Thermal runaway properties of Ag/Bi-2212 tape cooled by a cryocooler have been studied experimentally under the condition of magnetic fields up to 15T at 4K. To investigate the stability of the tape, Joule heating and a sample temperature were measured as a function of time at a fixed operating current. As a result, if cooling capacities are higher than Joule heating, it is found that thermal runaway current, Itr, is higher than critical current, Ic, which is defined by 1μV/cm. Furthermore, MRE (Minimum Runaway Energy) was measured as a function of operating current ratio, Iop/Itr, and the magnetic fields. The MRE decreased with increasing magnetic field in the same operating current ratio.
