Abstract
In a cylindrical metal tube a beam-plasma system exhibits an instability in the neighbourhood of the ion-plasma frequency. The instability is studied as a function of different parameters, such as B-field and plasma density.
The frequency of the observed instability and its amplitude are in semi-quantitative agreement with the theory for a homogeneous filled waveguide.
From wavelength measurements using a double probe, it is deduced that the interaction is excited by the slow electron-cyclotron wave on the beam. Due to the very small transverse dimensions of our beam-plasma system this instability is observable near the ion-plasma frequency.