Search results for "Applied Physics"
showing 10 items of 1226 documents
Self-consistent non-stationary theory of the gyrotron
2016
For a long time, the gyrotron theory was developed assuming that the transit time of electrons through the interaction space is much shorter than the cavity fill time. Correspondingly, it was assumed that during this transit time, the amplitude of microwave oscillations remains constant. A recent interest to such additional effects as the after-cavity interaction between electrons and the outgoing wave in the output waveguide had stimulated some studies of the beam-wave interaction processes over much longer distances than a regular part of the waveguide which serves as a cavity in gyrotrons. Correspondingly, it turned out that the gyrotron theory free from the assumption about constant amp…
Risk Assessment of Electron Induced SEE during the JUICE Mission
2018
The SEE sensitivity of electronic devices to high energy electrons has been put in evidence experimentally. Several ground experiments have shown that electron induced SEE could occur in recent technologies. In the case of the JUICE mission, the expected electron environment is harsher than for Earth orbits. The impact of such electron fluxes on the embedded electronics was assessed in this work. The study focused on SRAM memories SEU sensitivity. Three different device references were tested under electrons, as well as under protons and heavy ions. The electron and the low energy proton direct ionization contributions to the total SEU rate have been studied in more detail.
Effects of magnetic configuration on hot electrons in a minimum-B ECR plasma
2020
International audience; To investigate the hot electron population and the appearance of kinetic instabilities in highly charged electron cyclotron resonance ion source (ECRIS), the axially emitted bremsstrahlung spectra and microwave bursts emitted from ECRIS plasma were synchronously measured on SECRAL-II (Superconducting ECR ion source with Advanced design in Lanzhou No. II) ion source with various magnetic field configurations. The experimental results show that when the ratio of the minimum field to the resonance field (i.e. Bmin/Becr ) is less than ~0.8, the bremsstrahlung spectral temperature Ts increases linearly with the Bmin/Becr –ratio when the injection, extraction and radial mi…
Topological two-dimensional Su–Schrieffer–Heeger analog acoustic networks: Total reflection at corners and corner induced modes
2021
In this work, we investigate some aspects of an acoustic analogue of the two-dimensional Su-Schrieffer-Heeger model. The system is composed of alternating cross-section tubes connected in a square network, which in the limit of narrow tubes is described by a discrete model coinciding with the two-dimensional Su-Schrieffer-Heeger model. This model is known to host topological edge waves, and we develop a scattering theory to analyze how these waves scatter on edge structure changes. We show that these edge waves undergo a perfect reflection when scattering on a corner, incidentally leading to a new way of constructing corner modes. It is shown that reflection is high for a broad class of edg…
Enhanced acoustic pressure sensors based on coherent perfect absorber-laser effect
2021
Lasing is a well-established field in optics with several applications. Yet, having lasing or huge amplification in other wave systems remains an elusive goal. Here, we utilize the concept of coherent perfect absorber-laser to realize an acoustic analog of laser with a proven amplification of more than 10 4 in terms of the scattered acoustic signal at a frequency of a few kHz. The obtained acoustic laser (or the coherent perfect absorber-laser) is shown to possess extremely high sensitivity and figure of merit with regard to ultra-small variations of the pressure (density and compressibility) and suggests its evident potential to build future acoustic pressure devices such as precise sensor…
Thermal cloaking of complex objects with the neutral inclusion and the coordinate transformation methods
2019
We explore the cloaking of a complex shape by either the neutral inclusion or the transformation thermodynamics (TT) methods. Thin cloaks are built and the heat cloaking efficiency is investigated for both the steady-state and the transient regimes. We show that the neutral inclusion cloak is more efficient in both regimes, though it has the drawback that the thermal conductivity of the cloaked shape must be known. In practice, the neutral inclusion method is more flexible and easier to implement than the coordinate transformation method, especially for complex shapes.We explore the cloaking of a complex shape by either the neutral inclusion or the transformation thermodynamics (TT) methods…
Fundamental Noise Limits and Sensitivity of Piezoelectrically Driven Magnetoelastic Cantilevers
2020
International audience; Magnetoelastic sensors for the detection of low-frequency and low-amplitude magnetic fields are in the focus of research for more than 30 years. In order to minimize the limit of detection (LOD) of such sensor systems, it is of high importance to understand and to be able to quantify the relevant noise sources. In this contribution, cantilever-type electromechanical and magnetoelastic resonators, respectively, are comprehensively investigated and mathematically described not only with regard to their phase sensitivity but especially to the extent of the sensor-intrinsic phase noise. Both measurements and calculations reveal that the fundamental LOD is limited by addi…
A summary of expressions for central performance parameters of high efficiency solar cell concepts
2019
This work reviews expressions for central performance parameters of various types of PV-concepts when operating at the radiative limit. Some new expressions not published elsewhere are also included. The performance parameters include the short circuit current density, the open circuit voltage, the maximum power density and the optimal voltage. The cell concepts include single junction cells, cells optically coupled to up- and down-converters, intermediate band solar cells and a couple of implementations of multijunction devices. The Lambert W function is used to express the maximum power density.
Real space observation of two-dimensional Bloch wave interferences in a negative index photonic crystal cavity
2008
We report here the direct observation of two-dimensional (2D) Bloch wave interferences in a negative index photonic crystal by using optical near-field microscopy techniques. The photonic crystal is formed by a defectless honeycomb lattice of air holes etched in III-V semiconductor slab. A scanning near-field optical microscope is used to visualize spatially, as well as spectrally, the light distribution inside the photonic crystal. The recorded near-field spectra and maps presented here unambiguously demonstrate the Bloch wave interferences within the photonic crystal. Then, the spectral and spatial evolution of these interferences allows us to recover experimentally the 2D band diagram of…
Using of reflections for expansion of frequency tuning in a THz-band gyrotron
2017
Effect of delayed reflection on operation of a second-harmonic THz-band gyrotron is studied. Theoretical analysis, numerical calculations and experimental observations for the 0.394 THz FU CW IIB gyrotron are presented.