Generation of VHF oscillations in beam-plasma systems with nonuniform magnetic field

The problem of more effective application of intense electron beams to, in particular, generation of VHF oscillations has become most urgent in connection of extensive use of such beams in various types of experiments. The relevant studies have shown that the efficiency of particle energy transformation in VHF fields is still rather low in case of electromagnetic field generation using powerful relativistic beams. For example, the efficiency is ∼ 10% for unlimited plasma systems /1, 2/. The situation is, however, more favourable in plasma waveguides; in this case, the field energy flux can reach ∼ 20% of the beam power /3/. One of the reasons for such low an efficiency is associated with beam deceleration (due to the loss of particle translation energy for the heating of the plasma and beam itself and for VHF-field “pumping”) and with the weakening of the resonant interactions between the generated oscillation mode and particles. In connection with this, consideration was given to the concept of resonance “tuning” /4/ by varying the parameters of the system at the generation process.