Electrostatic cyclotron harmonic wave instabilities in beam‐plasma systems

The cyclotron harmonic wave instabilities of a weak electron beam and a warm plasma system having a finite cross section in a finite magnetic field are investigated. Experimentally, it is shown, by using a test wave method, that the unstable cyclotron harmonic waves are observed in each cyclotron harmonic band and their dispersion curves have harmonic structure. Theoretical studies show that the observed instabilities are ascribed to the Cerenkov and cyclotron excitations (normal and anomalous Doppler effects), where the negative energy waves on the beam are coupled to the obliquely propagating cyclotron harmonic waves in the warm plasma in a magnetic field.