AbstractThe frequency spectrum of cyclotron emission resonantly heated electrons in a magnetic mirror is investigated. In an experiment, a very strong emission is observed in a narrow frequency band just higher than the frequency of a heating wave, in addition to radiation with a broad frequency spectrum. The cyclotron emission spectrum from resonantly heated electrons is theoretically calculated with a velocity distribution of electrons bouncing in a magnetic mirror and experiencing multiple heating. The calculation shows that the observed narrow spectrum is attributed to cyclotron emission from heated electrons that are magnetically reflected and accumulated within a narrow region around the resonant heating layer.