Effect of helical slow-wave structure parameter variations on TWT cold-test characteristics

In this paper, the quasi-periodic boundary conditions in the computer code MAFIA is used to determine the effect on dispersion and on-axis interaction impedance of helical slow-wave structure and the finite element method software-ANSYS is used to simulate the helix pressure distortion. The result is that, with the variations of axial width and height of the helical tape, only a slight effect in the phase velocity, but more effect in the interaction impedance. There is a best point on both axial width and height of the helical tape for the interaction impedance. Both dispersion and on-axis interaction impedance are increased with helix deformation, in which the radial relative deformation is less then 1%. While radial relative deformation is more then 1%, the on-axis interaction impedance is decreased.