A Method for Calculating Resonant Frequencies, Mode Structure and Field Flatness in an Alvarez Type Linac Cavity

The method of Walkinshaw, Sabel and Outram has been extended to cavities consisting of drift tube loaded cells with varying lengths in order to determine the field flatness and sensitivity to errors for the various modes of a realistic linac. A computational program has been written which gives the resonant frequency and field pattern for a multi-cell cavity with arbitrary drift tube lengths and gap lengths. The object of the study is to obtain the following information: 1) Mode structure and resonant frequencies of a cavity consisting of several identical cells in order to obtain the dispersion curve. 2) Sensitivity of the field flatness to dimensional errors for the zero and 7/2 modes. 3) Mode structure and field flatness for a cavity consisting of several cells with differing geometrical parameters. Results of these computations are presented and discussed.