Design aspects of a large toroidal stabilizing shell and vacuum liner assembly

The design and manufacturing problems of toroidal shell/liner system with major/minor liner radii of 180/60cm for a High Beta Reversed Field Pinch Device with a maximum plasma current of 2MA, are considered. The stress analysis figures for the shell show that because of the vacuum load the net forces on the bolting system do not impose undue restraints. The key problems on the shell are the electrical insulation and cooling at the overlap, vacuum sealing and for a fabricated vessel the integrity of the welding for high vacuum conditions. Alternatively, a cast aluminium alloy shell should prove an attractive proposition, but is dependent upon satisfactory vacuum properties being achieved. From analysis of the dynamic forces on the liner induced by the magnetic fields diffusing through its wall, the buckling stresses have an adequate margin of safety over the critical case and the problem is one of supporting the liner. Because of the size of the liner and the thin sheet metal construction, manufacturing problems will be concerned with maintaining the overall dimensional accuracy and achieving the high standard of welding required