The magnetic field impact on the thermal conductivity of superconducting niobium

Abstract Particle accelerators extensively use superconducting radio frequency (SRF) cavities as essential components. The performance of the SRF cavities hinges critically on the thermal conductivity of the superconducting materials they are composed of. Previous research has thoroughly investigated this matter. In the meantime, magnetic fields’ influence on Cooper pairs in superconductors significantly affects thermal conductivity. With advancements in processing technology, the performance of SRF cavities has considerably improved. This has led to a significant increase in the acceleration gradient of the cavities, resulting in a magnetic field strength of almost 200 mT on the inner surface. This development has made the situation more critical. Thus, a more comprehensive and systematic study is needed to understand better the impact of magnetic fields on thermal conductivity and its effect on SRF performance. Therefore, we introduced a thermal conductivity model for superconductors, including a magnetic field correction in the thermal conductivity calculations. The study involves theoretical calculations and experimental measurements on the thermal conductivity of small niobium samples at varying magnetic fields and temperatures. A comparative analysis was conducted to assess the congruence between the experimental results and our theoretical predictions. Finally, these results were used to estimate SRF cavities’ performance, thereby enhancing their overall efficacy and reliability.