Classification of eigenmodes in rf cavities using the group theory

For many damped-accelerating cavities for high-intensity beams, classifications of eigenmodes according to azimuthal indices are generally insufficient due to a lack of their axial symmetry. To classify the eigenmodes in such cavities having general symmetry, the application of group theory is studied. By taking basis functions from a complete set of eigenmodes, one can form a representation of the symmetry group of the cavity. The eigenmodes can then be classified according to irreducible representations of the symmetry group. This method is particularly useful for classifying the eigenmodes in complicated cavities, and for understanding the effects of perturbations on the eigenmodes.