High purity niobium for tesla test facility

High purity Nb for Tesla Test Facility (TTF) cavities should meet well specified tight requirements. The acceptance tests include the RRR measurement, microstructure analysis analysis of interstitial and metallic impurities, hardness measurement, tensile test, examination of the surface roughness and search of clusters of foreign material inclusions. The purity of niobium can be additionally improved by a purification heat treatment (solid state Bettering). Pure titanium is used for solid state gettering of TTF cavities. The RRR after post purification reaches normally values of 500-600. The properties of niobium are analyzed regarding the fabrication of high gradient superconducting cavities. The fabrication of seamless cavities by hydro-forming as alternative to standard fabrication procedure (deep drawing and electron beam welding of half cells) was taken into consideration. Fabrication of seamless tubes suitable for hydro-forming is one of the challenges in development of this technique. (author)