Helical peniotron backward wave oscillators

Summary form only given, as follows. We propose to utilize the helical beam which is a natural beam formation from a helical wiggler and a vaned waveguide for peniotron interaction. In the medium beam energy regime, the advantage of a helical peniotron in comparison with a conventional peniotron is very significant. The latter interaction tends to increase the beam longitudinal energy while the former interaction converts both the transverse and longitudinal beam energy into wave energy. As a result the difference in overall efficiency can be as large as a factor of two. To illustrate this, the following parameters were used in our simulations: beam voltage=225 kV, beam current=50 A, 6 vanes, /spl pi/ modes, /spl alpha/=v/sub /spl perp//v/sub /spl par//=0.6, f/sub 0/spl sime//31 GHz, guide field=15 kG, wiggler field=2.2 kG, and wiggler period=1 cm. The resulting efficiency of the helical peniotron oscillator was 30% while that of the conventional peniotron oscillator was 16%.