Jyh-Chyuan Jan

Mini-pole Superconducting Undulator for X-Ray Synchrotron Light Source

A mini-pole planar vertically-wound racetrack coil undulator was studied to determine its potential for use as a hard X-ray source in a 3 GeV storage ring. A field strength of 1.4 T can be obtained for a superconducting undulator with a periodic length of 1.5 cm and a fixed magnetic gap of 5.6 mm. The magnetic circuit was optimized and a current density of 1090 A/mm2, at 80% of the critical current, meets the field strength requirement. A prototype with 40 poles was constructed to verify the design of the magnet and the performance of NbTi superconductor. Additionally, the magnetic field shimming method was developed for spectrum shimming. This study discusses the design of the magnetic circuit and the structure of the magnetic array, the field shimming technique, and the test results of the prototype magnet

Design, Fabrication, and Performance Tests of a HTS Superconducting Dipole Magnet

The use of HTS (high-temperature superconductor) coils for accelerator magnets decreases significantly the power consumption and operating cost. Therefore, a preliminary study was launched and a prototype of a dipole magnet with HTS coils has been designed and fabricated by NSRRC and HTS-110 Ltd. Although 2G YBCO wire is expected to be used in future HTS applications, it currently requires more joints to form the completed coils. For this reason, we chose 1G BSCCO wires for the HTS coils. Two single-stage pulse-tube refrigerators with one compressor serve to cool the HTS coils of the magnet, but we shall use LN2 to replace the pulse-tube refrigerators in the future. The HTS magnet is designed to provide a stable field of strength 1.19 T with field homogeneity better than 1.5 × 10-4 in the range of the transverse -20 ≤ x ≤ 20 mm direction when it operates at 50 K with a current of 110 A. To compare with the field features of copper-coil dipole magnets, a Hall-probe measurement system was used to measure the detailed magnetic field and B-I characteristics of the HTS dipole magnet at NSRRC.

A Superconducting Magnetization System With Hybrid Superconducting Wire for the Study and Application of Superconductivity

For the study of high-temperature superconductors and for the application of superconductivity, a superconducting high-field magnetization system with a hybrid superconducting coil was designed. This coil is composed of superconducting wires of three kinds-HTS YBCO 2G-wire, high-field and low-field NbTi wires. Three principal purposes of building this system are to inspect the characteristics of disk-shape bulk YBCO, to develop a HTS-bulk undulator, and to magnetize a portable HTS-bulk high-field magnet for application to a resonant X-ray scattering experiment. With four steps of temperature decrease, a two-stage GM-type cryocooler and liquid nitrogen provide cooling for the magnetization system. The hybrid superconducting coil, two cryogenic systems for the magnetization system and the portable HTS-bulk magnet, and the control and monitor systems that were designed are discussed.

Design of a HTS Magnet for Application to Resonant X-Ray Scattering

In material research, the characteristics of novel materials vary greatly with the environment. A magnet with a strong field will be developed for an experimental station for resonant X-ray scattering to investigate the magnetic properties of materials. This magnet will be developed with high-temperature superconductor (HTS) bulk YBa2Cu3O7 and magnetized with a HTS coil magnet wound with 2G HTS wire. HTS (RE) BCO will be selected to construct the coil of this magnet. Both the bulk and coil magnets will be assembled on the same movable system. The bulk HTS magnet will provide flux density greater than 4 T with a gap 34 mm that can accommodate the sample holder of the experimental station. The bulk magnet will be cooled with cryocoolers to 29 K and the coil magnet to 4.2 K; the coil magnet is separable from the bulk magnet after the field is trapped. We describe the concept of the magnetic-field calculation, the overall design of these magnets, and the cooling algorithm for the bulk HTS magnet system.

