Rippled-Field Magnetron with a Transparent Cathode

The rippled field magnetron is a source of millimeter-wave radiation theoretically described and experimentally verified by Bekefi [1]. It uses an array of azimuthally periodic permanent magnets to modulate electrons and allow them to become synchronous with a fast TM or TE electromagnetic mode in a smooth interaction space. The azimuthally periodic permanent magnets create an azimuthally periodic magnetic field (wiggler). Due to the radial component of the wiggler B
r
, electrons undergoing an azimuthal
$\text{ve}=\mathrm{E}_{\mathrm{r}}\text{xH}$
, drift will experience an extra force
$\mathrm{v}\theta\text{xB}_{\mathrm{r}},$
causing them to oscillate in the axial direction and bunching them in the azimuthal direction.