Complete overlapping of the electron and positron bunches at colliding point can be attained by using the strong time-depending electromagnetic RF field in the superconducting crab cavity. Commissioning of the crab cavities started in February 2007 at KEKB. Effective head-on collision of electron and positron has been achieved successfully. After introduction of crab crossing and crab cavity, the structure and the fabrication of the KEKB superconducting crab cavity are discussed.
A kenaf fiber-ice composite system can be used as a substitute for glass-fiber-reinforced plastics (GFRP). At the present time, electrical insulating systems at cryogenic temperature mainly use GFRP. However, GFRP dose not decompose naturally. A large negative environmental impact of GFRP has been pointed out as a problem to be solved. We have been suggesting the application of a natural fiber-ice composite system as an electrical insulating system in the cryogenic region. Kenaf is candidate of the natural material that has a low negative environmental impact. We pay attention to kenaf because it decomposes naturally and is characterized by its excellent elasticity and water absorption properties. In this study, we report the AC electrical breakdown strength (Fb) of a kenaf pulp-ice composite system is almost the same as that of GFRP. We consider that a kenaf fiber-ice composite system is promising as a substitute for the GFRP in electrical insulating systems used in the cryogenic region.
Research and development that attempts to reduce the weight of railroad vehicle and improve efficiency is being advanced by applying high-temperature superconducting wire material to the winding of 4 MVA-class traction transformer. To compose a cooling system that absorbs the generation of heat due to AC loss, a refrigerator that has the refrigerating capacity corresponds to the calorific value becomes indispensable. In this report, we described the results from the development stage of a 65 K,1 kW-class active-buffer, pulse-tube refrigerator.
PLD-RE1Ba2Cu3Oy (REBCO) coated conductors (CCs) manufactured using a reel-to-reel (RTR) system are inexpensive, can be produced in long lengths and have a high critical current (Ic), making them an excellent choice for industrial applications such as cables, transformers and superconducting magnetic energy storage (SMES) devices. Reducing the approach gap between the target and substrate (dT-S) is one effective technique to increase the production rate for CCs made using the RTR system. Generally, the critical current density (Jc) of PLD-REBCO CCs using a RTR-system decreases as dT-S decreases, because the amount of dead layer, such as a-axis-oriented grains, increases and the composition of the superconductor becomes off-stoichiometic. We speculated that the formation of a-axis-oriented grains in PLD-REBCO CCs fabricated at a short dT-S is due to a high deposition rate (i.e., high supersaturation). In this work, we fabricated PLD-Gd1Ba2Cu3Oy (GdBCO) CCs using a RTR system by varying the target composition and moving speed, to control superconductor composition, and suppress the formation of a-axis-oriented grains. As a result, the PLD-GdBCO CCs have the following characteristics: Ic=312 A/cm-width (Jc=2.6 MA/cm2) with a 1.2 µm thickness and 1 m length when manufactured at 2 m/h (deposition area = 1-turn×6.5 cm = 6.5 cm2, laser power = 300 mJ, ƒ=4-plums×30 Hz). This production rate and Jc value are 3.0 times and 1.8 times higher, respectively, compared to those before controlling the target composition and moving speed. We suggest that our technique is effective for not only increasing the production rate, but also enhancing the Jc of PLD-REBCO CCs manufactured using the RTR system.