Abstract :
A new helix configuration is used which reduces the phase velocity dispersion of the helix at lower frequencies. Dispersion shaping is accomplished with axial slots in the external helix shield, so that the conduction in the shield becomes anisotropic. This offers the advantage that large bandwidth operation becomes available in the low frequency region of the helix, where the interaction is much stronger. It is then possible to achieve high efficiency for octave bandwidth tubes. Very high efficiencies are achievable when methods of velocity resynchronization, such as a velocity taper or a voltage jump, are used also.
