68 research outputs found
Depth-resolving the redox compensation mechanism in LixNiO2
The performances of lithium-ion batteries are set by the electrodes materials
capacity to exchange lithium ions and electrons faster and reversibly. To this
goal Ni-rich layered metal oxides, especially LiNiO2, are attractive electrode
candidate to achieve both high voltage and capacities. Despite its
attractiveness, several drawbacks for its industrialization are related to
different form of surface and bulk instabilities. These instabilities are due
to redox process involving the charge transfer between cations and anions.
Therefore, a fundamental understanding based on further experimental evidence
is required to resolve of charge transfer between the cation and anion from the
surface to the bulk in LiNiO2. Herein, we resolve the role of nickel and oxygen
in the charge compensation process in LixNiO2 electrodes from the extreme
surface down to 30 nm by energy-dependent core-level HAXPES supported by ab
initio simulation. We emphasize the central role of oxygen in the bulk charge
compensation mechanism from LiNiO2 to NiO2 due to the negative charge transfer
and bond/charge-disproportionation characters of LiNiO2. This bulk behavior is
in turn responsible for surface deoxygenation and nickel reduction upon
delithiation
Advanced Simulations of Optical Transition and Diraction Radiation
Charged particle beam diagnostics is a key task in modern and future accelerator installations. The diagnostic tools are practically the “eyes” of the operators. The precision and resolution of the diagnostic equipment are crucial to define the performance of the accelerator. Transition and diffraction radiation (TR and DR) are widely used for electron beam parameter monitoring. However, the precision and resolution of those devices are determined by how well the production, transport and detection of these radiation types are understood. This paper reports on simulations of TR and DR spatial-spectral characteristics using the physical optics propagation (POP) mode of the Zemax advanced optics simulation software. A good consistency with theory is demonstrated. Also, realistic optical system alignment issues are discussed
Beam size measurements based on movable quadrupolar pick-ups
Quadrupolar pick-ups (PU) have been widely studied as candidates for non-intercepting beam size and emittance measurements. However, their application has been proven to be limited. Two fundamental factors make quadrupolar measurements exceptionally challenging: first, the low quadrupolar sensitivity of PUs and second, the parasitic position signal incorporated into the measured quadrupolar measurement. In this paper, an alignment technique, based on movable PUs, is proposed to efficiently cancel the parasitic position signal. Tests have been performed using PUs embedded in collimators in the Large Hadron Collider. Beam measurements demonstrate promising results.peer-reviewe
Diffractive shadowing of coherent polarization radiation
We report on the study of shadowing of electromagnetic fields radiated in the Terahertz (THz) region from two consecutive sources of coherent diffraction and transition radiation. In these conditions, the formation length is predicted to be 100 m, and shadowing effects should result in an almost complete suppression of radiated fields within distances of the order of tens of centimeters. We experimentally measured that shadowing effects disappear for distances significantly shorter than those predicted. We propose a new model that explains our experimental observations by taking into account 3D diffraction effects. These findings will have a positive impact on the beneficial use of consecutive radiators both for the generation of intense electromagnetic radiation and for beam diagnostics using coherent polarization radiation from ultra-relativistic charged particles
CERN’s beam instrumentation R&D study for FCC-ee
The Future Circular Collider (FCC) R&D study was started in 2021 as a comprehensive feasibility analysis of CERN’s future accelerator project encompassing technical, administrative and financial aspects. As part of the study, Beam Instrumentation (BI) is a key technical infrastructure that will have to face unprecedented challenges. In the case of electron-positron FCC-ee, these are represented, among others, by the size of the accelerator, the amount of radiation produced along the ring and in machine-detector interaction region, the presence of the top-up booster and collider ring in the same tunnel. In this contribution we will present the current FCC-ee BI study and discuss its status and perspectives
The status of the energy calibration, polarization and monochromatization of the FCC-ee
The Future Circular electron-positron Collider, FCC- ee, is designed for unprecedented precision for particle physics experiments from the Z-pole up to above the top-pair-threshold, corresponding to a beam energy range from 45.6 to 182.5 GeV. Performing collisions at various particle-physics resonances requires precise knowledge of the centre-of-mass energy (ECM) and collision boosts at all four interaction points. Measurement of the ECM by resonant depolarization of transversely polarized pilot bunches in combination with a 3D polarimeter, aims to achieve a systematic uncertainty of 4 and 100 keV for the Z-pole and W-pair-threshold energies respectively. The ECM itself depends on the RF-cavity locations, beamstrahlung, longitudinal impedance, the Earth’s tides, opposite sign dispersion and possible collision offsets. Application of monochromatization schemes are envisaged at certain beam energies to reduce the energy spread. The latest results of studies of the energy calibration, polarization and monochromatization are reported here
Summary of LHC MD:377: Schottky pick-up
The main objective of this MD was to record Schottky spectra under well known machine conditions. In summary, 7 set-points for the chromaticity and 8 for the emittance have been established and Schottky spectra have been recorded for each setting. The data will be used to benchmark and develop different fitting algorithms. This note presents the initial attempt of curve-fitting and discusses its shortcomings
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