Yukihiro Murata

A Novel Design Method of Shapes of Ferromagnetic Materials for the Superconducting MRI Magnets

We present a novel non-stochastic method for optimizing the shapes of ferromagnetic materials to generate a target static magnetic field. A magnetizing current corresponding to an error field is calculated as an inverse problem and then the current is replaced with an equivalent ferromagnetic material. Iteration of this process leads to an error field of almost zero. It should be noted that the initial condition of the material shape is critical for convergence. Consequently, we propose a combined method: the initial shape of the material is generated with a stochastic optimization algorithm, and then the shape is updated using an explicit method. We show that this method works well with a test 2D axisymmetric magnet.

Design of a Superconducting Wiggler for the Saga Light Source Storage Ring

A hybrid three-pole wiggler for generating hard X-rays in the range 4-40 keV was designed for the 1.4-GeV storage ring of a synchrotron radiation facility, i.e., the Saga Light Source. The wiggler consists of a superconducting main pole with a peak field of 4 T and two normal-conducting side poles with peak fields of 1 T. The normal-conducting side poles were used to reduce the heat load on the cryogenic system for the wiggler. A cryogen-free system was used to ensure long-term operational stability of the wiggler system. The superconducting coil and iron poles of the main pole are cooled by a Gifford-McMahon cryocooler via mechanical contact. To suppress the first and second field integrals of the main pole, we designed the main pole with relatively large field clamps and with no transverse return yoke. This pole structure was effective in suppressing beam displacement due to the wiggler field and in reducing the side pole volume. The beam effects due to the multipole fields of the wiggler were estimated and were found to be small or controllable. Based on these results, the storage ring with the designed wiggler is considered to be an effective hard-X-ray source.

Magnetic Field Design of a Superconducting Wiggler in the SAGA-LS Storage Ring

A magnetic field design for a superconducting (SC) wiggler system, which has been installed in the Saga light source storage ring, was described. The wiggler is a three-pole type, consisting of a 4.0-T SC center magnet and two normal-conducting side magnets; thus, each pole forms a magnet. Since the wiggler consists of isolated magnets, reduction of the first field integral of the center SC magnet was important from the viewpoint of suppression of the orbit displacement. For this purpose, the center SC magnet was designed to have a separated iron core with field clamps and no transverse return yoke. This concept made magnetic field negative regions near the center peak magnetic field on the electron beam orbit to reduce the first field integral and beam meandering. Heat generations due to eddy currents and the magnetic field due to supporting structures were calculated to have ignorable effects. The appropriateness of the design has been confirmed through daily stable operation at the light source.

Coupled Thermal-Magnetic Analysis on Thermally Actuated Superconducting Flux Pump

This paper presents numerical analysis of the thermally actuated superconducting flux pump. Visualization of the behavior of the magnetic flux helps our understanding of flux injection mechanism. In addition, in order to confirm validity of the result, we conducted a preliminary flux pump experiment. This result qualitatively agrees well with the experimental one. The flux pump system utilizes a particular behavior that permeability of some materials such as Gadolinium is sensitive to the temperature. In this paper a simple heater is used to control the flux pump system.

Design and Performance Test of Superconducting Transport Solenoid for D-Line at J-PARC Muon Science Facility

A superconducting transport solenoid for Decay Muon Line (D-line) at J-PARC Muon Science Facility was newly designed and manufactured. It was designed to generate a magnetic field in relatively large region (warm bore diameter 0.2 m), while keeping the same outer dimensions, connection interfaces to the existing refrigerator and the power supply of the previous machine [1-3]. Major changes of both solenoids are the reduction of the central magnetic field, the equipment of a warm bore and the adoption of the high Tc current leads. After the installation to the beam line, the initial cooling test, the excitation test and the emergency shutdown test at the rated current were conducted by KEK in order to confirm cryogenic and magnetic performance. These tests were successfully performed with no damege and indicated the solenoid was precisely manufactured and fulfilled the requirements. The solenoid has been under operation since July, 2015. This report describes the design, the manufacturing process, the magnetic field measurement at room temperature and the results of performance tests conducted by KEK.

Design Optimization for Superconducting Bending Magnets using Pareto Front Curve

A novel limit design method for superconducting magnets is presented. It is particularly suitable for ion core magnets such as those used in accelerator magnets. In general, a stochastic optimization whose objective functions consist of values, e.g., the magnetic field, experience field of superconducting coils, current density, and multipole field integral, is often used. However, it is well known that the obtained solution strongly depends on the initial one. Furthermore, once the calculation model is fixed, the range of solutions is also fixed, i.e., there are times when it may be impossible to find the global optimum solution even with a lot of parameter sweeps. In this study, we draw the Pareto front curve to obtain the range and infer whether the solution is an optimum one. In addition, the Pareto front curve indicates the neighborhood solution that is substituted for the initial one. After this process a stochastic optimization is implemented with its initial design parameters. To confirm the validity, we designed a superconducting bending magnet, and it showed that this method works well.