<p>For some cases of lattice layout in particle accelerators, the major part of the energy deposition coming from the collision is located in the midplane of the magnets. The heat produced might result in a quench in superconducting magnets. One solution for reducing the energy deposition in the coil is to introduce an opening in the midplane, which will lead away most of the particles to a safe zone instead of hitting the superconductors in the magnets.</p><p>The aim of this work is to optimize the field quality in dipoles based on the cosθ-design, where an opening in the midplane has been inserted. The equations for finding the solutions for the coil layout for different sizes of the opening are studied, and the solution giving the best field quality for each case is presented. Then, optimization procedures are applied to lay-outs with Rutherford cables. Finally, the resulting field strength from the solutions obtained is presented.</p>

For some cases of lattice layout in particle accelerators, the major part of the energy deposition coming from the collision is located in the midplane of the magnets. The heat produced might result in a quench in superconducting magnets. One solution for reducing the energy deposition in the coil is to introduce an opening in the midplane, which will lead away most of the particles to a safe zone instead of hitting the superconductors in the magnets. The aim of this work is to optimize the field quality in dipoles based on the cosθ-design, where an opening in the midplane has been inserted. The equations for finding the solutions for the coil layout for different sizes of the opening are studied, and the solution giving the best field quality for each case is presented. Then, optimization procedures are applied to lay-outs with Rutherford cables. Finally, the resulting field strength from the solutions obtained is presented.

Le travail effectué dans cette thèse a pour thème central la conception d’un aimant quadripolaire supraconducteur en Nb-Ti destiné à remplacer à l’horizon 2014 les aimants d’insertions actuellement utilisés dans le grand collisionneur de Hadrons (LHC) du CERN de Genève. Ce nouveau quadripôle, caractérisé par un diamètre d’ouverture encore jamais atteint (120 mm), ouvre la voie vers les quadripôles à grandes ouvertures. Tout d’abord, pour rapidement estimer l’énergie magnétique stockée dans un quadripôle de type cos2?, une formule analytique basée sur la décomposition en série de Fourier du courant et permettant d’estimer l’énergie avec une précision de 10 % est développée. Le design magnétique de la section transverse de la bobine du quadripôle est ensuite réalisé en utilisant une nouvelle méthode d’optimisation basée sur les équations analytiques du champ magnétique. Puis, pour la première fois, une estimation de la reproductibilité dans le positionnement des blocs de conducteurs dans des aimants Nb3Sn est faite. Elle a été réalisée à l’aide d’une méthode existante et grâce à la production récente de deux séries d’aimants Nb3Sn. Une comparaison avec les valeurs obtenues pour des aimants en Nb-Ti est présentée. Ensuite, une méthode analytique basée sur les statistiques et permettant d’expliquer certains phénomènes observés sur la dispersion des mesures magnétiques dans une série de quadripôles est développée. Enfin, on montre que l’incertitude sur la moyenne des harmoniques de champ est due pour la majorité des harmoniques à un phénomène statistique lié au nombre limité d’aimants dans la série et non à des erreurs systématiques / The main objective of the work presented in this thesis is the design of a quadrupole magnet based on Nb-Ti. It aims at replacing the current insertion quadrupoles used in the Large Hadron Collider (LHC) at CERN by 2014. This new quadrupole features an unprecedented large aperture (120 mm) and opens the way toward large aperture quadrupoles. First, to rapidly estimate the magnetic energy stored in a cos2?-type quadrupole, an analytical formula based on the Fourier transform of the current is developed. It allows estimating the energy with a precision of 10 %. Secondly, the magnetic design of the quadrupole coil cross-section is realized using a novel optimization method based on analytical equations of the magnetic field. Subsequently, for the first time, an estimate of the reproducibility in the coil-blocks positioning in Nb3Sn magnets is given. The estimate has been obtained by using an existing method and from tow recently built Nb3Sn magnet series. A comparison with values obtained for Nb-Ti magnets is also presented. Following this, an analytical method based on statistics is developed. It makes possible to explain some phenomenon observed on the dispersion of the magnetic measurement in a quadrupole series. Finally, we show that the uncertainty in the mean of the magnetic field errors is for most of the harmonics related to statistical errors due to the limited number of magnets in the series, and not because of systematic defects in the coil