RIGOROUS AND NUMERICALLY EFFICIENT COMPUTATION OF THE IRROTATIONAL ELECTRIC AND MAGNETIC EIGENFUNCTIONS OF COMPLEX GYROTRON CAVITIES

For the modal analysis of complex gyrotron cavities, complete sets of eigenfunctions of the corresponding completely shielded cavity are req uired. In this contribution, it is shown that the generalized scatteri ng matrix method which is well-known for the computation of the resona nce modes can also be applied to the calculation of the irrotational e lectric and magnetic eigenfunctions, The irrotational eigenfunctions a re computed for some circularly symmetrical structures. The validity o f the method is checked by investigating a spherical cavity for which the analytical solution is known. Furthermore, a special subdivision o f tapered cavity sections is presented which considerably improves the numerical efficiency of the method, For a standard gyrotron cavity, t he field in the source region is computed with and without making use of irrotational electric eigenfunctions. It is demonstrated that the a ccuracy and the numerical efficiency of the modal expansion of the cav ity field in the source region is improved if these eigenfunctions are included in the analysis.