Field Trimming by Iron Pieces and Coils in a Superconducting Undulator

Trim-iron-pieces and trim-coils were used to correct the magnetic field error in a superconducting undulator with a magnet period of 15 mm. The main-coils were wound with NbTi wires of 0.77 times 0.51 mm2 rectangular cross section. The entire iron pole array was electrically insulated from the main-coils using Teflon to avoid degradation of the superconducting wire when the main-coils were trained to a large current. The trim-coils were wound with NbTi wires of 0.33 mm diameter. The trim-iron-pieces and trim-coils were mounted directly on the iron pole. The electric current of these trim-coils were generated by a single power supply with a constant voltage. A variable resistor and two golden-case resistors were connected in parallel to adjust the current that passed through each trim-coil. In this work, three trim-iron-pieces and one trim-coil were fabricated and mounted on each of the upper and lower arrays, and their effect on correcting the magnetic field error of the undulator is measured and compared to a model simulation.

Design and Improvement of a Mini-Pole Superconducting Undulator at NSRRC

The wire windings and magnetic performance of the mini-pole superconducting undulator (SCU) at the National Synchrotron Radiation Research Center (NSRRC) are being improved. NbTi superconducting (SC) wire with a rectangular cross section 0.51 mm 0.77 mm was wound on a racetrack iron pole. The designed field strength was 1.4 T at excitation current 510 A. The bath LHe-cryostat cools the SC wire directly and uniformly using LHe. A stainless-steel (SS) beam duct (thickness 0.3 mm) is designed to separate the ultra-high vacuum (UHV) from the storage ring and the LHe. The SS beam duct is glued to the dummy arrays with resin epoxy. The dummy arrays provide a strong support for the beam duct, providing against deformity from a pressure differential. A vacuum test was performed with a short version of a beam duct (length 400 mm) at low temperature. This paper describes the construction of the magnet, the measurement of the field and the testing of the SS beam duct.

Preliminary Test Results Concerning the “Within-Achromat”Superconducting Wiggler at NSRRC

A 0.96 m with 16 poles superconducting wiggler is fabricated in-house at NSRRC. The wiggler produced a magnetic field of 3.1 T for a 61 mm period with a pole gap of 19 mm. Three 5-pole prototype magnets using various pole materials from low carbon steel, vanadium permendure steel and holmium are tested and measured to verify the magnetic field performance in the testing dewar. This work describes the design and construction of a magnet and cryostat system. Furthermore, this work presents the results of magnet tests and the field performance of the compact superconducting wiggler

Magnetic-Field Shimming and Field Measurement Issue of the 130-Pole Superconducting Undulator

A 130-pole superconducting undulator with NbTi wires was wound and tested at National Synchrotron Radiation Research Center (NSRRC). The magnetic field was measured with a cryogenic mini-Hall sensor in a vertical dewar. The difference of total length between the nominal design and that measured experimentally with the Hall probe is approximately 1.2 mm; this discrepancy arises from the thermal contribution during the field measurement in the test dewar. The reliability of the measurement system is confirmed, and is discussed in terms of the field-mapping spectrum. The measurement of the field strength revealed a non-uniform distribution of the field in the 1 m long arrays. An iron pole piece was used to shim the on-axis field strength of the undulators. We discuss the thermal effect of the measurement system, a useful shimming method and its results for the superconducting undulator.

Design, Construction, and Performance Testing of a 6.5 T Superconducting Wavelength Shifter

A compact three-pole superconducting magnet with an aluminum warm beam duct was designed and fabricated as an X-ray source in a 1.5 GeV Taiwan Light Source (TLS) or the 3 GeV Taiwan Photon Source (TPS). Three pairs of racetrack NbTi superconducting coils were connected to one main power supply to create a central field of over 6.5 T. Two low current trim power supplies were connected in parallel to the two side pairs of the coil to eliminate the first and second field integrals. The wavelength shifter magnet was cooled in a pool boiling helium bath. Helium boils off at 1.3 L/hr. The vapor-cooled current lead is used to pass the 350 A excitation current. The magnetic field strength was measured at room temperature using a Hall probe and a stretched wire system. The magnet was tested successfully to 308 A, at which the central field exceeded 6.5 T, and the peak field on coil was 8.2 T. The design and construction of the magnet and the cryostat, the quenching protection, and field measurement results will be presented and discussed.

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.