Experimental study of microwave generation and suppression in a non-neutral e-layer

Abstract

Broadband microwave radiation in the X and KA bands was observed from a non‐neutral electron layer prepared by passing a 2.5‐MeV straight hollow electron beam through a narrow magnetic cusp. The mean beam radius shrank from 6 to 4.5 cm and the beam radial width increased from less than 1 to 2.7 cm in the postcusp e‐layer drift region. When the beam was passed through a thin scattering foil prior to cusp transmission, the observed radiation decreased by two orders of magnitude and the beam width and radius remained at values consistent with single‐particle calculations. Results are discussed in terms of the negative‐mass instability.