ABSTRACT
Two typical assumptions are the neglection of structure appendices, especially couplers, and the idealization of pure rotational symmetry. In this paper we are going to describe the application of a method, denoted here as Coupled-S-Parameter-Calculation (CSC), on resonators where none of both simplifications are possible. esc is based on the partitioning of the entire structure in segments, being small enough to calculate their rfscattering properties - the frequency-dependent S-matrices - on standard hardware with commonly used field solving codes like MAFIA, CST Microwave Studio ™ [ 1], etc. Afterwards the calculation scheme of CSC is used to combine the segments to build up the entire structure, independent from its topology and the number of waveguide modes needed to describe the segment's interactions. esc is able to handle both kind of structures: a. with open ports, delivering the overall S-matrix, and b. completely closed resonators, calculating their eigenfrequencies and internal wave amplitudes. For a detailed description of esc and its theory see [2, 3]. The first example is the TESLA-9-cell structure l4l (section 3) fully equipped with Higher Order Mode-(HOM-) and input-couplers, that showed to have resonances with tmexpected high quality factors in the 2.6 GHz-range [5]. A similar study was presented in l6]. Here three different arrangements of HOM-and input-couplers were analyzed and the according Q-factors were determined. The latter step was performed by applying a fitting procedure (section 2) on the S-parameter-spectra found with CSC. A significant variation of the Q-values was found here. ln the second part (section 4) focus is laid on structures that are derived from ideally circular symmetric geometries, but experienced slight elliptical deformations. Two types of structures are considered: one denoted as ''waist-structure", having a big circular cross section at the connecting planes and a small inner cylinder of elliptical shape; the second being derived from an inner cell of the TESLA-resonator with a circular waist, but a slightly elliptical body. For both structure types eigenresonances of chains built from 3, 4 and 6 cells were studied, the cells being skewed one to the next by angles between 0° and 90°. Front-to-end differences of wave polarizations are calculated for all anangements and a certain set of dipole modes. Furthermore escresults of an unskewed 9-element-chain of the TESLA-type cell is compared with reference frequencies [7]. The 4-element chain is investigated in further detail, regarding the fields in all cutting planes.
