The instability near the ion plasma frequency in a beam-plasma system

In a beam-plasma experiment the instability near the ion plasma frequency is studied. In a helium plasma under our experimental conditions this instability has a frequency below 10 MHz. Wavelength measurements at this instability were made by a double probe. Excitation of the ion waves is brought about by the slow cyclotron harmonic waves on the electron beam. Multiple modes of the interaction peak have been observed and are caused by interactions, which are determined by different order Bessel-functions.