Superconducting materials for SCRF cavity applications and future direction

There has been remarkable progress in the field of superconducting radio frequency (SCRF) cavity technology over the past decades, and the type-II superconductor niobium (Nb) in its highly pure and bulk form is currently the material of choice for the fabrication of high accelerating gradient SCRF cavities. Accelerating gradients approaching 50 MVm^-1 in elliptical shaped single-cell 1.3 GHz TESLA Nb-SCRF cavities and gradients up to 45 MV m^-1 in nine-cell 1.3 GHz TESLA Nb-SCRF cavities with quality factor Q ∼10¹⁰ have been reported. However, reproducibility of such cavity performance reliably and regularly, depends on several factors starting from the Nb materials used in the formation of such SCRF cavities to the fabrication process and the post fabrication chemical and thermal treatment of the SCRF cavities