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As the “low activation” superconductor, Mg 11 B 2 has a potential application in superconducting coils for fusion reactor. In present work, the sintering process and critical current density of low activation Mg 11 B 2 superconductors were systemically studied from low temperature to high temperature. It was found that the J c and H irr values of Mg 11 B 2 bulks in present work are both obviously higher than that of those samples prepared in previous studies. Furthermore, the low-temperature sintered samples exhibit better J c performance at high fields than the high-temperature sintered samples, due to strong grain boundaries pinning. On the other hand, the high-temperature sintered samples have higher J c at low fields compared to low-temperature sintered samples, mainly owing to their better crystallinity and grain connectivity. The highest J c value (2.20 ×10 5 A cm −2 at 20 K, self-field) is obtained in the Mg 11 B 2 sample sintered at 850 °C for 45 min. [ABSTRACT FROM AUTHOR]

Highlights: [•] Histidine is an effective dopant for improving the critical current density. [•] The dominating pinning effects are provided by nano-scale MgO pinning centers. [•] MgO performed stronger pinning effects than defects caused by C substitution. [•] We clarified how to select the amino acid for doping. [Copyright &y& Elsevier]