Basic research of cryogenic low contact resistance switches for persistent operation of superconducting coil

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 06452436
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Nuclear fusion studies
• Research Institution: NATIONAL INSTITUTE FOR FUSION SCIENCE
• Principal Investigator: TANAHASHI Shugo National Institute for Fusion Science, Safety and Environmental Research Center, Professor, 安全管理センター, 教授 (30023683)
• Co-Investigator(Kenkyū-buntansha): CHIKARAISHI Hirotaka National Institute for Fusion Science, Research associate, 大型ヘリカル研究部, 助手 (60249969) ; YAMADA Shuichi National Institute for Fusion Science, Associate Professor, 大型ヘリカル研究部, 助教授 (50249968)
• Project Period (FY): 1994 – 1996
• Keywords: superconducting coil / disconnector / persisten current operation / cryogenic temperature / low resistance / contact point / contact resistance

Research Abstract

It is necessary to be able to keep coil currents constant in the experimental devices such as Large Helical Device which has large current superconducting coils. Persistent current operation is obviously preferable to constant current control operation, if possible. However, the persistent current operation is nowadays impossible because there is no such a high current persistent current switch as its current capacity of 30kA class. Because at the present stage of superconducting technology, there are no switches which have dielectric strength of several thousand volts in the open state and zero resistance and current capacity of several ten kA in the closed state. Then we chose development of normal conductive mechanical switches. Present results of are as follows ;
The contact points are made of copper base and their contact surface are plating with Pb-Sn solder. The contact points are formed from both a drum shaped projection (radius of curvature : 20mm, length : 20mm) and a flat plate. These contactors are used in the liquid helium bath and contacted and then slides each other. The thickness of the solder plating is 0.15-0.5mm. The contacting force is 70-80kg. Obtained contact resistance are 0.01 micro ohm at 100A,0.1 micro ohm at 200A,0.3 micro ohm at 300A.It seems almost zero ohm in the range less than 100A.If 100 contacts are operated at parallel connection and each contactor is flowed 300A,then 30kA,0.003 micro ohm. If it is used in the circuit of 1H class coil, the dumping time constant is 10 years.