A persistent current switch (PCS) is used for superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of YBCO bulk as a mechanical PCS. This paper focused on the current carrying area (called a-spot) on contact interfaces and presented an effect of interface condition on electrical contact characteristics in order to clarify the contact mechanism. The authors prepared various samples with different surface treatments (roughness and washing), and measured the contact voltage with a four-terminal method. YBCO deposited with metal (silver and indium) layer samples were similarly subjected to the contact voltage measurements. It was found that the contact interface conditions strongly affect the contact characteristics.
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