A Multi-Objective Genetic Algorithm for Optimizing Dispersion and Coupling Impedance in Helix TWTs

Optimization techniques have been used in traveling wave tubes design for the slow-wave circuit phase velocity taper and collector stages (Wilson, 2001; Chevalier et al., 2003). In the slow-wave circuit design, the objective function aims to minimize the difference between dispersions versus different frequency, and maximize the on-axis interaction impedance in a specified bandwidth. This is a double-objective optimizing problem. Unfortunately, the objective functions are conflicting. The small difference between dispersions comes with the decrease of interaction impedance. The single-objective optimization, therefore, is not suitable to pose this problem. However, to our knowledge, these multi-objective optimization techniques have not been applied to general slow-wave circuit design until now. The expression of evaluating interaction impedance in the sheath helix model was also presented