Abstract
The rippled-field magnetron is a novel crossed-field millimeter wave source in which electrons move in nearly circular paths under the combined action of a radial electric field, an axial magnetic field, and an azimuthally periodic wiggler magnetic field, Bw cos (Nϑ) oriented transversely to the flow. Estimates are given of the frequency and growth rate of the free-electron laser (FEL) type of instability excited in this smooth-bore magnetron configuration.