EFFICIENT COGENERATION OF 7TH-HARMONIC RADIATION IN CYCLOTRON AUTORESONANCE ACCELERATION

It is shown that the lowest TE(s,l) mode in a cylindrical waveguide at frequency s omega, with group velocity nearly identical to group velo city for the TE(11) mode at frequency omega, is that with s = 7, l = 2 . This allows coherent radiation to be generated at the seventh harmon ic during electron cyclotron autoresonance acceleration. Conditions ar e found where such co-generation of 7th harmonic power at 20 GHz is po ssible with overall efficiency greater than 80%. This mechanism could make possible high efficiency cm-wavelength high power rf sources suit able for driving a future multi-TeV electron-position collider.