## 5 Effects of Magnetic Fields on Quenching Characteristics of Superconducting Tapes
### Effects of Magnetic Fields on the Quenched Characteristics of Superconducting Tapes  
The same testing method was used to obtain the limited current, the voltage of the tape, and the quenched resistance of the SC_SH and SC_8602 superconducting tapes under magnetic fields of 0, 42.4, 75.9, and 122.9 mT. The relationship between prospecting current, transport current, magnetic fields, and the quenched resistance of superconducting tapes was investigated. Figure 7 shows the relationship between the prospective current and the quenched resistance per meter of eight testing tapes. The experimental results show that the quenched resistance of these two tapes increased when the prospective current increased. The higher prospective current caused higher Joule heat, which resulted in a higher temperature of the tapes. Thus, the quenched resistance of these two tapes increased when the prospective current increased. When the prospective current was around 300 A, the testing superconducting tapes either did not quench or the quenched resistance was very small, which cannot be tested. Thus, the resistance of the eight superconductor tapes was 0 \(\Omega\) when the prospective current was lower than 300 A. The rate of increase was different between the two tapes, as shown in Table 2. For the SC_SH superconducting tapes, when the prospective current changed from 400 A to 900 A, the quenched resistance increased faster than when the prospective current was more than 900 A. For SC_8602 superconducting tapes, the quenched resistance increased faster when the prospective current changed from 620 A to 900 A than when the prospective current was more than 900 A. The rising rate of SC_8602 was low when the prospective current changed from 400 to 620 A.  
Figure 6: Current, voltage, and resistance waveforms of 75.9 mT. (**a**) SC_SH. (**b**) SC_8602. Table 3 shows the amplitudes of the quenched resistance of two tapes when the prospective current was 1200 A. For SC_SH superconducting types, the quenched resistance increased with the increase of the magnet fields. The magnetic fields influenced both the amplitude and the rising rate of quenched resistance of the SC_SH tape. However, magnetic fields had little effects on the quenched resistance of SC_8602 superconducting types. The quenched resistance of SC_8602 was almost same at different magnetic fields. The superconducting resistance was about 100 m\(\Omega\)/m at room temperature (25 \({}^{\circ}\)C). As shown in Table 3, for the SC_SH, when the current was 1200 A, the resistance was 53 m\(\Omega\)/m. The resistance was about 62 m\(\Omega\)/m when the magnetic field was 122.9 mT. The increased ratio of SC_SH is 13.9%. The quenched resistance of the superconducting tapes is in direct proportion to the superconducting length. For a long superconducting tape, the quenched resistance of SC_SH under a magnetic field will increase significantly. However, the magnet field has little effect on the SC_8602. Figure 8a shows the effects of transport current on the voltage of superconducting tapes. Experimental results shows that the rising rate of the quenched resistance of SC_SH was always higher than SC_8602 under different magnetic fields. The amplitude and the rising rate of voltage of \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Rising Rate of Quenched Resistance (m\(\Omega\)/A)**} \\ \cline{2-5}
**Magnet Field (mT)** & **SC\_SH** & \multicolumn{4}{c}{**SC\_8602**} \\ \cline{2-5}  & **400–900 (A)** & **>900 (A)** & **400–620 (A)** & **620–900 (A)** & **>900 (A)** \\ \hline
0 & 0.0289 & 0.0208 & 0.0068 & 0.0571 & 0.0127 \\
42.4 & 0.0292 & 0.0183 & 0.0077 & 0.0583 & 0.0125 \\
75.9 & 0.0450 & 0.0244 & 0.0071 & 0.0574 & 0.0118 \\
122.9 & 0.0336 & 0.0165 & 0.0125 & 0.0613 & 0.0175 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Distribution of Rising Rate of Quenched Resistance.