RFQ Solver based on the Method of Moments

The aim of this research is to improve the accuracy and the simulation time of solvers devoted to Radio Frequency Quadrupoles (RFQ). The Method of Moments is a full-wave method used to solve scattering problems. Its main advantage over FE or FDTD solvers is that unknowns are limited to the boundaries of the object. The resulting dense system of equations can be solved very rapidly with the help of domain-decomposition approaches (e.g. Macro Basis Functions*), especially when the level of detail is very fine compared to the wavelength, which is definitely the case for RFQ’s. Such a method however needs a first regularization method to overcome the low-frequency breakdown in order to compute the Macro Basis Functions. The respective field contributions of different parts of the global structure (e.g. rods vs. stems) can also easily be finely investigated. Numerical results will be presented based on the Myrrha RFQ. The low-frequency breakdown issue due to the very fine mesh will be discussed and a solution based on the so-called Loop-Tree** decomposition will be detailed.