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)
We are developing a new type of photon detector for an experiment to search for muons decaying into a positron and a gamma ray. In this experiment, the photon detector will utilize liquid xenon (Xe) as the scintillation material. Good transparency of the liquid Xe is required in order to gain the highest performance out of the detector. Impurities like water and oxygen must be removed efficiently for this purpose. We have developed a new purification system, dedicated to removing water from liquid Xe, by employing a cryogenic centrifugal pump and molecular sieves. The performance of the system will be described in this article.
The operation tests of the 10 kWh-class flywheel energy storage system equipped with radial-type superconducting magnetic bearings (SMBs) experimentally manufactured under the NEDO project on “Superconducting bearing technologies for flywheel energy storage" were conducted. In the tests, we successfully achieved energy storage amounting to 5.0 kWh at high-speed rotation as high as 11,250 rpm. The radial-type SMBs are considered promising bearings suitable for high-capacity systems. However, compared to axial-type SMBs, not many radial-type SMBs have been experimentally manufactured; much less the full-scale outer-rotor-type rotating machines that use these bearings. Therefore, there were many unknown problems related to evaluating the practicality of these machines. The major issues in conducting the operation tests were to control the shaft descent of the radial-type SMB, and to control vibrations in the rotating system supported by the SMB with a small damping ratio. We solved these problems; the former using a pre-loading method, and the latter by using nonlinear zero-power control capable of controlling not only the rigid body vibration mode but also the elastic vibration mode of the rotor. The successful operation achieved in the tests proved the practicality of the radial-type SMBs as well as the feasibility of the outer rotor-type high-speed rotation systems using these bearings.
We have investigated YBa2Cu3O7-X (YBCO) coated conductor fabricated using a multi-plume and multi-turn (MPMT) pulsed-laser deposition (PLD) method. MPMT-PLD has been improved to a technique that enables the fast deposition of high critical current (Ic) YBCO layer for a long coated conductor fabrication. We used a substrate that a CeO2 cap layer deposited by PLD method on a Gd2Zr2O7 (GZO) buffered Hastelloy tape using the ion-beam assisted deposition (IBAD) method. The YBCO layer was deposited using MPMT-PLD and reel-to-reel tape transfer system. We attained the highest Ic of 313 A at a tape speed of 3.33 m/h using the MPMT-PLD method on a short sample. Then, we successfully deposited a 212.6 m-long YBCO layer at a tape speed of 3.75 m/h using the MPMT-PLD method. This YBCO coated conductor had a high Ic as high as 245 A, and the multiplication of Ic and length exhibited a high value of 52,087 A·m.