Cheng-Ying Kuo

Multipole Errors and Methods of Correction for TPS Lattice Magnets

Taiwan Photon Source (TPS) is a synchrotron radiation facility of medium energy, 3 GeV, and low emittance, under construction at National Synchrotron Radiation Research Center (NSRRC). The multipole errors of lattice magnets were rigorously examined and corrected so as to maintain the dynamic aperture of the electron beam in the storage ring. The lattice magnets were fully inspected at both the vendor and vendee sites. The multipole errors of the lattice magnets were tested and corrected. In particular, the sextupole magnets have the pole position adjusted to correct the multipole errors so as to conform to the specification. The yoke cutting is to correct the octupole error of the long-quadrupole magnets. The shimming of the magnetic center and the final examination of the magnets will be undertaken at NSRRC. In this paper, we report the methods of correcting the multipole errors, the magnetic center, and the performance of the TPS lattice magnets.

Design and Measurement of the Septum Magnet for the Taiwan Photon Source

The septum magnet bends the injection beam before the kicker magnet. The septum magnet is located near the storage ring in the Taiwan Photon Source (TPS). As the space from the magnet wall to the vacuum chamber of the ring is less than 3 mm, the leakage field of the septum magnet thus influences the stability of the electron beam in the storage ring. The main field and the leakage field of a septum of the direct-drive type are compared to one of the eddy-current type. The effects of the vacuum chamber and μ-metal are simulated with full-sine and half-sine current pulses with the OPERA-2D TR analysis module; measurement results are presented in this paper.

Crosstalk Issues of Vicinity Magnets Studied With a Novel Rotating-Coil System

Taiwan Photon Source (TPS) is a low-emittance synchrotron radiation factory. The lattice magnets are located compactly within the limited space in the storage ring. The mutual proximity of the magnets induces field crosstalk and influences the dynamic aperture of the electron beam. The field becomes distorted, induced by the crosstalk within not only the iron yoke but also the edges of the magnets. Precise measurements with rotating-coil systems were conducted to characterize the integral field quality of the magnets; a new method to detect the center of magnets is presented. Simulation with TOSCA software was undertaken for comparison with these experimental results. We report the field distortions induced by crosstalk on the basis of our measurements and simulations. A misalignment effect between the quadrupole and sextupole magnets is discussed.

Design of a magnetic circuit for a cryogenic undulator in Taiwan photon source

The plan for beamlines in Phase II at Taiwan Photon Source is to construct two new BioSAXS and nano-ARPES beamlines. A highly brilliant light source can be produced with a cryogenic undulator, and many synchrotron facilities have been developed and operated with these in their storage rings. The development of a cryogenic undulator became a target for a light source in TPS phase II. A cryogenic undulator with period of length 15 mm will be made in a hybrid magnetic structure, and use PrFeB permanent-magnet materials. A maximum magnetic field 1.31 T is estimated at gap 4 mm and temperature about 100 K. The spectral performance of a TPS cryogenic undulator is presented in this paper.

A prototype phase shifter for phase matching between undulators at TPS

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.

