Thermal, electrical properties and microstructure of high purity niobium for high gradient superconducting cavities

Publisher Summary This chapter describes the development of cryogenic thermal conductivity measurement system, a DC and an AC RRR measurement techniques for niobium quality control. The thermal conductivity, RRR distribution, and microstructure of electron beam welding niobium are investigated, and their correlation is observed by experiments. For controlling niobium properties for the fabrication of superconducting cavity, the systems for quick measurement of Nb thermal conductivity and residual resistivity ratio RRR are created. Thermal conductivity test can be done in a 100 1 transport liquid helium tank. An innovative cryogenic thermal conductivity measurement system based on transport liquid helium cryostat is described. Thermal conductivity distribution of electron beam welding sample is investigated. Below 3K, the thermal conductivities dependence on grain sizes is observed. Thermal break down is one of the main limitations on the way to high gradient superconducting cavity. To avoid thermal break down, high thermal conductivity of niobium is needed.