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Undulator Radiation Sources

Description:

Advanced undulator radiation sources are required for current and future light sources. Grant applications are sought for the development of:

(1) Superconducting undulators (SCUs) that can generate tunable, monochromatic x-ray beams in the 2-30 keV photon energy range of medium-energy (2-3 GeV) synchrotrons. These requirements demand that the undulators have a short period (around 1.5 cm) and high peak magnetic fields (around 1.6 tesla). The permanent-magnets commonly used in undulators do not produce sufficiently high magnetic fields to fully cover the desired photon energy range without gaps in the spectrum. Development efforts are underway at several national laboratories and in industry to develop SCUs that promise to overcome these deficiencies. However, current designs suffer from an inability to operate without quenching in the presence of the heat induced by the stored electron beam current and by synchrotron radiation encountered in modern synchrotron light sources. This heat load can be up to 10 watts per meter of undulator length. Novel ideas for SCU design, construction, and thermal management are needed to meet these challenging requirements.

(2) Superconducting undulators with time varying fields. This technology is in its infancy and could offer interesting possibilities for insertion-device radiation sources

(3) Cryogenically-Cooled Permanent Magnet Undulators (CPMUs). When permanent magnet materials are cooled to low temperatures, they exhibit a large coercivity (5-10%) for conventional materials, such as NdFeB or CoSm, and up to 20% for more exotic materials. To make use of this effect, undulators must be cooled to cryogenic temperatures, and, in the cooled down stage, magnetic measurements and adjustments of the permanent magnet must be performed. This requires a complex design.

(4) High coercivity permanent magnet materials for CPMUs. To take full advantage of CPMUs, sintering and manufacturing procedures need to be developed for permanent magnet material like PrFeB, which exhibits large increases in coercivity at cryogenic temperatures.

(5) New superconducting materials for undulator applications. Three types of materials promise a considerable enhancement of undulator performance: High temperature superconducting materials such as YBCO, which operate at about 90K, would allow current densities up 100kA/mm2. The challenge here is to optimize the conductor design to maximize the current density and the transport current, leading to the development of coil manufacturing techniques based on such materials (as the next step). Thin film high temperature superconducting materials such as MgB2, which are operated at ~39K, may become a good material for undulator magnets, depending upon the choice of substrate material, which will determine the mechanical properties of the  superconductor. The challenge here is the production of thin films and the choice of optimum substrate materials. APC (artificially enhanced pinning center) NbTi superconductor, which would allow super-high current densities that exceed the Jc of conventional NbTi superconductor by a large factor (14 kA/mm2 at 2 T). In particular, the high current density might offer an advantage for the design of magnet coils for undulator magnets.

(6) Undulators with period < 1 cm. The resonant condition requires undulator radiation at short wavelength (approximately 1 nm), with low energy electron beams (of 1-2 GeV), and with a shorter period than generally available from existing synchrotron radiation sources. The undulators should be designed with K-value ~1, impedance shielding of pole faces, and a gap that is greater than 2.25 mm.

Questions – contact Eliane Lessner, Eliane.Lessner@science.doe.gov

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