Aimant | EPFL Graph Search

Un aimant permanent, ou simplement aimant dans le langage courant, est un objet fabriqué dans un matériau magnétique dur, c’est-à-dire dont l'aimantation rémanente et le champ coercitif sont grands (voir ci-dessous). Cela lui donne des propriétés particulières liées à l'existence du champ magnétique, comme celle d'exercer une force d'attraction sur tout matériau ferromagnétique. Étymologie Le mot aimant est, comme le mot diamant, dérivé du grec ancien ἀδάμας, adámas (« fer particulièrement dur ou diamant »), apparenté à l'adjectif ἀδάμαστος, adámastos, (« indomptable »), en raison de la dureté de la pierre d'aimant. Histoire L'histoire des aimants commence dans l'Antiquité. En Chine, puis un peu plus tard en Grèce, des hommes découvrent une pierre noire, la pierre d'aimant, qui a le pouvoir d'attirer le fer. Qui plus est, cette pierre a la capacité de transmettre son pouvoir au fer. Dans l'Antiquité, selon Plutarque, la pierre d'aimant s'appelait os d'Horus e

Magnetic Model of the CERN Proton Synchrotron

Mariusz Juchno

In this thesis, we present development of the first magnetic model of the main Proton Synchrotron magnets. The operation of the machine and conducting research on increasing its performance require a significant amount of the magnetic field data for the optics modelling. For magnets of the Proton Synchrotron, such amount of data cannot be provided by the magnetic measurements, therefore, we have to rely on magnetic models. We have developed the model based on the numerical analysis of the magnetic field in the magnet and performed the validation with the use of the available magnetic measurements data. The results of the 2D quasi-static analysis were used to decompose the multipolar contributions of different magnet circuits on different levels fo the iron core magnetization within the whole range of the PS operation energies. Established formulas of every circuit contributions take into account the global magnetization of the yoke and its saturation as well as a local magnetization changes caused by contributions of other circuits. The 3D numerical analysis was setup to study the influence of the magnet stray field and gaps between the magnet blocks on the integrated multipolar field. Its results were used to derive appropriate model corrections of the integrated multipolar field with respect to the field in the reference cross-section and to approximate the effective magnetic lengths of the auxiliary circuits of the PS magnet. In order to perform a non-linear chromaticity analysis and to take the full advantage of the developed model, we have modified the existing optics model of the PS lattice. We have integrated magnetic model into the optics calculation with two simulation adjustment methods, which optimize the main coil current in similar way as it is done for the real magnets and adjust four free parameters to match the measured parameters of the initial working point. We have successfully validated the combined magnetic and optics models for various beam momentum levels and magnet powering conditions. With the use of the new magnetic model, for the first time in the history of the PS we are able to predict a higher-order chromaticity function for any energy. Base on the optics modelling results, we have derived working point transfer matrices for the non-linear chromaticity, which allow to predict a set of powering current offsets required to apply foreseen working point adjustment. We were also able to model an offset of the measured transfer matrices due to a change of the radial position chosen for the beam production.

EPFL2013

Optics design and performance of an ultra-low emittance damping ring for the compact linear collider

A high-energy (0.5-3.0 TeV centre of mass) electron-positron Compact Linear Collider (CLIC) is being studied at CERN as a new physics facility. The design study has been optimized for 3 TeV centre-of-mass energy. Intense bunches injected into the main linac must have unprecedentedly small emittances to achieve the design luminosity 1035cm-2s-1 required for the physics experiments. The positron and electron bunch trains will be provided by the CLIC injection complex. This thesis describes an optics design and performance of a positron damping ring developed for producing such ultra-low emittance beam. The linear optics of the CLIC damping ring is optimized by taking into account the combined action of radiation damping, quantum excitation and intrabeam scattering. The required beam emittance is obtained by using a TME (Theoretical Minimum Emittance) lattice with compact arcs and short period wiggler magnets located in dispersion-free regions. The damping ring beam energy is chosen as 2.42 GeV. The lattice features small values of the optical functions, a large number of compact TME cells, and a large number of wiggler magnets. Strong sextupole magnets are needed for the chromatic correction which introduces significant nonlinearities, decreasing the dynamic aperture. The nonlinear optimization of the lattice is described. An appropriate scheme of chromaticity correction is determined that gives reasonable dynamic aperture and zero chromaticity. The nonlinearities induced by the short period wiggler magnets and their influence on the beam dynamics are also studied. In addition, approaches for absorption of synchrotron radiation power produced by the wigglers are discussed. Realistic misalignments of magnets and monitors increase the equilibrium emittance. The sensitivity of the CLIC damping ring to various kinds of alignment errors is studied. Without any correction, fairly small vertical misalignments of the quadrupoles and, in particular, the sextupoles, introduce unacceptable distortions of the closed orbit as well as intolerable spurious vertical dispersion and coupling due to the strong focusing optics of the damping ring. A sophisticated beam-based correction scheme has been developed in order to bring the design target emittances and the dynamic aperture back to the ideal value. The correction using dipolar correctors and several skew quadrupole correctors allows a minimization of the closed-orbit distortion, the cross-talk between vertical and horizontal closed orbits, the residual vertical dispersion and the betatron tune coupling. The small emittance, short bunch length, and high current in the CLIC damping ring could give rise to collective effects which degrade the quality of the extracted beam. A number of possible instabilities and an estimate of their impact on the ring performance are briefly surveyed. The effects considered include fast beam-ion instability, coherent synchrotron radiation, Touschek scattering, intrabeam scattering, resistive-wall wake fields, and electron cloud.

EPFL2006

Long Spin Lifetime in Rare-Earth Single-Atom Magnets at Surfaces

Boris Sorokin

Further miniaturisation of magnetic storage devices requires an advent of new types of magnets, since classical ferromagnetic materials show lack of remanence at nano- and subnanoscale. A single atom can represent the smallest possible bit of information. Even though the isolated single atoms are paramagnetic, the interaction of surface adsorbed atoms with a substrate can result in high magnetic anisotropy energy and long magnetisation lifetime. In this thesis the magnetic properties of surface supported rare-earth single atoms are investigated with X-ray absorption spectroscopy, X-ray magnetic circular dichroism and multiplet simulations. The first goal of the project was to find new adatom/substrate combinations that exhibit a long adatom magnetic lifetime, possibly extending the current limits of the atomic magnetic moment stability to higher temperatures and longer spin relaxation times. The second objective was to implement the external electric field control of the adatom magnetic properties.Firstly, we present the experimental and theoretical research on Dy and Ho single atoms deposited on BaO. A comparison of our results with similar studies sheds light on the impact of the substrate crystal field, in particular Dy-O bond covalency, on the magnetic stability of the rare-earth adatoms. Next, the detailed experimental investigation of Dy single atoms on ZnO is presented. This adatom/substrate pair is used as first attempt to implement the electric field control of the adatom magnetic properties. Lastly, we study the Dy adatoms on graphene layers grown on various metals. The vibrational modes of the metallic substrates are shown to strongly affect the Dy spin lifetime, while addition of a second graphene layer does not allow to significantly improve the adatom magnetic stability.

EPFL2022

Magnetic Model of the CERN Proton Synchrotron

Mariusz Juchno

EPFL2013

Optics design and performance of an ultra-low emittance damping ring for the compact linear collider

EPFL2006