Coherent fast wave radiation from spatiotemporally modulated gyrating relativistic electron beams

Generation of radiation is described at a harmonic of the rotation frequency for a spatiotemporally modulated gyrating electron beam. Cumulative energy flow into the wave occurs when its group velocity matches the beam´s axial velocity. Fifth harmonic wave growth at 94 GHz in a cylindrical waveguide is shown to be relatively free of mode competition for a device employing a 150 kV, 6.7 A beam. Non-linear simulations show a saturated efficiency of 56% for a linear magnetic field taper in this device. The saturated efficiency only drops to 50% for an axial velocity spread of 10%.