Japanese intense spallation neutron source (JSNS) driven by 3 GeV protons with power of 1 MW is constructed under the joint project of Japan Atomic Energy Agency and High Energy Accelerator Research Organization. Supercritical hydrogen of around 20K with 2 MPa is selected as a neutron moderator material and cryogenic hydrogen transfer lines are constructed from the moderators to the refrigerator. Then, a super insulator (SI) is adopted to reduce heat load in the hydrogen transfer lines. We performed irradiation test of SI using 60Co gamma ray to evaluate the irradiation effect. Two kinds of super insulator (polyimide and polyester) coated both sides by aluminum with thickness of 5 x 10-8 m were irradiated. After gamma ray irradiation, tensile test and gas yield measurement of super insulator were performed. Polyester based SI became brittle at about 10 MGy, on the other hand, polyimide based SI did not loss ductility so much even 80 MGy. Polyester based SI generated gas yield higher than that of polyimide based SI about one order of magnitude. We developed the gas analysis method by using a Q-mass and a mass-flow, providing to identify the unknown gas (i.e. H2O) effectively compared to a gas chromatography method.
Japan Atomic Energy Agency (JAEA) has developed leak detection technology for liquid helium temperature experiments in large-scale superconducting magnet test facilities. In JAEA, a cryosorption pump that uses an absorbent cooled by liquid nitrogen with a conventional helium leak detector, is used to detect helium gas that is leaking from pressurized welded joints of pipes and valves in a vacuum chamber. The cryosorption pump plays the role of decreasing aerial components, such as water, nitrogen and oxygen, to increase the sensitivity of helium leak detection. The established detection sensitivity for helium leak testing is 10-10 to 10-9 Pam3/s. A total of 850 welded and mechanical joints inside the cryogenic test facility for the ITER Central Solenoid Model Coil (CSMC) experiments have been tested. In the test facility, 73 units of glass fiber-reinforced plastic (GFRP) insulation break are used. The amount of helium permeation through the GFRP was recorded during helium leak testing. To distinguish helium leaks from insulation-break permeation, the helium permeation characteristic of the GFRP part was measured as a function of the time of helium charging. Helium permeation was absorbed at 6 h after helium charging, and the detected permeation is around 10-7 Pam3/s. Using the helium leak test method developed, CSMC experiments have been successfully completed.
The effects of artificial pinning centers (APCs) in ErBa2Cu3O7-δ films are discussed. The APC used for this research was BaZrO3 which was mixed into an ErBa2Cu3O7-δ ceramic target. The target was ablated and the films were grown on substrates with APCs. The X-ray diffraction patterns show that there were no other phases than ErBa2Cu3O7-δ and BaZrO3. Transmission electron microscopy (TEM) revealed that the BaZrO3 APSs grow along the c-axis of the films. The introduction of APCs decreases the surface resistance of the ErBa2Cu3O7-δ film and dramatically increases the critical current density (JC). Strong JC enhancement at the B¦¦ c-axis coincides with the growth direction of the APCs.
The Japan Atomic Energy Agency (JAEA) has developed a cryogenic structural steel to be used in large superconducting magnets for a fusion machine, and achievements from this development work will be utilized in the International Thermonuclear Experimental Reactor (ITER). Low carbon and boron-added JK2 (JK2LB), which has high strength, fracture toughness at 4K and thermal contraction from room temperature to 4K lower than that of conventional 316LN steel, has been developed as a conduit material for the ITER Central Solenoid (CS) conductor, which is based on ordinary JK2. In order to achieve the ITER requirements (0.2% yield strength ≥1,000 MPa, fracture toughness KIC(J) ≥130 MPa√m) of CS conduit material, chemical components such as carbon, nitrogen and boron, were optimized. In addition, since the CS will be operated under load cycles of 6 x 104 with a maximum principal stress of 490 MPa, fatigue crack growth assessment of the CS jacket was performed. As a result, JK2LB with a nitrogen content of 0.2%, boron of 15-40ppm and low carbon was produced to achieve the strength and fracture toughness requirements. Concerning the welding of JK2LB, a filler wire of JK2LB with a low nitrogen content of 0.13% was developed and fracture toughness of more than 130 MPa√m was confirmed in a weld metal. Measured fatigue crack growth rates of the base and weld metal at 4 K are low enough to achieve the operation cycle of the CS coil.