Microwave Emission Produced by the Interaction of an Intense Relativistic Electron Beam with a Spatially Modulated Magnetic Field

Intense microwave emission was detected when a pulsed relativistic electron beam traversed a spatially modulated magnetic field. The microwave intensity was $\gtrsim 70$ dB above the noise level. The wavelength of the electromagnetic radiation was equal to the characteristic length of the rippled magnetic field. At a critical averaged magnetic field, the radiation appeared to be almost monochromatic ($\frac{\Delta \lambda }{\lambda }\lesssim 0.5\%$); below the critical field, a broad spectrum appeared ($\frac{\Delta \lambda }{\lambda \gtrsim 10\%}$).