Développement d'un onduleur cryogénique à aimants permanents à l'ESRF

Un nouveau concept d'onduleur courte période et fort champ a été proposé par Toru Hara à SPring-8 en 2004 : l'onduleur cryogénique à aimants permanents (CPMU). Il s'agit de refroidir des aimants Néodyme-Fer-Bore autour de 150 K. Cela permet d'utiliser ces aimants qui ont une rémanence jusqu'à 40% supérieure à celle des aimants utilisés conventionnellement dans les onduleurs. Pour évaluer les difficultés technologiques et la faisabilité de tels onduleurs, un CPMU de 2 m de long et de 18 mm de période a été lancé à l'ESRF. Ce travail présente le design et la réalisation du CPMU à l'ESRF. Un modèle magnétostatique du CPMU est présenté, il est basé sur des mesures de courbe d'aimantation à température cryogénique réalisées au laboratoire Louis Néel. Le modèle prévoit une augmentation du champ crête de l'onduleur de 8% autour de 150 K et de l'intégrale de champ de 20 Gcm. Un banc de mesure magnétique spécifique a également été développé à l'ESRF. Ce banc permet la mesure du champ local et des intégrales de champ sous vide. Son design et sa construction sont revus. Finalement les mesures magnétiques réalisées à température ambiante et à température cryogénique sont présentées. Ces mesures valident le modèle magnétostatique et les performances attendues.In 2004, at SPring-8, Toru Hara proposed a new concept of undulator with a short period and a high field: the Cryogenic Permanent Magnet Undulator (CPMU). The purpose of this concept is to cool Nd2Fe14B magnets at 150 K. This cooling allows magnets which have a higher remanence to be used, up to 40% higher than that of the magnets traditionally used in undulators. In order to assess the technological possibility of producing such undulator, a 2 m long undulator with a 18 mm period has been proposed at the ESRF. This piece of work presents the design and the construction of this CPMU at the ESRF. First a magnetic model of the CPMU is introduced; it is based on measurements of the magnetization curve at cryogenic temperature performed at the Louis Néel Laboratory. This model forecasts an increase of the peak field of 8% and of the field integral of 0.2 Gm at around 150 K. A unique magnetic measurement bench has been developed at the ESRF. This bench allows both the in vacuum local field and field integral to be measured. Its design and construction are presented. Finally we have reviewed the measurements at room and cryogenic temperature. These measurements are in agreement with the magnetic model.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Cross talks between storage ring magnets at the Extremely Brilliant Source at the European Synchrotron Radiation Facility

International audienceSignificant magnetic cross talks were observed between neighboring magnets on the Extremely Brilliant Source (EBS) low emittance storage ring. The main sources for these cross talks are the short longitudinal distances between magnets, which reach 47 mm in some cases. It affects mainly the dipole bending angles and the quadrupole gradients. A 1% bending angle correction was applied to the (permanent) bending magnets before their installation in the storage ring to compensate for the cross talks, while gradient errors as high as 1.8% were observed on quadrupoles. Intensive 3D magnetic simulations gave the longitudinal distribution of the cross talk errors for various magnet pairs and current settings. The error distribution depends on the magnet pairs: cross talks may create errors at magnet edges or all along the magnets, with same or opposite polarity. The simulations were validated by magnetic measurements, the discrepancies between measured and simulated values being in the 10-4 range with respect to the nominal gradients. Cross talk induced gradient errors were added to all quadrupoles and neighboring magnets in the lattice model. Even if it complicated the commissioning, the cross talks have no impact on the final performances of the lattice as the design machine parameters were reached for the most part