Electron-positron linear colliders have been under development since about 20 years ago and are the strongest candidates as future accelerators for high-energy physics. Two different technologies, normal and superconducting, have been competing. Regardless of the technology used, it was anticipated that the colliders would be too expensive to be afforded by one country or one region, and the decision was made to construct a single collider under international collaboration. The world high-energy physics community decided last summer that the next linear collider should be built utilizing the superconducting technology. Since then an international team has worked intensely studying the design of the collider. This article briefly describes the machine and summarizes the current status of the design.
We have reported the superconducting properties of Sm1+xBa2-xCu3Oy (SmBCO; x=0.08) thin films prepared by the low-temperature growth (LTG) technique. To investigate the effect of the Sm/Ba composition ratio (x) in the SmBCO, we deposited an upper layer with the Sm/Ba composition of x=0.00-0.12. From the result of the etch pit and composition analysis, we found that the Sm/Ba composition ratio in the SmBCO film influenced possible pinning centers, such as linear defects including screw dislocation and edge dislocation, and nano-size low-critical temperature (Tc) phase acting as a field-induced pinning center. Moreover, we noticed the Sm/Ba composition ratio in the SmBCO film influenced Tc and critical current density (Jc). As a result, the SmBCO films with x=0.04 and 0.08 showed Jc=2.8 × 105 A/cm 2 and 1.7 × 105 A/cm2 (77 K, B//c, 8 T), respectively.
We have found the condition to remove Sn from bronze by oxidation. The reactions are the oxidation of Sn at the surface of bronze and the diffusion of Sn from inside bronze toward the surface. The reaction rate is dominated by the later. This technique has been adapted to the internally stabilized Nb3Sn wires. It has been expected that the removal of Sn is perfect and the volume fraction of Cu increases from 19.2% to more than 65%. However, Sn removal enhances the conductivity of the wire at low temperature by no more than 40%. The theoretical estimation about the volume fraction of each component after the reactions suggests that (6∼10)% of volume fraction of Kirkendall voids remain in the Cu matrix. (Translation of the article originally published in Cryogenics 45 (2005) 645-652)