Vacuum furnace: design, installation and commissioning

To increase the mass acceptance of the heavy-ion superconducting LINAC booster at PLF, Mumbai, it has been decided to replace the existing Pb plated (β=0.1) cavities in the first accelerating module by low beta (β=0.07) bulk Nb cavities. Fabrication of bulk Nb superconducting radiofrequency cavity is now a mature technology and is a key building block in accelerators worldwide. During fabrication of Nb cavities, it is required to process and heat treat the components at elevated temperatures; for both stress relieving and surface degassing. We report in this paper a bottom loading, high vacuum, high temperature furnace suitable for our requirement and designed to operate at a maximum of 1200°C. The design was optimized to provide a vertical hot zone of 600 mm diameter and 1000 mm high with a load capacity of 100 kg. The size and the overall power requirement were restricted keeping in view the space constraint and available power in the laboratory. The heat shields were optimized to achieve the maximum operating temperature at a modest power of less than 20kW. Thus a total of 14 shield-layers were incorporated: with initial two layers each being of Lanthanated Molybdenum and Molybdenum, and the rest being of SS310. The furnace has three independent temperature controlled zones to achieve 1% accuracy and stability of the job temperature. The PLC system, safety interlocks and the furnace have been fully installed and commissioned. The system achieves a base vacuum better than 5x10^-7 mbar. At the maximum operating temperature of 1200°C, the system consumes only 17.5 kW of heater power. (author)