A Study on Quenching Characteristics of YBaCuO Bulk Superconductor with Deposited Ag Layer

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 Y-Ba-Cu-O (YBCO) bulk as a mechanical PCS. In previous reports, in order to investigate the contact characteristics of the switch, 50 A current test was performed and the contact resistance between two contacts was measured by four terminal method. As a result, it became clear that polishing and metal depositing on contact surfaces was effective methods to reduce the residual resistance, and the authors achieved to reduce this resistance to 0.64 muOmega, which was less than our target value of 1 muOmega. This paper focused on the greater current test (above 50 A) in order to perform more practical experiment as PCS used for SMES. In this experiment, the authors examined the characteristics to normal conductive state in the YBCO, which was not obtained by former 50 A current test. As a result, the transfer current is found to have a relationship with the layer thickness of deposited Ag on contact surfaces. The value of transfer current was rose by increasing the layer thickness of deposited silver, but saturated at around 0.60 mum.