Magnetron operation near the drift-cyclotron resonances

Summary form only given, as follows. In addition to the pure drift resonance w-ku/spl sime/0, where magnetrons usually operate, slow wave excitation may also occur near the Doppler shifted cyclotron resonance w-ku/spl sime//spl plusmn//spl Omega/, for fast (+) and slow (-) "drift-cyclotron" operation. In the slow drift cyclotron case the electrostatic energy is converted into radiation and cyclotron energy. In the fast drift cyclotron case both electrostatic and cyclotron rotation energy are converted into radiation. Thus operation at the fast mode offers (a) higher frequency at given B/sub 0/ (or lower B/sub 0/ for given frequency) (b) high efficiency through the conversion of cyclotron energy to wave energy (in addition to the conversion of the GC potential energy taking place during usual magnetron operation). In all cases, the non-relativistic gain curve is symmetric relative to the frequency detuning with maximum at resonance, in contrast to the antisymmetric gain of other microwave devices. The fast branch, which is linearly stable in the cold beam limit, is destabilized by finite Larmor radius k/spl rho/>1 and/or by relativistic effects. By averaging-out the fast cyclotron time one obtains nonlinear, slow-time scale equations describing the coupling of the guiding center drift with the Larmor radius variations. The solutions of the equations of motion are employed to address the spoke formation and the efficiency optimization under different operation scenarios. We also present proof-of-principle small signal gain simulations using the particle code MASK.