Mechanical Properties of High RRR Niobium at Cryogenic Temperatures

Abstract

High RRR niobium superconducting rf cavities are fast becoming the basic accelerator structures of a new breed of particle accelerators. Mechanical properties of the high RRR niobium play a critical role in the physical integrity of these structures. The mechanical properties, yield strength, ultimate tensile strength and percent of elongation of Nb are routinely measured at CEBAF in the temperature range 300 to 4.2 K as a quality assurance measure. In this paper the mechanical properties of high purity niobium from Fansteel and Teledyne are presented as a function of temperature between 300 and 4.2 K. As can be expected the yield and tensile properties improve with a decrease in temperature. However, a dip in the elongation versus temperature curve is observed at about 100 K. This seems to be attributable to the presence of interstitial hydrogen. A detailed investigation of the Q-degradation of the Nb cavities also observes a dip in the Q 0 versus temperature curve at about 100 K.