Twin-Helix Undulator for Round Beam-Related Light Sources

14 Vol. 31, No. 3, 2018, Synchrotron radiation newS Introduction Due to the strong demand for circularly polarized radiation, insertion devices (ID) have been used to provide elliptical fi elds since the late 1980s. The trend is to increase the degree of circular polarization and also the brightness of the radiation. ID design, therefore, evolved early from an asymmetric wiggler [1] to elliptical wigglers [2] and fi nally to helical undulators. For third-generation light sources, a variety of helical undulator designs have been developed and implemented [3– 5]. Among them, the design of the APPLE II [6] provides the highest fi elds and thus has become the workhorse in several facilities. Development of helical undulators was greatly facilitated thanks to improvements in magnetic materials, especially in rare-earth permanent magnet materials. A neodymium-iron-boron (NdFeB) magnet is preferred due to its higher remanence and its robust mechanical properties. Since the development of the NdFeB magnet by Sagawa in 1983 [7], the magnet has been widely used in the construction of IDs. For ultimate storage rings or linac-driven free electron lasers (FELs), a round vacuum pipe allows the placement of more magnetic materials close to the electron beam. A round-gap ID signifi cantly facilitates a design with enhanced magnetic fi eld properties. Bahrdt proposed the APPLE III [8], which chamfers the magnets for a round vacuum pipe; by tilting the magnetization direction to 45°, the magnetic fi eld could be enhanced for the BESSY soft-X-ray FEL. A Delta undulator [9] was proposed for the Cornell energy recovery linac and is implemented in the Linac Coherent Light Source (LCLS) for the afterburner confi guration [10]. Both types of undulators are used as a radiator for full control of the polarization. More recently, permanent magnet planar undulators have been preferred as modulators for the electron bunching process in FELs because their mature technology is fully understood. Nevertheless, there has been recent interest in the use of helical undulators for more compactness and for a more effi cient FEL [11]. Since commissioning of the Taiwan Photon Source (TPS) in December 2014, three APPLE IIs were installed in Phase I [12], and two or more are being constructed to fulfi ll the requirements of the community using radiation from the EUV to soft X-rays. Based on the construction and commissioning experience, an APPLE II can be improved by optimizing the mechanical design of the keeper structure, which holds the magnet blocks, to reduce effects on beam dynamic effects in various operation modes [13]. Moreover, an exotic twin-helix undulator (THU) has been proposed for the VUV FEL project [14]. The THU is a hybrid structure and has a round gap. The poles and magnet blocks are shaped into a helix to produce a purely helical fi eld, as well as improving the strength and homogeneity of the magnetic fi eld.

Reduction of dynamic multipole content in insertion devices using flat wires

Multipole errors of an insertion device are generally corrected based on measurements and analysis of the magnetic field integrals. Multipole components in a strong and narrow non-uniform field of an insertion device appear as dynamic multipoles. Flat wires were installed and commissioned to determine if the dynamic multipoles can be eliminated in an APPLE-II type undulator. In this work, we will discuss and compare the reduction of the dynamic multipole content and its beam dynamics effects with the flat wire through an analysis of field calculations and beam-based measurements in the storage ring.

Constructing a Permanent Magnet Phase Shifter

A permanent-magnet (PM) phase shifter has been constructed for tandem elliptically polarizing undulators at the Taiwan photon source. To increase the magnetic field reproducibility and to allow installation in a limited space, a robust mechanical structure is desired. To decrease multipole errors and optimize the magnetic field, algorithms for magnet sorting were used and magnetic field shimming was done. The start-to-end construction of a PM phase shifter will be discussed and explained in detail.

Design, Fabrication and Measurement of Gradient Damping Wiggler for the ALPHA Storage Ring

A 3-pole gradient-damping wiggler (GDW) was developed for the ALPHA storage ring at Indiana University. The GDW is effective in modifying the momentum-compaction factor and the damping partition number in the ALPHA storage ring. The yokes of GDW are made by lamination of silicon steel sheets (50CS1300) with a thickness 0.5 mm. Glue (3M 2216) is used to paste the lamination sheets together to create a block using a punch fixture. The C-shape structure and the pole profile of the damping wigglers are cut from the silicon-steel blocks with the wire-cutting machine. One middle pole and two outer poles are assembled on the same girder as the set of GDW. The oblique of pole profile of middle and outer poles is different to obtain the same polarity of gradient field. The magnet gaps of the middle and outer poles are 40 and 35.87 mm; respectively to obtain the same dipole field strength. The field strengths of dipole and gradient-field of the middle (outer) pole are 0.67 T (0.67 T) and 1.273 T/m (1.273 T/m), by keeping the integral ratio of (dB/dx)/B = 1.9 m-1 constant. The three combined functions of the dipole magnet can be charged in 1 Hz with a single power supply. There are trim coils on the three poles to adjust the first and second integral fields to zero. The good field region of the middle and outer poles along the transverse x-axis (ΔB/B = 0.%) are ±50 and ±40 mm respectively. After fabrication of one set GDW magnet, a Hall probe measurement system was used to measure the magnetic field to verify the design and construction performance of the magnet.