EFFICIENCY OF THE EMISSION OF ELECTROMAGNETIC-WAVES EXCITED IN THE INTERACTION OF AN ELECTRON-BEAM WITH A RADIALLY BOUNDED PLASMA IN A NONUNIFORM AXIAL MAGNETIC-FIELD

Results of experimental studies of the interaction of an electron beam with a radially bounded plasma are presented. It is shown that, for t he given beam parameters, the efficiency of the excitation of plasma o scillations can be substantially increased through an appropriate choi ce of the plasma radius. By adjusting the radial plasma density gradie nt, it is possible to achieve a high efficiency of the conversion of b eam-excited oscillations into electromagnetic waves. It is demonstrate d that the directional diagram of the electromagnetic radiation emitte d from the beam-plasma system can be controlled by varying the longitu dinal plasma inhomogeneity, i.e., by varying the longitudinal profile of the axial magnetic field. It is shown that the radial inhomogeneity of the plasma density can suppress ion-acoustic and drift instabiliti es. Electromagnetic radiation is observed against the background of th e excitation of lower hybrid oscillations and acceleration of plasma i ons in the fields of these oscillations in the direction of beam propa gation. The level of low-frequency ion-acoustic, drift, and lower hybr id oscillations determines the maximum power of high-frequency oscilla tions excited in a beam-plasma system.