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An undulator composed of an electromagnet (EM) and a permanent magnet (PM) has been developed to switch rapidly the right- or left-circularly polarized radiation. The polarization switching is achieved using the rapid change of polarity of excitation currents in the EM, which provides a vertical field in a fixed gap. A horizontal field is generated with a PM; the field strength is adjusted on altering its horizontal gaps. In addition to circularly polarized radiation, the structure fulfills the needs of horizontal and vertical linear polarization. In this paper, we discuss the compact structure and show a design to provide soft X-rays for TPS. The design considerations for this magnet include the design concept, magnetic materials, mechanical and coil structure, all of which are discussed in this paper.

The advantages of an APPLE-II elliptically polarized undulator (EPU) are a wide range of tuneable energy and a large polarization rate. National Synchrotron Radiation Research Center (NSRRC) therefore decided to install a 4-m EPU with period length 46 mm at a beamline for soft x-rays in Taiwan Photon Source. Magnetic-field shimming was developed; the final magnetic performances of the phase error, electron trajectory and multipole errors are presented in this paper.

Phase shifters of various kinds have been studied to match the double undulators that were installed in the same double-mini Betay-function straight section in TPS. A prototype phase shifter, designed to satisfy the requirement for phase matching between two undulators, comprises three C-type dipole magnets for convenient operation and tuning of the magnetic field to cover photon energies over a wide range. The phase shifter, operating at 5 A, provides phase delay 555° for minimal photon energy 300 eV. A trim current at the side coils serves to compensate for the first and second field integrals. The main current is varied to cover photon energies 0.3–20 keV. Our design takes into account an effect of cross talk with nearby magnets.

A superconducting, elliptically polarized undulator (SEPU24) with a period of length 24 mm was developed to provide first-harmonic photons from a 0.8 GeV storage ring for extreme-ultraviolet (EUV) lithography experiment. In SEPU24, two layers of a magnet array structure – with and without rotated magnet arrays – are combined to generate a helical field that provides radiation with wavelength 13.5 nm in the in-band energy. The arrays of iron and aluminium poles were wound with a racetrack coil vertically as for the magnet pole array. The elliptical field is created when the up and down magnet-pole arrays pass excitation currents in alternate directions. SEPU24 is designed with a magnet of gap 6.8 mm, yielding magnetic flux density Bx=Bz=0.61 T of the helical field. A prototype magnet was fabricated with a diode for quench protection, and assembled in a test dewar to test the magnet performance. A cryogenic Hall-probe system with a precise linear stage was used to measure the distribution of the magnetic field. We describe the design concept and algorithm, the engineering design, the calculation of the magnetic field, the construction and testing of the 10-pole prototype magnet and related issues.