104 research outputs found
Strategy for allocating the MSD magnets and vacuum chambers
An analogous strategy as applied for the MSI septum magnets allows an optimisation of the installation of the MSD septa regarding magnet and chamber allocation. Even if the gain in aperture is small, of the order of half a millimetre, it is not negligible and- being essentially for free - should nevertheless be implemented
RF Structures for Linac4
Linac4 is proposed to replace the existing proton linac at CERN (Linac2). Using an increased injection energy of 160 MeV instead of 50 MeV, Linac4 is expected to double the beam intensity in the PS Booster (PSB) and will thus be the first step towards higher brightness beams in the LHC. In this paper we re-assess the choice of RF structures for Linac4. Different accelerating structures for different energy ranges are compared in terms of RF efficiency, ease of construction and alignment, and necessary infrastructure. Eventually we present the final choice for Linac4
Integrated Design of Superconducting Magnets with the CERN Field Computation Program ROXIE
The program package ROXIE has been developed at CERN for the field computation of superconducting accelerator magnets and is used as an approach towards the integrated design of such magnets. It is also an example of fruitful international collaborations in software development.The integrated design of magnets includes feature based geometry generation, conceptual design using genetic optimization algorithms, optimization of the iron yoke (both in 2d and 3d) using deterministic methods, end-spacer design and inverse field calculation.The paper describes the version 8.0 of ROXIE which comprises an automatic mesh generator, an hysteresis model for the magnetization in superconducting filaments, the BEM-FEM coupling method for the 3d field calculation, a routine for the calculation of the peak temperature during a quench and neural network approximations of the objective function for the speed-up of optimization algorithms, amongst others.New results of the magnet design work for the LHC are given as examples
Deconstructing Magnetization Noise: Degeneracies, Phases, and Mobile Fractionalized Excitations in Tetris Artificial Spin Ice
Direct detection of spontaneous spin fluctuations, or "magnetization noise",
is emerging as a powerful means of revealing and studying magnetic excitations
in both natural and artificial frustrated magnets. Depending on the lattice and
nature of the frustration, these excitations can often be described as
fractionalized quasiparticles possessing an effective magnetic charge. Here, by
combining ultrasensitive optical detection of thermodynamic magnetization noise
with Monte Carlo simulations, we reveal emergent regimes of magnetic
excitations in artificial "tetris ice". A marked increase of the intrinsic
noise at certain applied magnetic fields heralds the spontaneous proliferation
of fractionalized excitations, which can diffuse independently, without cost in
energy, along specific quasi-1D spin chains in the tetris ice lattice.Comment: published in PNAS (2023
Translation of circRNAs
Circular RNAs (circRNAs) are abundant and evolutionarily conserved RNAs of largely unknown function. Here, we show that a subset of circRNAs is translated in vivo. By performing ribosome footprinting from fly heads, we demonstrate that a group of circRNAs is associated with translating ribosomes. Many of these ribo-circRNAs use the start codon of the hosting mRNA, are bound by membrane-associated ribosomes, and have evolutionarily conserved termination codons. In addition, we found that a circRNA generated from the muscleblind locus encodes a protein, which we detected in fly head extracts by mass spectrometry. Next, by performing in vivo and in vitro translation assays, we show that UTRs of ribo-circRNAs (cUTRs) allow cap-independent translation. Moreover, we found that starvation and FOXO likely regulate the translation of a circMbl isoform. Altogether, our study provides strong evidence for translation of circRNAs, revealing the existence of an unexplored layer of gene activity
MICE: the Muon Ionization Cooling Experiment. Step I: First Measurement of Emittance with Particle Physics Detectors
The Muon Ionization Cooling Experiment (MICE) is a strategic R&D project intended to demonstrate the only practical solution to providing high brilliance beams necessary for a neutrino factory or muon collider. MICE is under development at the Rutherford Appleton Laboratory (RAL) in the United Kingdom. It comprises a dedicated beamline to generate a range of input muon emittances and momenta, with time-of-flight and Cherenkov detectors to ensure a pure muon beam. The emittance of the incoming beam will be measured in the upstream magnetic spectrometer with a scintillating fiber tracker. A cooling cell will then follow, alternating energy loss in Liquid Hydrogen (LH2) absorbers to RF cavity acceleration. A second spectrometer, identical to the first, and a second muon identification system will measure the outgoing emittance. In the 2010 run at RAL the muon beamline and most detectors were fully commissioned and a first measurement of the emittance of the muon beam with particle physics (time-of-flight) detectors was performed. The analysis of these data was recently completed and is discussed in this paper. Future steps for MICE, where beam emittance and emittance reduction (cooling) are to be measured with greater accuracy, are also presented
Magnet Acceptance and Allocation at the LHC Magnet Evaluation Board
The normal and superconducting magnets for the LHC ring have been carefully examined to insure that each of about 1900 assemblies is suitable for the operation in the accelerator. Hardware experts and accelerator physicists have contributed to this work that consisted in magnet acceptance, and sorting according to geometry, field quality and quench level. This paper gives a description of the magnet approval mechanism that has been running since four years, reporting in a concise summary the main results achieved
Crystal-Chemical Origins of the Ultrahigh Conductivity of Metallic Delafossites
Despite their highly anisotropic complex-oxidic nature, certain delafossite
compounds (e.g., PdCoO2, PtCoO2) are the most conductive oxides known, for
reasons that remain poorly understood. Their room-temperature conductivity can
exceed that of Au, while their low-temperature electronic mean-free-paths reach
an astonishing 20 microns. It is widely accepted that these materials must be
ultrapure to achieve this, although the methods for their growth (which produce
only small crystals) are not typically capable of such. Here, we first report a
new approach to PdCoO2 crystal growth, using chemical vapor transport methods
to achieve order-of-magnitude gains in size, the highest structural qualities
yet reported, and record residual resistivity ratios (>440). Nevertheless, the
first detailed mass spectrometry measurements on these materials reveal that
they are not ultrapure, typically harboring 100s-of-parts-per-million impurity
levels. Through quantitative crystal-chemical analyses, we resolve this
apparent dichotomy, showing that the vast majority of impurities are forced to
reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly
pure (~1 ppm impurity concentrations). These purities are shown to be in
quantitative agreement with measured residual resistivities. We thus conclude
that a previously unconsidered "sublattice purification" mechanism is essential
to the ultrahigh low-temperature conductivity and mean-free-path of metallic
delafossites
Small Polarons in Transition Metal Oxides
The formation of polarons is a pervasive phenomenon in transition metal oxide
compounds, with a strong impact on the physical properties and functionalities
of the hosting materials. In its original formulation the polaron problem
considers a single charge carrier in a polar crystal interacting with its
surrounding lattice. Depending on the spatial extension of the polaron
quasiparticle, originating from the coupling between the excess charge and the
phonon field, one speaks of small or large polarons. This chapter discusses the
modeling of small polarons in real materials, with a particular focus on the
archetypal polaron material TiO2. After an introductory part, surveying the
fundamental theoretical and experimental aspects of the physics of polarons,
the chapter examines how to model small polarons using first principles schemes
in order to predict, understand and interpret a variety of polaron properties
in bulk phases and surfaces. Following the spirit of this handbook, different
types of computational procedures and prescriptions are presented with specific
instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure
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