Consistent modelling for magnetic flux in rotationally symmetric systems

In finite-element analysis of rotationally symmetric systems, the use of local co-ordinates can obscure some properties of the solution and can impede the deduction of flux density components which are consistent with the vector potential. A simple model for flux is proposed which uses global co-ordinates, is electromagnetically valid within each element, allows consistent flux density components to be deduced and can be applied over elements of any shape. In a test on a known magnetic lens, the COFEM model produced a physically more probable result and faster convergence than the standard FOFEM method.