Manufacturing experience and commissioning of large size (volume >180 m3) UHV class vacuum vessel for Indian test facility (INTF) for neutral beam

Indian Test Facility (INTF) designed for the "Full characterization of the Diagnostic Neutral Beam (DNB)" for ITER, which includes the beam production, neutralization and its transportation over a length of 20.67 m. Test Facility consists of a vacuum vessel, designed and manufactured as per ASME Sec. VIII Div. 1, to accommodate DNB components and to provide an ultra-high vacuum (UHV) environment for its operation. Considering the functional requirements, vessel is fabricated from AISI 304 L, in cylindrical configuration with the diameter of 4.5 m and length of 9 m. Vessel has a 'detachable top lid' to provide access for internal components during their installation and maintenance. To manufacture this configuration, cutting of top lid is made from the shell itself that demands controlling the distortion, arisen from stress relaxation caused by welding and shell rolling. Weld distortion was measured for the large flange welding and post-welding, machining parameters was optimized to get the flatness of 1.2 mm over the size 9 m x 5 m. Vacuum demonstration of 1E-05 mbar was done with leak rates of 10(-9) mbar l/sec (local) and 10(-6) mbar l/sec (global) with the UHV requirements. Learning experience and methodology generated in establishing the fabrication practices for the distortion and deflection control and vacuum integrity are presented in the paper.