“role of Metallurgy in the Thermal Conductivity of Superconducting Niobium”

Superconducting radio frequency (SRF) cavities for particle accelerators are fabricated using high purity niobium to allow for continuous high power operation. A hot-spot generated at a surface defect during accelerator operation can quench superconductivity and limit its performance. Increased heat conduction to the liquid helium bath dissipates hot spots, maintaining performance. Properly treated niobium may exhibit a local maximum (i.e., phonon peak) in thermal conductivity at T ≈1.8 K, the accelerator operating temperature. Conductivity with a phonon peak may be more than ten times that without the peak. Fabrication from ingot to cavity involves substantial processing, which in turn defines the metallurgical state of the niobium. Understanding the role of metallurgy and processing on conduction in the phonon regime can lead to improved accelerator performance.