THE ELECTRON CYCLOTRON MASER INSTABILITY

P. Sprangle , V. Granatstein , A. Drobot

The cyclotron maser instability has a two-fold importance, first, there is fundamental scientific interest in this strong instability of an ensemble of spiralling electrons in a magnetic field ; second, this instability is the basis for a new class of powerful millimeter wave generators (gyrotrons) which are finding application to r.f. heating of plasma in controlled fusion research devices. In this paper, both the linear theory and the nonlinear theory of the instability are considered. Relativistic effects associated with the spiralling electrons are responsible for amplification of a transverse electric waveguide mode. The temporal nonlinear evolution of the field amplitude and frequency of a single wave is described. The nonlinear wave dynamics are selfconsistently determined from the nonlinear particle orbits through the force and wave equations. Two mechanisms for saturation of wave growth are fond : (1) depletion of the available free energy associated with the rotating electrons ; (2) phase trapping of the electrons in the wave. Competition between the two saturation mechanisms leads to a peaking in the energy conversion efficiency as a function of beam energy. The theory has been used to design a nonlinear gyrotron amplifier with 340 kW output power at 35 GHz with efficiency optimized at 51 % in the laboratory frame.

Domaines: Articles anciens

P. Sprangle, V. Granatstein, A. Drobot. THE ELECTRON CYCLOTRON MASER INSTABILITY. Journal de Physique Colloques, 1977, 38 (C6), pp.C6-135-C6-152. ⟨10.1051/jphyscol:1977613⟩. ⟨jpa-00217197⟩