Force between magnets | EPFL Graph Search

Magnets exert forces and torques on each other due to the rules of electromagnetism. The forces of attraction field of magnets are due to microscopic currents of electrically charged electrons orbiting nuclei and the intrinsic magnetism of fundamental particles (such as electrons) that make up the material. Both of these are modeled quite well as tiny loops of current called magnetic dipoles that produce their own magnetic field and are affected by external magnetic fields. The most elementary force between magnets is the magnetic dipole–dipole interaction. If all magnetic dipoles for each magnet are known then the net force on both magnets can be determined by summing all the interactions between the dipoles of the first magnet and the dipoles of the second magnet. It is often more convenient to model the force between two magnets as being due to forces between magnetic poles having magnetic charges spread over them. Positive and negative magnetic charge is always connected by a str

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

Canted antiferromagnetic phases in the candidate layered Weyl material EuMnSb2

Xiao Wang

EuMnSb2 is a candidate topological material which can be tuned towards a Weyl semimetal, but there are differing reports for its antiferromagnetic (AFM) phases. The coupling of bands dominated by pure Sb layers hosting topological fermions to Mn and Eu magnetic states provides a potential path to tune the topological properties. Here we present single-crystal neutron diffraction, magnetization, and heat-capacity data as well as polycrystalline 151Eu M??ssbauer data which show that three AFM phases exist as a function of temperature, and we present a detailed analysis of the magnetic structure in each phase. The Mn magnetic sublattice orders into a C-type AFM structure below TNMn = 323(1) K with the ordered Mn magnetic moment ??Mn lying perpendicular to the layers. AFM ordering of the Eu sublattice occurs below TNEu1 = 23(1) K with the ordered Eu magnetic moment ??Eu canted away from the layer normal and ??Mn retaining its higher temperature order. ??Eu is ferromagnetically aligned within each Eu layer but exhibits a complicated AFM layer stacking. Both of these higher-temperature phases are described by magnetic space group (MSG) Pn'm'a' with the chemical and magnetic unit cells having the same dimensions. Cooling below TNEu2= 9(1) K reveals a third AFM phase where ??Mn remains unchanged but ??Eu develops an additional substantial in-plane canting. This phase a' . We also find some evidence of short-range magnetic correlations associated with the Eu between 12 K ??? T ??? 30 K. Using the determined magnetic structures, we postulate the signs of nearest-neighbor intralayer and interlayer exchange constants and the magnetic anisotropy within a general Heisenberg model. We then discuss implications of the various AFM states in EuMnSb2 and their potential for tuning topological properties.

AMER PHYSICAL SOC2022

Beam Dynamics Studies in Recirculating Machines

Dario Pellegrini

The LHeC and the CLIC Drive Beam share not only the high-current beams that make them prone to show instabilities, but also unconventional lattice topologies and operational schemes in which the time sequence of the bunches varies along the machine. In order to asses the feasibility of these projects, realistic simulations taking into account the most worrisome effects and their interplays, are crucial. These include linear and non-linear optics with time dependent elements, incoherent and coherent synchrotron radiation, short and long-range wakefields, beam-beam effect and ion cloud. In order to investigate multi-bunch effects in recirculating machines, a new version of the tracking code PLACET has been developed from scratch. PLACET2, already integrates most of the effects mentioned before and can easily receive additional physics. Its innovative design allows to describe complex lattices and track one or more bunches accordingly to the machine operation, reproducing the bunch train splitting and recombination to and from multiple beamlines. After some initial testing, PLACET2 has been applied to the LHeC Energy Recovery Linac design in order to complete the first end-to-end tracking simulation. The transport of the beam to the dump has been verified in presence of incoherent synchrotron radiation, wakefields and beam-beam effect. Unexpected high radiation losses have been found in specific sections of the lattice, solutions have been proposed to improve both the machine performance and the beam quality. These include a new design of the spreading sections and return arcs based on combined function magnets. The detector bypass, that was originally missing, have now been designed and integrated in the lattice. Tracking simulations have also been performed for PERLE, which have been developed to validate on a smaller scale the technology and the operation of the LHeC. Its performances have been assessed and the design has been consolidated and improved. The work at CTF3 focused on the Combiner Ring. Its length plays a crucial role in the phase structure of the combined beam and must be carefully tuned. The control of the ring length by means of optics scaling, has been measured on the machine and reproduced with the PLACET2 model. Moreover the code has been used to verify a multi-bunch instability that appeared during the commissioning of the ring.