Design and fabrication of a high-temperature high-vacuum furnace to heat treat niobium for superconducting radio frequency cavities

The noble metal niobium is increasingly used for the fabrication of superconducting radio frequency (SRF) cavities, which accelerate charged atomic and sub-atomic particles to speeds between 5 and 100% of the speed of light. The fabrication of SRF cavities typically involves large deformation of niobium sheet, introducing large strain in the metal. Strain produces dislocations in the metal, which is known to degrade the heat transfer properties of the metal. For improved thermal performance, annealing at 600°C to 800°C in vacuum can be done to stress relieve the deformed metal.;With high energy physics research aiming at higher accelerating gradients for larger particle accelerators, like the International Linear Collider (ILC), high purity niobium is desired for its improved thermal performance. One of the well known methods of increasing the purity of niobium is to heat treat the metal at temperatures between 1200°C and 1500°C, in vacuum and with a coating of a getter, like titanium or yttrium.;To advance the research capabilities of the SRF cavity group at the National Superconducting Cyclotron Laboratory at Michigan State University, a high-temperature high-vacuum heat treating furnace was designed and constructed for heat treating niobium samples used for materials and heat transfer research. A prototype furnace was also constructed to demonstrate novel technologies in a cost effective manner. The scale of the prototype and the sample heat treating furnace was such that most of the required equipment were available in-house. A furnace to heat treat full-size cavities can be fabricated by scaling the design of the sample heat treatment furnace.