Chin-Kang Yang

A Measurement System In Situ to Measure the Magnetic Field of an In-Vacuum Undulator

Two in-vacuum undulators (length 2 m) with period 22 mm (IU22) are constructed to be installed in the Taiwan Photon Source (TPS, 3 GeV) to provide a highly brilliant light source at hard X-ray energies. To verify ultimately the magnetic fields of these IU before installation in the storage ring, we have developed a system to measure the magnetic field in vacuum. To avoid contamination of the vacuum chambers, all components of the system are compatible with high vacuum. During actuation along the longitudinal direction, the positions of the Hall probe are monitored with optical devices and corrected with three two-axis stages. The deviations of position of the Hall probe with dynamic correction are less than 5 μm. The phase error reproducibility of this system is 0.15° and the first integral reproducibility is 13 G·cm. We applied this system to measure the magnetic performance of our in-vacuum undulators at varied gaps of the magnet array. The results of those measurements show no significant difference after assembly of the magnet arrays inside the chamber. The details of design and construction of this system are described, together with the results of measuring the magnetic field of the IU22.

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.

Design Improvement of a Staggered YBCO Undulator

A strong field and short period undulator can be a desirable light source device in a storage ring or a free-electron laser. Bulk YBCO can be used to construct a high-temperature-superconducting undulator in a staggered array structure. The YBCO material in form of 32 mm diameter and 2.5 mm thick was used to assemble a staggered magnet array. The period length is 5 mm and the magnet gap is 4 mm. To estimate the strength of a sinusoidal field and to optimize the end-pole design to minimize the first (i.e., electron angle) and second field integral (electron position), an energy-minimization method (EM-method) based on Beans model to simulate the field trapped in the HTS-Block is introduced. In this paper, we focus on promoting the practical value of the EM-method simulation. Combining the experimental experience of a YBCO staggered undulator and the simulation experience based on the EM-method, we address some issues to enhance the efficacy of this undulator design.

Optimized undulator to generate low energy photons from medium to high energy accelerators

While emitting low energy photons from a medium or high energy storage ring, the on-axis heat load on the beam line optics can become a critical issue. In addition, the heat load in the bending magnet chamber, especially in the vertical and circular polarization mode of operation may cause some concern. In this work, we compare the heat loads for the APPLE-II and the Knot-APPLE, both optimized to emit 10 eV photons from the 3 GeV TPS. Under this constraint the heat load analysis, synchrotron radiation performance and features in various polarization modes are presented. Additional consideration is given to beam dynamics effect.

Temperature Control of a Baking System for an Ultrahigh-Vacuum Insertion Device

Baking an undulator artificially accelerates outgassing, and is one of the most important and difficult factors in constructing an in-vacuum undulator. The total duration of baking was 76 h and each component in the undulator required a separate temperature for baking. Automatic procedures and devices for temperature control during baking were constructed and continually applied to achieve the required ultrahigh vacuum (pressure P < 2 × 10−10 Torr). This chapter describes details of the baking and the devices used and constructed in National Synchrotron Radiation Research Center.

Dynamic Field Integrals in Taiwan Photon Source Undulators

In an insertion device, the electrons wiggle with finite amplitudes because of the periodic magnetic field. The field integral is contributed from the static field integrals of construction field errors and intrinsic dynamic field integrals. From a flip coil or stretched wire, it is impossible to obtain a true integrated field along the electron trajectory. The dynamic field integral is derived from the nonuniformity in the transverse distribution of the magnetic field. The influence of the dynamic field integral on the spectral broadening of undulator radiation and the tune shift due to oscillation of the beam might produce a degraded performance of an undulator or a storage ring. In this paper, the tune shifts and spectral broadening of two Taiwan Photon Source undulators, an in-vacuum undulator and an elliptically polarized undulator, are discussed based on dynamic field integrals.

Field Measurement System in Vacuum for a Cryogenic Permanent-Magnet Undulator at NSRRC

A recent trend toward building an undulator for a mid-energy storage ring is a small period length and a large magnetic field, which typically requires a vacuum and cryogenic environment. To measure the magnetic field of such undulators, we designed and fabricated a Hall-probe measurement system in vacuum. All components of this system are installed in a vacuum chamber and are compatible with a high-vacuum and a low-temperature environment; the deployment of all parts is designed to fit a cryogenic permanent-magnet undulator that is now under construction at the National Synchrotron Radiation Research Center. The details of the design, completed fabrication, and test results are presented in this paper.

Performance of a NSRRC In-Vacuum Undulator

An advanced undulator technology is critical for highly brilliant synchrotron radiation in a third-generation light source. Taiwan Photon Source (TPS) is a light source of intermediate energy, and a short magnet period of an undulator is desired for experimental stations using hard X-rays. In-vacuum undulators have been delivered and tested at the NSRRC site before installation in the storage ring. The vacuum tests were performed first to ensure an ultra-high vacuum (below 2 ×10-10 torr). Magnetic measurement is comprised of laser alignment system that was developed at NSRRC. The results show satisfactory field repeatability after assembly of the vacuum chamber, because phase errors of both undulators are less than 3°. Baking an undulator was performed to achieve an ultra-high vacuum. Here, we describe the results from the acceptance tests.

Feasibility and Features of a Staggered Undulator Constructed With HTS YBCO Bulks

A staggered undulator with high-temperature superconducting bulks might be a solution to achieve an undulator with an extremely short period for a synchrotron light source. YBCO bulk was thus selected to investigate the feasibility. This bulk (diameter 32 mm, thickness 2.5 mm) was used to build a staggered-magnet array structure and a mock-up staggered undulator of period 5 mm and fixed gap 4 mm was designed for this test. The potential generation of a sinusoidal field was tested in a 3-T magnetization system with field-cooling magnetization (FCM). The practicability of a HTS undulator is discussed in regard to the possibility of correction of the local field, repetition of field trapping and long-term stability. In addition, a field simulation concept was developed for designing the staggered undulator with YBCO bulks.