A STUDY ON THE BUCKLING BEHAVIOR OF A BELLOWS-TYPE VACUUM VESSEL WITHTORUS SHAPE IN A REVERSED-FIELD PINCH DEVICE

Buckling strength of a thin bellows vacuum vessel with torus shape is studied for design work on a reversed field pinch (RFP) fusion experim ental device. In the RFP both toroidal and poloidal magnetic fields mu st be rapidly changed in the initial setting-up phase of the magnetic field configuration and high one-turn resistances of the vessel in bot h directions are required. Thus a very thin bellows with shallow convo lution has to be used and the mechanical strength of the bellows-type vessel is a crucial design point. Here the buckling strength of the ve ssel is analysed numerically by applying the finite element method to a half-pitch of the bellows in torus shape. Results show that the buck ling strength of the bellows torus is proportional to the third power of the equivalent bending thickness and approximately equal to that fo r a straight cylindrical tube having the same plate thickness as the e quivalent bending thickness. Thus the torus effect seems to be unimpor tant in a bellows torus. This result is different from the previous st udy for simple toroidal vessels, where the buckling strength is increa sed by the torus effect.