A large vacuum chamber of the SSC for HIRFL

The vacuum chamber of the Separated Sector Cyclotron (SSC) for Heavy Ion Research Facility Lanzhou (HIRFL) to have been built is described. It is a large monolithic ultra-high vacuum vessel with 10 m in diameter and 4.5 m high, weighing 65 tn. The total volume is about 100 m3. There are 234 ports on it for various purpose. The mechanical analysis of the vacuum chamber is completed using a finite element method by means of the procedure SAP-5C on a computer. Uddholm 316 L super-low carbon stainless steel made in Sweden was selected as a structure material. Because of very big size, the monolithic vacuum chamber is divided into eight bigger and several smaller pieces to fabricate in the factory. Then it is transported by a train and a truck to the institute. Finally it is welded as a single vessel and machined in situ. In the interests of economy, the manual electric arc welding is the best choice in our case. It is paid great attention to strict technological process during welding. Owing to high requirements for ultrahigh vacuum, all of tight welded seams are inspected and checked by liquid peretration testing, X-ray examination and helium mass spectrometer detecting. All of the flanges are machined before welding as far as possible at the factory. Some big flanges are cut by special way in situ. The pressure of 8 x 10-6 Pa for sufficient beam transmission in the vacuum chamber is obtained in September of 1986