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大強度陽子加速器施設(J-PARC)物質・生命科学実験施設において1MWの陽子ビームで駆動する核破砕中性子源では、水銀ターゲットで発生した高速中性子を冷中性子に冷却するために、液体水素(1.5MPa, 20K以下)を3基のモデレータに供給し、そこで発生する核発熱(3.8kW)を強制方式で冷却する低温水素システムを備えている。この低温水素システムでは、核発熱に伴う系内の圧力変動を低減するためにベローズ構造で圧力を吸収するアキュムレータを採用していることが特徴である。しかしながら、初期に使用したベローズで不具合が生じたため、高耐圧, 長寿命のアキュムレータが必要となった。厚肉プレートによる高耐圧性を有する溶接ベローズ(内ベローズ)の要素技術開発を行い、最適条件を見出すことができた。内ベローズの試作機を製作し、2MPaの圧力印加を繰り返す耐久試験により、設計寿命(1万回以上)を満たすことを確認した。また、その製作法による内ベローズを導入したアキュムレータの組立時、溶接歪等によって内ベローズの機能性や寿命に影響しないように、水平・垂直度を0.1$^{\circ}$以内に抑えた。改良したアキュムレータは既に約25,000時間(繰り返し伸縮約16,000回(運転中40mm伸縮の設計寿命は50万回))の運転を実現できており、2019年1月現在、500kWビーム出力で運転中である。2018年7月には932kWビーム入射した運転を行い、アキュムレータの圧力変動抑制機能が設計どおりの性能を有することを確認し、今後の高出力において安定運転ができる見通しを得た。, At Materials and Life Science experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC), a 1-MW pulsed spallation neutron source is equipped with a cryogenic hydrogen system which circulates liquid hydrogen (20 K and 1.5 MPa) to convert high energy neutrons generated at a mercury target to cold neutrons at three moderators with removing nuclear heat of 3.8 kW deposited there. The cryogenic system includes an accumulator with a bellows structure in order to absorb pressure fluctuations generated by the nuclear heat deposition in the system. Welded inner bellows of the first accumulator was failured during operation, forcing us to improve the accumulator to have sufficient pressure resistance and longer life-time. We have developed elemental technologies for manufacturing welded bellows of the accumulator by a thick plate with high pressure resistance, succeeding to find optimum welding conditions. We fabricated a prototype bellows block and carried out an endurance test by adding a pressure change of 2 MPa repeatedly. As a result, the prototype bellows was successfully in use exceeding the design life of 10,000 times. Since distortions given during welding and assembling affect functionality and lifetime of the bellows, we set the levelness of each element of the bellows as within 0.1$^{\circ}$. The improved accumulator has already been in operation for about 25,000 hours as of January 2019, resulting that the number of strokes reached to 16,000. In July 2018, we demonstrated that the accumulator could suppress the pressure fluctuation generated by the 932 kW beam injection as designed. As current operational beam power is 500 kW, the current cryogenic hydrogen system could be applicable for stable operation at higher power in the future.

Joint Research on Environmental Science and Technology for the Earth

Liquid hydrogen (LH₂), which has large latent heat, low viscosity coefficient, is expected to be a candidate for a cryogen for superconducting wires, not only MgB₂ but also other HTC superconductors. LH₂ cooled superconducting wires are expected to have excellent electro-magnetic characteristics, which is necessary to be clear for cooling stability design of LH₂ cooled superconducting device, however, due to handling difficulties of LH₂, there are only few papers on the properties of LH₂ cooled superconductors, especially under external magnetic field. We designed and made an experimental setup which can energize superconducting wires immersed in LH₂ with the current of up to 500A under the condition of external magnetic field up to 7 T and pressure up to 1.5 MPa. In order to confirm experimental method and safety operation of the setup, over current tests were carried out using MgB₂ superconducting wires under various external magnetic field conditions. Critical current of the test wire at the temperature 21, 24, 27, 29 K under external magnetic fields up to 1.2 T was successfully measured. The resistance of the wire also was measured, while the transport current exceeded the critical current of the wire., 11th European Conference on Applied Superconductivity (EUCAS2013)

To clarify the mechanism by which Cd initiates rat testicular cancer, the ability of Cd or H2O2 to induce DNA single strand breakage was evaluated in testicular Leydig cells using a simple and rapid DNA precipitation method. Effects of Cd, Fe, Zn and Ca on the oxidant-induced DNA damage and effects of reduced glutathione (GSH) on the genotoxicity caused by the peroxide and/or Fe were also assessed. H2O2 induced strong DNA single strand breakage. Cd alone did not exhibit such a genotoxicity nor did it enhance the peroxide-induced DNA damage. Ca and Fe(II) potentiated the oxidant-induced DNA single strand breakage, while Zn partially protected cells from the oxidative damage of DNA caused by the peroxide. GSH attenuated single strand breaks of DNA brought about by H2O2 and/or Fe. These results suggest that the initiation of carcinogenesis in the rat testis by Cd is triggered by active oxygen species such as H2O2, which is generated by the metal exposure, rather than by a direct genotoxicity of Cd. The oxidantmediated initiation is clearly a complicated event accomplished by multiple factors.