Ching-Shiang Hwang

Design and construction performance of a compact cryogen-free superconducting wavelength shifter

A compact cryogen-free superconducting wavelength shifter with a warm bore for electron beam has been constructed for generating synchrotron radiation hard X-rays. This magnet consists of three pairs of racetrack NbTi superconducting coils that can produce a maximum magnetic field of 6.0 Tesla at the central pole. The superconducting coils, the aluminum supporting block, and the return iron yokes are cooled to 4 K, and the thermal shielding and HTS current leads to 60 K, by using a 1.5 W Gifford-McMahon type cryocooler. The technical issues on the magnet design and the construction process are presented. Several different measurement systems are used to characterize the magnetic field performance.

Performance of an advanced elliptically polarized undulator with shimming

A 4-m-long elliptically polarizing undulator (EPU5.6) device with an Apple-II structure is installed in the Synchrotron Radiation Research Center storage ring. This is the longest EPU device with an Apple-II structure worldwide. The errors of the magnet construction and the assembly process are among the several factors that can degrade the spectral performance. This study describes the mechanical design concept and construction that reduce magnetic field errors to keep high performance of the magnet. The electron orbit distortion in various polarization radiation modes is discussed with reference to a global feedback system and a feed forward table with following gap and phase. The beam dynamic effects are also investigated when the phase and magnetic gap are changed.

Design of a superconducting multipole wiggler for synchrotron radiation

A 32-pole superconducting magnet with a 12 /spl times/ 80 mm/sup 2/ cold bore aperture was designed to serve as a multipole wiggler in the Taiwan synchrotron light source. The magnet consists of 32 pairs of racetrack NbTi superconducting coils with a periodic length of 60 mm, and can produce a maximum magnetic field of 3.2 Tesla at a pole gap of 18 mm. The superconducting coils, the aluminum-supporting block, and the return iron yokes are cooled to 4.4 K in LHe bath. The temperature of cold bore beam duct will be at 70 K using liquid nitrogen. Technical issues concerning the design of the magnet and its construction are discussed. A prototype magnet with five poles was also constructed to characterize the magnet design by means of various methods of magnetic field measurement.

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

Development of an Algorithm for Magnet Sorting and Field Shimming for TPS Elliptically Polarized Undulators

A spatially periodic magnetic field is essential to cause an electron beam to wiggle and to emit electromagnetic radiation in a synchrotron (SR) source of radiation, and to provide fully coherent light in free electron lasers (FEL). To create this field, permanent magnets (PM) or electromagnets are patterned in a device commonly called an insertion device for SR and a radiator or modulator for FEL. In reality, magnet blocks or iron poles are not identical, in terms of geometry and magnetic properties, even with progressive manufacture. Compensatory methods are thus desired to recover the magnetic field and also to decrease the duration of construction. Magnet sorting is a pre-process that aims to eliminate the effect of manufacturing error. Before assembly of an insertion device, data of each component, especially the magnetic properties of each magnet block and the gap variation of mechanical structure, are organized to optimize the performance of the magnetic field. After that process, there is sometimes an optimization to shim the magnetic field. An effective algorithm of both processes is significant, particularly for a long undulator and an elliptically polarized undulator (EPU).

Field Correction of an Elliptically Polarized Undulator

The correction of the magnetic field of an elliptically polarized undulator (EPU) decreases the phase errors, the RMS trajectory and multipole magnetic components. The conventional method to correct the field involves tedious work with much trial and error. Based on field-shimming procedures and a field-shimming simulator proposed in National Synchrotron Radiation Research Center, the duration of field correction of EPU46 becomes decreased. The first field integral and the kicker value at each magnet pole determine the amount of adjustment of vertical and horizontal positions of the magnet. The final result of correcting a single pair of a magnet array shows a phase error less than 5 and a variation of the RMS trajectory less than 5 , in both circular and linear polarization modes for single pair of magnet array. Here we describe a standard operating procedure of EPU field correction that is becoming established, which will be beneficial for a future mass-production stage and for training purposes.

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.

Analysis of Heat Load in a Superconducting Wiggler With a Semi-Cold UHV Beam Duct

A superconducting wiggler with a magnetic period of 6.0 cm (SW6) and a peak field of 3.2 T has been designed and fabricated in the National Synchrotron Radiation Research Center (NSRRC). The beam duct separates the electron beam from the cryogenic system of the magnet. The heat load on the beam duct should be low to stabilize the operation of the superconducting magnets. However, outgassing caused by synchrotron radiation at an electron energy of 1.5 GeV and a current of 200 mA must be reduced. Accordingly, operating the system at a higher temperature can minimize the adsorption of molecules on the beam duct. Therefore, the beam duct system and its connection by finite element analysis are designed to optimize the operating temperature of the beam duct at between 100 and 120 K. Performance of the beam duct is established to comply with specifications during the operation of magnet

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