From the viewpoint of a cryogen-free high-field superconducting magnet, the thermal stability properties of YBa 2 Cu 3 O 7 (Y123) coated conductor tapes before thermal runaway are examined under the conduction-cooling condition by a GM-cryocooler. Under such cryocooling condition, Ag-sheathed Bi 2 Sr 2 CaCu 2 O 8 (Bi2212) wires with c 10 4 A cm 2 reveal stable behaviors of 3 times larger current properties before thermal runaway than critical currents, although conventionalNb 3 Sn wires with c 10 4 A cm 2 quench almost at their critical currents under the cryocooling condition. In order to determine the maximum current-carrying capacity of the Y123 tape in high fields, we use a zero-dimensional heat balance model. On the basis of the measured basic properties for the Y123 tape, the calculations were done at = 20 T, bath temperature 0 = 4 2 K, c 10 7 A cm 2 , and cryocooling heat transfer coefficient = 10 3 W cm 2 K. We found that the Y123 tape with c 10 7 A cm 2 does not have the over-critical current but rather the sub-critical current before thermal runaway.Index Terms-Critical current property, cryogen-free superconducting magnet, high field, thermal stability, YBa 2 Cu 3 O 7 coated conductor.

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