposition of porous PbZrxTi1-xO3 (x = 0.45, 0.15) thin films on platinized silicon wafers. Addition of a polymer as a volatile phase to the precursor sol prior to spin coating has been proved an excellent method to synthesize PZT-porous films. Introduction of pores creates a matrix void composite resulting in high figures of merit for pyroelectric applications. The dielectric constant was found to be strongly dependent to the porosity, whereas the pyroc

In ferroelectric materials, domain wall displacement plays a key role in the dielectric properties measured with respect to the driving field amplitude and frequency. The low to medium field dielectric response in many ferroic systems can be often described by classical Rayleigh model, which is rate-independent i.e., it depends only on the strength of ac signal. However experiments show that the nonlinear parameters are frequency dependent. Thus a more general approach, which can describe both purely nonlin

A review of the properties of ferroelectric materials that are relevant to microwave tunable devices is presented: we discuss the theory of dielectric response of tunable bulk materials and thin films; the experimental results from the literature and from own work are reviewed; the correspondence between the theoretical results and the measured properties of tunable materials is critically analyzed; nominally pure, real (defected), and composite bulk materials and thin films are addressed. In addition, tech

PbTiO3 thin films were prepared from alkoxide solution precursors and crystallized onto Pt/TiO2/SiO2/Si substrates. Microscopy observations revealed that the complexity of the domain walls structure decreased with the grain size. Dielectric, electrostrictive, and piezoelectric properties of the films were characterized in details. A shift of the temperature of the dielectric permittivity maximum due to stresses in the plane of films has been observed. Electrostrictive M and Q coefficients were estimated by

The printing of lead zirconate titanate (PZT, Pb(Zr,Ti)O-3) piezoelectric thick films on silicon substrates is being studied for potential use as microactuators, microsensors, and micro.. transducers. A fundamental challenge in the fabrication of useful PZT thick-film devices on silicon is to sinter the PZT to high density at sufficiently low temperature to avoid mechanical or chemical degradation of the silicon substrate. The goal of the present study is to develop and implement suitable electrodes and PZT

A study of the complex permittivity in bismuth titanate was conducted to reveal the nature of an anomaly in the real part of the permittivity, which occurs below the Curie temperature. This anomaly is frequency dependent and is caused by a combination of two relaxation phenomena that appear in the imaginary part of the permittivity. One of the relaxations showed classic characteristics of an ion-jump process. Niobium doping suppressed this relaxation and eliminated the nonferroelectric anomaly in permittivi

Pb(Zr, Ti)O-3 (PZT) and Pb(Zr, Ti, Nb)O-3 (PNZT) thin films have been deposited on platinized silicon substrates by sputtering followed by a postannealing treatment. The Nb concentration in the films varied between 1 and 7 at. % with increments of 1 at. %. The effects of Nb modification on the piezoelectric response, and particularly on the longitudinal piezoelectric coefficient d(33), have been investigated. The introduction of Nb enhances the dielectric and piezoelectric properties of the PZT films. The b

The non-linear dielectric properties of single crystals of PbMg1/3Nb2/3O3 relaxer ferroelectric were investigated experimentally by using measurements of the dielectric permittivity of this material as a function of the DC bias and the AC driving fields. The results were analyzed using four models of the dielectric response of relaxors currently discussed in the literature, It was shown that among them only one model was consistent with the experimental data. This provides strong evidence that the mechanism

The effective piezoelectric coefficient e(31) has been measured on sol-gel processed Pb(ZrxTi1-x)O-3 thin films with Zr concentrations ranging from 45 to 60%. The largest value was observed at 45% Zr, although dielectric constant and effective d(33) peak at 53% Zr. The findings suggest that the optimal composition for microactuators and sensors is less than or equal to 45% Zr, i.e., in the tetragonal part of the phase diagram.

Demonstration of microwave generation by a ferroelectric-cathode tube

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The Diocotron Instability in the Trapped Electrons Experiment T-REX and its Relevance to Electron Clouds in Gyrotron Guns

Unusual dielectric behavior and domain structure in rhombohedral phase of BaTiO3 single crystals

The realization and performance of vibration energy harvesting MEMS devices based on an epitaxial piezoelectric thin film

Multi-Scale Assessment of Cr Contamination Levels in SOFC Cathode Environment

Calculation of Stray Magnetic Field Effects on the Operation of the ITER Electron Cyclotron System

Dielectric and acoustical high frequency characterisation of PZT thin films

Design studies of the dual-frequency operation of the W7-X/140GHz/1MW gyrotron at 126GHz for TCV and 168GHz for ITER

Monte Carlo ICRH simulations in fully shaped anisotropic plasmas

Amorphous hafnium silicates: structural, electronic and dielectric properties

Atomic-scale modelling of the Si(100)-SiO2 interface

Dielectric effect of a thin SiO2 interlayer at the interface between silicon and high-k oxides

Enhanced performance of pyroelectric microsensors through the introduction of nanoporosity

Analysis of the non linear domain wall response in ferroelectric thin films

Ferroelectric materials for microwave tunable applications

Properties of ferroelectric PbTiO3 thin films

Processing and properties of screen-printed lead zirconate titanate piezoelectric thick films on electroded silicon

Niobium doping and dielectric anomalies in bismuth titanate

Evaluation of niobium effects on the longitudinal piezoelectric coefficients of Pb(Zr, Ti)O-3 thin films

Mechanism of polarization response and dielectric non-linearity of PbMg1/3Nb2/3O3 relaxor ferroelectric

In-plane piezoelectric coefficient of PZT thin films as a function of composition