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

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.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

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

Skew Quadrupole Effect of Laser Plasma Electron Beam Transport

International audienceLaser plasma acceleration (LPA) capable of providing femtosecond and GeV electron beams in cm scale distances brings a high interest for different applications, such as free electron laser and future colliders. Nevertheless, LPA high divergence and energy spread require an initial strong focus to mitigate the chromatic effects. The reliability, in particular with the pointing fluctuations, sets a real challenge for the control of the dispersion along the electron beam transport. We examine here how the magnetic defects of the first strong quadrupoles, in particular, the skew terms, can affect the brightness of the transported electron beam, in the case of the COXINEL transport line, designed for manipulating the electron beam properties for a free electron laser application. We also show that the higher the initial beam divergence, the larger the degradation. Experimentally, after having implemented a beam pointing alignment compensation method enabling us to adjust the position and dispersion independently, we demonstrate that the presence of non-negligible skew quadrupolar components induces a transversal spread and tilt of the beam, leading to an emittance growth and brightness reduction. We are able to reproduce the measurements with beam transport simulations using the measured electron beam parameters

Construction and Optimization of Cryogenic Undulators at SOLEIL

International audienceWith permanent magnets undulator operation at cryogenic temperature, the magnetic field and the coercivity can be enhanced, enabling shorter periods with high magnetic fields. The first full scale (2 m long, 18 mm period) hybrid cryogenic undulator [1] using PrFeB [2] magnets operating at 77 K was installed at SOLEIL in 2011. Photon spectra measurements, in good agreement with the ex-pectations from magnetic measurements, were used for precise alignment and taper optimization. The second and third 18 mm PrFeB cryogenic undulators, modified to a half-pole/magnet/half-pole structure, were optimized without any magnet or pole shimming after assembly but mechanical sortings and some geometrical corrections had been done before assembly. A systematic error on individual magnets on the third U18 was also compensated. In-situ measurement benches, including a Hall probe and a stretched wire to optimize the undulator field at room and cryogenic temperature are presented. An upgrade of these in-situ benches will be detailed with the fabrication of a 15 mm 3 m long PrFeB cryogenic undulator at SOLEIL

Transportation and Manipulation of a Laser Plasma Acceleration Beam

International audienceThe ERC Advanced Grant COXINEL aims at demonstrating free electron laser amplification, at a resonant wavelength of 200 nm, based on a laser plasma acceleration source. To achieve the amplification, a 10 m long dedicated transport line was designed to manipulate the beam qualities. It starts with a triplet of permanent magnet with tunable gradient quadrupoles (QUAPEVA) that handles the highly divergent electron beam, a demixing chicane with a slit to reduce the energy spread per slice, and a set of electromagnetic quadrupoles to provide a chromatic focusing in a 2 m long cryogenic undulator. Electrons of energy 176 MeV were successfully transported throughout the line, where the beam positioning and dispersion were controlled efficiently thanks to a specific beam based alignment method, as well as the energy range by varying the slit width. Observations of undulator radiation for different undulator gaps are reported

SOLEIL Status Report

International audienceSOLEIL is both a synchrotron light source and a research laboratory at the cutting edge of experimental techniques dedicated to matter analysis down to the atomic scale, as well as a service platform open to all scientific and industrial communities. This French 2.75 GeV third generation synchrotron light source provides today extremely stable photon beams to 29 beamlines (BLs) complementary to ESRF. We report facility performance, ongoing projects and recent major achievements. A significant work was performed in order to secure the operation of the two canted 5.5 mm in-vacuum cryogenic permanent magnet undulators (CPMUs). Major R&D areas will also be discussed, and progress towards a lattice baseline for making SOLEIL a diffraction limited storage ring

Study of the Electron Transport in the COXINEL FEL Beamline Using a Laser-Plasma Accelerated Electron Beam

International audienceThe ERC Advanced Grant COXINEL aims at demonstrating free electron laser (FEL) at 200 nm, based on a laser-plasma accelerator (LPA). To achieve the FEL amplification a transport line was designed to manipulate the beam properties. The 10 m long COXINEL line comprises a first triplet of permanent-magnet variable-strength quadrupoles (QUAPEVA), which handles the large divergence of LPA electrons, a magnetic chicane, which reduces the slice energy spread, and finally a set of electromagnetic quadrupoles, which provides a chromatic focusing in a 2-m undulator. Electrons were successfully transported through the line from LPA with ionization-assisted self-injection (broad energy spectra up to~250 MeV, few-milliradian divergence)