Development of ingot niobium technology for efficient and economic SRF linacs

The SRF cavities for all completed discovery science programs have been built with high purity polycrystalline niobium with residual resistance ratio greater than 250. The XFEL at DESY is again based on 300 RRR polycrystalline niobium. The procedures and processes used from production of the polycrystalline niobium sheets to finished cavities are complex, numerous and expensive thereby making this technology unfriendly for the vast majority of possible technology spin-offs. CBMM and Jefferson Lab have invented ingot niobium technology and this holds a promise of changing the SRF Technology outlook with fewer, and more streamlined cost effective production processes and generate high yield. In this talk we will show that less stringent commercial niobium specifications are acceptable. We will also describe the development of large diameter (∼ 500 mm) high purity ingots suitable for 650 MHz cavities. Further, we will explore other simpler processes and procedures, which may lay the foundation for producing SRF cavities with improved quality factors at high peak magnetic fields. As a result SRF technology will become friendlier for future scientific and technological applications. (author)