Thermal Stability Properties of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7}$ Coated Conductor Tape Under the Cryocooling Condition

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
J
_c
~ 10
⁴
A/cm
²
reveal stable behaviors of 3 times larger current properties before thermal runaway than critical currents, although conventional Nb
₃
Sn wires with
J
_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
B
=20 T, bath temperature
T
₀
=4.2 K,
J
_c
~ 10
⁷
A/cm
²
, and cryocooling heat transfer coefficient
h
=10
^-3
W/cm
²
K. We found that the Y123 tape with
J
_c
~ 10
⁷
A/cm
²
does not have the over-critical current but rather the sub-critical current before thermal runaway.