Structure analysis and experiment research of the welded bellows for the ports of the HT-7U vacuum vessel

Vacuum vessel of the HT-7U is a fully welded toroidal structure with noncircular cross-section nested in the bore of the TF coils. According to the requirement of the physics design, sixteen horizontal ports on outboard mid-plane and thirty-two vertical ports on the top and bottom are designed for diagnostics, plasma heating, current driving, vacuum pumping and gas puffing. Bellows on these ports are used for flexible components to absorb the relative displacement in radial and vertical directions due to the external load, thermal expansion or contraction, assembly toleration and as well as for isolation of mechanical vibration. Some three-dimension finite element COSMOS models were performed to analysis its structural strength, stiffness and fatigue life, laying the emphasis on these bellows static stress analysis. The load case spectra during vacuum vessel operation were also simulated on a model from the view of fatigue design. It was confirmed that these bellows have sufficient strength in range of the design load conditions. The results showed the bellows peak stress was 87 MPa and its fatigue cumulative usage factor was only 0.01, which was less than critical value of 1. Now all kinds of bellows have been designed. In order to accumulate some engineering experiences and probe into some molding die and welding technologies, a prototypical bellows have been fabricated. At the same time a mechanical testing apparatus was designed for proof tests on the prototypical bellows to verify its functional and structure capability. The experimental data indicated that the results of finite element analysis were coincident with experimental test results. It has been proved that the present vacuum vessel's bellows are reasonable and feasible.