Efficient Co-Generation of Seventh-Harmonic Radiation in Cyclotron Autoresonance Acceleration.

Abstract

It is shown that the lowest ${\mathrm{TE}}_{s,l}$ mode in a cylindrical waveguide at frequency $s\ensuremath{\omega}$, with group velocity nearly identical to group velocity for the ${\mathrm{TE}}_{11}$ mode at frequency $\ensuremath{\omega}$, is that with $s\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}7$, $l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$. This allows coherent radiation to be generated at the seventh harmonic during electron cyclotron autoresonance acceleration. Conditions are found where such co-generation of 7th harmonic power at 20 GHz is possible with overall efficiency greater than 80%. This mechanism could make possible high efficiency cm-wavelength high power rf sources suitable for driving a future multi-TeV electron-position collider.