We experimentally studied the quench properties of REBa2Cu3Oy (RE-123) coated conductors with various plated-copper thicknesses (20 and 40 μm). A short sample of coated conductors was conduction-cooled to 45 K, a magnetic field (μ0H, up to 2 T) was applied perpendicular to its wide face to control the critical current, an operating current was supplied, and subsequently quench was initiated using a small heater. Normal zone propagation velocities (NZPVs) were measured at various operating currents, and the NZPVs of coated conductors with various copper thicknesses were compared with each other. To understand the impact of the copper stabilizer on quench protection, hot-spot temperatures were measured during the processes that simulate quench detection using voltage taps and protection using dump resistor. The maximum hot-spot temperatures were plotted against the operating current as well as the overall current density, and the impact of the thickness of the copper stabilizer on hot-spot temperature was examined. The impact of the initial temperature on hot-spot temperature was also studied.
Three YBCO thin films on sapphire substrate with widths of 3, 5, and 10 mm were prepared, and their AC loss characteristics were studied experimentally. The total AC loss dissipated in samples carrying AC transport current in an AC transverse magnetic field was measured by an electromagnetic method. The total AC loss in YBCO film is proportional to the film width and the perpendicular magnetic field component, a component of the transverse magnetic field that is perpendicular to the film wide face. Reduction of the film width and/or the perpendicular magnetic field component is an essential means of decreasing the total AC loss. When plotting the total AC loss divided by film width against the perpendicular magnetic field component, curves for various film widths and field angles almost agree with each other. The total AC loss can be estimated by analytical expressions except in an intermediate range of the perpendicular magnetic field component. The experimental results indicate two engineering approaches for reducing the total AC loss in YBCO film: decreasing the film width and decreasing the perpendicular magnetic field component. Findings have shown empirically that decreasing the film width and decreasing sinα, where α is the field angle, are equivalently effective in reducing the total AC loss.
The committee on applied superconducting apparatuses and characteristics of superconductors, the Institute of Electrical Engineers of Japan (IEEJ) has made a database on superconducting magnets which were built over last ten years in Japan. The outline of the database is explained part I. In part II, stability and hot-spot temperature of a magnet are investigated. Minimum quench energies, minimum propagating zones, and Stekly's stability factors are calculated using the database. Dependence of those stability parameters on the magnet scale is studied and the design trends of the stability are discussed. Hot-spot temperatures of the pool-cooled magnets at quench and energy dump process are also calculated based on the database, and the trends of design rules for the quench protection are studied.
When a normal zone is produced in one or a few strands in a multi-strand superconducting cable by a localized disturbance, the current in the normal-transited strand transfers to the others via contact resistance between strands. Heat generated in the normal zone also diffuses to the other strands. The stability of the multi-strand superconducting cable against local disturbances is much influenced by these current transfer and thermal diffusion. The influence of the copper resistivity on current transfer and stability is studied. When we plot the MQE on "contact resistivity"-"contact thermal conductivity"-plane, there are a stable region with large MQE and an unstable region with small MQE. The small contact resistance and small contact thermal conductivity between strands are preferable from the view point of stability. If the contact thermal conductivity is small, the transition from the stable region to the unstable region is drastic.< >
For accelerator magnets, high Tc superconductors (HTS) are a remarkable option comparing with low Tc superconductors (LTS), since they possess several distinctive characteristics, such as good thermal stability and high cooling efficiency. On the other side, HTSs have strong mechanical constraints which make them hard to shape, like bending and winding. In this paper, a method is proposed to solve the mechanical constraint problems of HTSs, and the feasibility of applying HTSs to combined-function accelerator magnets is proved. The detailed method is presented to apply coated conductors into the design of a combined function accelerator magnet containing both dipole and quadrupole magnetic field components, which is named 2+4 pole magnet in this paper. This method takes electromagnetic characteristics of coated conductors into account, and it is capable of solving their mechanical constraint problems. First a 2D cross-sectional design of the straight section was completed, with a layout in the form of multi-layers to generate required magnetic fields. Then a 3D design was carried out to wind coil ends considering flat-wise/edge- wise bending and torsion tolerance. The locations and angles of coated conductors were optimized to improve the efficiency of field generation and minimize the field error. Results show that coil ends can be successfully designed, and electromagnetic analyses show that the designed magnet can properly generate required magnetic field.
We report the progress of an R&D project of fundamental technologies for cryocooler-cooled accelerator magnets using coated conductors funded by the Japan Science and Technology Agency under its S-Innovation Program. Its target applications include carbon cancer therapy and accelerator-driven subcritical reactor. We have been carrying out design studies of HTS magnets for spiral sector fixed-field alternating gradient accelerators to show their feasibility for the target applications and to clarify the requirements of winding technologies. A three-dimensional winding machine has been developed to fabricate a model magnet in which winding technologies required for the designed magnet are implemented. With respect to the large magnetization of coated conductors, which is one of the big concerns on their uses in accelerator magnets, the magnetic field measurements using rotating pick-up coils have been made to clarify its influence on the multipole components of the magnetic field. A method for numerical electromagnetic field analyses of coils with three-dimensional shapes has been developed to predict the influence of magnetization on the field quality of magnets.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)