Design and fabrication of insertion fixture for dressing of 1.3 GHZ 9-cell SCRF cavities

RRCAT is working on infrastructure and technology development, required for fabrication of SCRF cavities, to support their future accelerator programme involving SC LINAC. Initially as part of this, 1.3GHz 9-cell SCRF cavity has been fabricated. Each cavity is enclosed within titanium vessel and cooled by liquid helium to maintain 2K temperature. Dressing is defined as integration of VTS qualified cavity and titanium vessel (with bellows) while maintaining co-centricity. For dressing, an insertion fixture was designed for rigidity criteria and fabricated using extruded aluminium sections. This fixture consists of a bench, a trolley, a cantilever end support, one column support and alignment brackets. The overall size of fixture is 4x0.5x0.9m height up to trolley base. The helium vessel mounted on trolley, travels in the slotted guide, is passed over the cavity to match with transition ring on the main coupler end. The adjustable adapter ring at the field probe end (installed over boom prior to mounting the helium vessel) is then assembled precisely with vessel and cavity. Then tack welding is done with suitable argon purging, to lock the alignment. After the tack welds have cooled down, the assembly is ready to be moved to the glove box for complete welding. This paper covers the dressing requirements of cavity and vessel, design and fabrication of insertion fixture. In future, the experience will be helpful for insertion fixture design and dressing of 650 MHz SCRF cavity. (author)